Flavour compounds in tomato fruits: identification of loci and potential pathways affecting volatile composition

The dissection of tomato flavor: biochemistry, genetics, and omics

Flavor and quality are the major drivers of fruit consumption in the US. However, the poor flavor of modern commercial tomato varieties is a major cause of consumer dissatisfaction. Studies in flavor research have informed the role of volatile organic compounds in improving overall liking and sweetness of tomatoes. These studies have utilized and applied the tools of molecular biology, genetics, biochemistry, omics, machine learning, and gene editing to elucidate the compounds and biochemical pathways essential for good tasting fruit. Here, we discuss the progress in identifying the biosynthetic pathways and chemical modifications of important tomato volatile compounds. We also summarize the advances in developing highly flavorful tomato varieties and future steps toward developing a "perfect tomato".

Natural overexpression of CAROTENOID CLEAVAGE DIOXYGENASE 4 in tomato alters carotenoid flux

Carotenoids and apocarotenoids function as pigments and flavor volatiles in plants that enhance consumer appeal and offer health benefits. Tomato (Solanum lycopersicum.) fruit, especially those of wild species, exhibit a high degree of natural variation in carotenoid and apocarotenoid contents. Using positional cloning and an introgression line (IL) of Solanum habrochaites "LA1777', IL8A, we identified carotenoid cleavage dioxygenase 4 (CCD4) as the factor responsible for controlling the dark orange fruit color. CCD4b expression in ripe fruit of IL8A plants was ∼8,000 times greater than that in the wild type, presumably due to 5' cis-regulatory changes. The ShCCD4b-GFP fusion protein localized in the plastid. Phytoene, ζ-carotene, and neurosporene levels increased in ShCCD4b-overexpressing ripe fruit, whereas trans-lycopene, β-carotene, and lutein levels were reduced, suggestive of feedback regulation in the carotenoid pathway by an unknown apocarotenoid. Solid-phase microextraction-gas chromatography-mass spectrometry analysis showed increased levels of geranylacetone and β-ionone in ShCCD4b-overexpressing ripe fruit coupled with a β-cyclocitral deficiency. In carotenoid-accumulating Escherichia coli strains, ShCCD4b cleaved both ζ-carotene and β-carotene at the C9-C10 (C9'-C10') positions to produce geranylacetone and β-ionone, respectively. Exogenous β-cyclocitral decreased carotenoid synthesis in the ripening fruit of tomato and pepper (Capsicum annuum), suggesting feedback inhibition in the pathway. Our findings will be helpful for enhancing the aesthetic and nutritional value of tomato and for understanding the complex regulatory mechanisms of carotenoid and apocarotenoid biogenesis.

Effect of Methyl Jasmonate on the Biosynthesis of Volatile Compounds Associated with the Ripening of Grape Tomato Fruits

The present work aims to evaluate the roles of methyl jasmonate (MeJA) in the formation of volatile organic compounds (VOC) from grape tomatoes during ripening. Fruits were treated with MeJA, ethylene, 1-MCP (1-methylcyclopropene), and MeJA+1-MCP, with analyses of the VOC and levels of the gene transcripts for the enzymes lipoxygenase (LOX), alcohol dehydrogenase (ADH), and hydroperoxide lyase (HPL). An intimate relationship between MeJA and ethylene in aroma formation was detected, mainly among the VOC from the carotenoid pathway. Expression of the fatty acid transcripts, LOXC, ADH, and HPL pathway genes, was reduced by 1-MCP, even when associated with MeJA. In ripe tomato, MeJA increased most of the volatile C6 compounds, except 1-hexanol. The MeJA+1-MCP treatment followed most of the increases in volatile C6 compounds that were increased by MeJA alone, which evidenced some ethylene-independent mechanism in the production of the volatile C6 compounds. In ripe tomato, MeJA and MeJA+1-MCP increased the levels of 6-methyl-5-hepten-2-one, which is derived from lycopene, evidencing an ethylene-independent biosynthetic process.

Thorough Characterization of ETHQB3.5, a QTL Involved in Melon Fruit Climacteric Behavior and Aroma Volatile Composition

The effect of the QTL involved in climacteric ripening ETHQB3.5 on the fruit VOC composition was studied using a set of Near-Isogenic Lines (NILs) containing overlapping introgressions from the Korean accession PI 16375 on the chromosome 3 in the climacteric 'Piel de Sapo' (PS) genetic background. ETHQB3.5 was mapped in an interval of 1.24 Mb that contained a NAC transcription factor. NIL fruits also showed differences in VOC composition belonging to acetate esters, non-acetate esters, and sulfur-derived families. Cosegregation of VOC composition (23 out of 48 total QTLs were mapped) and climacteric ripening was observed, suggesting a pleiotropic effect of ETHQB3.5. On the other hand, other VOCs (mainly alkanes, aldehydes, and ketones) showed a pattern of variation independent of ETHQB3.5 effects, indicating the presence of other genes controlling non-climacteric ripening VOCs. Network correlation analysis and hierarchical clustering found groups of highly correlated compounds and confirmed the involvement of the climacteric differences in compound classes and VOC differences. The modification of melon VOCs may be achieved with or without interfering with its physiological behavior, but it is likely that high relative concentrations of some type of ethylene-dependent esters could be achieved in climacteric cultivars.

Multifaceted effects of difenoconazole in tomato fruit ripening: Physiology, flavour and nutritional quality

Difenoconazole is widely used in crop growth, however, its effects on the quality of agricultural products are poorly studied. In this study, the application of difenoconazole on tomato plants could increase soluble sugar content, reduce organic acid and raise accumulation of nutrient-related metabolites during late fruit ripening. Consumer surveys in our study showed that the treatment of difenoconazole tomatoes group had higher sweetness and lower acidity, and those tomatoes were preferred by consumers. Alterations in fruit flavor-related attributes were at least in part corroborated by the abundance of transcripts related to sucrose (SlLin5, SlLin7, SlSuS2, SlSuS6, SlSPS1, SlSPS3) and organic acids (CS, ICDH, cMDH) anabolism. Furthermore, the difenoconazole also significantly promoted the expression of phytohormones synthesis genes, and consequently increased abscisic acid and ethylene levels. Our study not only provides theoretical support for the use of difenoconazole on tomatoes at the level of flavor quality and nutritional health, but also provides valuable information on the mechanism of triazole fungicides in the flavor quality of tomato fruits.

Targeted approaches to improve tomato fruit taste

Tomato (Solanum lycopersicum) is the most valuable fruit and horticultural crop species worldwide. Compared with the fruits of their progenitors, those of modern tomato cultivars are, however, often described as having unsatisfactory taste or lacking flavor. The flavor of a tomato fruit arises from a complex mix of tastes and volatile metabolites, including sugars, acids, amino acids, and various volatiles. However, considerable differences in fruit flavor occur among tomato varieties, resulting in mixed consumer experiences. While tomato breeding has traditionally been driven by the desire for continual increases in yield and the introduction of traits that provide a long shelf-life, consumers are prepared to pay a reasonable premium for taste. Therefore, it is necessary to characterize preferences of tomato flavor and to define its underlying genetic basis. Here, we review recent conceptual and technological advances that have rendered this more feasible, including multi-omics-based QTL and association analyses, along with the use of trained testing panels, and machine learning approaches. This review proposes how the comprehensive datasets compiled to date could allow a precise rational design of tomato germplasm resources with improved organoleptic quality for the future.

