Editorial: Bioactive Compounds Biosynthesis and Metabolism in Fruit and Vegetables

Metabolomics-Driven Mining of Metabolite Resources: Applications and Prospects for Improving Vegetable Crops

Vegetable crops possess a prominent nutri-metabolite pool that not only contributes to the crop performance in the fields, but also offers nutritional security for humans. In the pursuit of identifying, quantifying and functionally characterizing the cellular metabolome pool, biomolecule separation technologies, data acquisition platforms, chemical libraries, bioinformatics tools, databases and visualization techniques have come to play significant role. High-throughput metabolomics unravels structurally diverse nutrition-rich metabolites and their entangled interactions in vegetable plants. It has helped to link identified phytometabolites with unique phenotypic traits, nutri-functional characters, defense mechanisms and crop productivity. In this study, we explore mining diverse metabolites, localizing cellular metabolic pathways, classifying functional biomolecules and establishing linkages between metabolic fluxes and genomic regulations, using comprehensive metabolomics deciphers of the plant’s performance in the environment. We discuss exemplary reports covering the implications of metabolomics, addressing metabolic changes in vegetable plants during crop domestication, stage-dependent growth, fruit development, nutri-metabolic capabilities, climatic impacts, plant-microbe-pest interactions and anthropogenic activities. Efforts leading to identify biomarker metabolites, candidate proteins and the genes responsible for plant health, defense mechanisms and nutri-rich crop produce are documented. With the insights on metabolite-QTL (mQTL) driven genetic architecture, molecular breeding in vegetable crops can be revolutionized for developing better nutritional capabilities, improved tolerance against diseases/pests and enhanced climate resilience in plants.

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.

Fractional Separation and Characterization of Cuticular Waxes Extracted from Vegetable Matter Using Supercritical CO2

Cuticular waxes can be used in high-value applications, including cosmetics, foods and nutraceuticals, among the others. The extraction process determines their quality and purity that are of particular interest when biocompatibility, biodegradability, flavor and fragrance are the main features required for the final formulations. This study demonstrated that supercritical fluid extraction coupled with fractional separation can represent a suitable alternative to isolate cuticular waxes from vegetable matter that preserve their natural properties and composition, without contamination of organic solvent residues. Operating in this way, cuticular waxes can be considered as a fingerprint of the vegetable matter, where C27, C29 and C31 are the most abundant compounds that characterize the material; the differences are mainly due to their relative proportions and the presence of hydrocarbon compounds possessing other functional groups, such as alcohols, aldehydes or acids. Therefore, selectivity of supercritical fluid extraction towards non-polar or slightly polar compounds opens the way for a possible industrial approach to produce extracts that do not require further purification steps.

Total Phenolic, Anthocyanins HPLC-DAD-MS Determination and Antioxidant Capacity in Black Grape Skins and Blackberries: A Comparative Study

Anthocyanins are flavonoids with an antioxidant effect. They are the pigments that give rich colours to berries, red onions, pomegranates, and grapes. In addition to acting as antioxidants and fighting free radicals, anthocyanins may offer anti-inflammatory, anti-viral, and anti-cancer benefits. Among various types of fruits, blackberries and grapes are distinguished by their rich content in polyphenols, including anthocyanins. The purpose of this study was the identification and quantification of the anthocyanins in black grape skins and blackberries, but also the determination of the total phenolic content and total antioxidant capacity. The grape skins and blackberry extracts were prepared by an ultrasound-assisted acidified ethanol and methanol extraction method, with the 80% methanol solution being the most effective. Alcoholic extracts of blackberries and grape skins were analysed by the HPLC-DAD-MS method. There were five glycosylated anthocyanin compounds in blackberries, eight glycosylated anthocyanins compounds, and seven fragments of anthocyanin derivatives in grape skins identified. It was concluded that the anthocyanin profile of blackberries and grapes revealed mainly anthocyanin monoglycosides and acetylglycosides. Cyanidin-3-glucoside was the main component (86.49%) in blackberries, while, in the grape skins, the main component was delphinidin-3-O-glucoside (about 40.64%). Principal component analysis (PCA) was carried out on the basis of the 13 identified compounds in order to separate the extracts and describe the anthocyanins characteristics of different groups, the findings being in agreement with the experimental results. Compared to methanol extracts, ethanol extracts showed higher antioxidant activity, being related to the total phenolic content for the blackberries. Overall, the obtained results indicated that the blackberries and grapes skins possessed a high antioxidant content, similar to other berries, highlighting their potential use as fresh functional foods or fruit-derived products.

Breeding Tomato Hybrids for Flavour: Comparison of GWAS Results Obtained on Lines and F1 Hybrids

Tomato flavour is an important goal for breeders. Volatile organic compounds (VOCs) are major determinants of tomato flavour. Although most tomato varieties for fresh market are F1 hybrids, most studies on the genetic control of flavour-related traits are performed on lines. We quantified 46 VOCs in a panel of 121 small fruited lines and in a test cross panel of 165 hybrids (the previous panel plus 44 elite cherry tomato lines crossed with a common line). High and consistent heritabilities were assessed for most VOCs in the two panels, and 65% of VOC contents were strongly correlated between lines and hybrids. Additivity was observed for most VOCs. We performed genome wide association studies (GWAS) on the two panels separately, along with a third GWAS on the test cross subset carrying only F1 hybrids corresponding to the line panel. We identified 205, 183 and 138 associations, respectively. We identified numerous overlapping associations for VOCs belonging to the same metabolic pathway within each panel; we focused on seven chromosome regions with clusters of associations simultaneously involved in several key VOCs for tomato aroma. The study highlighted the benefit of testcross panels to create tasty F1 hybrid varieties.