| The purpose of this study was to prepare low-lactose milk by hydrolysis of lactose in milk withβ-galactosidase.Hydrolysis properties ofβ-galactosidase and its hydrolysis conditions were investigated. Results showed that commercialβ-galactosidase Maxlact from Kluveromyces lactis exhibited an optima pH 6.6-6.8 and an optima temperature 39-41℃. The optima pH was in the range of nature pH of milk, so it is applicable to hydrolyze lactose in milk.At 39℃more than 70% hydrolysis lactose could be reached in 2,3,3 hours with 2000,1500,1000NLU/Lβ-galactosidase,Respectively.2000,1500, 1000 NLU/Lβ-galacto- sidase were added to pasteuriz ed milk, and after treatment for 24,46,46 hours at 4℃, the lactose hydrolysis more than 70%. 750,500,250NLU/Lβ-galactosidase were added to UHT milk aseptically and after 1 week treatment at room temperature, the lactose hydrolysis reached more than 90%.The properties of immobilizedβ-galactosidase were investigated.The kinetics of immobilizedβ-galactosidase Km and Vmax were 304.87mmol/L and 0.10mmol/g·min, respectively. In continuous flow stirred tand reactor, the half-life of immobilizedβ-galactosidase at 37℃was 14 days. In packed bed reactor, the half-life at 10℃and 37℃were 304 days and 7 days, respectively. The results showed that lactose was hydrolyzed effectively by the immobilizedβ-galactosidase.This paper also studied the change in quality during storage of low-lactose milk treated by aseptically addition of lactase. The results showed that during storage, the quality decreased, browning of low lactose milk increased, pH value decreased, viscosity decreased , and the changes were significantly (p<0.05).
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