Effects of methyl salicylate pre-treatment on the volatile profiles and key gene expressions in tomatoes stored at low temperature

Tomato is one of the most widely cultivated horticultural plants in the world, while the key volatile compounds of tomato fruits generally derive from fatty acid, carotenoid, phenylalanine, and branched-chain amino acid pathways. As an important endogenous signal molecule, methyl salicylate (MeSA) plays a crucial role in the fruit ripening process of plant. Recently, it has been demonstrated that MeSA can maintain the flavor quality of full ripe tomatoes after cold-storage preservation. However, few research teams attempted to investigate the effects of MeSA plus low temperature treatment on the different volatile biosynthetic pathways of tomatoes previously. Therefore, in this study, the effects of methyl salicylate pre-treatment (0.05 mM MeSA, 24 h) on the volatile profile and flavor-related key gene expressions of tomato fruits stored at 10°C were evaluated for the first time. Our results showed that the loss of volatile compounds in low temperature-treated tomato fruits could be effectively alleviated by MeSA pre-treatment. Although MeSA had no remarkable effect on the formation of carotenoid pathway- and branched-chain amino acid pathway-related volatiles in tomatoes subjected to low temperature, the content of fatty acid pathway-related volatiles (including cis-3-hexenal, hexanal, and trans-2-hexenal) in full red fruits of 10°C MeSA group was remarkably higher than that of 10°C control group. Furthermore, MeSA pre-treatment significantly up-regulated the expression of LOXC or LOXD gene in low temperature-treated fruits at breaker or full red stage, respectively. In conclusion, pre-treatment with MeSA might avoid the loss of aromatic compounds in tomato fruits stored at low temperature by activating the fatty acid pathway.

Comparative Studies on the Physicochemical and Volatile Flavour Properties of Traditional Deep Fried and Circulating-Air Fried Hairtail (Trichiurus lepturus)

The aim of this study is to investigate the effects of deep frying (DF) and air frying (AF) on the quality and flavour profile of hairtail (Trichiurus lepturus) fillets. The changes of some physicochemical indices such as moisture content, oil content, colour, thiobarbituric acid reactive substances (TBARS) and peroxide values (POV) in hairtail fillets were detected with increasing frying time. According to these physicochemical indices and sensory evaluation, deep frying for 7 min under 190 °C (DF7) and air frying for 24 min under 190 °C (AF24) were selected as samples for their great quality. The flavour fingerprint of hairtail (Raw, DF7, AF24) was developed and volatile compounds were investigated by HS-GC-IMS. A total of 28 volatile substances including aldehydes, alcohols, ketones and others were identified both in the DF7 and AF24 samples. There are differences in the aroma fingerprint between the DF7 and AF24 samples. DF was characterised by 2-Heptanone, (E)-2-Heptenal, 2-Pentyfuran and 1-Pentanol, AF was characterised by 2-methylbutanol, Ethyl methyl ketone-M and 3-hydroxy-2-butanone. These findings suggest that the aroma of hairtail fillets after DF7 and AF24 was significantly different and supply flavour information and practical applications of the fried hairtail fillets.

Inheritance of Secondary Metabolites and Gene Expression Related to Tomato Fruit Quality

Flavour and nutritional quality are important goals for tomato breeders. This study aimed to shed light upon transgressive behaviors for fruit metabolic content. We studied the metabolic contents of 44 volatile organic compounds (VOCs), 18 polyphenolics, together with transcriptome profiles in a factorial design comprising six parental lines and their 14 F1 hybrids (HF1) among which were five pairs of reciprocal HF1. After cluster analyses of the metabolome dataset and co-expression network construction of the transcriptome dataset, we characterized the mode of inheritance of each component. Both overall and per-cross mode of inheritance analyses revealed as many additive and non-additive modes of inheritance with few reciprocal effects. Up to 66% of metabolites displayed transgressions in a HF1 relative to parental values. Analysis of the modes of inheritance of metabolites revealed that: (i) transgressions were mostly of a single type whichever the cross and poorly correlated to the genetic distance between parental lines; (ii) modes of inheritance were scarcely consistent between the 14 crosses but metabolites belonging to the same cluster displayed similar modes of inheritance for a given cross. Integrating metabolome, transcriptome and modes of inheritance analyses suggested a few candidate genes that may drive important changes in fruit VOC contents.

Patterns of Volatile Diversity Yield Insights Into the Genetics and Biochemistry of the Date Palm Fruit Volatilome

Volatile organic compounds are key components of the fruit metabolome that contribute to traits such as aroma and taste. Here we report on the diversity of 90 flavor-related fruit traits in date palms (Phoenix dactylifera L.) including 80 volatile organic compounds, which collectively represent the fruit volatilome, as well as 6 organic acids, and 4 sugars in tree-ripened fruits. We characterize these traits in 148 date palms representing 135 varieties using headspace solid-phase microextraction gas chromatography. We discovered new volatile compounds unknown in date palm including 2-methoxy-4-vinylphenol, an attractant of the red palm weevil (Rhynchophorus ferrugineus Olivier), a key pest that threatens the date palm crop. Associations between volatile composition and sugar and moisture content suggest that differences among fruits in these traits may be characterized by system-wide differences in fruit metabolism. Correlations between volatiles indicate medium chain and long chain fatty acid ester volatiles are regulated independently, possibly reflecting differences in the biochemistry of fatty acid precursors. Finally, we took advantage of date palm clones in our analysis to estimate broad-sense heritabilities of volatiles and demonstrate that at least some of volatile diversity has a genetic basis.

A flavin-dependent monooxygenase produces nitrogenous tomato aroma volatiles using cysteine as a nitrogen source

Aroma is an important factor in consumer perception and acceptance of fresh tomatoes and involves a cocktail of several dozen compounds. Tomato fruits produce uncommon nitrogen-containing volatiles derived mainly from the amino acids leucine and phenylalanine. These volatiles have strong positive correlations with consumer liking. We show that an enzyme active in ripening tomatoes is responsible for the production of all nitrogenous volatiles in tomato fruit, at the expense of substrates derived from cysteine and volatile aldehydes. This discovery defines a cysteine-dependent route to nitrogenous volatiles in plants, prompting a reconsideration of the impact of sulfur metabolism on tomato flavor and quality.

Tomato (Solanum lycopersicum) produces a wide range of volatile chemicals during fruit ripening, generating a distinct aroma and contributing to the overall flavor. Among these volatiles are several aromatic and aliphatic nitrogen-containing compounds for which the biosynthetic pathways are not known. While nitrogenous volatiles are abundant in tomato fruit, their content in fruits of the closely related species of the tomato clade is highly variable. For example, the green-fruited species Solanum pennellii are nearly devoid, while the red-fruited species S. lycopersicum and Solanum pimpinellifolium accumulate high amounts. Using an introgression population derived from S. pennellii, we identified a locus essential for the production of all the detectable nitrogenous volatiles in tomato fruit. Silencing of the underlying gene (SlTNH1;Solyc12g013690) in transgenic plants abolished production of aliphatic and aromatic nitrogenous volatiles in ripe fruit, and metabolomic analysis of these fruit revealed the accumulation of 2-isobutyl-tetrahydrothiazolidine-4-carboxylic acid, a known conjugate of cysteine and 3-methylbutanal. Biosynthetic incorporation of stable isotope-labeled precursors into 2-isobutylthiazole and 2-phenylacetonitrile confirmed that cysteine provides the nitrogen atom for all nitrogenous volatiles in tomato fruit. Nicotiana benthamiana plants expressing SlTNH1 readily transformed synthetic 2-substituted tetrahydrothiazolidine-4-carboxylic acid substrates into a mixture of the corresponding 2-substituted oxime, nitro, and nitrile volatiles. Distinct from other known flavin-dependent monooxygenase enzymes in plants, this tetrahydrothiazolidine-4-carboxylic acid N-hydroxylase catalyzes sequential hydroxylations. Elucidation of this pathway is a major step forward in understanding and ultimately improving tomato flavor quality.

