Evolution of the aroma volatiles of pear fruits supplemented with fatty acid metabolic precursors

Application of a metabolomics method in the study of pear fruit storage

The entire transportation process of 'crown' pears from harvest to consumption is primarily refrigerated. However, the impact of refrigeration time and temperature on fruit quality remains unclear. In this study, metabolites of 'crown' pears were analyzed using UHPLC-Q-Exactive and GC-MS/MS techniques under cold storage, at room temperature, and at different cold storage durations. A total of 372 substances were identified, including sugars, amino acids, and flavonoids, among others. Among these substances, 27 were identified as significant biomarkers affecting pear quality. An accurate quantitative method for amino acids was established to systematically verify the change trend of L-aspartic amide, glycine, glutamic acid, and other amino acids. The results indicated that after 30 days of storage at 0 °C, there was a relatively small change in the quality and substance content of 'crown' pears with little effect on their nutritional value. These findings could serve as a reference for optimizing the refrigeration time and temperature for pear fruit.

Synergistic variation in abscisic acid and brassinolide treatment signaling component alleviates fruit quality of 'Shine Muscat' grape during cold storage

Grape fruit are harvested in the late summer or early fall and need to be stored at low temperatures to prevent enfeeblement and prolong their shelf-life. This study aimed to determine the effects of abscisic acid (ABA), brassinolide (BR) and ABA + BR (ABR) treatment on the berry quality of 'Shine Muscat' under low temperatures. ABA and BR maintained fruit appearance, cellular structure, weight, firmness. ABR treatments reduced the loss of fruit aroma. Furthermore, the transcriptome and metabolome analysis revealed that ABA, BR, and ABR treatments maintained the quality of fruits during the low temperatures period by influencing chlorophyll metabolism, carotenoid metabolism, flavonoid metabolism, unsaturated fatty acid, and terpene metabolism. These findings identify key genes and metabolites for ABA and BR-induced maintenance of grape fruit quality during cold storage, expanding our understanding of postharvest storage quality maintenance of grape fruit at the transcript and metabolic levels.

Volatile Profile Characterization of Jujube Fruit via HS-SPME-GC/MS and Sensory Evaluation

Current research does not fully elucidate the key compounds and their mechanisms that define the aroma profile of fresh jujube fruits. Therefore, this study conducted a comprehensive analysis of both free and glycosidically bound aroma compounds in fresh jujube fruits of ten cultivars. Utilizing gas chromatography-mass spectrometry (GC-MS), we identified 76 volatile free aroma compounds and 19 glycosidically bound volatile compounds, with esters, aldehydes, and ketones emerging as the predominant volatile compounds in the jujube fruits. Odor activity value (OAV) analysis revealed that the primary aroma profile of the jujubes is characterized by fruity and fatty odors, with β-damascenone being a key contributor to the fruity aroma, and (E)-2-oct-en-1-al and nonanal significantly influencing the fatty aroma. Moreover, the integration of sensory evaluation and partial least squares regression (PLSR) analysis pinpointed octanal, (E)-2-oct-en-1-al, nonanal, β-damascenone, and pentanal as significant contributors to the jujube's characteristic aroma, while isoamyl acetate was identified as significantly influencing the fatty acid taste. This study not only underscores the complexity of the jujube aroma composition but also highlights the impact of environmental factors on aroma profiles, offering valuable insights into the sensory characteristics of jujube fruits.

bZIP transcription factor PubZIP914 enhances production of fatty acid-derived volatiles in pear

'Nanguo' pear emitted a rich aroma when entirely ripe. The six-carbon (C6) volatiles, including the aldehydes, 2-hexenal, and hexanal, as well as their corresponding alcohols and esters which are derived from lipoxygenase pathway are the important volatile components in 'Nanguo' pears. However, the transcriptional regulation mechanism of aroma synthesis of 'Nanguo' pears remains largely unknown. bZIP transcription factors (TFs) mediate different developmental processes in plants. In this study, we identified and characterized a bZIP TF that is highly expressed and induced in 'Nanguo' pear fruits at the mature stage. The content of fatty acid-derived volatiles increased significantly in transgenic pears and tomatoes of PubZIP914 overexpression. Meanwhile, PubZIP914 could regulate PuLOX3.1 by binding directly to PuLOX3.1 promoter. The results of this study provide evidence demonstrating how bZIP transcription factors regulate fatty acid-derived volatiles biosynthesis during pear fruit ripening.

