Splechtna Barbara, Nguyen Thu-Ha, Zehetner Romana, Lettner Hans Peter, Lorenz Werner, Haltrich Dietmar
Research Center Applied Biocatalysis, Graz, Austria.
Biotechnol J. 2007 Apr;2(4):480-5. doi: 10.1002/biot.200600230.
Galacto-oligosaccharides (GOS) are formed from lactose in discontinuous mode of conversion using beta-galactosidase from Lactobacillus sp. (beta-gal). The discontinuous process was optimized for technical application with regard to GOS yield, enzyme preparation, reaction temperature and substrate source. It proved to be advantageous to directly apply the crude cell-free enzyme extract for the conversion, since similar GOS yields and composition were obtained as when using the pure enzyme preparation, but expensive purification could be avoided. Reaction temperature was lowered to 17 degrees C to limit microbial contamination when using technical substrates. Thereby GOS yield decreased from 30% to 28% of total sugars and enzyme demand increased 2.7-fold. Whey permeate was compared to buffered lactose solution as a substrate source. The initial reaction rate was found to be 1.8 times higher for the whey permeate substrate; however, GOS yield was slightly lower (approximately 25% of total sugar at 17 degrees C) mainly due to smaller amounts of allolactose[beta-D-Galp-(1-->6)-D-Glc] and the trisaccharide beta-D-Galp-(1-->6)-D-Lac formed.
低聚半乳糖（GOS）是利用来自乳酸杆菌属的β-半乳糖苷酶（β-gal），以不连续转化模式由乳糖形成的。针对低聚半乳糖的产量、酶制剂、反应温度和底物来源，对该不连续过程进行了技术应用优化。结果表明，直接应用粗制无细胞酶提取物进行转化是有利的，因为与使用纯酶制剂时获得的低聚半乳糖产量和组成相似，但可避免昂贵的纯化过程。当使用工业底物时，将反应温度降至17℃以限制微生物污染。由此，低聚半乳糖产量从总糖的30%降至28%，酶需求量增加了2.7倍。将乳清渗透液与缓冲乳糖溶液作为底物来源进行了比较。发现乳清渗透液底物的初始反应速率高1.8倍；然而，低聚半乳糖产量略低（在17℃时约占总糖的25%），主要是由于异乳糖[β-D-吡喃半乳糖基-(1→6)-D-葡萄糖]和三糖β-D-吡喃半乳糖基-(1→6)-乳糖的量较少。