Metabolomic selection for enhanced fruit flavor

Consumers often regard heirloom fruit varieties grown in the garden as more flavorful than commercial varieties purchased at the grocery store. While plant breeders have historically focused on improving producer-orientated traits such as yield, consumer-oriented traits such as flavor have regularly been neglected. This is, in part, due to the difficulty associated with measuring the sensory perceptions of flavor. Here, we combine fruit chemical and consumer sensory panel information to train machine learning models that can predict how flavorful a fruit will be from its chemistry. By increasing the throughput of flavor evaluations, these models will help plant breeders to integrate flavor earlier in the breeding pipeline and aid in the design of varieties with exceptional flavor profiles.

Although they are staple foods in cuisines globally, many commercial fruit varieties have become progressively less flavorful over time. Due to the cost and difficulty associated with flavor phenotyping, breeding programs have long been challenged in selecting for this complex trait. To address this issue, we leveraged targeted metabolomics of diverse tomato and blueberry accessions and their corresponding consumer panel ratings to create statistical and machine learning models that can predict sensory perceptions of fruit flavor. Using these models, a breeding program can assess flavor ratings for a large number of genotypes, previously limited by the low throughput of consumer sensory panels. The ability to predict consumer ratings of liking, sweet, sour, umami, and flavor intensity was evaluated by a 10-fold cross-validation, and the accuracies of 18 different models were assessed. The prediction accuracies were high for most attributes and ranged from 0.87 for sourness intensity in blueberry using XGBoost to 0.46 for overall liking in tomato using linear regression. Further, the best-performing models were used to infer the flavor compounds (sugars, acids, and volatiles) that contribute most to each flavor attribute. We found that the variance decomposition of overall liking score estimates that 42% and 56% of the variance was explained by volatile organic compounds in tomato and blueberry, respectively. We expect that these models will enable an earlier incorporation of flavor as breeding targets and encourage selection and release of more flavorful fruit varieties.

Fingerprints and changes analysis of volatile compounds in fresh-cut yam during yellowing process by using HS-GC-IMS

The purpose of this study was to investigate the dynamic change in volatile components during the yellowing process. The volatile components were analyzed by headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) and the critical enzyme activities were determined by commercial kits. The results revealed that 29 signal peaks for 20 compounds were identified, which were quantified in all samples: 1 furan, 1 ester, 15 aldehydes, 3 ketones, and 9 alcohols. The contents of most of these compounds increased first and then decreased at 36 h, which were basically consistent with the enzyme activities of LOX, HPL, ADH and AAT. Subsequently, principal component analysis (PCA) results clearly showed that the fresh-cut yams for different yellowing processes were well distinguished by the volatile compounds. These results showed that the potential of HS-GC-IMS-based approaches to evaluate the volatile compound profiles of fresh-cut yam at different stages in the yellowing period.

Branched-Chain Volatiles in Fruit: A Molecular Perspective

Branched-chain volatiles (BCVs) constitute an important family of fruit volatile metabolites essential to the characteristic flavor and aroma profiles of many edible fruits. Yet in contrast to other groups of volatile organic compounds important to fruit flavor such as terpenoids, phenylpropanoids, and oxylipins, the molecular biology underlying BCV biosynthesis remains poorly understood. This lack of knowledge is a barrier to efforts aimed at obtaining a more comprehensive understanding of fruit flavor and aroma and the biology underlying these complex phenomena. In this review, we discuss the current state of knowledge regarding fruit BCV biosynthesis from the perspective of molecular biology. We survey the diversity of BCV compounds identified in edible fruits as well as explore various hypotheses concerning their biosynthesis. Insights from branched-chain precursor compound metabolism obtained from non-plant organisms and how they may apply to fruit BCV production are also considered, along with potential avenues for future research that might clarify unresolved questions regarding BCV metabolism in fruits.

Enhanced soluble sugar content in tomato fruit using CRISPR/Cas9-mediated SlINVINH1 and SlVPE5 gene editing

Soluble sugar is known to improve the sweetness and increase tomato sauce yield. Studies have focused on improving the content of soluble sugar in tomato fruits, usually by promoting functional genes. We studied two genes (SlINVINH1 and SlVPE5) that inhibited the accumulation of soluble sugar in tomato fruits and obtained two genes’ knocked-out lines (CRISPR-invinh1 or CRISPR-vpe5) using CRISPR/Cas9. Aggregated lines with CRISPR-invinh1 and CRISPR-vpe5 were gained by hybridization and self-pollination. Compared to wild-type lines, the glucose, fructose, and total soluble solid (TSS) contents of CRISPR-invinh1 and CRISPR-vpe5 increased significantly. Glucose, fructose, and TSS levels further improved simultaneously with CRISPR-invinh1 and CRISPR-vpe5 than with single gene knock-out lines. This indicates that these genes have a synergistic effect and will increase the soluble sugar content. Thus, the knock-out SlINVINH1 and SlVPE5 may provide a practical basis for improving the sweetness of tomato fruits and their processing quality.

Characterization of the Volatile Compounds of Zhenba Bacon at Different Process Stages Using GC-MS and GC-IMS

Zhenba bacon (ZB), a type of Chinese traditional bacon with a long history, has attracted considerable attention in the Southwest of China for its unique flavor. To elucidate the changing course of aroma components during the process of ZB, four stages of process stages were assessed by GC-MS and GC-IMS coupled with multivariate data analysis. A total of 44 volatile compounds were identified by GC-IMS, including 5 esters, 8 alcohols, 12 aldehydes, 3 ketones, 1 furan and 2 sulfides; 40 volatile compounds were identified by GC-MS, 4 ketones, 7 phenols, 8 alcohols, 6 esters, 6 aldehydes, and 6 other compounds were detected. During the curing period, the amount and content of esters in Zhenba bacon gradually increased. Phenols appear in large quantities during the smoking period. The VOCs (volatile organic compounds) in the gallery plots were the most diverse in YZ samples, which are mainly esters. POV (peroxide value) and TBARS (thiobarbituric acid reactive substance) showed that lipid oxidation played an important role in the formation of volatile flavor components of bacon. This study provides valuable analytical data to explain the flavor formation of Zhenba bacon.

Physico-Chemical, Nutritional, and Sensory Evaluation of Two New Commercial Tomato Hybrids and Their Parental Lines

Tomato (Solanum lycopersicum) is the globally most consumed vegetable. The objective of this research was to analyze physico-chemical, nutritional and sensorial components (taste and flavor) in two new commercial hybrids (AS 300 F1 and AS 400 F1) and their four F7 parental lines. Two widely grown F1 hybrids (Precos F1 and Addalyn F1) were used as controls. The results obtained for carbohydrates (HPLC-RID) indicated that the highest values (27.82 mg/g) were recorded in the paternal line AS 10 of the new hybrid AS 400 F1. The highest values of total organic acids (HPLC-VWD) were recorded in Addalyn F1 (5.06 m/g), while the highest value of phenolic compounds (HPLC-DAD-ESI⁺) were identified in the maternal line AS 09 of the hybrid AS 400 F1 (96.3 µg/g). Intrinsic sensory values were analyzed by male and female tasters of different ages using a hedonic scale. The tasters' perception revealed obvious taste differences between tomato genotypes. The study allowed determining genetic parameters of interest (heterosis and heterobeltosis) for the new hybrids, as well as a detailed characterization of the chemical composition and organoleptic quality of the parental breeding lines and their hybrids, which is useful in tomato breeding.