An overview of food lipids toward food lipidomics

Increasing evidence regarding lipids' beneficial effects on human health has changed the common perception of consumers and dietary officials about the role(s) of food lipids in a healthy diet. However, lipids are a wide group of molecules with specific nutritional and bioactive properties. To understand their true nutritional and functional value, robust methods are needed for accurate identification and quantification. Specific analytical strategies are crucial to target specific classes, especially the ones present in trace amounts. Finding a unique and comprehensive methodology to cover the full lipidome of each foodstuff is still a challenge. This review presents an overview of the lipids nutritionally relevant in foods and new trends in food lipid analysis for each type/class of lipids. Food lipid classes are described following the LipidMaps classification, fatty acids, endocannabinoids, waxes, C8 compounds, glycerophospholipids, glycerolipids (i.e., glycolipids, betaine lipids, and triglycerides), sphingolipids, sterols, sercosterols (vitamin D), isoprenoids (i.e., carotenoids and retinoids (vitamin A)), quinones (i.e., coenzyme Q, vitamin K, and vitamin E), terpenes, oxidized lipids, and oxylipin are highlighted. The uniqueness of each food group: oil-, protein-, and starch-rich, as well as marine foods, fruits, and vegetables (water-rich) regarding its lipid composition, is included. The effect of cooking, food processing, and storage, in addition to the importance of lipidomics in food quality and authenticity, are also discussed. A critical review of challenges and future trends of the analytical approaches and computational methods in global food lipidomics as the basis to increase consumer awareness of the significant role of lipids in food quality and food security worldwide is presented.

Advances in detecting fruit aroma compounds by combining chromatography and spectrometry

Fruit aroma is produced by volatile compounds, which can significantly enhance fruit flavor. These compounds are highly complex and have remarkable pharmacological effects. The synthesis, concentration, type, and quantity of fruit aroma substances are affected by various factors, both abiotic and biotic. To fully understand the aroma substances of various fruits and their influencing factors, detection technology can be used. Many methods exist for detecting aroma compounds, and approaches combining multiple instruments are widely used. This review describes and compares each detection technology and discusses the potential use of combined technologies to provide a comprehensive understanding of fruit aroma compounds and the factors influencing their synthesis. These results can inform the development and utilization of fruit aroma substances. © 2023 Society of Chemical Industry.

Metabolome and transcriptome profiling revealed the enhanced synthesis of volatile esters in Korla pear

BACKGROUND

Flavor contributes to the sensory quality of fruits, including taste and aroma aspects. The quality of foods is related to their flavor-associated compounds. Pear fruits have a fruity sense of smell, and esters are the main contributor of the aroma. Korla pear are well known due to its unique aroma, but the mechanism and genes related to volatile synthesis have not been fully investigated.

RESULTS

Flavor-associated compounds, including 18 primary metabolites and 144 volatiles, were characterized in maturity fruits of ten pear cultivars from five species, respectively. Based on the varied metabolites profiles, the cultivars could be grouped into species, respectively, by using orthogonal partial least squares discrimination analysis (OPLS-DA). Simultaneously, 14 volatiles were selected as biomarkers to discriminate Korla pear (Pyrus sinkiangensis) from others. Correlation network analysis further revealed the biosynthetic pathways of the compounds in pear cultivars. Furthermore, the volatile profile in Korla pear throughout fruit development was investigated. Aldehydes were the most abundant volatiles, while numerous esters consistently accumulated especially at the maturity stages. Combined with transcriptomic and metabolic analysis, Ps5LOXL, PsADHL, and PsAATL were screened out as the key genes in ester synthesis.

CONCLUSION

Pear species can be distinguished by their metabolic profiles. The most diversified volatiles as well as esters was found in Korla pear, in which the enhancement of lipoxygenase pathway may lead to the high level of volatile esters at maturity stages. The study will benefit the fully usage of pear germplasm resources to serve fruit flavor breeding goals.

The Molecular Network behind Volatile Aroma Formation in Pear (Pyrus spp. Panguxiang) Revealed by Transcriptome Profiling via Fatty Acid Metabolic Pathways

