Effect of ripening and inter-cultivar differences on strawberry quality

Conductivity at varying frequencies as a method for differentiating strawberry ripeness and association with colour acceptance of strawberry nectars

BACKGROUND

Identifying the best strawberries to produce colour stable nectars is a priority for the juice industry. Although riper strawberries produce nectars with better colour stability, variability between cultivars means that surface colour cannot be used as a single quality attribute to determine stability. Conductivity and bio-impedance measurements can be used to differentiate ripeness of strawberries. The commercially available PEF Control System (ELEA) can measure cell disruption by measuring conductivity at different frequencies. Updated software measured strawberry conductivity at 121 frequencies between 100 Hz and 1 MHz to determine whether conductivity at these frequencies could differentiate ripeness, and be compared with the colour acceptance and stability of nectars produced from these strawberries.

RESULTS

A high-low ratio (HLR) was calculated by dividing the conductivity at frequency 1 MHz by conductivity at 1 kHz. HLR could be used to separate five strawberry ripeness stages, with decreasing HLR associated with increasing ripeness. HLR was then compared with the colour of nectars produced from these strawberries. Although there was a good correlation between HLR and an acceptable colour to consumers on initial production (r = -0.823, P < 0.001) and after 12 weeks of storage (-0.759, P < 0.001), cultivars differed greatly in both HLR and colour stability. Additionally, HLR had a strong correlation with firmness.

CONCLUSION

The PEF Control System could be used to differentiate ripeness of strawberries by HLR, and therefore was associated with colour stability. However, no additional information on colour stability was gained from conductivity beyond what could already be deduced from differentiating ripeness based on surface colour. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Development and Optimization Method for Determination of the Strawberries' Aroma Profile

The strawberry (genus Fragaria) is a plant from the rose family (Rosaceae). As the fruits are likely to be picked mechanically, they are grown close to consumption centers. The aim of this work was to develop a suitable method for detecting as many molecules as possible in order to be able to distinguish between different strawberry cultivars and geographical origins in the future. Whole strawberries of the "Albion" cultivar, grown in the Jagodica Purgerica region of Zagreb, were used. Gas chromatography-mass spectrometry (GC-MS) in SCAN mode was used to analyze the aroma profile and to determine the proportion of individual components. The samples were prepared and analyzed using the solid-phase microextraction method (SPME). The impact of SPME fiber selection and GC column type was investigated, as well as sample weight, ionic strength, agitation temperature, and sampling time. A higher ionic strength was achieved by adding a 20% NaCl solution to the sample. The aroma profile of the studied strawberry cultivar consisted of furanone, esters, aldehydes, and carboxylic acids. Optimal results were achieved by adjusting the ionic strength during 15 min of extraction and incubation. The individual compounds were identified using NIST, Wiley libraries, and the "area normalization" method.

Advances in strawberry postharvest preservation and packaging: A comprehensive review

Strawberries spoil rapidly after harvest due to factors such as the ripening process, weight loss, and, most importantly, microbial contamination. Traditionally, several methods are used to preserve strawberries after harvest and extend their shelf life, including thermal, plasma, radiation, chemical, and biological treatments. Although these methods are effective, they are a concern from the perspective of safety and consumer acceptance of the treated food. To address these issues, more advanced environment-friendly technologies have been developed over the past decades, including modified and controlled atmosphere packaging, active biopolymer-based packaging, or edible coating formulations. This method can not only significantly extend the shelf life of fruit but also solve safety concerns. Some studies have shown that combining two or more of these technologies can significantly extend the shelf life of strawberries, which could significantly contribute to expanding the global supply chain for delicious fruit. Despite the large number of studies underway in this field of research, no systematic review has been published discussing these advances. This review aims to cover important information about postharvest physiology, decay factors, and preservation methods of strawberry fruits. It is a pioneering work that integrates, relates, and discusses all information on the postharvest fate and handling of strawberries in one place. Additionally, commercially used techniques were discussed to provide insight into current developments in strawberry preservation and suggest future research directions in this field of study. This review aims to enrich the knowledge of academic and industrial researchers, scientists, and students on trends and developments in postharvest preservation and packaging of strawberry fruits.

Changes in the Aroma Profile and Phenolic Compound Contents of Different Strawberry Cultivars during Ripening

Secondary metabolites, namely, phenolic and volatile organic compounds, contribute to the nutritional and organoleptic quality of the strawberry fruit. This study focuses on the changes in the content of phenolic compounds and volatile organic compounds during the ripening, from green to overripe fruit, of five strawberry cultivars ('Asia', 'CIVN 766', 'Aprica', 'Clery', and 'Malwina'). Additionally, these changes are compared with the colour of the fruit and peroxidase and polyphenol oxidase activity. Our results show that the accumulation of secondary metabolites (phenolic and volatile organic compounds) significantly changed during the ripening process for all of the studied cultivars. As for phenolic compounds, flavanols and hydroxybenzoic acid derivatives comprised between 87 and 95% of the total phenolic compound content in unripe green fruit. In contrast, anthocyanins and hydroxycinnamic acid derivatives comprised between 64 and 77% of the total phenolic compound content in overripe fruit, except in the fruit of the cultivar 'CIVN766'. When it comes to the aroma profile, the content of aldehydes decreased by 24-49% as the fruit ripened, and the accumulation of esters increased. Our study also shows that the ripening process differs among cultivars, and it is therefore necessary to define ripening indicators separately for each cultivar.