Use of metabolomics data analysis to identify fruit quality markers enhanced by the application of an aminopolysaccharide

Chitosan is a biostimulator that has a great effect either on plant physiology, productivity, or fruit quality. However, the metabolic mechanism regulated by chitosan still remains unknown. Untargeted metabolomics analysis, using LC-MS/MS mass spectrometry, was used to investigate fruit quality markers. Thus, this study was focused on the identification of untargeted metabolites of tomato fruits produced under the application of five doses of chitosan at different concentrations (0, 0.25, 0.50, 0.75, and 1 mg ml^-1) that was extracted from Parapenaeus longirostris shrimp shells. The identification was carried out using two ion modes (ESI^-/ESI⁺), a web application "Metfamily" to analyze signals, and reference libraries. The analysis of data using partial least squares discriminant analysis (PLS-DA) and hierarchical cluster analysis (HCA) showed that chitosan application, especially 0.75 mg ml^-1, had a clear and remarkable effect regarding the number of metabolite families identified in both ion modes. This treatment has increased the relative abundance of many metabolites that belong to anthocyanins decorated with sugars, terpenoids, phenylpropanoids, acylsugars, glucosinolates, folates, galactolipids, fatty acids, and phospholipids. Thus, these results showed that chitosan application increased the quality of tomato fruits due to its involvement in the regulation of many metabolic pathways that might be responsible for enhancing the nutritional characteristics as well as the defense of fruits.

Papaya (Carica papaya L.) Flavour Profiling

A major challenge to the papaya industry is inconsistency in fruit quality and, in particular, flavour, which is a complex trait that comprises taste perception in the mouth (sweetness, acidity, or bitterness) and aroma produced by several volatile compounds. Current commercial varieties vary greatly in their taste, likely due to historical prioritised selection for fruit appearance as well as large environmental effects. Therefore, it is important to better understand the genetic and biochemical mechanisms and biosynthesis pathways underpinning preferable flavour in order to select and breed for better tasting new commercial papaya varieties. As an initial step, objectively measurable standards of the compound profiles that provide papaya's taste and aroma, together with 'mouth feel', are required. This review presents an overview of the approaches to characterise the flavour profiles of papaya through sugar component determination, volatile compound detection, sensory panel testing, as well as genomics-based studies to identify the papaya flavour.

Effects of Harvest Maturity, Refrigeration and Blanching Treatments on the Volatile Profiles of Ripe "Tasti-Lee" Tomatoes

The interactive effects of six maturity stages and refrigerated storage (chilling)/blanching (heating) treatments on the volatile profiles of ripe tomatoes were studied. A total of 42 volatiles were identified, of which 19 compounds had odor activity values equal to or greater than 1. Of those, “green” and “leafy” aroma volatiles were most abundant. Chilling and heating treatments both suppressed overall volatile production, with chilling having the greater impact, regardless of harvest maturity. However, fruit harvested at the turning stage had the least volatile suppression by chilling and heating treatments in comparison with fruit harvested earlier or later, mostly in the fatty acid- and phenylalanine-derived volatiles. Volatiles derived from amino acids were promoted by heat treatment for fruit harvested at all maturities, and those derived from carotenoid and phenylalanine pathways and harvested at advanced harvest maturities were stimulated by chilling treatment. Volatile production is generally believed to be improved by delayed harvest, with vine-ripe being optimum. However, opposite results were observed possibly because the later-harvested fruit had longer exposure to open-field weather stress. The best harvest maturity recommendation is the turning stage where fruit developed abundant volatiles and were least impacted by chilling and heating treatments.

Gall- and erineum-forming Eriophyes mites alter photosynthesis and volatile emissions in an infection severity-dependent manner in broad-leaved trees Alnus glutinosa and Tilia cordata

Highly host-specific eriophyoid gall- and erineum-forming mites infest a limited range of broadleaf species, with the mites from the genus Eriophyes particularly widespread on Alnus spp. and Tilia spp. Once infected, the infections can be massive, covering a large part of leaf area and spreading through the plant canopy, but the effects of Eriophyes mite gall formation on the performance of host leaves are poorly understood. We studied the influence of three frequent Eriophyes infections, E. inangulis gall-forming mites on Alnus glutinosa, and E. tiliae gall-forming and E. exilis erineum-forming mites on Tilia cordata, on foliage morphology, chemistry, photosynthetic characteristics, and constitutive and induced volatile emissions. For all types of infections, leaf dry mass per unit area, net assimilation rate per area and stomatal conductance strongly decreased with increasing severity of infection. Mite infections resulted in enhancement or elicitation of emissions of fatty acid-derived volatiles, isoprene, benzenoids and carotenoid breakdown products in an infection severity-dependent manner for all different infections. Monoterpene emissions were strongly elicited in T. cordata mite infections, but these emissions were suppressed in E. inangulis-infected A. glutinosa. Although the overall level of mite-induced emissions was surprisingly low, these results highlight the uniqueness of the volatile profiles and offer opportunities for using volatile fingerprints and overall emission rates to diagnose infections by Eriophyes gall- and erineum-forming mites on temperate trees and assess their impact on the physiology of the affected trees.

The Genetic Basis of Tomato Aroma

Tomato (Solanum lycopersicum L.) aroma is determined by the interaction of volatile compounds (VOCs) released by the tomato fruits with receptors in the nose, leading to a sensorial impression, such as "sweet", "smoky", or "fruity" aroma. Of the more than 400 VOCs released by tomato fruits, 21 have been reported as main contributors to the perceived tomato aroma. These VOCs can be grouped in five clusters, according to their biosynthetic origins. In the last decades, a vast array of scientific studies has investigated the genetic component of tomato aroma in modern tomato cultivars and their relatives. In this paper we aim to collect, compare, integrate and summarize the available literature on flavour-related QTLs in tomato. Three hundred and 5ifty nine (359) QTLs associated with tomato fruit VOCs were physically mapped on the genome and investigated for the presence of potential candidate genes. This review makes it possible to (i) pinpoint potential donors described in literature for specific traits, (ii) highlight important QTL regions by combining information from different populations, and (iii) pinpoint potential candidate genes. This overview aims to be a valuable resource for researchers aiming to elucidate the genetics underlying tomato flavour and for breeders who aim to improve tomato aroma.

Can gene editing reduce postharvest waste and loss of fruit, vegetables, and ornamentals?

Postharvest waste and loss of horticultural crops exacerbates the agricultural problems facing humankind and will continue to do so in the next decade. Fruits and vegetables provide us with a vast spectrum of healthful nutrients, and along with ornamentals, enrich our lives with a wide array of pleasant sensory experiences. These commodities are, however, highly perishable. Approximately 33% of the produce that is harvested is never consumed since these products naturally have a short shelf-life, which leads to postharvest loss and waste. This loss, however, could be reduced by breeding new crops that retain desirable traits and accrue less damage over the course of long supply chains. New gene-editing tools promise the rapid and inexpensive production of new varieties of crops with enhanced traits more easily than was previously possible. Our aim in this review is to critically evaluate gene editing as a tool to modify the biological pathways that determine fruit, vegetable, and ornamental quality, especially after storage. We provide brief and accessible overviews of both the CRISPR-Cas9 method and the produce supply chain. Next, we survey the literature of the last 30 years, to catalog genes that control or regulate quality or senescence traits that are "ripe" for gene editing. Finally, we discuss barriers to implementing gene editing for postharvest, from the limitations of experimental methods to international policy. We conclude that in spite of the hurdles that remain, gene editing of produce and ornamentals will likely have a measurable impact on reducing postharvest loss and waste in the next 5-10 years.

