UTILIZATION OF ACID-STABLE A-AMYLASE FROM THE CITRIC ACID KOJI (Aspergillus usamii var.) AND PREPARATION OF EDIBLE MICROCAPSULE

在鹿儿岛，柠檬酸是利用淀粉生产工厂的甘薯废浆，由一种不同的usamii曲霉生产的商业基础上的柠檬酸。为了利用副产物，用柱层析法从曲霉的酸性提取物中获得了酸性稳定的α-淀粉酶(UAA)。该酶的最适pH为3~5.5时(37℃)，最适温度为60~70℃(pH 4.0时)，比普通中性α-淀粉酶(NA)高约15℃。N-末端的前20个氨基酸的序列以及约100,000个分子量与普通NA不同。在还原末端用14C-葡萄糖标记一系列低聚麦芽糖，测定其速率参数k0/Km和裂解频率。结果表明，活性中心由5个亚中心组成，催化中心位于非还原末端第3~4个亚中心之间。通过化学修饰，阐明了氨基酸在α-淀粉酶活性部位的作用。通过G3-CNP的半乳糖化反应合成了一种新的底物Gal-G3-CNP，使我们即使在糖化酶存在的情况下也能区分UAA和NA。UAA可提高糖化淀粉酶对生淀粉的消化速度。因此，以玉米淀粉为原料，用曲精粗提物消化玉米淀粉，制得可食用微胶囊的新型淀粉原料。消化后淀粉的链长分布等化学结构没有明显变化，而α-淀粉酶消化率和淀粉图最大粘度等物理性质有显著变化。对消化后的淀粉和染料化合物的掺入实验表明，消化产生的淀粉颗粒的空腔比阴离子化合物更容易吸收阳离子化合物。

In Kagoshima, citric acid was produced on a commercial basis by a koji of a variety of Aspergillus usamii, using waste pulp of sweet potato from starch production factories. For the utilization of by-product purified enzyme of acid-stable a-amylase (UAA) was obtained from the acidic extract of the koji by column chromatograph. The enzyme exhibited its optimum activity a pH of around 3-5.5 (at 37℃), and a temperature of 60-70℃ (at pH4.0), which is about 15℃ higher than the ordinary neutral a-amylase (NA). The sequence of the first 20 amino acids from the N-terminus as well as a molecular weight of about 100,000 differed from the ordinary NA. Using a series of maltooligosaccharides labeled with 14C-glucose at the reducing end, the rate parameter k0/Km and the cleavage frequency were determined. It was elucidated that the active center is composed of five subsites, with the catalytic site located between the 3-rd and the 4-th subsites from the nonreducing end. Chemical modification was performed to elucidate the role of the amino acids in the active site of a-amylase. A new substrate Gal-G3-CNP was synthesized by galactosylation of commercial G3-CNP, and allowed us to discriminate between UAA and NA even in the presence of glucoamylase. UAA was found to enhance the rate of digestion of raw starch by glucoamylase. Thus, the digested starch was prepared as a new starchy material of edible microcapsule from corn starch by digestion with the crude extract of the koji. No change in chemical structure was found such as distribution of chain length of the digested starch, while the significant change in the physical properties was found such as α-amylase digestibility and the maximum viscosity in amylogram. Incorporation experiment with the digested starch and the dye compounds revealed that the cavity of starch granule produced by the digestion absorbed cationic compounds easier than anionic compounds.