In vitro digestibility of kudzu starch by using α‐amylase and glucoamylase

Abstract

Kudzu starch is used as a nutritious food in East Asia, however, its impact on glycemic response is unclear. The objective was to investigate its susceptibility to digestive enzymes compared to other root starches. We investigated the enzyme kinetics and hydrolytic rate of porcine pancreatic α‐amylase, examined the in vitro starch digestibility using digestive enzymes, and measured rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) of kudzu starch. The results indicated that, compared to other root starches, the Km value of granular kudzu starch was the largest, but after gelatinization, the Km value significantly decreased. During the in vitro digestion, the crystallinity of granular kudzu starch increased from 34.8 to 38.4% and 43.6% after 20 and 120 min, respectively. The RDS, SDS, and RS of granular kudzu starch were 5.66, 25.88, and 68.46%, respectively. After gelatinization, RDS and SDS of kudzu starch increased to 48.79 and 39.83%, and the RS decreased to 11.38%. Thus, it is important to regulate gelatinization to keep the optimal RS and SDS levels of kudzu starch in order to maintain the balance in blood glucose levels. Incompletely gelatinized kudzu starch will be of interest from the viewpoint of developing slowly digestible starchy foods.