Abstract
The starch digestion processing of whole grain foods is associated with its health benefits in improving insulin resistance. This study modified the digestibility of whole quinoa flour (WQ) via heat-moisture treatment (HMT), HMT combined with pullulanase (HMT+P), HMT combined with microwave (HMT+M), and HMT combined with citric acids (HMT+A), respectively. Results showed that all the treatments significantly increased (p < 0.05) the total dietary fiber (TDF) content, amylose content, and resistant starch (RS) content, however, significantly decreased (p < 0.05) the amylopectin content and rapidly digestible starch (RDS) content of WQ. HMT+P brought the highest TDF content (15.3%), amylose content (31.24%), and RS content (15.71%), and the lowest amylopecyin content (30.02%) and RDS content (23.65%). HMT+M brought the highest slowly digestible starch (SDS) content (25.09%). The estimated glycemic index (eGI) was respectively reduced from 74.36 to 70.59, 65.87, 69.79, and 69.12 by HMT, HMT+P, HMT+M, and HMT+A. Moreover, a significant and consistent reduction in the heat enthalpy (ΔH) of WQ was observed (p < 0.05), after four treatments. All these effects were caused by changes in the starch structure, as evidenced by the observed conjunction of protein and starch by a confocal laser scanning microscope (CLSM), the decrease in relative crystallinity, and transformation of starch crystal.
Highlights
(p < 0.05), respectively, which was consistent with a previous report that the total dietary fiber (TDF) content in whole wheat flour significantly increased after heat-moisture treatment (HMT) [26]
The results agreed with the results of Niu et al who reported that HMT combined with microwave (HMT+M) increased the amylose content in potato starch [29]
whole quinoa flour (WQ): whole grain quinoa flour; HMT: heat-moisture treated whole grain quinoa flour; HMT+P: HMT combined with pullulanase treated whole grain quinoa flour; HMT+M: HMT combined with microwave treated whole grain quinoa flour; HMT combined with citric acids (HMT+A): HMT combined with acids treated whole grain quinoa flour
Summary
It was reported that various modification methods can affect the starch digestion process, and among them, heat-moisture treatment (HMT) has received increasing attention due to its features of high efficiency, safety, and environmental protection [5]. HMT was found to change the physicochemical property of starch, such as decreasing the relative crystallinity, changing the starch type from B to A, decreasing the swelling capacity and solubility, increasing the phase transition temperature, and widening the gelatinization temperature ranges [9]. Other treatments, such as physical, chemical, and enzymatic modifications, are usually combined with HMT to enhance the modification effects. Cheng et al found that parboiling-HMT resulted in the formation of rice amylose lipid complexes, and the SDS and RS content increased to 45.8%
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