乳糖
嗜热链球菌
乳糖酶
β-半乳糖苷酶
水解
发酵
生物化学
食品科学
发酵乳制品
乳糖不耐受
乳酸
生物
细菌
酶
微生物学
化学
乳酸菌
大肠杆菌
基因
遗传学
作者
Belay Tilahun,Ge Zhao,Paul J. Kempen,Christian Solem
标识
DOI:10.1021/acs.jafc.2c04191
摘要
Streptococcus thermophilus is a fast-growing lactic acid bacterium (LAB) used in yoghurt and cheese manufacturing. Recently, we reported how this bacterium could serve as a cell catalyst for hydrolyzing lactose when permeabilized by nisin A. To enhance the lactose hydrolyzing activity of S. thermophilus, we mutated a dairy strain and screened for variants with elevated β-galactosidase activity. Two isolates, ST30-8 and ST95, had 2.4-fold higher activity. Surprisingly, both strains were able to hydrolyze lactose when used as whole-cell lactase catalysts without permeabilization, and ST30-8 hydrolyzed 30 g/L lactose in 6 h at 50 °C using 0.18 g/L cells. Moreover, both strains hydrolyzed lactose while growing in milk. Genome sequencing revealed a mutation in l-lactate dehydrogenase, which we believe hampers growth and increases the capacity of S. thermophilus to hydrolyze lactose. Our findings will allow production of sweet lactose-reduced yoghurt without the use of costly purified lactase enzymes.
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