Nano-selenium repaired the damage caused by fungicides on strawberry flavor quality and antioxidant capacity by regulating ABA biosynthesis and ripening-related transcription factors

Recently, studies have shown that pesticides may have adverse effects on the flavor quality of the fruits, but there is still a lack of appropriate methods to repair the damage. This study investigated the effects and mechanism of applying the emerging material, nano‑selenium, and two fungicides (Boscalid and Pydiflumetofen) alone or together on the flavor quality and antioxidant capacity of strawberries. The results showed that the two fungicides had a negative impact on strawberry color, flavor, antioxidant capacity and different enzymatic systems. The color damage was mainly attributed to the impact on anthocyanin content. Nano‑selenium alleviated the quality losses by increasing sugar-acid ratio, volatiles, anthocyanin levels, enzyme activities and DPPH scavenging ability and reducing ROS levels. Results also showed that these damage and repair processes were related to the regulation of flavor and ripening related transcription factors (including FaRIF, FaSnRK1, FaMYB10, FaMYB1, FaSnRK2.6 and FaABI1), the upregulation of genes on sugar-acid, volatile, and anthocyanin synthesis pathways, as well as the increase of sucrose and ABA signaling molecules. In addition, the application of nano-Se supplemented the selenium content in fruits, and was harmless to human health. This information is crucial for revealing the mechanisms of flavor damage caused by pesticides to strawberry and the repaired of nano‑selenium, and broadens the researching and applying of nano‑selenium in repairing the damage caused by pesticides.

Early detection of Botrytis cinerea in strawberry fruit during quiescent infection using selected ion flow tube mass spectrometry (SIFT-MS)

Botrytis cinerea is a devastating pathogen that can cause huge postharvest losses of strawberry. Although this fungus usually infects strawberries through their flowers, symptoms mainly appear when fruit are fully mature. A fast and sensitive method to detect and quantify the fungal infection, prior to symptom development, is, therefore, needed. In this study, we explore the possibility of using the strawberry volatilome to identify biomarkers for B. cinerea infection. Strawberry flowers were inoculated with B. cinerea to mimic the natural infection. First, quantitative polymerase chain reaction (qPCR) was used to quantify B. cinerea in the strawberry fruit. The detection limit of qPCR for B. cinerea DNA extracted from strawberries was 0.01 ng. Subsequently, changes in the fruit volatilome at different fruit developmental stages were characterized using gas chromatography - mass spectrometry (GC-MS) and selected ion flow tube mass spectrometry (SIFT-MS). Based on GC-MS data, 1-octen-3-ol produced by B. cinerea was confirmed as a potential biomarker of B. cinerea infection. Moreover, the product ion NO⁺ 127, obtained by SIFT-MS measurements, was proposed as a potential biomarker for B. cinerea infection by comparing its relative level with that of 1-octen-3-ol (obtained by GC-MS) and B. cinerea (obtained by qPCR). Separate PLS regressions were carried out for each developmental stages, and 11 product ions were significantly altered at all developmental stages. Finally, PLS regressions using these 11 ions as variables allowed the discrimination between samples containing different amount of B. cinerea. This work showed that profiling the fruit's volatilome using SIFT-MS can be used as a potential alternative to detect B. cinerea during the quiescent stage of B. cinerea infection prior to symptom development. Moreover, the corresponding compounds of potential biomarkers suggest that the volatile changes caused by B. cinerea infection may contribute to strawberry defense.

"How sweet are your strawberries?": Predicting sugariness using non-destructive and affordable hardware

Global soft fruit supply chains rely on trustworthy descriptions of product quality. However, crucial criteria such as sweetness and firmness cannot be accurately established without destroying the fruit. Since traditional alternatives are subjective assessments by human experts, it is desirable to obtain quality estimations in a consistent and non-destructive manner. The majority of research on fruit quality measurements analyzed fruits in the lab with uniform data collection. However, it is laborious and expensive to scale up to the level of the whole yield. The "harvest-first, analysis-second" method also comes too late to decide to adjust harvesting schedules. In this research, we validated our hypothesis of using in-field data acquirable via commodity hardware to obtain acceptable accuracies. The primary instance that the research concerns is the sugariness of strawberries, described by the juice's total soluble solid (TSS) content (unit: °Brix or Brix). We benchmarked the accuracy of strawberry Brix prediction using convolutional neural networks (CNN), variational autoencoders (VAE), principal component analysis (PCA), kernelized ridge regression (KRR), support vector regression (SVR), and multilayer perceptron (MLP), based on fusions of image data, environmental records, and plant load information, etc. Our results suggest that: (i) models trained by environment and plant load data can perform reliable prediction of aggregated Brix values, with the lowest RMSE at 0.59; (ii) using image data can further supplement the Brix predictions of individual fruits from (i), from 1.27 to as low up to 1.10, but they by themselves are not sufficiently reliable.