Bibliometric study of volatile compounds in commercial fruits of the Solanaceae family

Abstract Bibliometric analysis is a discipline that allows us to identify knowledge trends, assesses scientific activity and the impact of research through its volume, evolution, visibility, and structure. The present study aimed to carry out a bibliometric study of scientific research that contributes to the knowledge of Volatile Organic Compounds (VOCs) of edible and commercial fruits of Solanaceae family. The research consisted of extracting the information from papers in the Web of Science database. We analyzed and performed the production, visibility, and impact of these papers, also relationships and collaboration between authors using BibExcel and VOSviewer software. As a result, 178 documents were obtained from 2001 to 2017. Tomato is the fruit with the largest number of related articles that are focused on studying compounds responsible for taste, aroma, and biotic and abiotic relationships, as well as studies for identification of the genes responsible for these organoleptic and ecological traits. Papers analyzed are related to the research studies of 491 authors from 239 different organizations distributed in 45 countries. This bibliometric study allowed to identify trends in the knowledge in VOCs with respect to Solanaceae fruits, as well as recognizing the location of the scientific material in this field.

Ethylene and Auxin: Hormonal Regulation of Volatile Compound Production During Tomato (Solanum lycopersicum L.) Fruit Ripening

As the auxin-ethylene interaction in climacteric fruit ripening has been highlighted, the hormonal regulation of aroma changes in climacteric fruits requires clarification. The influence of both phytohormones on the volatile organic compound (VOC) metabolism was evaluated during tomato (Solanum lycopersicum L.) fruit ripening. Tomato fruits cv. Micro-Tom and Sweet Grape at the mature green stage were randomly grouped according to treatment with ethylene (ETHY), auxin (IAA), or both (ETHY + IAA). At middle ripening, Micro-Tom ETHY + IAA fruits present VOC profiles similar to those of ETHY fruits, while Sweet Grape presents VOC profiles closer to those of IAA fruits. At full ripeness, Micro-Tom and Sweet Grape ETHY + IAA fruits show profiles closer to those of IAA fruits, suggesting that the auxin overlaps the ethylene effects. Aroma compounds positively correlated with consumer preferences (2-isobutylthiazole, 6-methyl-5-hepten-2-one, and others) are identified in both cultivars and have their contents affected by both hormone treatments. The transcription of genes related to the biosynthesis of important tomato VOCs that have fatty-acid and carotenoid precursors evidences their regulation by both plant hormones. Additionally, the results indicate that the observed effects on the VOC metabolism are not restricted to the Micro-Tom cultivar, as these are also observed in the Sweet Grape cultivar. In conclusion, ethylene and auxin directly regulate the metabolic pathways related to VOC formation, impacting tomato aroma formation during ripening since Micro-Tom fruits apparently at the same maturation stage have different aromas.

Functional divergence of principal alcohol o-acyltransferase for biosynthesis of volatile acetate esters among tomato wild species (Solanum Sect. Lycopersicon)

Volatile esters are the chemicals that have multiple physiological functions including plant defense responses and reproduction. From a human perspective, the esters largely contribute to the fruity aroma of freshy fruits. Composition of volatile esters show a significant diversity among the wild tomato species (Solanum sect. Lycopersicon). To address the basis for this divergence, here we conducted functional analysis of a gene encoding major alcohol o-acyltransferase (AAT1) that catalyzes volatile ester formation. Although AAT1 transcripts were highly expressed in the ripe fruits of all the wild species examined, their enzymatic properties significantly differed due to amino acid sequence variations. Notably, AAT1s from S. pennellii showed the highest ability to produce acetate esters whereas AAT1s from S. neorickii, S. chmielewskii and S. habrochaites had the lowest activities. Further, screenings using domain-swapped or point-mutated AAT1s allowed us to identify Met/Thr352 as one of the critical residues related to the transferase activity with acetyl-CoA. This finding is potentially applied to aroma engineering in which a site-directed mutagenesis at this position in alcohol o-acyltransferases could enable to manipulate volatile ester levels in ripe fruits.

Dynamic Changes of DNA Methylation Induced by Heat Treatment Were Involved in Ethylene Signal Transmission and Delayed the Postharvest Ripening of Tomato Fruit

Deoxyribonucleic acid (DNA) methylation plays an important role in fruit ripening and senescence. Here, the role of DNA methylation of the CpG island of SlACS10, LeCTR1, LeEIN3, LeERT10, and SlERF-A1 genes induced by heat treatment (37 °C) in postharvest ripening of tomato fruit was studied. After heat treatment, the firmness and vitamin C content showed higher levels, the loss of aldehydes in volatile components was delayed, and the activities of methylase and demethylase decreased in tomato fruit. Moreover, in heat-treated fruit, significant changes in DNA methylation of SlACS10, LeCTR1, LeEIN3, LeERT10, and SlERF-A1 were induced, the expression of LeERT10 and LeEIN3 was inhibited, the expression of SlERF-A1 was increased, by which ethylene signal transmission might be suppressed and the postharvest ripening of tomato fruit was delayed. The present study provided valuable information for understanding the essential role of DNA methylation in the postharvest ripening of tomato fruit.

NMR Metabolomics Applied on the Discrimination of Variables Influencing Tomato (Solanum lycopersicum)

Tomato composition and nutritional value are attracting increasing attention and interest from both consumers and producers. The interest in enhancing fruits' quality with respect to beneficious nutrients and flavor/aroma components is based not only in their economic added value but also in their implications involving organoleptic and healthy properties and has generated considerable research interest among nutraceutical and horticultural industries. The present article reviews up to March 2020 some of the most relevant studies based on the application of NMR coupled to multivariate statistical analysis that have addressed the investigation on tomato (Solanum lycopersicum). Specifically, the NMR untargeted technique in the agri-food sector can generate comprehensive data on metabolic networks and is paving the way towards the understanding of variables affecting tomato crops and composition such as origin, variety, salt-water irrigation, cultivation techniques, stage of development, among many others. Such knowledge is helpful to improve fruit quality through cultural practices that divert the metabolism towards the desired pathways and, probably more importantly, drives further efforts towards the differentiation of those crops developed under controlled and desired agronomical conditions.

The genetic and functional analysis of flavor in commercial tomato: the FLORAL4 gene underlies a QTL for floral aroma volatiles in tomato fruit

Tomato (Solanum lycopersicum L.) has become a popular model for genetic studies of fruit flavor in the last two decades. In this article we present a study of tomato fruit flavor, including an analysis of the genetic, metabolic and sensorial variation of a collection of contemporary commercial glasshouse tomato cultivars, followed by a validation of the associations found by quantitative trait locus (QTL) analysis of representative biparental segregating populations. This led to the identification of the major sensorial and chemical components determining fruit flavor variation and detection of the underlying QTLs. The high representation of QTL haplotypes in the breeders' germplasm suggests that there is great potential for applying these QTLs in current breeding programs aimed at improving tomato flavor. A QTL on chromosome 4 was found to affect the levels of the phenylalanine-derived volatiles (PHEVs) 2-phenylethanol, phenylacetaldehyde and 1-nitro-2-phenylethane. Fruits of near-isogenic lines contrasting for this locus and in the composition of PHEVs significantly differed in the perception of fruity and rose-hip-like aroma. The PHEV locus was fine mapped, which allowed for the identification of FLORAL4 as a candidate gene for PHEV regulation. Using a gene-editing-based (CRISPR-CAS9) reverse-genetics approach, FLORAL4 was demonstrated to be the key factor in this QTL affecting PHEV accumulation in tomato fruit.

