Glucoamylase and acid-stable alpha-amylase in koji for citric acid production
1995
Suganuma, T. (Kagoshima Univ. (Japan). Faculty of Agriculture) | Nishiyama, S. | Kitahara, K. | Nagahama, T.
Glucoamylase and acid-stable alpha-amylase were found in the acidic extract (pH 2.5) of koji for citric acid production after 6 days in solid culture of a variety of Aspergillus niger. The ratio of glucoamylase and alpha-amylase was estimated to be about 90:10, judging from productions of glucose and the reducing sugar determined by both the glucose-oxidase and Somogyi-Nelson methods, when soluble starch was digested at pH 4.0. Using a partially purified alpha-amylase (10.6 U/mg) from the citric acid-koji, its enzymes properties were compared with those of the neutral alpha-amylase from A. oryzae. HPLC analysis showed that the oligosaccharides were produced in their alpha-anomers on the enzymic digestion of soluble starch and its product pattern was very similar to that of the neutral alpha-amylase. It may be noted that the alpha-amylase is excellent for industrial use, since the enzyme is more acid-stable and more thermostable than the neutral alpha-amylase. The enzyme exerts its maximum activity at pH 3.5-4.5 and about 70 degrees C. With a slight modification of the manufacture processes, we could recover the amylases from the koji, as one of the by-products of citric acid-production. Hence procedure for co-recovery of citric acid and amylases was proposed
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