Pears are popular table fruits, grown and consumed worldwide for their excellent color, aroma, and taste. Volatile aroma is an important factor affecting fruit quality, and the fatty acid metabolism pathway is important in synthesizing volatile aromas. Most of the white pear varieties cultivated in China are not strongly scented, which significantly affects their overall quality. Panguxiang is a white pear cultivar, but its aroma has unique components and is strong. The study of the mechanisms by which aroma is formed in Panguxiang is, therefore, essential to improving the quality of the fruit. The study analyzed physiological and transcriptome factors to reveal the molecular network behind volatile aroma formation in Panguxiang. The samples of Panguxiang fruit were collected in two (fruit development at 60, 90, 120, and 147 days, and fruit storage at 0, 7, 14, 21, and 28 days) periods. A total of nine sample stages were used for RNA extraction and paired-end sequencing. In addition, RNA quantification and qualification, library preparation and sequencing, data analysis and gene annotation, gene co-expression network analysis, and validation of DEGs through quantitative real-time PCR (qRT-;PCR) were performed in this study. The WGCNA identified yellow functional modules and several biological and metabolic pathways related to fatty acid formation. Finally, we identified seven and eight hub genes in the fatty acid synthesis and fatty acid metabolism pathways, respectively. Further analysis of the co-expression network allowed us to identify several key transcription factors related to the volatile aroma, including AP2/ERF-ERF, C3H, MYB, NAC, C2H2, GRAS, and Trihelix, which may also be involved in the fatty acid synthesis. This study lays a theoretical foundation for studying volatile compounds in pear fruits and provides a theoretical basis for related research in other fruits.

Calcium Biofortification of Rocha Pear Fruits: Implications on Mineral Elements, Sugars and Fatty Acids Accumulation in Tissues

Following an agronomic approach for the Ca enrichment of Rocha pears, this study aimed to assess the interactions between mineral nutrients in fruit tissues at harvest and after storage for 5 months and to characterize the implications on the profile of sugars and fatty acids (FA). A total of seven foliar sprays (with concentrations of 0.1–0.6 kg·ha−1 Ca(NO3)2 and 0.8–8 kg·ha−1 CaCl2) were applied to pear trees. After harvest, the fruits were stored for 5 months, in environmentally controlled chambers, and the mineral contents in five regions (on the equatorial section) of the fruits were assessed, while the sugar and FA content were quantified. For both dates, all foliar sprayed treatments, at different extends, increased Ca content in the center and near the epidermis of Rocha pear fruits and the levels of K, Mn, Fe, Zn and Cu also varied. At harvest, the Ca treatments did not affect the levels of sucrose, glucose, fructose and sorbitol and, after storage, their concentrations remained higher in Ca-treated fruits. Additionally, the tendency of the relative proportions of FA was C18:2 > C18:1 > C16:0 > C18:3 > C18:0 > chains inferior to 16 C (<16:0), but after storage it was C18:2 > C16:0 > C18:3 > C18:0 > C18:1 > chains inferior to 16 C (<16:0). It is concluded that the heterogeneous distribution of Ca in the tissues of Rocha pear fruits results from its absorption in the peel after Ca(NO3)2 and CaCl2 sprays and from the xylemic flux in the core prior to maturity. Additionally, the hydrolysis of complex polysaccharides affects the contents of simpler sugars during maturation, ripening and senescence, while storage decreases the amount of total fatty acids (TFA), but the double bond index (DBI) indicate that cell membrane fluidity remains unaffected.

Integrated metabolome and transcriptome analysis of the regulatory network of volatile ester formation during fruit ripening in pear

'Nanguo' pear (Pyrus ussuriensis Maxim.) is a typical climacteric fruit with an attractive aroma after postharvest ripening. Esters are the key volatile compounds determining the typical aroma formation. However, the mechanism of aroma-related ester formation remains largely unknown. In this study, we performed transcriptome and metabolome analyses to reveal the changes of aroma-related compounds during pear ripening in the optimal taste period (OTP). During the pear ripening process, typical fatty acid-derived volatile organic compounds (VOCs) are transformed from aldehydes, alcohols, and ketones to esters, where ethyl hexanoate, hexyl acetate, and ethyl butanoate are the dominant esters in the OTP. Rich aroma-related esters in the OTP are associated with the accumulation of important precursors of aroma volatiles, including linoleic acid, α-linolenic acid, γ-linolenic acid, and oleic acid. Genes encoding key biosynthetic enzymes are associated with the altered levels of aroma-related esters. The candidate genes associated with the high levels of aroma-related esters in 'Nanguo' pears are PuFAD2, PuLOX2, PuLOX5, and PuAAT. Additionally, transcription factor (TF) genes such as PuWRKY24, PuIAA29, and PuTINY may play crucial roles in aroma formation during fruit ripening. Hence, we summarized the TFs that regulate VOC metabolism in different fruit species. The results provided a foundation for further research on aroma-related esters in 'Nanguo' pears and could help to elucidate the mechanisms regulating fruit quality improvement.

