产转糖基β-半乳糖苷酶菌株F3的鉴定、产酶条件及转糖基活性研究

菌株乃从土壤中筛选得到，具有产生转糖基β-半乳糖苷酶（β-galactosidase）的特性。根据形态观察及18S rDNA序列分析；菌株乃被鉴定为扩张青霉（Penicillumexpansum）。通过单因子试验和正交试验，对菌株乃产生转糖基阻半乳糖苷酶的培养基组成及发酵条件进行了优化。优化后的培养基组成为葡萄糖2％、酵母粉1％、蛋白胨1．5％、氯化钠0．3％。在初始pH6．0，28℃培养40h时，其产酶量为2245．2U／L，比优化前提高约3倍。菌株乃产生的转糖基肛半乳糖苷酶以pH4．5缓冲液配制的30％乳糖为底物，50℃反应24h，低聚半乳糖产量为30．6％，其中80％以上为三糖。

Identification of strain F3 producing transglycosyl β-galactosidase and the optimization of fermentation and galactosylation

Strain F3 was isolated from soil and produced transglycosyl β-galactosidase. It was identified as Penicillum expansum F3 by means of morphological characteristics and 18S rDNA sequence analysis. Medium and fermentation conditions for its β-galactosidase production were optimized by single factor and orthogonal experiments. The final yield of the enzyme reached 2 245.2 U/L in the medium composed of 2% glucose, 1% yeast extract, 1.5% peptone and 0.3% NaCl at initial pH 6.0 and 28℃ for 40 h, which increased three-fold compare to before optimization. The effects of pH, temperature and time on galactoohgosaccharides （GOS） synthesis were investigated. A purity of 30.6% （w/w） GOS was obtained from 30% lactose solution at pH 4.5 and 50 ℃ for 24 h. Transgalactosyl trisaccharides were the main products, accounting for more than 80% of the GOS product.