特异腐质霉葡糖化酶催化生淀粉一步糖化的酶学特征

Enzymatic characterization for catalysing saccharification of raw starch in a single step by glucase from Humicola insolens

从北京西郊森林土壤中分离到产生糖化生淀粉的葡糖化酶的特异腐质霉Humicola insolens HG‐618菌株。优化的产酶培养基如下:6%麦麸、2%玉米粉、0.7%磷酸氢二铵和1%玉米浆,p H 8.0,250m L三角瓶装40m L培养基,在40℃和280r/min培养90h。以生玉米淀粉为底物,发酵液中葡糖化酶活力为180U/m L。酶学性质试验表明,该酶的最适反应p H为6.0,最适反应温度为65℃;在p H 6.0–9.0范围酶活力稳定;酶热稳定性强,在60℃和p H 6.0保温8h,酶活力仍保留83%。一步糖化生玉米粉试验表明,在50m L 30%浓度生玉米粉浆和270U HG‐618葡糖化酶的反应体系中,采用自然p H 6.7,在55℃和100r/min条件下糖化40h。获得的糖化液还原糖浓度为17.1%(由酶产生的还原糖浓度为15.9%),生玉米粉中所含淀粉的糖化率为90%,且产生的糖全部为葡萄糖。因此,该葡糖化酶具有良好的一步糖化生玉米粉前景,它也可以用于生大米粉、生小麦粉和生马铃薯粉的直接糖化。

Humicola insolens strain HG-618 isolated from a forest soil can produce a raw starch saccharifying glucase.The optimal cultivating conditions for enzyme production were as follows： 6% wheat bran, 2% corn meal, 0.7% （NH4）2HPO4 and 1% corn steep liquor with pH 8.0, cultivating at 40°C and 280r/min on a rotary shaker for 90h. The glucase activity of culture supernatant toward raw corn starch was 180U/ml. The optimal conditions for enzyme action were pH 6.0 and 65°C. The enzyme was stable when pH ranged from 6.0 to 9.0. Thermostability of the enzyme was excellent since 83% of the enzyme activity remained after it was treated at 60°C and pH 6.0 for 8h. Fifty millilitres of a slurry containing 30% raw corn meal and 270U of HG-618 glucase （with natural pH value of 6.7） were saccharified at 55°C and 100r/min on a rotary shaker for 40h. The concentration of reducing sugar in the saccharification liquid was 17.1% （the concentration of resultant reducing sugar by enzyme was 15.9%） and saccharification efficiency of starch contained in the raw corn meal was 90%. Produced sugar was all glucose. The glucase can be also used for direct saccharification of raw rice meal, raw wheat meal and raw potato meal. Thus it showed good alternative processing in starch saccharifications.