Preparation of sweet milk and yogurt containing d-tagatose by the l-arabinose isomerase derived from Lactobacillus rhamnosus

Abstract

d-Tagatose is a novel low-calorie sweetener, but its application in milk and yogurt has not been explored. A novel l-arabinose isomerase gene was identified in Lactobacillus rhamnosus. The purified l-arabinose isomerase showed good thermal stability from 50 °C to 65 °C, and pH stability from 6.0 to 8.0. To prepare sweet milk, 3.77 × 10−7 kat/mL β-galactosidase and 9.02 × 10−8 kat/mL l-arabinose isomerase were added. After reaction at 65 °C for 3.5 h, the contents of glucose, d-galactose, and d-tagatose in milk were 25.00 g/L, 13.76 g/L, and 11.24 g/L, respectively, and lactose was not detected. Furthermore, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, with the respective characteristic of d-galactose, and glucose utilization were used as starters for sweet yogurt preparation. After fermentation, the yogurt contained 13.88 g/L of glucose, 10.13 g/L of d-galactose, and 10.90 g/L of d-tagatose, respectively. These results indicated the L. rhamnosusl-arabinose isomerase had a great potential for industrial application in sweetened milk and yogurt preparation.