Evaluation of the inhibitory effect of pistachio (Pistacia vera L.) green hull aqueous extract on mushroom tyrosinase activity and its application as a button mushroom postharvest anti-browning agent

The short shelf life of button mushroom is a serious problem in its postharvest distribution. One approach is the application of plant extract (mainly polyphenolic compounds) to inhibit tyrosinase activity. The inhibitory activity of pistachio green hull extract (PGHE), sodium metabisulfite (MET), and ascorbic-citric acids (ASC-CIT) on mushroom tyrosinase was investigated at different concentrations (0.05-0.8% w/v) and IC50 value was determined (0.07%). Prevention of button mushroom postharvest browning was investigated by vacuum impregnation pretreatment with PGHE, MET, and ASC-CIT. Physicochemical, organoleptic, and microbial properties of the treated mushrooms were determined over 10 d of storage (at 4 degrees C). The results of the browning index (BI) showed that the PGHE-treated mushrooms had lower BI than the other samples. On the 10th d, only the mushrooms treated with PGHE had highest phenolic content (10.4%). The antioxidant activity of PGHE-treated mushrooms was higher than the control (4.5%). The mushrooms treated by PGHE had 13.9% higher firmness than the control. The sensory evaluation results showed that the samples treated with PGHE had the highest sensory scores. Also, the main components of PGH extract determined by RP-HPLC-DAD were phloroglucinol, gallic acid, naringin, vanillic acid, catechin, and protocatechuic acid. The inhibitory activity of two main components, pure phloroglucinol, gallic acid and the mixture of them, on tyrosinase were 43.6, 24.4 and 42.5%, respectively. It could be concluded that these compounds have a synergistic effect. It can be concluded that pistachio green hull extract is a new natural tyrosinase inhibitor that can delay browning reactions in mushrooms.