Characterization of alpha-galactosidase from Lactobacillus reuteri L22 and its application in fermented soymilk

• Main Authors: Hui-Tzu Lu, 呂惠茲
• Other Authors: Wen-Zhe Hwang
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/20492805163755696533

碩士 === 國立中興大學 === 食品科學系 === 93 === Sixty six strains of lactic acid bacteria were screened for their -galactosidase activity with two kinds of substrates, 4MU-Gal and p-NPG, respectively. Among them, Lactobacillus reuteri L22 showed the highest activity and was chosen for further study. Alpha-Galactosidase from L. reuteri L22 was first demonstrated to be an intracellular enzyme. The optimal activity of the crude enzyme from L. reuteri L22 was characterized by using p-NPG as substrate at pH 5.0~5.5 and 45~50˚C. The crude enzyme retained good stability between pH 4.5 to 7.5 and showed high enzymatic activity at least 4 hr under the optimal temperature. When L. reuteri L22 was incubated with different -D-galactosyl oligosaccharides as carbon sources, the bacterial cells expressed higher -galactosidase activity, especially when raffinose was used (0.622 U/ml). All sugars could support the growth of L. reuteri L22, except for fructose. The results in this study also proved that -galactosidase from L. reuteri L22 could hydrolyze natural substrates, including melibiose, raffinose, and stachyose. The raffinose and stachyose in soymilk could be totally hydrolyzed when the soymilk was fermented 12 hours by L. reuteri L22 with the initial inoculation of 1.25x108 CFU/ml. When treated with 2 U of the crude enzyme from L. reuteri L22, after 8 hour of reaction, raffinose and stachyose in soymilk disappeared completely. The sensory evaluation of the fermented soymilk produced by L. reuteri L22 was conducted by a consumer sensory panel. Milk plus 20% fermented soymilk and fermented soymilk plus 10% fructose were the most favorite products and the unadorned fermented soymilk was not acceptable to the panelists. To summary, the -galactosidase of L. reuteri L22 was capable of degrading raffinose and stachyose and could be applied in soymilk fermentation for the removal of raffinose family oligosaccharides in soymilk to resolve the flatulence problem caused by them. It has the potential in the development of the lactic acid beverage-like or soyoghurt products.