Metabolomic insights into the browning inhibition of fresh-cut apple by hydrogen sulfide

Hydrogen sulfide (H2S) is known to effectively inhibit the browning of fresh-cut apples, but the mechanism at a metabolic level remains unclear. Herein, non-targeted metabolomics was used to analyze metabolic changes in surface and internal tissues of fresh-cut apple after H2S treatment. The results showed that prenol lipids were the most up-accumulated differential metabolites in both surface and inner tissue of fresh-cut apple during browning process, which significantly down-accumulated by H2S treatment. H2S treatment reduced the consumption of amino acid in surface tissue. Regarding inner tissue, H2S activated defense response through accumulation of lysophospholipid signaling and induced the biosynthesis of phenolic compounds. We therefore propose that H2S inhibited the surface browning of fresh-cut apple by reducing the accumulation of prenol lipids, directly delaying amino acid consumption in surface tissue and indirectly regulating defense response in inner tissue, which provides fundamental insights into browning inhibition mechanisms by H2S.

Effects of cellulose nanofibrils treatment on antioxidant properties and aroma of fresh-cut apples

Horticultural products tend to deteriorate during postharvest storage and processing. In this study, cellulose nanofibers (CNFs) were prepared from wood to investigate the effects of CNF treatment on the storage quality, aroma composition, and antioxidant system of fresh-cut apple (Malus domestica) wedges. Compared with control treatment, CNF coating treatment significantly improved the appearance of apple wedges; reduced the decay rate of apple wedges; and delayed the decline in weight loss, firmness, and titratable acid during storage. Gas chromatography-mass spectrometry showed that CNF treatment could maintain the aroma components of apple wedges (stored for 4 days). Further investigations showed that CNF treatment increased the antioxidant system level and decreased reactive oxygen species content and membrane lipid peroxidation level of apple wedges. Overall, this study showed that CNF coating could effectively maintain the quality of fresh-cut apples during cold storage.

Integration of transcriptome, miRNA and degradome sequencing reveals the early browning response in fresh-cut apple

Surface browning negatively impacts the shelf-life of fresh-cut apple. Herein, we found that the browning of fresh-cut apple aggravated rapidly after 24 h post-cutting, then the transcriptomic and miRNA expression profiles of fresh-cut apple immediately after cutting (T0) and 24 h post-cutting (T24) were analyzed to explore the molecular mechanism of early browning response. A total of 3156 differentially expressed mRNAs (DEGs) and 23 differentially expressed miRNAs (DEmiRNAs) were identified in T24 vs T0. Most DEGs related to respiratory, energy, antioxidant, lipid and secondary metabolism were activated in the early stage of browning. There were 63 target genes of 10 DEmiRNAs validated by degradome sequencing and among them, mdm-miR156aa_L + 1_1 targets 12-oxophytodienoate reductase, ptc-miR6478_R-1 targets patatin-like protein, mdm-miR156aa_L + 1_1 and mdm-miR156aa_L + 1_2 co-target SPLs might participate in the early browning response through regulating antioxidant, lipid and secondary metabolism. Our results will be beneficial for the technological innovation of browning amelioration for fresh-cut apple.

Effects of tea polyphenols on physicochemical and antioxidative properties of whey protein coating

Effects of tea polyphenols (TP) incorporation on physicochemical and antioxidative properties of whey protein isolate (WPI) coating were studied. Two WPI coating solutions were prepared by heating WPI solutions (pH 8, 90 °C) for 30 min and then TP was incorporated. TP addition could increase the negative zeta potential of 5% solution. The surface hydrophobicity index of both solutions was increased and intrinsic fluorescence intensity decreased greatly after addition of TP. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis (2 ethylbenzothiazoline-6-sulfonate) (ABTS) radical scavenging capacities of both solutions increased with increasing TP. Compared with apple pieces coated with whey protein only, those with TP containing whey protein coatings showed lower browning index and slight changes in weight loss during 24 h storage. Data indicated that TP could influence the physicochemical properties and improve the antioxidant activity of WPI coating solutions and can be used to retard the enzymatic browning of fruit during storage.

Ultrasound-assisted vacuum impregnation on the fortification of fresh-cut apple with calcium and black carrot phenolics

This study evaluated the simultaneous effect of ultrasound on vacuum impregnation process to enhance infusion of calcium lactate and black carrot phenolics into ready to eat apple tissues. A vacuum - ultrasonic equipment was developed for this purpose and effects of different ultrasound powers (96-198 W) at 35 kHz and stage of ultrasound application at vacuum and restoration periods were investigated. The simultaneous application of 130 W ultrasound during vacuum impregnation did not rupture cellular integrity, but it led to increases in calcium content (13.8%), total phenolics (11.8%), total flavonoids (17.3%), total anthocyanins (24.6%) and antioxidant capacities (23.6%) of apple discs compared to non-ultrasound vacuum impregnation. In addition, total population of psychrophilic and mesophilic microorganisms were enumerated in both black carrot infused and non-infused samples and results showed that ultrasound-assisted vacuum impregnation treatment in the presence of black carrot phenolics were highly effective on inhibition of microorganisms growth in apple discs over storage period.

Evaluation of microbial quality and yeast diversity in fresh-cut apple

The present work's aim was to study the microbial quality of minimally processed apples commercialized in Portugal. Sixty eight samples of fresh-cut apple were analyzed before their best-before date in 2011 and 2012 for aerobic mesophilic and psychrotrophic microorganisms, total coliforms, lactic-acid bacteria (LAB), coagulase-positive staphylococci and fungi. The parameters of food safety studied were Cronobacter sakazakii, Salmonella spp. and Listeria sp. Samples were analyzed according to standard methodologies and using Chromocult Agar for coliforms and Escherichia coli. The yeasts were identified by restriction analysis of the ITS-5.8S rDNA-region and 26S rDNA partial sequencing. The mesophilic and psychrotrophic microorganisms ranged from 3.3 to 8.9 and from 4.9 to 8.4 log CFU/g, respectively. Coliforms were detected in all the samples and staphylococci in 5.8% of them. LAB numbers varied from 2.8 to 8.7 and fungi (yeast and molds) from 3.6 to 7.1 log CFU/g. The most common yeasts were Candida sake and Pichia fermentans followed by Hanseniaspora spp., Candida spp., Meyerozyma guilliermondii, Metschnikowia pulcherrima, Cryptococcus spp. and the psychrotrophic Cystofilobasidium infirmominiatum. Foodborne bacteria and opportunistic pathogenic yeasts were not detected in the apples studied. The results obtained respected the European Commission regulation regarding criteria of food hygiene and safety.