Enzymatic determination of total starch and degree of starch gelatinization in various products

Abstract The degree of starch gelatinization (DSG) affects not only structural, physicochemical and organoleptic properties but also susceptibility to enzymatic digestion and thus nutritional values of starchy products. DSG determination has been conducted in many laboratories, entailing measurements of both gelatinized and total starch. However, current enzymatic methods are complex and inaccurate. For addressing the problems, this study was conducted. Results show that gelatinized and native starch solubilized maximally at different NaOH concentrations and that proper sample pretreatments to solubilize starch were important for obtaining accurate results. For gelatinized starch, optimal pretreatments entailed mixing in 40–80 mM NaOH solution at 150 rpm for 15–70 min. For total starch, mixing samples in 0.5 M NaOH for as short as 5 min or autoclaving for 60 min was optimal but boiling for 60 min was not. Consequently, a new method was proposed to measure DSG, consisting of differential alkaline pretreatments of samples for determining gelatinized starch and total starch, hydrolysis of solubilized starch by amyloglucosidase, and colorimetric measurement of d -glucose released by glucose oxidase-peroxidase. Furthermore, DSG calculation was significantly simplified by using absorbance ratio of gelatinized starch over total starch and omitting a correction factor for limited hydrolysis of native starch. This calculation eliminates the need for assessing absolute contents of gelatinized and total starch and determining the correction factor. The new method was validated and compared with a prior method. It enabled simple and accurate analysis of gelatinized starch, total starch, and DSG in various products in situ.