Relationship of the methanol production, pectin and pectinase activity during apple wine fermentation and aging.

Understanding pectin structure and pectinase activity was important to control methanol content in apple wine. Therefore, this study compared inoculated fermentation (I), spontaneous fermentation (S) and inoculated fermentation combined with CaCl treatment (I & CaCl) to explore their differences in methanol production, pectin peak molecular weight (Mp), and the activities of pectin methyl esterase (PME), pectin lyase (PL) and polygalacturonase (PG). The results showed that the activities of PME, PL and PG were intensively inhibited during fermentation; however, they still retained 3.41-5.84% (PME), 9.46-17.71% (PL) and 9.17-10.31% (PG) of the initial activities after aging for 30 days. Therefore, the methanol content was increased in all three aged wines even aging at 4 °C. CaCl promoted the PME and PL activities, and thus accelerated the methanol production. Because the pectin with Mp 3.07 kDa was retained by CaCl, the highest pectin content was found in wine I & CaCl (160.69 mg/L), which was 95.47 mg/L higher than that in wine I, and 107.03 mg/L higher than that in wine S. In group S, the long lag period allowed pectin to withstand the pectinases inherent in apple juice for a long time, which was conducive to the cleavage of pectin to Mp lower than 3 kDa continuously, its further degradation led to the lowest pectin content (53.65 mg/L) in wine. Hence, inhibiting the pectinases activities, or shortening the aging period would play an important role in decreasing the methanol content in apple wine.