Effects of Shear and Heat Milling Treatment on Thermal Properties and Molecular Structures of Rice Starch

• Published in: Starch - Stärke Vol. 70; no. 3-4
• Main Authors: Murakami, Seigo, Fujita, Naoko, Nakamura, Yasunori, Inouchi, Naoyoshi, Oitome, Naoko F., Koda, Tomonori, Nishioka, Akihiro
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.03.2018
• Subjects: amorphous; Amylopectin; Crystal structure; Crystallinity; Flour; Glucans; Grain; Heat treatment; High temperature; Milling (machining); Moisture content; Molecular weight; Mortars (material); Rice; rice flour; rice starch; shear and heat; Starch; Temperature effects; Thermal properties; Thermodynamic properties; Water content; Weight reduction
• ISSN: 0038-9056; 1521-379X
• DOI: 10.1002/star.201700164

The effects of a previously reported shear and heat milling machine (SHMM) on the crystallinity and molecular architecture of starch are examined. The SHMM produces amorphous starch flour from rice grains containing crystalline starch. A high temperature of 120 °C and a distance of 10 µm between milling mortars were essential for the complete conversion of crystalline starch to amorphous starch. The effects of increasing the gap between mortars to 100 µm and decreasing the temperature to 15 °C were tested. The use of highly dried rice flour containing only 1% water (w/w) was also examined. The results suggest that the transition from crystalline starch to amorphous starch produced by the SHMM is a gelatinization process because a significant amount of water in the rice grains contributes to the formation of amorphous starch. It was also found that high temperature milling specifically, but only partially, cleaved the cluster‐interconnecting chains of amylopectin, resulting in the formation of glucans smaller than normal amylopectin. Novel finding from these results is that the coordinated action of high temperature milling, a small gap, and endogenous water in amylopectin induces gelatinization, accompanied by a reduction in the molecular weight of amylopectin cut at the B2‐3 branches. Effect of simultaneous shear and heat milling on the crystallinity and molecular architecture of starch was examined. It was found that high temperature milling partially cleaved the cluster‐interconnecting chains of amylopectin, resulting in the formation of glucans smaller than normal amylopectin.