4.6 Article

Increasing Protein Content of Rice Flour with Maintained Processability by Using Granular Starch Hydrolyzing Enzyme

Journal

MOLECULES
Volume 28, Issue 8, Pages -

Publisher

MDPI
DOI: 10.3390/molecules28083522

Keywords

rice flour; rice protein; granular starch hydrolyzing enzyme; hydrolytic mechanism; physicochemical property

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In this study, rice flour (RF) with higher protein content was prepared using a granular starch hydrolyzing enzyme (GSHE). The hydrolytic mechanism of RF and rice starch (RS) was established through characterization of particle size, morphology, crystallinity, and molecular structures. Processability of RF was evaluated through thermal, pasting, and rheological properties. The GSHE treatment resulted in sequential hydrolysis of crystalline and amorphous areas on the starch granule surface, leading to changes in amylose content and protein content in RF. However, the processability of RF was properly maintained.
Rice flour (RF) has become a promising food material. In the present study, RF with higher protein content was prepared using a granular starch hydrolyzing enzyme (GSHE). Particle size, morphology, crystallinity, and molecular structures of RF and rice starch (RS) were characterized to establish a hydrolytic mechanism; thermal, pasting, and rheological properties were determined to evaluate processability using differential scanning calorimetry (DSC), rapid viscosity analysis (RVA), and rheometer, respectively. The GSHE treatment resulted in pinholes, pits, and surface erosion through sequential hydrolysis of crystalline and amorphous areas on the starch granule surface. The amylose content decreased with hydrolysis time, while the very short chains (DP < 6) increased rapidly at 3 h but decreased slightly later. After hydrolysis for 24 h, the protein content in RF increased from 8.52% to 13.17%. However, the processability of RF was properly maintained. Specifically, the data from DSC showed that the conclusion temperature and endothermic enthalpy of RS barely changed. The result of rapid RVA and rheological measurement indicated that RF paste viscosity and viscoelastic properties dropped rapidly after 1 h hydrolysis and thereafter recovered slightly. This study provided a new RF raw material useful for improving and developing RF-based foods.

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