Abstract
From a commercial enzyme from Aspergillus niger on marketing as a maceration agent of various plant tissues, several enzyme preparations were made which had relatively high activity of pectin depolymerase(poly(l, 4-α-galacturonide)glycanohydrolase, EC 3.2. 1.15), xylanase(1, 3-β-D-xylane xylanohydrolase EC 3.2.1.32) or cellulase (1, 4(1, 3; 1, 4)-β-D-glucan 4-hydrolase), and examined for maceration effect on sliced or disrupted sweet potato. The preparation which was strong in the activity of pectin depolymerase caused a rapid maceration at pH 4.5 and 40°C while the enzyme preparation which was high in xylanase and cellulase activities but slight in pectin depolymerase was almost sluggish in the effect. Sweet potato was steeped in 0.15% H2SO4 overnight to sterilize. Then, 0.1% each of maceration enzyme and glucoamylase (5000 units of pectin depolymerase and 3000 units of glucoamylase) was added to the grated potato and the mixture was incubated at pH 4.5 and 45°C. Two hours later, the mash was cooled at 30°C and yeast was added in a proportion of 10 g as dry weight per kg potato for alcohol fermentation. The alcohol produced in 6-day incubation was 14.5-15.5% (v/v). In order to shorten the fermentation period, the macerated mixture with pectin depolymerase was adjusted to pH 5.2-5.4 with sodium hydroxide, added with bacterial α-amylase, and the mixture was pumped through a chamber heated at 88-90°C with a retention time of 5 min. The dextrinized mash was acidified at pH 4.5 with sulfuric acid and subjected to alcohol fermentation after addition of glucoamylase and yeast. The fermentation by this method was completed in 42-44 hr and the alcohol produced was 17% (v/v).