Insights into the Mechanism of Flavor Loss in Strawberries Induced by Two Fungicides Integrating Transcriptome and Metabolome Analysis

Consumers have been complaining about the deterioration of the flavor of strawberries. The use of pesticides could have potential impacts on fruit flavor but the mechanisms are unclear. Here, we spayed boscalid and difenoconazole on the small green fruit of strawberries to investigate their effect on fruit flavor quality and the mechanism. The results indicated that both fungicides decreased the contents of soluble sugar and nutrients but increased acids in mature fruits, changed the levels of volatiles, and caused oxidative damage, which ultimately reduced the flavor quality of strawberries, and the negative effect of boscalid was greater. Combined with transcriptome and metabolome, boscalid altered the genes in sugar-acid metabolism (SUT, SPS, and INV), volatiles (FaQR, FaOMT, FaLOX, and FaAAT), and amino acid synthesis pathways and metabolites. This study elaborated on the effects of fungicides on the flavor quality of strawberries from physiological-biochemical and molecular levels and laid the foundation for improving the strawberry flavor quality.

Changes in Volatile Compounds in Short-Term High CO2-Treated 'Seolhyang' Strawberry (Fragaria × ananassa) Fruit during Cold Storage

'Seolhyang' strawberry is harvested before it is fully ripened and treated with CO₂ to extend the shelf-life. However, the volatile changes in the 'Seolhyang' strawberry after short-term CO₂ treatment have not been investigated, although the volatile profile is an important quality attribute. Herein, we investigated the effect of short-term high CO₂ treatment on the changes in the composition of volatile compounds in 'Seolhyang' strawberries at two ripening stages (i.e., half-red and bright-red) during cold storage using headspace solid-phase microextraction and gas chromatography-mass spectrometry. Furthermore, the effect of CO₂ treatment on fruit quality with respect to the aroma was investigated. A total of 30 volatile compounds were identified. Storage increased the volatile compound concentrations, and the total concentration of volatiles in the CO₂-treated strawberries was lower than that of the untreated strawberries during storage. The production of some characteristic strawberry volatiles (e.g., 4-methoxy-2,5-dimethyl-3(2H)-furanone) was inhibited in CO₂-treated strawberries. However, CO₂ treatment helped maintain the concentrations of hexanal and 2-hexenal, which are responsible for the fresh odor in strawberries. Interestingly, CO₂ treatment suppressed the production of off-odor volatiles, acetaldehyde, and hexanoic acid during strawberry storage. Thus, short-term CO₂ treatment may help maintain the fresh aroma of strawberries during cold storage.

Integrated metabolomic and transcriptomic analysis reveals factors underlying differences in fruit quality between Fragaria nilgerrensis and Fragaria pentaphylla

BACKGROUND

Strawberries have become one of the most popular fruits because of their unique flavor and high nutritional value. Fruit quality and price are the most important criteria that determine consumer acceptability. Fragaria nilgerrensis and Fragaria pentaphylla are two wild Asian diploid strawberry species that differ in fruit color, taste, and aroma. To understand the molecular mechanisms involved in the formation of high-quality strawberry fruit, we integrated transcriptomics and metabolomics research methods to compare the metabolic and biosynthetic mechanisms of the two Fragaria species.

RESULTS

F. nilgerrensis fruit has higher amino acid and lipid contents and a higher sugar-to-acid ratio than F. pentaphylla fruit does, underlying their superior nutritional value, aroma, firmness, and taste. Compared with F. nilgerrensis fruit, F. pentaphylla fruit contained more flavonoids, indicating its enhanced color and health benefits. In addition, candidate structural genes that regulate the biosynthesis of flavonoids, amino acids, and glycerophospholipids in the two strawberry fruit were screened.

CONCLUSIONS

The differences in aroma, firmness, and taste between F. nilgerrensis fruit and F. pentaphylla fruit are probably due to differences in their amino acid and lipid contents, as well as the difference in their sugar-to-acid ratios. Eight key structural genes that may play important roles in the biosynthesis of amino acids, lipids, and flavonoids were identified. © 2021 Society of Chemical Industry.

