Mechanism of browning occurring during the processing of semi-dried persimmons.

摘要

To investigate the mechanism of browning occurring during the processing of semi-dried 'Atago' persimmon (Diospyros kaki) fruit, the changes in several components related to enzymatic and non-enzymatic browning were determined. The browning of semi-dried persimmons developed when the water content of fruit decreased to about 50% or less, and hand massage (HM) treatment promoted both the drying process and development of browning. The polyphenol content as a substrate of polyphenol oxidase (PPO) markedly decreased during the first 7 days of drying before the occurrence of browning. PPO activity gradually decreased and was lower in dry+HM than dry treatment alone during drying. The ascorbic acid (AsA) content decreased and HM accelerated the reduction by 7 days of drying. Dehydroascorbic acid (DHA) also decreased with stagnation in the mid-stage during 14 days of drying and was lower in dry+HM than dry treatment alone during the latter period of drying. Furfural, a non-oxidative degradation product of AsA, started to increase from 4 or 10 days of drying in dry+HM or dry treatment, respectively. Reducing sugars, fructose and glucose, markedly increased for the first 4 days with a concomitant decrease in the sucrose content, and were higher in dry+HM than dry treatment. The content of amino acids gradually decreased, and no difference was observed between treatments. Hydroxymethylfurfural (HMF), as an intermediate product from fructose to brown pigments, decreased during drying and was lower in dry+HM than dry treatment alone. These results suggest that the oxidative and non-oxidative degradation of AsA would contribute markedly to the browning of semi-dried persimmon fruit, and enzymatic browning by PPO and the Maillard reaction between amino acids and reducing sugars might not play an important role.