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For the selection of suitable enzymes for the solubilization of onion, degree of solubilization (DS) values were measured. The DS values of Pectinex and Viscozyme were 75.8 and 78.4%, respectively, which indicates they have higher specific activities than Cereflo and Celluclast. The enzyme mixture of Pectinex and Viscozyme (relative ratio of 1:3) had higher DS values and reducing sugar content than Pectinex alone. The enzyme mixture degraded onions with a synergistic effect, solubilizing 85% of the onion. The DS values and reducing sugar content at the optimal condition (pH 4.5 and 45 °C) reached a maximum of 85% and 494.8 mg g–1 of onion, respectively. The DS values and reducing sugar content increased with increasing reaction time, reaching a maximum of 89% and 517.5 mg g–1 of onion, respectively. When cooking pork, onion appeared to be preferable to onion hydrolysate, however there was no significant difference. The sweetness and preference of pork cooked with 3% addition of hydrolysate per gram of pork meat were the highest but those were not different significantly from those cooked with less than 10% addition of hydrolysate per pork meat.

Summary To increase the industrial applications of sweet potato, a rice beverage was prepared by adding barley sprouts, sweet potato, or a mixture of barley sprouts and sweet potato (1:1). Amylases from barley sprouts and sweet potatoes had a similar hydrolysis pattern to β‐amylase. Heat stability of this enzyme in sweet potato was higher than that in barley. Reducing sugar content in the mixture of barley sprouts and sweet potato was higher than in either barley sprouts or sweet potato alone. After the preparation of the rice beverage, the maltose content of the mixture with barley sprouts, either barley sprouts and sweet potato, or sweet potato was 37.2, 44.1 and 40.3 mg mL−1 after 6 h, respectively. The amylase activity in the mixture with barley sprouts and sweet potato decreased more than that of the mixture with only sweet potato. The use of sweet potato resulted in an increase of sweetness, flavour and improved preference in rice beverage.