Polymorphism of the FaOMT and FaFAD1 genes for fruit flavor volatiles in strawberry varieties and wild species from the genetic collection of the Michurin Federal Research Center

Fruit aroma is an important consumer attribute of strawberry varieties. The key volatile compounds of the aromatic complex of strawberry fruit are mesifurane (fruity and caramel aromas) and γ-decalactone (fruity, sweet, or peachy aroma). The mesifurane content in strawberry fruit is controlled by the FaOMT gene, which is mapped to the distal region of the long arm of chromosome VII-F.1. The γ-decalactone content in strawberry fruit is controlled by the FaFAD1 gene, mapped to the distal region of the long arm of chromosome III-2. Identification of forms carrying genes for fruit flavor volatiles is an important step in breeding varieties with fragrant fruit. The use of molecular markers allows highly reliable detection of target gene alleles in a genome at early developmental stages. This study involves molecular genotyping of Fragaria L. varieties for the FaOMT and FaFAD1 genes, analysis of polymorphism of the loci in question, and identification of genotypes valuable for breeding. The objects of our study were wild species of the genus Fragaria L. and strawberry varieties (Fragaria × ananassa Duch.) of different ecological and geographic origins. To assess the allelic states of the FaOMT gene, the codominant marker FaOMT-SI/NO was used, and for the FaFAD1 gene, the dominant marker FaFAD1. The functional allele of the FaOMT gene (FaOMT+) in the heterozygous state (FaOMT+FaOMT– genotype) was detected in 34.9 % of the accessions tested. The functional allele of the FaOMT gene in the homozygous state (FaOMT+FaOMT+ genotype) was detected in 51.2 % of the accessions. The homozygous state of the inactive allele (FaOMT–FaOMT– genotype) was detected in 13.9 % of the studied strawberry accessions. The FaFAD1 gene was identified in 25.6 % of the analyzed collection of strawberry genotypes, including the wild species F. orientalis Los., F. moschata Duch., F. ovalis Rydb. The combination of functional alleles of the FaOMT and FaFAD1 genes was detected in 16.3 % of the analyzed forms. The wild species F. orientalis Los. and F. moschata Duch. and strawberry variety Red Gauntlet combine the functional allele of the FaFAD1 gene with the homozygous state of the active allele of the FaOMT gene; therefore, we recommend them as promising sources of high contents of mesifurane and γ-decactone in fruit in breeding programs for fruit aroma.

Assessing Volatiles in Three Chinese Dwarf Cherry Cultivars during Veraison and Maturation Using Headspace-Solid Phase Microextraction with Gas Chromatography-Mass Spectrometry

Chinese dwarf cherry is a native shrub in northwest China with a rich and unique fruit aroma. This study aims to determine the changes in volatile profiles during the maturation period, which provides a theoretical basis for the optimal harvest times and the breeding of aroma-rich varieties. The variation in the production of 164 volatile compounds from three Chinese dwarf cherry cultivars, namely, "Jing'ou 1", "Jing'ou 2", and "Jing'ou 3", were investigated by headspace-solid phase microextraction (HS-SPME)-GC-MS. These volatiles mainly constituted alcohols, carbonyls, esters, terpenoids, and hydrocarbons. Their maturation process could be divided into three stages, namely prophase, metaphase, and anaphase. Prophase contained an abundance of hydrocarbons and carbonyls, primarily benzaldehyde being dominant among all volatiles. During metaphase, volatiles remained at a low level of abundance and diversity. Anaphase coincided with full maturation and was associated with esters and terpenoids; in particular, "Jing'ou 3" presented more compound diversity and a high level of acetate esters. The periods including the week prior to veraison and the week during maturation were particularly critical in volatile formation in Chinese dwarf cherries. This study reveals that the low level or lack of hexanal might be one of the distinctive characteristics separating Chinese dwarf cherries from other Cerasus or Rosaceae fruits.

Analysis of flavor and taste attributes differences treated by chemical preservatives: a case study in strawberry fruits treated by 1-methylcyclopropene and chlorine dioxide

Flavor and taste attributes of fruits varied by different preservatives treatments. Changes in sugars, organic acids, amino acids as well as volatiles of strawberries treated with 1-methylcyclopropene (1-MCP) and/or chlorine dioxide (ClO₂) were evaluated during storage period in this study. Our results revealed that the decreases of tartaric acid, malic acid, citric acid, titratable acidity (TA), sucrose and soluble sugar contents were significantly inhibited by 1-MCP + ClO₂. The fructose and glucose contents of all groups remained stable and slightly increased at the last period of 10 days. However, different treatments had no influence on content of succinic acid. Moreover, the highest sweet taste (77.37 mg 100 g^-1 fresh weight) and lowest bitter taste (3.44 mg 100 g^-1 fresh weight) free amino acids (FAA) were observed in the strawberries treated by 1-MCP combined with ClO₂ treatment as compared to other treatments and control. (E)-2-hexenal was the most abundant volatile and showed a significant increase trend during strawberry storage. More interestingly, ethyl butyrate, fruit-like aroma, could be recovered in content by 1-MCP, ClO₂ alone and their combination treatment. Compared with other treatments, the significant different flavor in ClO₂ treatment was identified by principle component analysis. In addition, methyl hexanoate and 4-methoxy-2,5-dimethylfuran-3(2H)-one (DMMF) were the major factors that affected the volatile organic compounds (VOCs) of strawberries through the whole storage. Taken together, 1-MCP coupled with ClO₂ could be a complex preservative to maintain strawberries quality by regulating the flavor and taste attributes.

