Abstract: In order to study the starch-metabolizing ability of lactic acid bacteria with specific starch-binding activity, Lactobacillus paracasei L1 was evaluated for its ability to produce raw starch-degrading amylase by utilizing raw starch. The conditions for enzyme production were optimized and the molecular mass of the amylase was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The production and utilization of carbohydrates and organic acids were determined by high performance liquid chromatography (HPLC). The results showed that raw starch-degrading amylase existed on the cell surface and in the culture supernatant of L1. The enzyme could hydrolyze raw starch from different sources to a certain extent, and raw starch could induce the production of the enzyme. The highest enzyme activity of (191.64 ± 0.63) U/mL was achieved under the following conditions: initial medium pH 6.5, 68% starch in total carbon source, and 2.03% carbon source. Glucose and maltose were the final products of carbohydrate hydrolysis, and malt oligosaccharide was the intermediate product. Lactic acid was the main product of organic acid hydrolysis while citric acid was the secondary product. This study proved that L1 can combine and utilize raw starch, which is of great significance to the application of lactic acid bacteria in starch matrices.

Key words: Lactobacillus paracasei L1; raw starch-degrading amylase; enzyme production optimization; metabolites