Pear genetics: Recent advances, new prospects, and a roadmap for the future

Pear, belonging to the genus Pyrus, is one of the most economically important temperate fruit crops. Pyrus is an important genus of the Rosaceae family, subfamily Maloideae, and has at least 22 different species with over 5000 accessions maintained or identified worldwide. With the release of draft whole-genome sequences for Pyrus, opportunities for pursuing studies on the evolution, domestication, and molecular breeding of pear, as well as for conducting comparative genomics analyses within the Rosaceae family, have been greatly expanded. In this review, we highlight key advances in pear genetics, genomics, and breeding driven by the availability of whole-genome sequences, including whole-genome resequencing efforts, pear domestication, and evolution. We cover updates on new resources for undertaking gene identification and molecular breeding, as well as for pursuing functional validation of genes associated with desirable economic traits. We also explore future directions for "pear-omics".

Recognition of pathogens in food matrixes based on the untargeted in vivo microbial metabolite profiling via a novel SPME/GC × GC-QTOFMS approach

Foodborne diseases incurred by pathogenic bacteria are one of the major threats in food safety, and thus it is important to develop facile and effective recognition methodology of pathogens in food. Herein, a new automatic approach for detection of in vivo volatile metabolites emitted from foodborne pathogens was proposed by coupling solid phase microextraction (SPME) technique with a comprehensive two-dimensional gas chromatography quadrupole time-of-flight mass spectrometry (GC × GC-QTOFMS). A novel polymer composite based SPME probe which possessed high-coverage of microbial metabolites was utilized in this contribution to realize the sensitive extraction of untargeted metabolites. As a result, a total of 126 in vivo metabolites generated by the investigated pathogens were detected and identified, with 33, 29, 25, 21 and 18 volatile metabolites belonging to Shigella sonnei, Escherichia coli, Salmonella typhimurium, Vibrio parahaemolyticus and Staphylococcus aureus, respectively. Multivariate statistical analyses were applied for further analysis of metabolic data and separation of responsive metabolic features among different microbial systems were found, which were also successfully verified in foodstuffs contaminated by microorganisms. The growth trend of the potential volatile markers of each pathogen in food samples kept consistent with that of the pure strain incubated in medium during the whole incubation time. This study promotes the application of SPME technology in microbial volatile metabolomics and contributes to the development of new approaches for foodborne pathogens recognition.

Pollen Source Affects Development and Behavioral Preferences in Honey Bees

Simple Summary

Pollinators adjust their foraging preference based on the pollen cues of foraging plants. Honey bees, for example, prefer to collect one type of pollen from plants that bloom at the same time. In northern China, apricot and pear trees are the two main foraging plants in the early spring. However, honey bees tend to collect pollen from apricot trees. It is interesting to understand what affects the foraging decision of honey bees regarding these two pollen types. In this study, we observed the foraging preference of Apis mellifera workers with respect to apricot and pear pollen under laboratory conditions. The effect of pollen on the development of the hypopharyngeal gland (HG) and ovary was measured. The number of visits made to apricot pollen was significantly higher than that to pear pollen. Furthermore, the response of the HG and ovary to these two pollens was different. The development of the HG was significantly affected by pollen diet treatments. However, there was no significant difference in the ovarian development of caged workers supplied with the two different pollen diets. Overall, honey bees showed a significant preference for apricot pollen over pear pollen. Compared with the ovary, the HG of honey bee workers may be more sensitive to pollen nutrition.

Abstract

With the availability of various plants in bloom simultaneously, honey bees prefer to collect some pollen types over others. To better understand pollen’s role as a reward for workers, we compared the digestibility and nutritional value of two pollen diets, namely, pear (Pyrus bretschneideri Rehd.) and apricot (Armeniaca sibirica L.). We investigated the visits, pollen consumption, and pollen extraction efficiency of caged Apis mellifera workers. Newly emerged workers were reared, and the effects of two pollen diets on their physiological status (the development of hypopharyngeal glands and ovaries) were compared. The choice-test experiments indicated a significant preference of A. mellifera workers for apricot pollen diets over pear pollen diets (number of bees landing, 29.5 ± 8.11 and 9.25 ± 5.10, p < 0.001 and pollen consumption, 0.052 ± 0.026 g/day and 0.033 ± 0.013 g/day, p < 0.05). Both pollen diets had comparable extraction efficiencies (67.63% for pear pollen and 67.73% for apricot pollen). Caged workers fed different pollen diets also exhibited similar ovarian development (p > 0.05). However, workers fed apricot pollen had significantly larger hypopharyngeal glands than those fed pear pollen (p < 0.001). Our results indicated that the benefits conferred to honey bees by different pollen diets may influence their foraging preference.

