Expression and Characterization of L-Arabinose Isomerase and Its Enzymatic Recycling of the Expired Milk

As global milk production continues to rise, the disposal of expired milk contributes to environmental pollution and valuable resource wastage. This study presents the development of a novel L-arabinose isomerase, designated <i>Bm</i>AIase12, and its application in the enzymatic recycling of expired milk. <i>Bm</i>AIase12 exhibited a specific activity of 10.7 U/mg and showed optimal performance at 50 °C and pH 7.0. Furthermore, it exhibited higher activity than most other L-arabinose isomerases. It converted D-galactose into D-tagatose with a high conversion ratio of 53.3% after 48 h at 50 °C. The conversion efficiency of expired milk to D-tagatose was recorded at 40.62%, resulting in a maximum tagatose yield of 1.625 g/L. This was accomplished through the incorporation of β-galactosidase (120 U/mL) and <i>Saccharomyces cerevisiae</i> (30 mg/mL) to hydrolyze lactose and metabolize glucose, followed by the addition of 3 U/mL of <i>Bm</i>AIase12. Ultimately, following purification, the purity of tagatose was determined to be 98%, and the final yield was 29.8%. These results suggest that <i>Bm</i>AIase12 may serve as a promising enzyme for D-tagatose production due to its high conversion yield.