Metabolic Profile of Strawberry Fruit Ripened on the Plant Following Treatment With an Ethylene Elicitor or Inhibitor

Strawberry is the most studied nonclimacteric fruit for understanding the role ethylene has in ripening regulation. However, previous studies on the effects of ethylene on strawberry ripening were conducted with detached fruit. Thus, the aim of this work was to determine the effect of ethylene and the ethylene-action inhibitor 1-methylcyclopropene (1-MCP) applied at different developmental stages on important physical-chemical attributes of ripe 'Albion' strawberry. Fruit at four developmental stages that remained attached to the plant were dipped in one of three treatment solutions (Ethephon, 1-methylcyclopropene, and water), plus one absolute control that received no dip. Following treatment, when immature fruit were fully red or 24 h after treatment for red-treated fruit, strawberry fruit were assessed for physicochemical properties (mass, length, diameter, firmness, color, titratable acidity, soluble solids, pH, total phenolics, sugar, organic acid, amino acid, and volatile composition). The days following treatment required for fruit to ripen were also recorded. Treatments did not affect the rate of ripening nor fruit color, titratable acidity, pH, soluble solids, total phenolics, sugars, or organic acids of ripe fruit. Ethephon affected fruit mass, diameter, length, firmness, anthocyanins, amino acids, and volatiles, but these effects were dependent on fruit developmental stage at which the treatment was applied. When green fruit were treated with ethephon, ripe fruit had larger diameter and mass. Ethephon treatment of white fruit resulted in ripe fruit having greater anthocyanin content. Treatment of pink fruit resulted in ripe fruit having smaller diameter, length, and mass and greater firmness. Treatment of red fruit with ethephon altered fruit volatile composition, increasing concentrations of ethyl- and acetate-esters, which were reduced by the 1-MCP treatment. Ethephon treatment increased concentrations of 11 of the 19 free amino acids measured in ripe fruit with treatment of green and white fruit having the greatest effect. A total of 41 volatile compounds had significant correlations with 14 amino acids. While ethylene did not stimulate typical ripening of strawberry fruit, it does appear to alter fruit development and metabolism. The physiological effects of ethylene on strawberry fruit appear to depend on the developmental stage of the fruit.

Volatile Profiling of Strawberry Fruits Cultivated in a Soilless System to Investigate Cultivar-Dependent Chemical Descriptors

Volatile compounds are essential for food organoleptic characteristics and of great utility for the food industry as potential markers for authenticity purposes (e.g., variety, geographical origin, adulteration). The aim of this study was to determine the characteristic volatile compounds of strawberry samples grown in a soilless system by using headspace solid phase micro-extraction coupled with gas chromatography and to investigate the influence of cultivar (Festival, Candonga, Camarosa) on this volatile profile. We observed that Festival and, to a lesser extent, Candonga varieties were characterized by the richest aroma-related profiles, including higher levels of esters, furanones and terpenes. In particular, methyl butyrate, hexyl hexanoate, linalool, geraniol and furaneol were the most abundant aromatic compounds detected in the three varieties of strawberries. Complementarily, the application of pattern recognition chemometric approaches, including principal component analysis and linear discriminant analysis, demonstrated that concentrations of specific volatiles can be employed as chemical descriptors to discriminate between strawberry cultivars. Accordingly, geraniol and hexyl hexanoate were found to be the most significant volatiles for the discrimination of strawberry varieties.

Evaluation and optimization of air-based precooling for higher postharvest quality: literature review and interdisciplinary perspective

Precooling is of significant importance for postharvest fruits and vegetables to control the quality degradation and prolong the shelf-life. Current precooling methods include room cooling, forced-air cooling, hydrocooling, vacuum cooling, contact or package icing, and cryogenic cooling, all of which have their advantages and disadvantages. The first two methods with the cooling medium of air are extensively used because of the wide applicable range of fruits and vegetables. Numerous studies have been devoted to cope with the drawbacks of these two air-based precooling methods with various evaluation criteria and optimization methods. A systematic literature review on these studies is firstly conducted with respect to experimental and numerical investigations respectively for the two methods. The main contributions from the previous studies are also summarized respectively with the research objectives and performance metrics. The literature review indicates that the current performance evaluation is limited to apparent parameters and the optimal design is only proposed based on the performance evaluation and comparison. Furthermore, with inspiration from the research in other domains, a scheme of advanced evaluation and optimization for air-based precooling methods is proposed with thermodynamic evaluation metrics and constructal optimization methods from the interdisciplinary perspective.

