Role of amylolytic activities during pregermination on rice kernel morphology and physicochemical properties of isolated starch

Abstract

Background and objectives:The role of amylolytic activities during four stages of pregermination varying on embryonic growth length between 0.5 and 7.0 mm on dynamic changes of rice kernel morphology and chemical composition, crystallinity, and thermal properties of isolated starches from three different Thai rice cultivars-SPT1 (waxy), PTT1 (low amylose), and PNL2 (high amylose)-were investigated. Findings: Amylolytic activities of all rice cultivars significantly increased at each progressive stage, whereas SPT1 showed the highest increase in alpha-amylase activity as the first stage of pregermination. Scanning electron micrographs showed the radial crack of kernel, appearance of individual and nonuniform starch granules after pregermination, particularly of the SPT1 cultivar. Molecular weight distribution of pregerminated brown-rice starch (PGBRS) indicated the partial hydrolysis of starch molecules especially amylopectin, resulting in a decrease fraction of high MW molecules after pregermination. All PGBRS had A-type X-ray diffraction patterns with higher relative crystallinity than their natives, except that of PNL2 cultivar. Pregermination led to the change onset temperature (To) of starch gelatinization (gel_p1) and retrograded amylopectin melting (ret_p1) of PGBRS for all rice cultivars and peak temperature (Tp) of gel_p1 and ret_p1 of PGBRS for only SPT1 cultivar, whereas SPT1 was found at the lower stage than other cultivars. PGBRS at the second and third stage for SPT1, after the third stage for PTT1, and after the second stage for PNL2 had lower enthalpy (DH) of ret_p1 than their natives. Conclusions: Alpha-amylase activity plays a role in partial hydrolysis of amylopectin at amorphous region during rice pregermination which resulted in significant changes of thermal properties for all rice, especially SPT1 cultivar. Pregermination with 2-3-mm EGL of all rice could be used as starch bio-modification to obtain a lower retrograded starch as a functional ingredient of rice-based products. Significance and novelty: The change in thermal properties of waxy SPT1 rice cultivar, which mostly contained amylopectin and highly increased alpha-amylase activity after first stage of pregermination, was more pronounced than those of nonwaxy PTT1 and PNL2 rice cultivars. Cereal Chemistry. 2018;95:543-554. wileyonlinelibrary.com/journal/cche © 2018 AACC International | 543 K E Y W O R D S amylolytic activities, isolated rice starch, kernel morphology, physicochemical properties, pregermination How to cite this article: Kupkanchanakul W, Thongngam M, Shi Y-C, Naivikul O. Role of amylolytic activities during pregermination on rice kernel morphology and physicochemical properties of isolated starch. Cereal Chem. 2018;95:543-554.

Effects of high hydrostatic pressure on structures, properties of starch, and quality of cationic starch

“…The gelatinization characteristics of starch were determined by a differential scanning calorimeter (200PC; Netzsch, Germany) according to the method of Kupkanchanakul et al (). 5.00 mg (dry basis) of starch samples was accurately weighed in aluminum pan with 15 μl deionized water and was stayed for 12 hr at 4°C.…”

“…The X-ray patterns of starch were obtained using an X-ray diffractometer (D8 ADVANCE; Bruker AXS GMBH, Germany) under the following conditions: radiation source: Cu Kα; angle of diffraction scanned: 1-40° (Kupkanchanakul, Thongngam, Shi, & Naivikul, 2018).…”

Gluten-Free Rice Breading Using Composited Rice Flour and Pre-Germinated Brown Rice Flour for Health Benefits

“…In addition, the PGBRF substitu-tion in rice bread formula led to the increase in yellowness and redness of C-RB and the decrease in lightness, which was closely similar to that of C-WB (Table 4). The increasing yellowness of RB after PGBRF substitution was probably due to the PGBRF containing sugar, which was the product of partial degradation of starch during pre-germination (9).…”

“…Germination process has been widely reported to induce chemical changes of rice due to a complex biochemical process of starch, protein and other components being considerably activated, particularly during rice paddy growth at 0.5-7 mm of embryonic growth length (EGL), which is called pre-germination process (8,9). Pre-germinated brown rice flour (PGBRF) from 24-48 h of germination, which were substituted in the composited wheat-rice bread formula, were reported to reduce hardness of bread after baking and to reduce staling rate after storage (10).…”