Flavor-Related Quality Attributes of Ripe Tomatoes Are Not Significantly Affected Under Two Common Household Conditions

Consumer complaints about the flavor of fresh tomato fruits (Solanum lycopersicum L.) have increased in the past few decades, and numerous studies have been done on the flavor of tomatoes and how it is influenced. However, it has not yet been taken into account how consumer handling affects the flavor when considering the complete post-harvest chain-from retailer (distributor) to retail to consumer. In this study, the impact of two household storage regimes on the volatile profile and important flavor-related compounds were examined, considering the entire post-harvest handling. New breeding lines (n = 2) and their parental cultivars (n = 3) were evaluated. Fruits were harvested ripe and stored at 12.5°C for 1 day, at 20°C for 2 days, and afterward at either 20 or 7°C for another 4 days. The aroma volatile profile was measured using GC-MS and GC-FID. A trained panel was used to characterize the sensory attributes of the fruits. In both storage regimes, the relative amount of hexanal increased during the storage period in three of the five cultivars/breeding lines while benzaldehyde was the only volatile compound that decreased significantly in four cultivars/breeding lines. The relative concentration of the precursors of lipid-derived volatiles-linoleic (C18:2) and linolenic (C18:3) acid-did not change in both storage regimes. The lycopene and β-carotene contents increased slightly during storage (20 and 7°C), as the carotenoid-derived volatile 6-methyl-5-hepten-2-one did. The fructose and glucose concentrations did not vary significantly, while the content of total soluble solids increased during both storage regimes. No significant difference could be found between the fruits stored at 20 or 7°C for 4 days after the post-harvest handling in all the parameters analyzed, including the sensory analysis, considering all cultivars/breeding lines. A storage temperature of 7°C is not detrimental for the flavor of ripe fruits under the experimental conditions used. The genetic background of the studied cultivars/breeding lines have a higher impact on the flavor variation than the two common household storage conditions when storing ripe fruits and taking the entire post-harvest handling into account.

Dissection of complex traits of tomato in the post-genome era

We present the main advances of dissection of complex traits in tomato by omics, the genes identified to control complex traits and the application of CRISPR/Cas9 in tomato breeding. Complex traits are believed to be under the control of multiple genes, each with different effects and interaction with environmental factors. Advance development of sequencing and molecular technologies has enabled the recognition of the genomic structure of most organisms and the identification of a nearly limitless number of markers that have made it to accelerate the speed of QTL identification and gene cloning. Meanwhile, multiomics have been used to identify the genetic variations among different tomato species, determine the expression profiles of genes in different tissues and at distinct developmental stages, and detect metabolites in different pathways and processes. The combination of these data facilitates to reveal mechanism underlying complex traits. Moreover, mutants generated by mutagens and genome editing provide relatively rich genetic variation for deciphering the complex traits and exploiting them in tomato breeding. In this article, we present the main advances of complex trait dissection in tomato by omics since the release of the tomato genome sequence in 2012. We provide further insight into some tomato complex traits because of the causal genetic variations discovered so far and explore the utilization of CRISPR/Cas9 for the modification of tomato complex traits.

Network Analysis Provides Insight into Tomato Lipid Metabolism

Metabolic correlation networks have been used in several instances to obtain a deeper insight into the complexity of plant metabolism as a whole. In tomato (Solanum lycopersicum), metabolites have a major influence on taste and overall fruit quality traits. Previously a broad spectrum of metabolic and phenotypic traits has been described using a Solanum pennellii introgression-lines (ILs) population. To obtain insights into tomato fruit metabolism, we performed metabolic network analysis from existing data, covering a wide range of metabolic traits, including lipophilic and volatile compounds, for the first time. We provide a comprehensive fruit correlation network and show how primary, secondary, lipophilic, and volatile compounds connect to each other and how the individual metabolic classes are linked to yield-related phenotypic traits. Results revealed a high connectivity within and between different classes of lipophilic compounds, as well as between lipophilic and secondary metabolites. We focused on lipid metabolism and generated a gene-expression network with lipophilic metabolites to identify new putative lipid-related genes. Metabolite–transcript correlation analysis revealed key putative genes involved in lipid biosynthesis pathways. The overall results will help to deepen our understanding of tomato metabolism and provide candidate genes for transgenic approaches toward improving nutritional qualities in tomato.

Tomato Fruit Development and Metabolism

Tomato (Solanum lycopersicum L.) belongs to the Solanaceae family and is the second most important fruit or vegetable crop next to potato (Solanum tuberosum L.). It is cultivated for fresh fruit and processed products. Tomatoes contain many health-promoting compounds including vitamins, carotenoids, and phenolic compounds. In addition to its economic and nutritional importance, tomatoes have become the model for the study of fleshy fruit development. Tomato is a climacteric fruit and dramatic metabolic changes occur during its fruit development. In this review, we provide an overview of our current understanding of tomato fruit metabolism. We begin by detailing the genetic and hormonal control of fruit development and ripening, after which we document the primary metabolism of tomato fruits, with a special focus on sugar, organic acid, and amino acid metabolism. Links between primary and secondary metabolic pathways are further highlighted by the importance of pigments, flavonoids, and volatiles for tomato fruit quality. Finally, as tomato plants are sensitive to several abiotic stresses, we briefly summarize the effects of adverse environmental conditions on tomato fruit metabolism and quality.

Salmonella adapts to plants and their environment during colonization of tomatoes

Humans and animals are considered typical hosts for Salmonella, however, also plants can be colonized. Tomatoes were linked to salmonellosis outbreaks already on several occasions. The aim of this study was, therefore, to establish a comprehensive view on the interaction between Salmonella enterica and tomatoes, and to test the hypothesis that colonization of plants is an interactive process. We assessed the persistence of Salmonella in agricultural soil, the colonization pattern in and on tomatoes, as well as the reciprocal responses of tomatoes to different Salmonella strains and Salmonella to root exudates and tomato-related media. This study revealed that Salmonella can persist in the soil and inside the tomato plant. Additionally, we show that Salmonella strains have particular colonization pattern, although the persistence inside the plant differs between the tested strains. Furthermore, the transcriptome response of tomato showed an up-regulation of several defense-related genes. Salmonella transcriptome analysis in response to the plant-based media showed differentially regulated genes related to amino acid and fatty acid synthesis and stress response, while the response to root exudates revealed regulation of the glyoxylate cycle. Our results indicate that both organisms actively engage in the interaction and that Salmonella adapts to the plant environment.

Distribution of Volatile Compounds in Different Fruit Structures in Four Tomato Cultivars

Distribution of volatile compounds in different fruit structures were analyzed in four tomato cultivars by headspace-solid-phase microextraction (SPME)-gas chromatography-mass spectrometry (GC-MS). A total of 36 volatile compounds were identified in fruit samples, which were primarily aldehydes, hydrocarbons, alcohols, ketones, furans, esters, nitrogen compounds, and sulfur and nitrogen-containing heterocyclic compounds. The volatile compositions in pericarp (PE), septa and columella (SC), locular gel and seeds (LS), and stem end (SE) tissues showed different profiles. The PE tissue showed the highest total volatile concentration due to a high abundance of aldehydes, especially cis-3-hexenal and benzaldehyde. Meanwhile, it showed higher aromatic proportion and herbaceous series intensity than other tissues. Floral and fruity series showed higher intensity in SC and LS tissues. The concentration of alcohols in the LS was higher than that in other tissues in association with the higher abundances of 2-methyl propanol, 3-methyl butanol, and 2-methyl butanol. However, the numbers and concentrations of volatile compounds, especially cis-3-hexenal, benzaldehyde, and geranyl acetone were lower in SE than in the other tissues, indicating less tomato aromas in SE. SE tissues were also lacking in floral and fruity characteristic compounds, such as geranyl acetone, 1-nitro-pentane, and 1-nitro-2-phenylethane. "FL 47" contained more volatile compounds than the other three, and the contents of aldehydes, ketones and oxygen-containing heterocyclic compounds in the "Tygress" fruit were higher than the other cultivars.