Co-expression network analysis uncovers key candidate genes related to the regulation of volatile esters accumulation in Woodland strawberry

FveERF (FvH4_5g04470.1), FveAP2 (FvH4_1g16370.1) and FveWRKY (FvH4_6g42870.1) might be involved in fruit maturation of strawberry. Overexpression of FveERF could activate the expression of AAT gene and ester accumulation. Volatile esters play an important role in the aroma of strawberry fruits, whose flavor is the result of a complex mixture of various esters. The accumulation of these volatiles is closely tied to changes in metabolism during fruit ripening. Acyltransferase (AAT) is recognized as having a significant effect in ester formation. However, there is little knowledge about the regulation network of AAT. Here, we collected the data of RNA-seq and headspace GC-MS at five time points during fruit maturation of Hawaii4 and Ruegen strawberry varieties. A total of 106 volatile compounds were identified in the fruit of woodland strawberries, including 58 esters, which occupied 41.09% (Hawaii4) or 33.40% (Ruegen) of total volatile concentration. Transcriptome analysis revealed eight transcription factors highly associated with AAT genes. Through the changes in esters and the weight co-expression network analysis (WGCNA), a detailed gene network was established. This demonstrated that ERF gene (FvH4_5g04470.1), AP2 gene (FvH4_1g16370.1) and one WRKY gene (FvH4_6g42870.1) might be involved in expression of AAT genes, especially ERF genes. Overexpression of FveERF (FvH4_5g04470.1) does activate expression of AAT genes and ester accumulation in fruits of strawberry. Our findings provide valuable clues to gain better insight into the ester formation process of numerous fruits.

Analysis of Volatile Compounds and Sugar Content in Three Polish Regional Ciders with Pear Addition

Aroma plays important part in cider acceptability to the consumer. In this study, techniques such as headspace solid-phase microextraction (HS-SPME), which has been coupled with gas chromatography and mass spectrometry, have been used to assess what changes in the volatilome occur during fermentation of three apple cultivars (Cortland, Gala, Idared) with and without addition of pear (Konferencja) juice addition. Analysis of volatiles has shown that temperature of fermentation, apple variety and pear juice addition have significant influences on the volatile compositions of the acquired ciders. Ciders prepared in laboratory conditions fermented at 15 °C were characterized by a greater share of esters, such as ethyl hexanoate, ethyl decanoate and ethyl dodecanoate, in volatile profile (66.24–79.58%) than ciders fermented at 20 °C (58.81–77.22%). Ciders fermented at a higher temperature were characterized by a greater share of alcohols, such as phenylethyl alcohol and hexan-1-ol (18.34–36.7%) than ciders fermented at a lower temperature (16.07–25.35%). In the ciders prepared from pear (20% w/w) and apple (80% w/w) juice, the presence of esters, such as ethyl (2E, 4Z)-deca-2,4-dienoate, characterized by a pear aroma, could be noted.

Genome-wide identification and comparative analysis of the ADH gene family in Chinese white pear (Pyrus bretschneideri) and other Rosaceae species

Alcohol dehydrogenase (ADH) is essential to the formation of aromatic compounds in fruits. However, the evolutionary history and characteristics of ADH gene expression remain largely unclear in Rosaceae fruit species. In this study, 464 ADH genes were identified in eight Rosaceae fruit species, 68 of the genes were from pear and which were classified into four subgroups. Frequent single gene duplication events were found to have contributed to the formation of ADH gene clusters and the expansion of the ADH gene family in these eight Rosaceae species. Purifying selection was the major force in ADH gene evolution. The younger genes derived from tandem and proximal duplications had evolved faster than those derived from other types of duplication. RNA-Seq and qRT-PCR analysis revealed that the expression levels of three ADH genes were closely correlated with the content of aromatic compounds detected during fruit development.

Variation Patterns of the Volatiles during Germination of the Foxtail Millet (Setaria Italic): The Relationship between the Volatiles and Fatty Acids in Model Experiments

Functional and nutritional compounds are increased during foxtail millet germination while bad smell is produced due to the fatty acid oxidation. To eliminate the unpleasant aroma, the origins of the volatiles must be known. A comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry showed forty-nine volatiles containing 8 ketones, 10 aldehydes, 20 alkanes, 4 alcohols, 5 alkenes, and 2 furans were tentatively identified, and they increased during the germination of the foxtail millet. To identify the origin of some volatiles, model experiments by adding 6 fatty acids to the crude enzymes of the foxtail millet was designed, and 17 volatiles could be detected. The saturated fatty acids (palmitic acid and stearic acid) had no contributions to the formation of the volatiles, whereas the unsaturated fatty acid played important roles in the formation of volatiles. Among the unsaturated fatty acids, palmitoleic acid and linoleic acid produced most aldehydes, alcohols, and ketones, while linolenic acid produced the most alkanes and alkenes. This study will be helpful for controlling the smell of germinated seeds from the raw material selection.

