Evaluating the effect of bentonite, malic acid on pectin methyl esterase, methanol in fermented apple juice

Abstract

To elucidate the effect of bentonite and pH of apple juice on pectin methyl esterase (PME) activity and methanol content, apple juice was treated with bentonite and malic acid and incubated for 24.0 h at 20 °C and 10 °C, respectively. The treated juice was fermented at 20 °C and 10 °C, respectively. Results showed that bentonite absorbed 28.9–31.5 % of pectin and reduced 56 % of PME activity in apple juice. Whereas pH 3.0 regulated by malic acid inhibited 95.8–96.6 % of PME activity and the activity increased during fermentation owing to the increase of pH. Consequently, the lowest pectin and PME activity caused methanol content to decrease by 33.4–34.3 % in bentonite treated apple wine; while a lower PME activity caused methanol content to decrease by 11.9 % in malic acid treated fermented apple juice. A longer fermentation period at 10 °C led to a higher methanol content than that at 20 °C. Structural equation model indicated that the methanol content was directly affected by pectin in the three treatments. Whereas the PME activity directly affected the methanol content in malic acid treatment at 10 °C.