From Acetoin to ( Z)-3-Hexen-1-ol: The Diversity of Volatile Organic Compounds that Induce Plant Responses

Evidence that plants can respond to volatile organic compounds (VOCs) was first presented 35 years ago. Since then, over 40 VOCs have been found to induce plant responses. These include VOCs that are produced not only by plants but also by microbes and insects. Here, we summarize what is known about how these VOCs are produced and how plants detect and respond to them. In doing so, we highlight notable observations we believe are worth greater consideration. For example, the VOCs that induce plant responses appear to have little in common. They are derived from many different biosynthetic pathways and have few distinguishing chemical or structural features. Likewise, plants appear to use several mechanisms to detect VOCs rather than a single dedicated "olfactory" system. Considering these observations, we advocate for more discovery-oriented experiments and propose that future research take a fresh look at the ways plants detect and respond to VOCs.

Quantitative Trait Loci Analysis Identifies a Prominent Gene Involved in the Production of Fatty Acid-Derived Flavor Volatiles in Tomato

To gain insight into the genetic regulation of lipid metabolism in tomato, we conducted metabolic trait loci (mQTL) analysis following the lipidomic profiling of fruit pericarp and leaf tissue of the Solanum pennellii introgression lines (IL). To enhance mapping resolution for selected fruit-specific mQTL, we profiled the lipids in a subset of independently derived S. pennellii backcross inbred lines, as well as in a near-isogenic sub-IL population. We identified a putative lecithin:cholesterol acyltransferase that controls the levels of several lipids, and two members of the class III lipase family, LIP1 and LIP2, that were associated with decreased levels of diacylglycerols (DAGs) and triacylglycerols (TAGs). Lipases of this class cleave fatty acids from the glycerol backbone of acylglycerols. The released fatty acids serve as precursors of flavor volatiles. We show that LIP1 expression correlates with fatty acid-derived volatile levels. We further confirm the function of LIP1 in TAG and DAG breakdown and volatile synthesis using transgenic plants. Taken together, our study extensively characterized the genetic architecture of lipophilic compounds in tomato and demonstrated at molecular level that release of free fatty acids from the glycerol backbone can have a major impact on downstream volatile synthesis.

Canalization of Tomato Fruit Metabolism

To explore the genetic robustness (canalization) of metabolism, we examined the levels of fruit metabolites in multiple harvests of a tomato introgression line (IL) population. The IL partitions the whole genome of the wild species Solanum pennellii in the background of the cultivated tomato (Solanum lycopersicum). We identified several metabolite quantitative trait loci that reduce variability for both primary and secondary metabolites, which we named canalization metabolite quantitative trait loci (cmQTL). We validated nine cmQTL using an independent population of backcross inbred lines, derived from the same parents, which allows increased resolution in mapping the QTL previously identified in the ILs. These cmQTL showed little overlap with QTL for the metabolite levels themselves. Moreover, the intervals they mapped to harbored few metabolism-associated genes, suggesting that the canalization of metabolism is largely controlled by regulatory genes.

Volatile metabolite profiling reveals the changes in the volatile compounds of new spontaneously generated loquat cultivars

In recent years, the advantageous traits of three new loquat cultivars have drawn the attention of breeders and growers. All three have spontaneously arisen from the 'Algerie' cultivar: the new 'Xirlero' cultivar is a bud mutant of 'Algerie', while 'Amadeo' and 'Raúl' arose as chance seedlings. Following a non-targeted approach based on HS-SPME-GC-MS, the volatile compounds profile of the fruits from the new cultivars were obtained and compared to the original 'Algerie' cultivar. Carboxylic acids clearly dominated the volatile profile of all the loquat cultivars, but esters, aldehydes, ketones and alcohols were also predominant compounds. Interestingly when the bud mutant event did not lead to marked changes in the volatile compounds complement, pronounced changes in the volatile composition of chance seedling-generated cultivars 'Amadeo' and 'Raúl' were observed. 'Amadeo' fruits showed lower levels of 2-methyl butanoic acid and much higher levels of methylhexanoate, methylbutanoate and 2-hydroxy-5-methylacetophenone. The 'Raúl' cultivar also had a distinctive volatile profile characterised by high levels of C6-aldehydes, (E)-2-hexanal, 2-hexenal, (Z)-3-hexenal and hexanal, and several carotenoid-derived volatiles; e.g. 2-pentene-1,4-dione 1-(1,2,2-trimethylcyclopentyl), (S)-dihydroactinidiolide, isodurene, cis-geranyl acetone, β-damascenone, β-ionone, α-ionone and 3,4-dehydro-β-ionone. These changes in volatiles were associated with a more intense flavour in cultivars 'Amadeo' and 'Raúl', according to the sensory evaluation of the flavour intensity carried out by a semi-trained panel. A metabolomic correlation network analysis provided insights as to how volatiles were regulated, and revealed that the compounds modified in 'Amadeo' were uncoupled from the rest of the volatilome, while the volatiles modified in 'Raul' changed according to specific groups. To conclude, this work provides a holistic view of how the loquat volatilome was affected, and this information was integrated with the physical-chemical-sensory attributes to understand the changes that occur in the new cultivars.

Identification of major loci and genomic regions controlling acid and volatile content in tomato fruit: implications for flavor improvement

Plant metabolites are important to world food security due to their roles in crop yield and nutritional quality. Here we report the metabolic profile of 300 tomato accessions (Solanum lycopersicum and related wild species) by quantifying 60 primary and secondary metabolites, including volatile organic compounds, over a period of 2 yr. Metabolite content and genetic inheritance of metabolites varied broadly, both within and between different genetic groups. Using genotype information gained from 10 000 single nucleotide polymorphism markers, we performed a metabolite genome-wide association mapping (GWAS) study. We identified 79 associations influencing 13 primary and 19 secondary metabolites with large effects at high resolution. Four genome regions were detected, highlighting clusters of associations controlling the variation of several metabolites. Local linkage disequilibrium analysis and allele mining identified possible candidate genes which may modulate the content of metabolites that are of significant importance for human diet and fruit consumption. We precisely characterized two associations involved in fruit acidity and phenylpropanoid volatile production. Taken together, this study reveals complex and distinct metabolite regulation in tomato subspecies and demonstrates that GWAS is a powerful tool for gene-metabolite annotation and identification, pathways elucidation, and further crop improvement.