Effects of palmitic acid (16:0), hexacosanoic acid (26:0), ethephon and methyl jasmonate on the cuticular wax composition, structure and expression of key gene in the fruits of three pear cultivars

The chemical composition, crystal morphology and expression levels of associated genes involved in the cuticular wax of three pear cultivars 'Housui', 'Cuiguan' and 'Yuluxiang' after treatment with palmitic acid (PA), hexacosanoic acid (HA), ethephon and methyl jasmonate (Meja) were determined. A total of 59 cuticular wax compounds were detected across all samples. The wax coverage of 'Housui' fruits increased by 71.74, 93.48 and 89.13% after treatment with PA, ethephon and Meja, respectively, and treatment with PA, HA and Meja also increased the wax coverage in 'Cuiguan' (65.33, 20.00 and 21.33% respectively) and in 'Yuluxiang' (38.60, 63.16 and 42.11% respectively) fruits. Heatmap clustering analysis and partial least-squares-discriminate analysis (PLS-DA) also revealed that the different treatments exerted various influences on cuticular wax among the different cultivars. In addition, the wax component coverage and wax crystal structures showed variations among the different cultivars as well as different treatments. Gene expression analysis revealed 11 genes likely to be involved in pear fruit wax synthesis, transport and regulation. Taken together, the results of this study demonstrate that the differences in the cuticular waxes of the fruits of different cultivars after treatment with PA, HA, ethephon or Meja might lead to a better understanding of the regulatory effect of a substrate or elicitor on the composition and deposition of cuticular waxes.

Dietary fatty acids promote sleep through a taste-independent mechanism

Consumption of foods that are high in fat contribute to obesity and metabolism-related disorders. Dietary lipids are comprised of triglycerides and fatty acids, and the highly palatable taste of dietary fatty acids promotes food consumption, activates reward centers in mammals and underlies hedonic feeding. Despite the central role of dietary fats in the regulation of food intake and the etiology of metabolic diseases, little is known about how fat consumption regulates sleep. The fruit fly, Drosophila melanogaster, provides a powerful model system for the study of sleep and metabolic traits, and flies potently regulate sleep in accordance with food availability. To investigate the effects of dietary fats on sleep regulation, we have supplemented fatty acids into the diet of Drosophila and measured their effects on sleep and activity. We found that flies fed a diet of hexanoic acid, a medium-chain fatty acid that is a by-product of yeast fermentation, slept more than flies starved on an agar diet. To assess whether dietary fatty acids regulate sleep through the taste system, we assessed sleep in flies with a mutation in the hexanoic acid receptor Ionotropic receptor 56D, which is required for fatty acid taste perception. We found that these flies also sleep more than agar-fed flies when fed a hexanoic acid diet, suggesting the sleep promoting effect of hexanoic acid is not dependent on sensory perception. Taken together, these findings provide a platform to investigate the molecular and neural basis for fatty acid-dependent modulation of sleep.

Investigations into the production of volatile compounds in Korla fragrant pears (Pyrus sinkiangensis Yu)

The composition of volatile compounds in Korla fragrant pears was determined using headspace solid-phase microextraction followed by a gas chromatography-mass spectrometry analysis using fruits at 30, 90, and 150 days after bloom. Hexanal, (E)-2-hexenal, 1-hexanol, (E)-2-hexen-1-ol, (Z)-3-hexen-1-ol, and hexyl acetate were identified as the major compounds. The composition of volatile compounds was associated with fatty acid concentrations and key enzyme activity in the lipoxygenase pathway. In vitro linoleic and linolenic acid feeding experiments conducted using cubes of fruit flesh demonstrated that the concentrations of volatile esters, such as hexyl acetate, in the treated fruits increased significantly after incubation for 12 h compared with those in the control fruits, which was accompanied by a reduction in aldehyde and alcohol concentrations (p < 0.05 or p < 0.01). However, the treatments did not significantly influence the enzyme activity and expression of genes encoding the enzymes.

