Lu Lili, Xiao Min, Xu Xiaodong
State Key Laboratory of Microbial Technology, National Glycoengineering Research Center, Shandong University, Jinan 250100, China.
Wei Sheng Wu Xue Bao. 2008 Jan;48(1):38-44.
Galacto-oligosaccharides (GOS) are promising non-digestible oligosaccharides recognized as prebiotics. Commercial GOS containing galactose as subunit, are synthesized from lactose using the galactosyl-transferase activity of beta-galactosidase. A strain producing beta-galactosidase with transglycosylation activity was screened from the soil. Phenotypic analysis including morphology and physiology characteristics and 16S rDNA sequence analysis were carried out. Based on taxonomy results, the strain was identified as Enterobacter agglomerans B1. Medium and fermentation conditions were optimized by single factor and orthogonal experiments. The enzyme reached 9.7 U/mL in the medium (pH 7.5) containing 1% lactose, 1% yeast extract, and 0.5% peptone when cultured at 25 degrees C for 26 h. Effects of pH, temperature, lactose concentration, and reaction time on transgalactosylation by whole cells were studied. Yield of GOS reached 40.7% in 30% lactose (pH 7.5) at 50 degrees C for 12 h, as analyzed by HPLC and TLC. The results of an MS analysis showed that GOS were composed of di, tri-, and tetrasaccharides.
低聚半乳糖（GOS）是一种很有前景的不可消化性低聚糖，被认为是益生元。以半乳糖为亚基的商业GOS是利用β-半乳糖苷酶的转糖基化活性由乳糖合成的。从土壤中筛选出一株具有转糖基化活性的β-半乳糖苷酶产生菌。进行了包括形态学和生理学特征在内的表型分析以及16S rDNA序列分析。根据分类学结果，该菌株被鉴定为成团肠杆菌B1。通过单因素和正交试验对培养基和发酵条件进行了优化。当在25℃培养26 h时，在含有1%乳糖、1%酵母提取物和0.5%蛋白胨的培养基（pH 7.5）中，酶活达到9.7 U/mL。研究了pH、温度、乳糖浓度和反应时间对全细胞转糖基化的影响。通过高效液相色谱（HPLC）和薄层色谱（TLC）分析，在50℃、pH 7.5的30%乳糖中反应12 h时，GOS的产率达到40.7%。质谱分析结果表明，GOS由二糖、三糖和四糖组成。