Fragaria Genus: Chemical Composition and Biological Activities

The strawberries represent in our days one of the main fresh fruits consumed globally, inevitably leading to large amounts of by-products and wastes. Usually appreciated because of their specific flavor, the strawberries also possess biological properties, including antioxidant, antimicrobial, or anti-inflammatory effects. In spite of the wide spread of the Fragaria genus, few species represent the subject of the last decade scientific research. The main components identified in the Fragaria species are presented, as well as several biological properties, as emerging from the scientific papers published in the last decade.

Effect of Mesoporous Silica Nanoparticles on The Physicochemical Properties of Pectin Packaging Material for Strawberry Wrapping

Citrus peel pectin was used to prepare films (cast with or without glycerol) containing mesoporous silica nanoparticles. Nanoparticles reduced significantly the particle size, and had no effect on the Zeta potential of pectin solutions. Mechanical characterization demonstrates that pectin+nanoparticles containing films slightly increased tensile strength and significantly decreased the Young's modulus in comparison to films made only of pectin. However, elongation at the break increased in the pectin+nanoparticles films cast in the presence of glycerol, while both Young's modulus and tensile strength were reduced. Moreover, nanoparticles were able to reduce the barrier properties of pectin films prepared with or without glycerol, whereas positively affected the thermal stability of pectin films and the seal strength. The 0.6% pectin films reinforced or not with 3% nanoparticles in the presence of 30% glycerol were used to wrap strawberries in order to extend the fruit's shelf-life, over a period of eighty days, by improving their physicochemical properties.

Novel Strategy to Decipher the Regulatory Mechanism of 1-Naphthaleneacetic Acid in Strawberry Maturation

1-Naphthaleneacetic acid (NAA) has long been used to regulate strawberry growth. However, its regulatory mechanisms are unclear. Here, a nuclear magnetic resonance (NMR)-based metabolomics approach was utilized to capture differential metabolites, then matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and transcriptomics as assisted methods to validate the significant findings of metabolomics. The metabolomics results suggested that NAA regulated strawberry growth via multiple metabolic pathways, and different NAA application times also influenced these regulatory effects. We also found an interesting phenomenon that citric acid had completely opposite changes when NAA was sprayed at two different ripening stages of the strawberries. Furthermore, MALDI-TOF MS validated the changes of citric acid and transcriptomics identified the related genes. The study demonstrated that the novel strategy of "metabolomics capture-MALDI-TOF MS and transcriptomics assisted validation" could offer a fresh insight for understanding the mechanism of the plant growth regulator in strawberry maturation.

A Comparison of Temporal Dominance of Sensation (TDS) and Quantitative Descriptive Analysis (QDA™) to Identify Flavors in Strawberries

Temporal dominance of sensations (TDS) is a rapid descriptive method that offers a different magnitude of information to traditional descriptive analysis methodologies. This methodology considers the dynamic nature of eating, assessing sensory perception of foods as they change throughout the eating event. Limited research has applied the TDS methodology to strawberries and subsequently validated the results against Quantitative Descriptive Analysis (QDA™). The aim of this research is to compare the TDS methodology using an untrained consumer panel to the results obtained via QDA™ with a trained sensory panel. The trained panelists (n = 12, minimum 60 hr each panelist) were provided with six strawberry samples (three cultivars at two maturation levels) and applied QDA™ techniques to profile each strawberry sample. Untrained consumers (n = 103) were provided with six strawberry samples (three cultivars at two maturation levels) and required to use TDS methodology to assess the dominant sensations for each sample as they change over time. Results revealed moderately comparable product configurations produced via TDS in comparison to QDA™ (RV coefficient = 0.559), as well as similar application of the sweet attribute (correlation coefficient of 0.895 at first bite). The TDS methodology however was not in agreement with the QDA™ methodology regarding more complex flavor terms. These findings support the notion that the lack of training on the definition of terms, together with the limitations of the methodology to ignore all attributes other than those dominant, provide a different magnitude of information than the QDA™ methodology.

PRACTICAL APPLICATION

A comparison of TDS to traditional descriptive analysis indicate that TDS provides additional information to QDA™ regarding the lingering component of eating. The QDA™ results however provide more precise detail regarding singular attributes. Therefore, the TDS methodology has an application in industry when it is important to understand the lingering profile of products. However, this methodology should not be employed as a replacement to traditional descriptive analysis methods.

