Structure identification of walnut peptides and evaluation of cellular antioxidant activity.

Walnut peptides are widely accepted as nutraceuticals with multiple health benefits. However, information about the structure and biological activity of walnut peptides is limited. In this work, walnut protein hydrolysate (WPH) was prepared by enzymatic hydrolysis. The total and free amino acids compositions in WPH were determined. The peptides sequence of WPH was analyzed by UPLC-MS/MS, and forty eight bioactive peptides were identified. Antioxidant activities were detected for WPH in both extracellular and intercellular assays. QGRPWG, PSRADIY and AYNIPVNIAR were the peptides that accounted for the antioxidant activity of WPH. Among them, QGRPWG showed the highest ORAC value (2801 µmol TE/g), and AYNIPVNIAR possessed the strongest protective effect against H2O2-induced oxidative stress in PC-12 cells in a dose-dependent manner. The results can aid in the recognition of peptides from walnut as nutraceuticals.

Effect of morin on the degradation of water-soluble polysaccharides in banana during softening.

The degradation of cell wall polysaccharides is highly associated with the softening process of banana. In this work, banana was treated by morin to delay softening during storage. Water-soluble polysaccharides were extracted from banana pulp at four storage stages. Their levels increased when the banana was green, but decreased when turned to yellow. Three types of polysaccharides were identified by nuclear magnetic resonance spectroscopy, including starches, homogalacturonans and arabinogalactan proteins. (1 → 4)-α-D-galacturonan constructed the backbone of homogalacturonans, which was the leading water-soluble polysaccharide in the last stage. Starch was the dominant polysaccharide at all stages in morin-treated banana. Deassembly of insoluble starch granules and degradation of soluble starches were responsible for its high level in banana. Arabinogalactan proteins were only detected in late stages, and could be a marker for banana deterioration. The inhibited degradation of cell wall polysaccharides contributed to the preservative effect of morin.

The structure changes of water-soluble polysaccharides in papaya during ripening.

Papaya is a fruit mainly grown in tropical and subtropical regions. The structural changes of polysaccharides are highly involved in the organoleptic property change of papaya. However, it remains unclear how the structure characteristics of water-soluble polysaccharides are changed during postharvest ripening. It is interesting to work on this topic. In this work, the dominant water-soluble polysaccharide in papaya was purified. It was identified to be α-(1→4)-D-galacturonan by NMR. It remained stable during postharvest ripening. ß-(1→4)-D-galactan was only detected in fully green papaya. Once the postharvest ripening initiated, this polysaccharide was rapidly degraded. There were no significant differences in the structure changes of water-soluble polysaccharides for the naturally ripening papaya and ethylene-treated papaya. These results extended the understanding about the relationship between polysaccharide structure and papaya ripening during postharvest storage.

Structure characterisation of polysaccharides in vegetable "okra" and evaluation of hypoglycemic activity.

Okra is a widely accepted vegetable in subtropical and tropical regions due to the good palatability. However, the polysaccharide compositions remain unclear. In this work, the water extract of okra pod was prepared and the leading polysaccharide fraction was purified. The precise structural characteristics were identified. It was a polysaccharide "rhamnogalacturonan" as shown below, and the structure was different to previously reported rhamnogalacturonans. The hypoglycemic effect of rhamnogalacturonan was determined in vivo. By comparing with streptozotocin-induced diabetic mice group, the high-dose group showed decreased blood glucose level and glucose tolerance. The body weight of all groups were not significantly different. The results indicated that the rhamnogalacturonan was responsible for the hypoglycemic effect of okra.

Application of Proteomics for the Investigation of the Effect of Initial pH on Pathogenic Mechanisms of Fusarium proliferatum on Banana Fruit.

Fusarium proliferatum is an important pathogen and causes a great economic loss to fruit industry. Environmental pH-value plays a regulatory role in fungi pathogenicity, however, the mechanism needs further exploration. In this study, F. proliferatum was cultured under two initial pH conditions of 5 and 10. No obvious difference was observed in the growth rate of F. proliferatum between two pH-values. F. proliferatum cultured under both pH conditions infected banana fruit successfully, and smaller lesion diameter was presented on banana fruit inoculated with pH 10-cultured fungi. Proteomic approach based on two-dimensional electrophoresis (2-DE) was used to investigate the changes in secretome of this fungus between pH 5 and 10. A total of 39 differential spots were identified using matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-TOF/TOF-MS) and liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Compared to pH 5 condition, proteins related to cell wall degrading enzymes (CWDEs) and proteolysis were significantly down-regulated at pH 10, while proteins related to oxidation-reduction process and transport were significantly up-regulated under pH 10 condition. Our results suggested that the downregulation of CWDEs and other virulence proteins in the pH 10-cultured F. proliferatum severely decreased its pathogenicity, compared to pH 5-cultured fungi. However, the alkaline environment did not cause a complete loss of the pathogenic ability of F. proliferatum, probably due to the upregulation of the oxidation-reduction related proteins at pH 10, which may partially compensate its pathogenic ability.