From Central to Specialized Metabolism: An Overview of Some Secondary Compounds Derived From the Primary Metabolism for Their Role in Conferring Nutritional and Organoleptic Characteristics to Fruit

Fruit flavor and nutritional characteristics are key quality traits and ones of the main factors influencing consumer preference. Central carbon metabolism, also known as primary metabolism, contributes to the synthesis of intermediate compounds that act as precursors for plant secondary metabolism. Specific and specialized metabolic pathways that evolved from primary metabolism play a key role in the plant's interaction with its environment. In particular, secondary metabolites present in the fruit serve to increase its attractiveness to seed dispersers and to protect it against biotic and abiotic stresses. As a consequence, several important organoleptic characteristics, such as aroma, color, and fruit nutritional value, rely upon secondary metabolite content. Phenolic and terpenoid compounds are large and diverse classes of secondary metabolites that contribute to fruit quality and have their origin in primary metabolic pathways, while the delicate aroma of ripe fruits is formed by a unique combination of hundreds of volatiles that are derived from primary metabolites. In this review, we show that the manipulation of primary metabolism is a powerful tool to engineer quality traits in fruits, such as the phenolic, terpenoid, and volatile content. The enzymatic reactions responsible for the accumulation of primary precursors are bottlenecks in the transfer of metabolic flux from central to specialized metabolism and should be taken into account to increase the yield of the final products of the biosynthetic pathways. In addition, understanding the connection and regulation of the carbon flow between primary and secondary metabolism is a key factor for the development of fruit cultivars with enhanced organoleptic and nutritional traits.

A comprehensive look into the volatile exometabolome of enteroxic and non-enterotoxic Staphylococcus aureus strains

Staphylococcal food poisoning is a disease that originates significant health and economic losses and is caused by Staphylococcus aureus strains able to produce enterotoxins. The aim of this work is to go further on the study of the volatile exometabolome of S. aureus using an advanced gas chromatographic technique. Enterotoxic and non-enterotoxic strains were assessed. The volatile exometabolome profile comprised 240 volatiles belonging to ten chemical families. This volatiles were mainly by-products of branched-chain amino acids and methionine degradation, pyruvate metabolism, diacetyl pathway, oxidative stress and carotenoid cleavage. Metabolites released by the first two pathways were produced in higher contents by the enterotoxic strains. This study add further insights to S. aureus volatile exometabolome, and also shows that by applying it, it is possible to distinguish strains of S. aureus by the number of produced enterotoxins, which is especially important from the food safety point of view.

1-MCP treatment affects peach fruit aroma metabolism as revealed by transcriptomics and metabolite analyses

1-methylcyclopropene (1-MCP) negatively affects peach aroma but the underlying molecular basis remains elusive. In this study, transcriptomics and metabolite analyses were carried out to investigate the regulatory mechanisms of 1-MCP on peach aroma from different standpoints: fatty acid (FA) metabolism, ethylene signal transduction and lipoxygenase/β-oxidation pathway during 20 °C storage. Results indicate that 1-MCP significantly postponed the ethylene climacteric peak appearance and reduced ethylene production through down-regulation of related biosynthesis and signal transduction genes including PpaSAMS1/2, PpaACS1/2, PpaACO1 together with PpaETR1/2, PpaERS1, PpaEIN4 and PpaCTR1. Decrease in the levels of FAs and PpaFADs was observed in treated fruit, except oleic acid and PpaFAD4/5, before day 5 of storage. In addition, 1-MCP-treated fruit also possessed higher levels of C6 aldehydes and alcohols and delayed the formation of volatile compounds characteristic of peach-like aroma by upregulation of PpaLOX1/2/3 and PpaHPL1 expression and down-regulation of PpaLOX5 expression. Our findings suggest that inhibition of peach-like volatiles and promotion of green-note volatiles by 1-MCP were associated with ethylene production and modulation of FA levels through transcriptional regulation.

Pollen trapping and sugar syrup feeding of honey bee (Hymenoptera: Apidae) enhance pollen collection of less preferred flowers

Pear (Pyrus bretschneideri) is characterized by being self-incompatible and dependent on cross-pollination to set fruit. Honeybee (Apis mellifera) is considered the most important pollinator of pear. Nevertheless, limited pollen transfer has been cited as the main cause of poor fruit set in many pear orchards. Here, we tested the following hypotheses: (i) colony manipulations increase the pollen collection tendency of honeybees and (ii) the proportion of pollen loads being returned to the hive is from the target plant. The technique reliably and rapidly estimates the pollination of honeybees tested under different colony manipulations: (1) using pollen trapping (PT); (2) PT with sugar syrup feeding (SS) (PTSS); (3) SS alone and (4) control without PT and SS. The results clearly show that the pollen collection of honeybees during the experiment was significantly affected (P < 0.05) by colony manipulations. The mean amount of pollen harvested daily was higher for PTSS (19.4 g) and PT (16.4 g) than for SS (12.85 g) and control (8.7 g) colonies. Therefore, PTSS was the most effective treatment for increasing pear pollen collection; other treatments such as PT and SS could also be useful. This study was important for determining how the behavior of honeybee colonies is shaped through colony manipulation to enhance pollen collection of less preferred pear flowers, which is critical when pollination is required.

