d-Allulose 3-epimerase of Bacillus sp. origin manifests profuse heat‐stability and noteworthy potential of d-fructose epimerization

BACKGROUND: d-Allulose is an ultra-low calorie sugar of multifarious health benefits, including anti-diabetic and anti-obesity potential. d-Allulose 3-epimerase family enzymes catalyze biosynthesis of d-allulose via epimerization of d-fructose. RESULTS: A novel d-allulose 3-epimerase (DaeB) was cloned from a plant probiotic strain, Bacillus sp. KCTC 13219, and expressed in Bacillus subtilis cells. The purified protein exhibited substantial epimerization activity in a broad pH spectrum, 6.0–11.0. DaeB was able to catalyze d-fructose to d-allulose bioconversion at the temperature range of 35 °C to 70 °C, exhibiting at least 50 % activity. It displaced excessive heat stability, with the half-life of 25 days at 50 °C, and high turnover number (k(cat) 367 s(− 1)). The coupling of DaeB treatment and yeast fermentation of 700 g L(− 1) d-fructose solution yielded approximately 200 g L(− 1) d-allulose, and 214 g L(− 1) ethanol. CONCLUSIONS: The novel d-allulose 3-epimerase of Bacillus sp. origin discerned a high magnitude of heat stability along with exorbitant epimerization ability. This biocatalyst has enormous potential for the large-scale production of d-allulose.