Effects of Exogenous Trisodium Phosphate on Activities of Key Enzymes of Reactive Oxygen Species and Phenylpropane Metabolism and Accumulation of Phenolic Compounds in Jujube Fruits

Jujube fruit (cv. Sanxing) were soaked in 0.5 mg/mL trisodium phosphate solution for 10 min after harvest to study its effects on key enzymes activities and phenolic compounds accumulation in reactive oxygen species metabolism and phenylpropanoid pathway during storage at room temperature. Results showed that trisodium phosphate promoted hydrogen peroxide content during the entire storage time and peaked at 4 d and 10 d. Additionally, trisodium phosphate treatment distinctly increased the activities of ascorbate peroxidase and glutathione reductase on days 4~12 d and 4~8 d of storage (P<0.05). Moreover, trisodium phosphate treatment increased the activities of phenylalanine ammonilyase, 4-coumarate/coenzyme A ligase and peroxidase in the middle and late storage period. A ligase and peroxidase activities in jujube fruit and peaked at 6, 8 and 8 d, respectively, which was 1.18, 1.16 and 1.40 times of those in control (P<0.05). The increase of these enzymes activities significantly accelerated total phenols and flavonoids accumulation in jujube fruit on 6~12 d and peaked on 8 d and 10 d, which was 1.38 and 1.29 times of those in control, respectively (P<0.05). These findings suggest that postharvest trisodium phosphate treatment can activate the activities of enzymes to eliminate reactive oxygen species, and enhance the activities of key enzymes and phenolic compounds accumulation in phenylpropanoid metabolism, thus enhancing disease resistance.