Metabolomic profiling reveals that natural biodiversity surrounding a banana crop may positively influence the nutritional/sensorial profile of ripe fruits

This study is part of an extensive project that evaluated the effects of a natural ecosystem on a healthy banana crop and the quality of its fruit. In particular, the study examined the influence of the maintenance of natural biodiversity (Atlantic forest) near a conventional banana crop on the metabolic profiling of ripe banana fruits. Results revealed differences between ripe fruits harvested from plants near the natural forest (Near-NF) and fruits harvested in areas distant from the natural forest (Distant-NF). A total of 76 metabolites were identified in ripe banana fruits. Bananas harvested from Near-NF plot showed increased levels of γ-aminobutyric acid and reduced levels of putrescine compared with fruits from Distant-NF plot. Furthermore, fatty acids profile suggests that ripe fruits harvested from Near-NF plot had increased nutritional quality compared with fruits from Distant-NF plot. Multivariate statistical analysis revealed that these metabolites, which potentially influence the nutritional/sensorial quality of ripe fruits, also contributed to distinguishing fruits harvested from Near-NF and Distant-NF plots. Collectively, the results suggest that the natural biodiversity surrounding a crop area could benefit ripe banana nutritional/sensorial quality. The maintenance of natural forest fragments thus appears to be a promising tool for increasing the quality of fruit crops.

Two ω-3 FADs Are Associated with Peach Fruit Volatile Formation

Aroma-related volatiles, together with sugars and acids, play an important role in determining fruit flavor quality. Characteristic volatiles of peach fruit are mainly derived from fatty acids such as linoleic acid (18:2) and linolenic acid (18:3). In the present study, six genes encoding fatty acid desaturases (FAD) were cloned, including two ω-6 FAD genes (PpFAD2, PpFAD6) and four ω-3 FAD genes (PpFAD3-1, PpFAD3-2, PpFAD7 and PpFAD8). Heterologous expression of peach FADs in tobacco plants showed that PpFAD3-1, and PpFAD3-2 significantly reduced contents of 18:2, and accumulated significant higher levels of 18:3. In the case of volatiles, transgenic plants produced lower concentrations of hexanal and higher levels of (E)-2-hexenal. Consequently, the ratio of the (E)-2-hexenal and hexanal was about 5- and 3-fold higher than that of wild type (WT) in PpFAD3-1 and PpFAD3-2 transformants, respectively. No significant changes in volatile profiles were observed in transgenic plants overexpressing the four other peach FAD genes. Real-time quantitative polymerase chain reaction (qPCR) analysis showed that ripe fruit had high PpFAD3-1 and low PpFAD3-2 transcript levels. In contrast, high PpFAD3-2 and low PpFAD3-1 transcript levels were observed in young fruit. These results indicate a temporal regulation of these two ω-3 FADs during development and ripening, influencing peach fruit volatile formation.

Microwave-Assisted Synthesis of Cinnamyl Long Chain Aroma Esters

Cinnamyl long chain aroma esters were prepared by using the conventional and microwave-assisted methods. The esterification reaction of naturally occurring 3-phenyl-prop-2-en-1-ol and different chain lengths acidic and diol reagents was carried out at the temperature of 140 °C under solvent free conditions. As acidic reagents, oxolane-2,5-dione, oxane-2,6-dione, hexanedioic acid and decanedioic acid were applied. Ethane-1,2-diol and 2,2'-[oxybis(2,1-ethandiyloxy)]diethanol were used as diol reagents. The synthesis of high molecular mass cinnamyl esters under conventional method conditions requires a long time to obtain high yields. The studies confirm that by using microwave irradiation, it is possible to reduce the reaction times to only 10-20 min. The structures of prepared esters were confirmed on the basis of FTIR, 1H-NMR and 13C-NMR. In addition, the newly obtained cinnamyl long chain esters were tested for their thermal properties. The TG studies proved the high thermal resistance of the obtained esters under inert and oxidative conditions.