Journal
JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY
Volume -, Issue -, Pages -Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jafc.2c04191
Keywords
chemical mutagenesis; EMS; S. thermophilus; lactose hydrolysis; beta-galactosidase
Funding
- Innovation Fund Denmark [1046-00008B]
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This study discovered that a mutated strain of Streptococcus thermophilus can efficiently hydrolyze lactose using whole-cell lactase catalysts. Genome sequencing revealed a mutation that affects the growth of the strain and increases its lactose hydrolyzing ability. These findings could potentially lead to the production of sweet lactose-reduced yoghurt without the need for expensive purified lactase enzymes.
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 beta-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 degrees 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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