A sarabande of tropical fruit proteomics: Avocado, banana, and mango

Multi-omic applications for understanding and enhancing tropical fruit flavour

Consumer trends towards nutrient-rich foods are contributing to global increasing demand for tropical fruit. However, commercial cultivars in the breeding pipeline that are tailored to meet market demand are at risk of possessing reduced fruit flavour qualities. This stems from recurrent prioritised selection for superior agronomic traits and not fruit flavour, which may in turn reduce consumer satisfaction. There is realisation that fruit quality traits, inclusive of flavour, must be equally selected for; but currently, there are limited tools and resources available to select for fruit flavour traits, particularly in tropical fruit species. Although sugars, acids, and volatile organic compounds are known to define fruit flavour, the specific combinations of these, that result in defined consumer preferences, remain unknown for many tropical fruit species. To define and include fruit flavour preferences in selective breeding, it is vital to determine the metabolites that underpin them. Then, objective quantitative analysis may be implemented instead of solely relying on human sensory panels. This may lead to the development of selective genetic markers through integrated omics approaches that target biosynthetic pathways of flavour active compounds. In this review, we explore progress in the development of tools to be able to strategically define and select for consumer-preferred flavour profiles in the breeding of new cultivars of tropical fruit species.

From fruit growth to ripening in plantain: a careful balance between carbohydrate synthesis and breakdown

In this study, we aimed to investigate for the first time different fruit development stages in plantain banana in order gain insights into the order of appearance and dominance of specific enzymes and fluxes. We examined fruit development in two plantain banana cultivars during the period between 2-12 weeks after bunch emergence using high-throughput proteomics, quantification of major metabolites, and analyses of metabolic fluxes. Starch synthesis and breakdown are processes that take place simultaneously. During the first 10 weeks fruits accumulated up to 48% of their dry weight as starch, and glucose 6-phosphate and fructose were important precursors. We found a unique amyloplast transporter and hypothesize that it facilitates the import of fructose. We identified an invertase originating from the Musa balbisiana genome that would enable carbon flow back to growth and starch synthesis and maintain a high starch content even during ripening. Enzymes associated with the initiation of ripening were involved in ethylene and auxin metabolism, starch breakdown, pulp softening, and ascorbate biosynthesis. The initiation of ripening was cultivar specific, with faster initiation being particularly linked to the 1-aminocyclopropane-1-carboxylate oxidase and 4-alpha glucanotransferase disproportionating enzymes. Information of this kind is fundamental to determining the optimal time for picking the fruit in order to reduce post-harvest losses, and has potential applications for breeding to improve fruit quality.

A spotlight on analytical prospects in food allergens: From emerging allergens and novel foods to bioplastics and plant-based sustainable food contact materials

The present review throws a spotlight on new and emerging food safety concerns in view of a well-established food allergen risk arising from global socio-economic changes, international trade, circular economy, environmental sustainability, and upcycling. Food culture globalization needs harmonization of regulations, technical specifications, and reference materials towards mutually recognised results. In parallel, routine laboratories require high-throughput reliable analytical strategies, even in-situ testing devices, to test both food products and food contact surfaces for residual allergens. Finally, the currently neglected safety issues associated to possible allergen exposure due to the newly proposed bio- and plant-based sustainable food contact materials require an in-depth investigation.

Fruit quality parameters and volatile compounds from 'Palmer' mangoes with internal breakdown

The internal breakdown (IB) is a premature and uneven mango pulp ripening physiological disorder that is noticed only when the fruit is sliced for consumption. Thus, there is a demand for analytical methods to detect IB in mangoes to avoid consumer dissatisfaction and reduce postharvest waste. In this work, physicochemical and volatile compounds were determined to evaluate the ability to predict pulp IB. Principal components analysis (PCA) and partial least squares discriminant analysis (PLS-DA) of the data show that color, firmness, and volatiles compounds are important to give some information about the physiological changes caused by IB. The volatile compounds methacrylic acid, ethyl ester, isopentyl ethanoate, limonene oxide, (E)-2-pentenal, tetradecane, and γ-elemene were identified as chemical markers of IB. Therefore, mango physical and chemical characteristics combined with PCA and PLS-DA were successfully employed for the identification of IB in mangoes, showing significant differences between healthy and IB fruits.

