A low-cost production, characterization, and application of raw starch degrading enzyme from the thermophilic filamentous bacterium, Laceyella sacchari P43

Abstract

Raw starch degrading enzyme (RSDE) is a group of enzymes that can directly degrade starch granules at low temperatures without the gelatinization process resulting in reduced cost and energy consumption. This work aimed to optimize the enzyme production, purification, and characterization of RSDE from Laceyella sacchari P43. The highest enzyme production was found at 171.8 ± 6.53 U/mL when using the low-cost agricultural crop and by-products from the brewing industry, including broken rice powder and dried brewer’s yeast at 8.0 and 4.7 g/L, respectively. The optimized medium resulted in a 5.03-fold improvement in RSDE production and an 8.5-fold reduction in cost compared to the non-optimized medium. The optimum physical factors enhancing RSDE production were pH at 6.5 and 50°C. The fed-batch fermentation was carried out in a 3.0 L airlift fermenter, which showed the highest enzyme production at 201 ± 11.53 U/mL. The purified enzyme has a molecular weight of 50 kDa and 35.2 purification folds with optimum activity at pH 6.0 and 55°C. The enzyme stimulated the activity by Co2+, Mn2+, and Ca2+ and was strongly inhibited by N-Bromosuccinimide, which confirmed that it was α-amylase. The crude enzyme could hydrolyze the low-grade broken rice powder, yielding 40.31 ± 2.21 g/L after incubating for 9 h. This study developed the enzyme production process using low-cost substrates and enzyme application for sugar syrup production, which could be applied for further industrial application.