As the unavoidable byproducts of alcoholic fermentation, higher alcohols are unhealthy compounds widespread in alcoholic drinks. To investigate the activity of apple crude enzymes toward higher alcohols in liquors, five kinds of apple peels, namely, Fuji, Gala, Golden Delicious, Red Star, and Jonagold, were chosen to prepare enzymes, and three kinds of Chinese liquors, namely, Xifeng (containing 45% ethanol), Taibai (containing 50% ethanol), and Erguotou (containing 56% ethanol), were tested. Enzymes were prepared in the forms of liquid solution, powder, and immobilized enzymes using sodium alginate (SA) and chitosan. The treatment was carried out at 37 °C for 1 h. The relative amounts of different alcohols (including ethanol, 1-propanol, isobutanol, 1-butanol, isoamylol, and 1-hexanol) were measured using gas chromatography (GC). Conditions for preparing SA-immobilized Fuji enzymes (SA-IEP) were optimized, and the obtained SA-IEP (containing 0.3 g of enzyme) was continuously used to treat Xifeng liquor eight times, 20 mL per time. Significant degradation rates (DRs) of higher alcohols were observed at different degrees, and it also showed enzyme specificity according to the apple varieties and enzyme preparations. After five repeated treatments, the DRs of the optimized Fuji SA-IEP remained 70% for 1-hexanol and >15% for other higher alcohols.
Keywords: Chinese liquor; apple; degradation; enzyme; higher alcohols.