Effect of water blanching on phenolic compounds, antioxidant activities, enzyme inactivation, microbial reduction, and surface structure of samnamul ( Aruncus dioicus var kamtschaticus )

Influence of blanching on the bioactive compounds of Terminalia ferdinandiana Exell fruit during storage

Changes in quality of fruits and vegetables during processing and storage might impact on the nutritional and economical value of food products. The present study aimed to evaluate the influence of blanching on the content of vitamin C and ellagic acid (EA) as the main bioactive compounds present in Kakadu plum (KP) fruits (Terminalia ferdinandiana) during storage at 40oC to mimic typical temperature when wild harvested. Changes in the profile of fatty acids, malondialdehyde (MDA) production, as a biomarker for lipid peroxidation, and antioxidant properties of KP fruits were evaluated. The results revealed that vitamin C decreased between 25 and 52% over the storage period. Statistically significant differences in the concentration of vitamin C were associated with temperature (p < 0.05) and blanching (p < 0.05), whereas no significant differences in EA during storage were observed. DPPH radical scavenging capacity and total phenolic content of both blanched and control samples decreased by 80% and 35%, respectively, at the end of the storage period compared to day 0. In addition, the change in DPPH activity is significantly correlated (Pearson R2 = 0.829, p ˂ 0.01) with the breakdown of ellagitannins. Furthermore, KP fruit demonstrated excellent antioxidative properties by reducing MDA production. It was concluded that blanching causes significant vitamin C loss whereas neither blanching nor long-term storage at elevated temperature affect the EA content. The results also indicate that the antioxidant compounds present in the KP fruits provided considerable protection against fatty acid oxidation during storage.

Inactivation of Endogenous Pectin Methylesterases by Radio Frequency Heating during the Fermentation of Fruit Wines

Pectin methylesterase (PME) is a methyl ester group hydrolytic enzyme of either plant or microbial origin. Importantly, endogenous PMEs in fruits can catalyze the demethoxylation of pectin with a bulk release of methanol, largely impacting the fruit juice and wine industries. Here, we demonstrated radio frequency (RF) heating for inactivation of endogenous PMEs and investigated the relevant mechanisms underpinning enzymatic inactivation. The RF heating curve indicated that the optimal heating rate was achieved at an electrode gap of 90 mm (compared to 100 mm and 110 mm) and that the inactivation rate of the enzyme increases with heating time. RF heating exhibited better effects on enzymatic inactivation than traditional water heating, mainly by changing the secondary structures of PMEs, including α-helix, β-sheet, β-turn, and random coil. Moreover, fluorescence spectroscopy indicated changes in the tertiary structure with a significant increase in fluorescence intensity. Significantly, application of RF heating for inactivation of PMEs resulted in a 1.5-fold decrease in methanol during the fermentation of jujube wine. Collectively, our findings demonstrated an effective approach for inactivating endogenous PMEs during the bioprocesses of fruits.