A Multidisciplinary Phenotyping and Genotyping Analysis of a Mapping Population Enables Quality to Be Combined with Yield in Rice

In this study a mapping population (F₈) of ca 200 progeny from a cross between the commercial rice varieties Apo and IR64 has been both genotyped and phenotyped. A genotyping-by-sequencing approach was first used to identify 2,681 polymorphic SNP markers which gave dense coverage of the genome with a good distribution across all 12 chromosomes. The coefficient of parentage was also low, at 0.13, confirming that the parents are genetically distant from each other. The progeny, together with both parents, were grown under irrigated and water restricted conditions in a randomised block design. All grain was harvested to determine variation in yield across the population. The grains were then polished following standard procedures prior to performing the phenotyping analyses. A Gas Chromatography—Mass Spectrometry approach was used to determine the volatile biochemical profiles of each line and after data curation and processing, discriminatory metabolites were putatively identified based on in-house and commercial spectral libraries. These data were used to predict the potential role of these metabolites in determining differences in aroma between genotypes. A number of QTLs for yield and for individual metabolites have been identified. Following these combined multi-disciplinary analyses, it proved possible to identify a number of lines which appeared to combine the favourable aroma attributes of IR64 with the favourable (higher) yield potential of Apo. As such, these lines are excellent candidates to assess further as potential genotypes to work up into a new variety of rice which has both good yield and good quality, thus meeting the needs of both farmer and consumer alike.

Use of Natural Diversity and Biotechnology to Increase the Quality and Nutritional Content of Tomato and Grape

Improving fruit quality has become a major goal in plant breeding. Direct approaches to tackling fruit quality traits specifically linked to consumer preferences and environmental friendliness, such as improved flavor, nutraceutical compounds, and sustainability, have slowly been added to a breeder priority list that already includes traits like productivity, efficiency, and, especially, pest and disease control. Breeders already use molecular genetic tools to improve fruit quality although most advances have been made in producer and industrial quality standards. Furthermore, progress has largely been limited to simple agronomic traits easy-to-observe, whereas the vast majority of quality attributes, specifically those relating to flavor and nutrition, are complex and have mostly been neglected. Fortunately, wild germplasm, which is used for resistance against/tolerance of environmental stresses (including pathogens), is still available and harbors significant genetic variation for taste and health-promoting traits. Similarly, heirloom/traditional varieties could be used to identify which genes contribute to flavor and health quality and, at the same time, serve as a good source of the best alleles for organoleptic quality improvement. Grape (Vitis vinifera L.) and tomato (Solanum lycopersicum L.) produce fleshy, berry-type fruits, among the most consumed in the world. Both have undergone important domestication and selection processes, that have dramatically reduced their genetic variability, and strongly standardized fruit traits. Moreover, more and more consumers are asking for sustainable production, incompatible with the wide range of chemical inputs. In the present paper, we review the genetic resources available to tomato/grape breeders, and the recent technological progresses that facilitate the identification of genes/alleles of interest within the natural or generated variability gene pool. These technologies include omics, high-throughput phenotyping/phenomics, and biotech approaches. Our review also covers a range of technologies used to transfer to tomato and grape those alleles considered of interest for fruit quality. These include traditional breeding, TILLING (Targeting Induced Local Lesions in Genomes), genetic engineering, or NPBT (New Plant Breeding Technologies). Altogether, the combined exploitation of genetic variability and innovative biotechnological tools may facilitate breeders to improve fruit quality tacking more into account the consumer standards and the needs to move forward into more sustainable farming practices.

Identification, introgression, and validation of fruit volatile QTLs from a red-fruited wild tomato species

Volatile organic compounds (VOCs) are major determinants of fruit flavor, a primary objective in tomato breeding. A recombinant inbred line (RIL) population consisting of 169 lines derived from a cross between Solanum lycopersicum and a red-fruited wild tomato species Solanum pimpinellifolium accession (SP) was characterized for VOCs in three different seasons. Correlation and hierarchical cluster analyses were performed on the 52 VOCs identified, providing a tool for the putative assignation of individual compounds to metabolic pathways. Quantitative trait locus (QTL) analysis, based on a genetic linkage map comprising 297 single nucleotide polymorphisms (SNPs), revealed 102 QTLs (75% not described previously) corresponding to 39 different VOCs. The SP alleles exerted a positive effect on most of the underlying apocarotenoid volatile QTLs-regarded as desirable for liking tomato-indicating that alleles inherited from SP are a valuable resource for flavor breeding. An introgression line (IL) population developed from the same parental genotypes provided 12 ILs carrying a single SP introgression and covering 85 VOC QTLs, which were characterized at three locations. The results showed that almost half of the QTLs previously identified in the RILs maintained their effect in an IL form, reinforcing the value of these QTLs for flavor/aroma breeding in cultivated tomato.

Effects of thermal processing and pulp filtration on physical, chemical and sensory properties of winter melon juice

BACKGROUND

Winter melon (Benincasa hispida) is a widely consumed crop in Asia, and believed to impart special benefits to human health. The nutritional composition and sensory properties of four juice types, resulting from a combination of pulp levels (low/high pulp, LP/HP) and thermal processing (with/without boiling, B/NB), LPNB, HPNB, LPB and HPB, were compared.

RESULTS

The juices had low sugars (< 20 g kg^-1 ) and low titratable acidity (about 2 g kg^-1 ). The insoluble solids, glucose, fructose and citric acid content in LP juice were significantly lower than in HP juice. The phenolic amino acids phenylalanine, tyrosine, and tryptophan were detected at 10-45 mg L^-1 levels, and the antioxidant activity ranged from 36 to 49 mg gallic acid L^-1 . C6 and C9 aldehydes were mainly found in HP juice, and boiling induced the accumulation of sulfur compounds and C5 aldehydes. The LPNB juice showed the highest acceptability in the sensory panel. The frozen concentrated orange juice (FCOJ) reconstituted with LPNB was preferable to regular FCOJ for 31% of panelists and not different for 20% of panelists.

CONCLUSION

The low sugar/low acid LPNB juice with 'fresh' flavor could be developed to replace water for reconstituting FCOJ with enhanced nutritional value. © 2016 Society of Chemical Industry.

Carotenoid Cleavage Oxygenases from Microbes and Photosynthetic Organisms: Features and Functions

Apocarotenoids are carotenoid-derived compounds widespread in all major taxonomic groups, where they play important roles in different physiological processes. In addition, apocarotenoids include compounds with high economic value in food and cosmetics industries. Apocarotenoid biosynthesis starts with the action of carotenoid cleavage dioxygenases (CCDs), a family of non-heme iron enzymes that catalyze the oxidative cleavage of carbon-carbon double bonds in carotenoid backbones through a similar molecular mechanism, generating aldehyde or ketone groups in the cleaving ends. From the identification of the first CCD enzyme in plants, an increasing number of CCDs have been identified in many other species, including microorganisms, proving to be a ubiquitously distributed and evolutionarily conserved enzymatic family. This review focuses on CCDs from plants, algae, fungi, and bacteria, describing recent progress in their functions and regulatory mechanisms in relation to the different roles played by the apocarotenoids in these organisms.

Sensory sacrifices when we mass-produce mass produce

Plant breeders have been extremely successful at driving genetic improvements in crops. However, 'improvements' are truly a question of perspective. Over the last one-hundred years most plant genetic innovations have been driven by industry demand. Larger fruits, heavier yields, uniformity, increased resistance to disease and better shipping quality are just a few of the traits that have ensured profits on the farm and affordable food for consumers. However, these milestones have come at the expense of sensory qualities, which have been sacrificed in exchange for practical production objectives. With a base of industry-sufficient genetics, today's breeders can now turn to the consumer for guidance in defining critical desires. New approaches to plant breeding start with the analysis of consumer preferences, and then merge them with modern genomics and analytical chemistry tools. The result is the next generation of crops that meet supply chain demands while presenting improvements in flavor, nutrition, color, aroma and texture. This review analyzes the approach of consumer-assisted selection as it has been applied to tomato and strawberry, two complementary annual crops that have been intensively bred to meet industry expectations. Current breeding efforts start with the consumer, with the objective of reclaiming lost sensory qualities.