Combinatorial peptides: A library that continuously probes low-abundance proteins

After a decade of experimental applications, it is the objective of this review to make a point on combinatorial peptide ligand libraries dedicated to low-abundance proteins from animals to plants and to microorganism proteomics. It is, thus, at the light of the recent technical developments and applications that we will examine the state of the art, its usage within the scientific community, and its openness to unexplored fields. The improvements of the methodology and its implementation in connection with analytical determinations of combinatorial peptide ligand library (CPLL)-treated samples are extensively reviewed and commented upon. Relevant examples covering few critical aspects describe the performance of the technology. Finally, a reflection on the technological future is attempted in particular by involving new concepts adapted to the limited availability of certain biological samples.

Isolation, Purification and Characterization of Proteins in “Señorita” Banana (Musa acuminata (AAA) ‘Señorita’) Pulp with Bioactive Peptides Exhibiting Antihypertensive and Antioxidant Activities

Banana is one of the most important crops, providing multiple benefits. Although it has been widely studied for its health benefits, little information can be found about its proteins. This study determined the antihypertensive and antioxidant activities of the crude, purified, and hydrolyzed protein extracts from ‘Señorita’ banana pulp. Crude proteins were extracted using Tris-HCl buffer and purified through ammonium sulfate precipitation, dialysis, and gel filtration chromatography. The protein content of the crude, partially purified, and purified extracts were found to be 167.32, 120.45, and 28.51 μg·mL−1, respectively, with major protein having an approximate molecular weight of 15 kDa. These extracts were then subjected to enzymatic hydrolysis for release of bioactive peptides prior to ACE inhibitory and antioxidant activities determination. Among these samples, the undigested crude extract had the highest ACE inhibitory activity (85.20%). There was also an observable increase in ACE inhibition of the digested samples with increased digestion time. Meanwhile, the 3-h and 4-h crude digests had the highest DPPH radical scavenging activity with 30.82% and 34.74%, respectively. These were not significantly different from the activity of the standard, ascorbic acid. A general decrease in DPPH radical scavenging activity of the samples was observed with increased digestion time. These observations were coherent with the in silico analysis of the putative major protein, lectin, which showed that its enzymatic hydrolysis releases ACE inhibitor and antioxidant peptides.

Effects of ozone treatment on the antioxidant capacity of postharvest strawberry

Strawberries are highly popular around the world because of their juicy flesh and unique taste. However, they are delicate and extremely susceptible to peroxidation of their membrane lipids during storage, which induces water loss and rotting of the fruit. This study investigated the effects of ozone treatment on the physiological traits, active oxygen metabolism, and the antioxidant properties of postharvest strawberry. The results revealed that the weight loss (WL) and respiration rate (RR) of strawberry were inhibited by ozone treatment (OT), while the decline of firmness (FIR) and total soluble solids (TSS) were delayed. Ozone also reduced the generation rate of superoxide radical anions , and the content of hydrogen peroxide (H₂O₂) enhanced the activity of superoxidase (SOD), catalase (CAT), ascorbate peroxidase (APX), and monodehydroascorbate reductase (MDHAR), as well as promoted the accumulation of ascorbic acid (ASA), glutathione (GSH), and ferric reducing/antioxidant power (FRAP). In addition, a total of 29 antioxidant-related proteins were changed between the OT group and control (CK) group as detected by label-free proteomics during the storage time, and the abundance associated with ASA–GSH cycle was higher in the OT group at the later stage of storage, and the qRT-PCR results were consistent with those of proteomics. The improvement of the antioxidant capacity of postharvest strawberry treated with ozone may be achieved by enhancing the activity of the antioxidant enzymes and increasing the expression of the antioxidant proteins related to the ascorbic acid–glutathione (ASA–GSH) cycle.

Strawberries are highly popular around the world because of their juicy flesh and unique taste.

