Lactase plays a significant role in the dairy industry.However, currently commercial lactase have low thermal stability and poor reusability.To convert these drawbacks, β-galactosidase (BgaS) from Pyrococcus furiosus was selected and heterologously expressed in Bacillus subtilis WB800.The optimum temperature and pH of BgaS were at 90 ℃ and 7.These enzymic properties showed a promising potential for application in lactose-free product processing.To enhance the reusability of the BgaS, chitosan microspheres were employed as carriers for enzyme immobilization using a cross-linking method, and the cross-linking conditions were optimized.The optimal conditions were as follows:26.50 g/L of glutaraldehyde, 35 ℃ of cross-linking temperature, 2.5 h of cross-linking time, and 5.94 U/mL of enzyme dosage.After optimization, the enzyme activity recovery reached 55.11%.Compared to free enzymes, immobilized enzymes had the same optimal pH and temperature.Moreover, under non-optimal pH conditions, the relative enzyme activity of immobilized enzymes generally increased by more than 18.23% compared to free enzymes.In terms of thermostability, immobilized enzymes retained over 80% relative activity after being incubated at 95 ℃ for 90 min, which was an improvement of 11.31% compared to free enzymes.Meanwhile, immobilized enzymes had a high recovery rate and good operational stability, and could reduce lactose in milk to below 0.5% in just 3 h under optimal conditions, achieving lactose-free levels.This provides technical support for potential industrial applications.
XU Huidong
,
YOU Yang
,
YOU Yingxin
,
WANG Zhouping
,
XIA Yu
. Heterologous expression and enzymatic characterization of a highly thermostable lactase and its immobilized enzyme[J]. Food and Fermentation Industries, 2024
, 50(21)
: 1
-8
.
DOI: 10.13995/j.cnki.11-1802/ts.037932
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