|LIU, QIAN - NORTHEAST AGRICULTURAL UNIVERSITY, CHINA|
Submitted to: Annual Meeting of the Institute of Food Technologists
Publication Type: Abstract Only
Publication Acceptance Date: 3/25/2019
Publication Date: 6/3/2019
Citation: Liu, K., Liu, Q. 2019. An improved enzymatic method for determining the degree of starch gelatinization in dry products. Annual Meeting of the Institute of Food Technologists. E03-359.
Technical Abstract: Introduction: Starch gelatinization is an important physical, chemical, and biochemical change during processing of starch-containing foods or feeds. The degree of starch gelatinization (DSG) not only determines textural and organoleptic properties of processed products but also affects their digestibility when ingested by humans and animals. There are many techniques for measuring DSG, but most are applicable to purified starch only. In our early work published in Journal of Agricultural and Food Chemistry (2012), we developed an enzymatic method for measuring the DSG of dried products in situ by adding a step of mixing samples in water to resolubilize gelatinized starch prior to enzymatic hydrolysis and expressing results as percentages of total starch after correcting for native starch. Yet, we have found that mixing samples slowly in water cannot fully resolubilize gelatinized starch and that correcting for native starch can be difficult. Thus, the method fails to measure DSG accurately for some starchy products. For the present study, our objective was to improve the enzymatic method developed previously in our lab for measuring DSG of dried starchy products. Method: To achieve this objective, we used native and fully gelatinized flours of corn and rice and subjected them to slow mixing in a NaOH solution with varying concentrations (20-140 mM) instead of water for varying time (5, 15 and 70 min). Solubilized starch was then hydrolyzed by amyloglucosidase and D-glucose released by glucose oxidase-peroxidase was measured. We also simplified DSG calculation by eliminating native starch correction. Results: Results show that slowly mixing a dried sample in a NaOH solution of low concentrations (< 100 mM) was able to maximize resolubilization of gelatinized starch while minimizing solubilization of native starch in the sample before enzymatic hydrolysis of solubilized starch. Significance: The new hydration step effectively addressed issues of insusceptibility of insoluble gelatinized starch and susceptibility of soluble native starch to enzymatic attacks and eliminated the need to isolate starch from dry samples when measuring DSG. Compared to our previous method, the improved method is simpler and more reliable for determining DSG in all kinds of starch and starchy products in situ.