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Hot water (HW) pre-treatment provides tolerance to chilling injury (CI) in tomato fruit, but little is known about the biochemical bases of this tolerance. The aim of this study was to identify proteins associated with CI tolerance in HW pre-treated tomato cv. Imperial. We used a comparative proteomic analysis between HW-treated (42 °C, 5 min) and non-treated fruit after cold storage (0, 10, and 20 days at 5 °C) and ripening (7 days at 21 °C); as well as real-time PCR to analyze the expression of genes encoding some selected proteins. Thirteen proteins were differentially expressed after 20 days of cold storage and 13 after the subsequent ripening period; polypeptides showing greater accumulation in HW-treated fruit included small heat shock proteins, antioxidant enzymes (thioredoxin peroxidase 1, superoxide dismutase, and ascorbate peroxidase), plant defense proteins (PR-10 and remorin 1) and RNA-binding chaperone protein (GR-RBP). In addition, non-treated fruit showed higher expression of enzymes involved in detoxification, carbohydrate, and energy metabolism, suggesting a low cellular efficiency in energy production due to severe structural damage. The hot water-induced chilling tolerance in tomato fruit appears to be related with the prevention of protein denaturation, activation of the antioxidant and defense systems, and the potential regulation of cold sensitive genes.

Spent coffee grounds (SCG) are residues generated during coffee beverage preparation that contain 12–17% protein and are a rich source of peptides. Bacteria can generate peptides with potential bioactivity through protein hydrolysis in a fermentation process. This study aimed to obtain digested protein hydrolysates with potential bioactivity from Bacillus clausii-fermented SCG. The fermentation was performed with 1.5 × 108 colony-forming units/mL of bacteria at 37 °C for 39 h. Total and soluble proteins and protein hydrolysates were quantified using spectrophotometric techniques. Pepsin/pancreatin protein hydrolysates were characterized using ultra-performance liquid chromatography-mass spectrometry. The physicochemical properties and potential bioactivity of peptides were evaluated using in silico analysis. The fermentation process increased the amounts of total proteins, soluble proteins, and protein hydrolysates by 2.7, 2.2, and 1.2-fold, respectively, compared to non-fermented SCG. Fermented SCG samples, increased the abundance of seven peptides that displayed potentially antioxidant capacity, angiotensin-converting enzyme activity, and dipeptidyl peptidase-IV-inhibitor activity. The YGF and GMCC peptide sequences presented the highest bioactivity scores (0.97 each), followed by the YWRYDCQ (0.65) and RMYRY (0.60) peptides. In summary, fermented SCG had increased abundance of peptides with high bioactive potential that may be exploited in managing oxidative stress, hypertension, and diabetes.

The application of a quarantine hot water treatment (HWT) induces chilling injury (CI) tolerance in mango fruit, but little is known about the mechanisms involved in this tolerance. The aim of this study was to identify metabolomic changes associated with HWT-induced CI tolerance in 'Keitt' mango fruit. Mature green fruit treated with hot water (HWT; 46.1 °C, 75-90 min) and non-treated (control) were stored for 20 d at 5 °C and ripened for 7 d at 21 °C. The incidence of chilling injury symptoms was registered as CI index. Methanol extracts of fruit peels were used for comparative metabolomics analyses by UPLC-DAD-MS and GC-MS. Total phenolics (TP) were analyzed by the Folin-Ciocalteu assay and the antioxidant activity (AA) was measured by ABTS, DPPH, and FRAP methods. HWT provided CI tolerance to mango fruit as evidenced by a low incidence of symptoms. Fifty-two and 14 metabolites were identified by UPLC-DAD-MS and GC-MS, respectively. These metabolites were classified as galloylquinic acids, gallic acid esters, gallotannins, gallic acid derivatives, benzophenone derivatives, xanthones, flavonoids, organic acids, sugars, fatty acids, and other metabolites (myo-inositol). The HWT before cold storage increased the abundance of galloylquinic acids, gallic acid esters, gallotannins, quercetin 3-O-rhamnoside, and myo-inositol; and it decreased the levels of mangiferin, ribose, malic acid, and palmitic acid. After cold storage and ripening, HWT fruit maintained higher levels of galloylquinic acids, gallic acid esters, gallotannins, quercetin 3-O-rhamnoside, mangiferin, myo-inositol, linolenic acid, and sugars than those in control fruit. HWT fruit also had higher values of TP and AA by the three methods. Control fruit had higher levels of citric acid, malic acid, palmitic acid, and ribose, as well as lower unsaturated/saturated fatty acid ratio. The HWT-induced CI tolerance in mango fruit appears to be associated with an increased content of antioxidants and osmoprotectant metabolites and a higher ratio of unsaturated/saturated fatty acids.

Genetic analysis using quality protein maize (QPM) recombinant inbred lines derived from K0326Y QPM and W64Ao2 identified three quantitative trait loci (QTL) in bins 1.06, 7.02 and 9.03 associated with opaque2 endosperm modification. We evaluated the effects of these QTLs on protein accumulation and starch physicochemical properties. The QTL in bin 1.06 is close to α-zein genes, and vitreous individuals with this QTL had increased accumulation of 19-kDa α-zein, 27-kDa γ-zein and legumin-1. The QTL in bin 7.02 corresponds to the γ-zein locus, and greater accumulation of this protein was found in vitreous individuals. The QTL in bin 9.03 is close to starch biosynthetic genes; greater accumulation of granule-bound starch synthase and amylose was observed in vitreous kernel samples with this locus and that in bin 1.06, as well as less gelatinization enthalpy and crystallinity. Vitreous kernels contained angular-shaped/compact starch granules and more short-intermediate length chains of amylopectin. These results support that endosperm modification in QPM is associated with increased accumulation of γ-zein and other storage proteins, but also show that synthesis of less crystalline starch with more amorphous regions at the periphery of granules, which favor their packing and association with endosperm proteins, may also be an important factor.

The opaque2 (o2) mutation in maize (Zea mays L.) increases the content of free amino acids (FAA) in the endosperm. We investigated the basis of this trait by using recombinant inbred lines from a cross of Oh545o2 (high FAA) and Oh51Ao2 (low FAA) to identify quantitative trait loci (QTL) for FAA content and to determine their effect on FAA composition and protein accumulation. Mapping identified six QTLs that accounted for 71% of the phenotypic variation. Two QTLs in bins 4.01 and 7.02 are close to α-zein genes; high FAA individuals with these QTLs had reduced accumulation of α-zein 19 kDa isoforms and increased FAA abundant in α-zeins. A QTL in bin 3.03 is close to a gene encoding triose phosphate isomerase (tpi4) and a higher expression of this enzyme was found in high FAA individuals. Other differentially expressed proteins included vicilin-like globulins and the enzymes glyceraldehyde-3-phosphate dehydrogenase, enolase-2, sorbitol dehydrogenase and granule-bound starch synthase. The results suggest that the increased levels of FAA in o2 endosperm are mainly due to the reduction of storage proteins and the failure to incorporate their amino acids into other proteins, as well as the alteration of carbohydrate metabolism that may favor amino acid biosynthesis.