Effect of bacterial β-amylase and fungal α-amylase on the digestibility and structural characteristics of potato and arrowroot starches

Abstract

Retrograded and debranched starch, known as resistant starch type 3 (RS3), is resistant to digestive enzymes and exhibits a behavior similar to that of dietary fibers. In this study, the effect of β- and α-amylase on the digestibility and structural characteristics of potato and arrowroot starches was evaluated and compared. Starch samples were gelatinized, hydrolyzed by β- or fungal α-amylase, debranched, cooled (4 °C/16 h), precipitated with ethanol, and dried. Debranched and gelatinized starch samples were used as control. The degrees of hydrolysis for the two starches were similar (~25%), regardless of enzyme used. In both starches, β-amylase resulted in a significant decreases in average degree of polymerization (DPn) of short chains (from 16.5 to 12) and in proportion of these chains, while fungal α-amylase caused a significant decrease in DPn of long chains (from 38.9 to 26.8 and from 35.1 to 28.2 for potato and arrowroot starches, respectively) plus a significant increase in proportion of short chains. Gelatinization enthalpy and relative crystallinity of modified starches increased with amylolysis, particularly when α-amylase was used. RS3 content was 20.2% in the debranched potato starch and increased to 36.5% with amylolysis, regardless of the enzyme used before debranching. However, slowly digestible starch content increased from 8.5% to 27.8% when α-amylase was used in this starch. Meanwhile, arrowroot starch had 47.5% and 53.4% RS3 contents when β- and α-amylase were used, respectively. Structural characteristics, particularly the amylopectin branch chain length distribution, are important factors responsible for RS3 formation when amylolysis precedes debranching.