This study aimed to investigate the effect of oligochitosan on purified polyphenol oxidase (PPO) from Fuji apple and the associated mechanisms. PPO was firstly separated and purified in a four‐step procedure and the molecular weight was estimated to be about 65 kDa by SDS‐PAGE. PPO showed an optimum activity at pH 7 and 35°C, and it was stable in the temperature range of 25–55°C with more than 50% residual activity. Thermal inactivation parameters indicated that the Fuji apple PPO was very heat‐labile. Using catechol as the substrate, the PPO activity decreased with the increase of oligochitosan concentration, and only 30% activity remained when the concentration reached 4mg/mL. Oligochitosan showed uncompetitive type reversible inhibition with Ki value of 0.26mg/mL. Data obtained in this study provided theoretical basis for controlling enzymatic browning during apple processing with oligochitosan.
Practical applications
Processing operations, such as peeling, cutting, and juicing have the same problem: enzymatic browning, which causes a decrease in market value and economic loss. The most common approach for preventing browning is using anti‐browning agents, however, consumers are demanding a reduction in the overall use of chemicals on foods safe and asking effective substitutes especially natural inhibitors with the increased health awareness. This research systematically characterizes the enzymatic browning related PPO from apple and demonstrated that oligochitosan can inhibited PPO activity as an uncompetitive inhibitor, which will help in the development of oligochitosan to be a new type of anti‐browning agent.
This study was conducted aiming at improving the quality of jujube juice by mixed fermentation of lactobacilli. Selection of favourable lactobacilli and addition of nitrogen sources were explored as an efficient method to improve the viability of probiotic in jujube juice. After fermentation, the viability increased to 9.15 AE 0.10 Log CFU mL À1 , while the content of lactic acid increased to 5.61 AE 0.03 mg mL À1 . The total phenolic and total flavonoid content were 2663.03 AE 11.95 lg mL À1 and 163.95 AE 0.47 lg mL À1 respectively. Moreover, the stability of fermented jujube juice during refrigeration was investigated, which showed that the viability dropped to 8.84 AE 0.6 Log CFU mL À1 and the concentration of lactic acid slowly increased to 6.51 AE 0.04 mg mL À1 ; the ABTS value showed a 4.26% reduction and FRAP value did not significantly (P < 0.05) change during refrigerated storage. In addition to the existing knowledge, our data aid to the future applications of the jujube as a potential ingredient in novel probiotic foods formulation.
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