Deciphering genetic factors that determine melon fruit-quality traits using RNA-Seq-based high-resolution QTL and eQTL mapping

Combined quantitative trait loci (QTL) and expression-QTL (eQTL) mapping analysis was performed to identify genetic factors affecting melon (Cucumis melo) fruit quality, by linking genotypic, metabolic and transcriptomic data from a melon recombinant inbred line (RIL) population. RNA sequencing (RNA-Seq) of fruit from 96 RILs yielded a highly saturated collection of > 58 000 single-nucleotide polymorphisms, identifying 6636 recombination events that separated the genome into 3663 genomic bins. Bin-based QTL analysis of 79 RILs and 129 fruit-quality traits affecting taste, aroma and color resulted in the mapping of 241 QTL. Thiol acyltransferase (CmThAT1) gene was identified within the QTL interval of its product, S-methyl-thioacetate, a key component of melon fruit aroma. Metabolic activity of CmThAT1-encoded protein was validated in bacteria and in vitro. QTL analysis of flesh color intensity identified a candidate white-flesh gene (CmPPR1), one of two major loci determining fruit flesh color in melon. CmPPR1 encodes a member of the pentatricopeptide protein family, involved in processing of RNA in plastids, where carotenoid and chlorophyll pigments accumulate. Network analysis of > 12 000 eQTL mapped for > 8000 differentially expressed fruit genes supported the role of CmPPR1 in determining the expression level of plastid targeted genes. We highlight the potential of RNA-Seq-based QTL analysis of small to moderate size, advanced RIL populations for precise marker-assisted breeding and gene discovery. We provide the following resources: a RIL population genotyped with a unique set of SNP markers, confined genomic segments that harbor QTL governing 129 traits and a saturated set of melon eQTLs.

Historical Review on the Identification of Mesifurane, 2,5-Dimethyl-4-methoxy-3(2 H)-furanone, and Its Occurrence in Berries and Fruits

Mesifurane, 2,5-dimethyl-4-methoxy-3(2 H)-furanone, is a natural compound used a worldwide as a flavoring for foods, beverages, and cosmetics. Global sales of mesifurane are around $100 million. Its significance as a flavor-impact compound in some Nordic berries was discovered in the early 1970s in Finland. Synthesized mesifurane was used as a key compound in aroma mixes exploited in a Finnish patent. Mesifurane is a significant flavorant in arctic brambles, mangoes, strawberries, and many other fruits and berries and is an enzymatic methylation product of 2,5-dimethyl-4-hydroxy-3(2 H)-furanone. Because of the obscurity of the information on the history of the commonly used trivial name, mesifurane, it is time to lift the veil and reveal the background of the present situation. The key player was a northern berry, arctic bramble ( Rubus arcticus), the Finnish name of which is mesimarja. Forty years ago, aroma research was limited by technical factors, but nowadays there is a surplus of information.

Identification of volatile compound markers during the ripening and senescence of lulo (Solanum quitoense Lam.)

Lulo (Solanum quitoense Lam.) is an exotic fruit cultivated in Colombia. During ripening and senescence, this climactic fruit undergoes biochemical processes that produce the volatiles responsible for its aroma. This study aimed to evaluate the changes in the volatile content during the ripening and senescence of lulo. Analysis of the volatile composition of lulo harvested in each of its five ripening stages and during its senescence time when stored at 18 ± 2 °C was performed using HS-SPME with GC-MS. Throughout ripening, the most notable change was the transformation of alcohols such as (Z)-3-hexen-1-ol and 1-penten-3-ol to afford esters such as (Z)-3-hexenyl acetate and ketones such as 1-penten-3-one. Some acids reacted with alcohols to produce acetate and hexanoate esters, concentrations which increased more than sixfold between stage one and five. Moreover, all the major compounds were C₆ straight chain compounds related to the lipoxygenase pathway. During senescence, majority of compounds were methyl esters, which increased in concentration consistently until day eight. Remarkably, the content of methyl butanoate increased from 0.9% of the total amount of volatiles on day two up to 76.4% on day eight. Some of these volatiles are probably contributors to the "off flavor" during senescence.

Aroma Profile of Rubus ulmifolius Flowers and Fruits During Different Ontogenetic Phases

The chemical composition of spontaneous volatile emission from Rubus ulmifolius flowers and fruits during different stages of development was evaluated by HS-SPME-GC/MS. In total, 155 chemical compounds were identified accounting 84.6 - 99.4% of whole aroma profile of flowers samples and 92.4 - 96.6% for fruit samples. The main constituents were α-copaene, β-caryophyllene, germacrene D, (E,E)-α-farnesene, 1,7-octadien-3-one,2-methyl-6-methylene, tridecane, (E)-2-hexenol acetate, (E)-3-hexenol acetate and cyperene. The results give a chemotaxonomic contribution to the characterization of the VOCs emitted from flowers and fruits during their ontogenic development.

