A novel cold-active type I pullulanase from a hot-spring metagenome for effective debranching and production of resistant starch

• Published in: Bioresource technology 2021-01, Vol.320 (Pt A), p.124288-124288, Article 124288
• Main Authors: Thakur, Monika, Sharma, Nitish, Rai, Amit K., Singh, Sudhir P.
• Format: Article
• Language: English
• Subjects: Cold-active; Crystallinity; Debranching; Glycoside Hydrolases - genetics; Metagenome; Pullulanase; Resistant Starch; Retrogradation; Starch
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2020.124288

•The study reports a novel cold-adaptive type I pullulanase (PulM).•PulM showed substantial enzymatic activity at low temperature, 4 °C.•PulM catalyzed hydrolysis of α-1,6 glucosidic bonds in starch.•PulM debranching caused a significant increase in amylose content of starch.•Retrogradation of the PulM debranched starch resulted in resistant starch 3. Pullulanase is a potent enzyme for starch debranching. In this study, a novel type I pullulanase (PulM) was identified from the metagenome of a thermal aquatic habitat that exhibits optimal activity of debranching at 40 °C temperature and pH 6.0 to 7.0. More than 50% enzymatic activity was detected at the low temperature of 4 °C, determining it a cold-active type I pullulanase. It was able to efficiently catalyze the hydrolysis of α-1,6-glycosidic linkages in pullulan, with a specific activity of 177 U mg−1. The results determined PulM to be a potential starch debranching biocatalyst, causing a significant increase of about 80% in the apparent amylose content of potato starch. Retrogradation of the debranched starch resulted in the formation of resistant starch 3. The yield of resistant starch was estimated to be about 45%. The resistant starch exhibited higher crystallinity, enhanced heat-stability, and resistance to α-amylase digestion, as compared to native starch.