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

Authors: Liu, Keshun; LIU, QIAN - Northeast Agricultural University, China

Submitted to: Food Hydrocolloids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2019
Publication Date: 1/3/2020
Citation: Liu, K., Liu, Q. 2020. Enzymatic determination of total starch and degree of starch gelatinization in various products. Food Hydrocolloids. 103. https://doi.org/10.1016/j.foodhyd.2019.105639.
DOI: https://doi.org/10.1016/j.foodhyd.2019.105639

Interpretive Summary: Starch is an important component of various food and feed products. The degree of starch gelatinization (DSG) affects not only physiochemical and sensory properties of starchy products but also their susceptibility to enzymatic digestion and thus nutritional properties for humans or animals. Therefore, measurements of total starch content as well as DSG have been routinely conducted in many laboratories. Over the years, enzymatic determination of DSG, which entails measurements of both gelatinized starch and total starch, has been a method of choice. However, many of enzymatic methods described previously fail to include proper sample pretreatments for measuring gelatinized starch and total starch and appropriate sample controls, and/or suffer from complex calculation for results based on contents of the two types of starch. To address these problems, we developed improved methods by pretreating samples with different alkaline concentrations for enzymatic analysis of gelatinized starch and total starch, respectively, and running proper blanks. The new procedures ensured accurate measurement of the two types of starch, resulting in accurate determination of DSG. Furthermore, we also significantly simplified the DSG calculation by using the absorbance ratio (instead of absolute contents) of gelatinized over total starch and eliminating a correction factor for limited hydrolysis of native starch. The new method enabled simple and accurate analysis of total starch and DSG in various products.

Technical 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, respectively, 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 by 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.