Validation of reference genes for accurate normalization of gene expression for real time-quantitative PCR in strawberry fruits using different cultivars and osmotic stresses

The increasing demand of strawberry (Fragaria×ananassa Duch) fruits is associated mainly with their sensorial characteristics and the content of antioxidant compounds. Nevertheless, the strawberry production has been hampered due to its sensitivity to abiotic stresses. Therefore, to understand the molecular mechanisms highlighting stress response is of great importance to enable genetic engineering approaches aiming to improve strawberry tolerance. However, the study of expression of genes in strawberry requires the use of suitable reference genes. In the present study, seven traditional and novel candidate reference genes were evaluated for transcript normalization in fruits of ten strawberry cultivars and two abiotic stresses, using RefFinder, which integrates the four major currently available software programs: geNorm, NormFinder, BestKeeper and the comparative delta-Ct method. The results indicate that the expression stability is dependent on the experimental conditions. The candidate reference gene DBP (DNA binding protein) was considered the most suitable to normalize expression data in samples of strawberry cultivars and under drought stress condition, and the candidate reference gene HISTH4 (histone H4) was the most stable under osmotic stresses and salt stress. The traditional genes GAPDH (glyceraldehyde-3-phosphate dehydrogenase) and 18S (18S ribosomal RNA) were considered the most unstable genes in all conditions. The expression of phenylalanine ammonia lyase (PAL) and 9-cis epoxycarotenoid dioxygenase (NCED1) genes were used to further confirm the validated candidate reference genes, showing that the use of an inappropriate reference gene may induce erroneous results. This study is the first survey on the stability of reference genes in strawberry cultivars and osmotic stresses and provides guidelines to obtain more accurate RT-qPCR results for future breeding efforts.

Nutritional and nutraceutical quality of strawberries in relation to harvest time and crop conditions

Three strawberry varieties cultivated in soilless systems were studied for their content of primary and secondary metabolites in relation to harvest time and crop conditions. The three varieties were chosen based on their sensitivity level to environmental stress: Palomar (very sensitive), Festival (sensitive), and Camarosa (resistant). Throughout the campaign, three samplings were performed: December (extra-early production), January, and March (early production). Differences among cultivars and harvest times were observed based on the contents of sugars, organic acids, phenolic compounds, and antioxidant capacity. The higher levels for total anthocyanins and flavan-3-ols were found in Camarosa and Festival strawberries, both in the January harvest. The Palomar variety showed higher total sugar/total organic acids ratio in the March harvest. The influence of cultivation practices and environmental conditions was assessed by nested ANOVA and PLS-DA. Differences in the sugar and phenolic content were observed depending upon variety and coverage type. TEAC was most influenced by the substrate type.

Influence of cultivar and culture system on nutritional and organoleptic quality of strawberry

BACKGROUND

Strawberries are widely appreciated and consumed as a pleasant-tasting fruit either in fresh form or as processed product. Of the many factors which can affect the quality of fruit (sensorial and nutritional), the cultivar is especially important, but it is also affected by crop conditions. The main characteristics related to the fruit quality and nutritional attributes were assessed in several varieties of strawberry grown in soilless and soil culture. The effect of different cultivars and cropping systems on selected quality parameters, were assessed by applying multivariate statistical methods, such as principal component analysis and partial least square discriminant analysis (PLS-DA).

RESULTS

Differences among cultivars were observed based on the mineral composition and glucose and fructose concentrations in both cultivation systems. However, no significant differences between cultivars were detected in sourness. Tamar and Camarosa were the sweetest cultivars among those grown in soilless and soil system, respectively. Both varieties also had the highest total sugars/total acids ratio. The comparison between strawberries cultivated in soil and soilless systems also revealed significant differences in the mineral composition, content of sugars and related parameters.

CONCLUSION

Good discrimination was observed between cultivars of conventional crops, whereas no clear separation between cultivars grown in the soilless system was achieved by PLS-DA. PLS-DA also allowed differentiation of samples by type of crop (soilless vs. conventional crop). This information could be useful for selection of growing conditions and high-quality cultivars.

Evaluation of the sensory characteristics of strawberry cultivars throughout the harvest season using projective mapping

BACKGROUND

Strawberry breeding programs should be able to rely on valid and simple methodologies for evaluating sensory quality of new cultivars. In this context, the aim of the present work was to evaluate the applicability of a simple sensory methodology, named projective mapping, to evaluate the sensory characteristics of strawberry cultivars and advanced selections throughout the harvest season. Three strawberry cultivars and two advanced selections were evaluated by an untrained assessor panel using projective mapping in three different moments of the harvest season: June (early season), August (mid-season) and September (peak harvest). Instrumental measurements were also performed.

RESULTS

Projective mapping enabled the identification of the main sensory characteristics of the strawberry cultivars and advanced selections, as well as the similarities and differences among them. Sensory characteristics of the five evaluated strawberry cultivars and advanced selections largely varied throughout the harvest season. Simple instrumental measurements were not able to predict the sensory characteristics of the strawberry cultivars, suggesting the importance of sensory methodologies for the evaluation of new cultivars in breeding programs.

CONCLUSIONS

Projective mapping consisted of a quick alternative for the evaluation of new cultivars relative to standard commercial cultivars. Its main advantage is that a large number of cultivars can be screened with minimal investment of time and resources.