Low-abundance plant protein enrichment with peptide libraries to enlarge proteome coverage and related applications

In plant tissues proteins are present in low amounts but in a very large number. To this peculiar situation many complex foreign components render protein extraction and purification very difficult. In the last several years interesting technologies have been described to improve the technical situation to the point that some methodologies allow reaching very low-abundance proteins and minor allergens. Among enrichment methods the one documented in this report is based on combinatorial peptide ligand libraries (CPLLs) that emerged in the last decade by contributing to largely improve the knowledge in plant proteomics. It is the aim of this review to describe how this technology allows detecting low-abundance proteins from various plant tissues and to report the dynamics of the proteome components in response to environmental changes and biotic attacks. Typical documented examples with the description of their scientific interest are reported. The described technical approach and selected applications are considered as one of the most advanced approaches for plant proteomics investigations with possibilities not only to enlarge the knowledge of plant proteomes but also to discover novel allergens as well as plant biomarkers subsequent to stressful situations.

Primary Metabolism in Avocado Fruit

Avocado (Persea americana Mill) is rich in a variety of essential nutrients and phytochemicals; thus, consumption has drastically increased in the last 10 years. Avocado unlike other fruit is characterized by oil accumulation during growth and development and presents a unique carbohydrate pattern. There are few previous and current studies related to primary metabolism. The fruit is also quite unique since it contains large amounts of C7 sugars (mannoheptulose and perseitol) acting as transportable and storage sugars and as potential regulators of fruit ripening. These C7 sugars play a central role during fruit growth and development, but still confirmation is needed regarding the biosynthetic routes and the physiological function during growth and development of avocado fruit. Relatively recent transcriptome studies on avocado mesocarp during development and ripening have revealed that most of the oil is synthesized during early stages of development and that oil synthesis is halted when the fruit is harvested (pre-climacteric stage). Most of the oil is accumulated in the form of triacylglycerol (TAG) representing 60-70% in dry basis of the mesocarp tissue. During early stages of fruit development, high expression of transcripts related to fatty acid and TAG biosynthesis has been reported and downregulation of same genes in more advanced stages but without cessation of the process until harvest. The increased expression of fatty acid key genes and regulators such as PaWRI1, PaACP4-2, and PapPK-β-1 has also been reported to be consistent with the total fatty acid increase and fatty acid composition during avocado fruit development. During postharvest, there is minimal change in the fatty acid composition of the fruit. Almost inexistent information regarding the role of organic acid and amino acid metabolism during growth, development, and ripening of avocado is available. Cell wall metabolism understanding in avocado, even though crucial in terms of fruit quality, still presents severe gaps regarding the interactions between cell wall remodeling, fruit development, and postharvest modifications.

Analysis of the molecular basis of fruit cracking susceptibility in Litchi chinensis cv. Baitangying by transcriptome and quantitative proteome profiling

Fruit cracking is a serious problem in Litchi chinensis cv. Baitangying orchards, but few advances have been made in understanding the molecular basis of cracking susceptibility in 'Baitangying'. In this work, we conducted transcriptome and quantitative proteome analyses of the pericarps of three kinds of litchi: noncracking 'Feizixiao' (cracking-resistant cultivar, F), noncracking 'Baitangying' (B), and cracking 'Baitangying' (CB). A total of 101 genes and 14 proteins with the same regulatory changes were found to overlap between CB vs. B and B vs. F, and we focused on these results to avoid the effects of passive progression after fruit cracking. The obtained data suggest that fruit cracking susceptibility in 'Baitangying' is related to pericarp photosynthetic characteristics and the oxidation of unsaturated fatty acids in this cultivar, which lead to changes in cuticle structure. Furthermore, differences in the pericarp hormone balance between 'Baitangying' and 'Feizixiao' may influence the susceptibility of 'Baitangying' to fruit cracking. This integrated analysis of transcriptomic and proteomic data indicates that susceptibility to fruit cracking in 'Baitangying' litchi is regulated both translationally and posttranslationally. Our results may help provide a new perspective for further study of the mechanisms that govern fruit cracking susceptibility in 'Baitangying' litchi and other fruits.