Structural Characteristics, Properties, and In Vitro Digestibility of Rice

Abstract

Using rice samples derived from normal rice cultivars and endosperm starch mutant, we investigated key factors contributing to the enzyme digestibility of steamed rice grains. The chemical composition of polished rice grains, structural features of endosperm starch, and enzyme digestibility of steamed rice grains were examined. The protein content of polished rice grains was 4.6–9.1%, amylose content was 4–27%, the DPn of purified amylose was 900–1,600, the amylopectin short/long chain ratio was 1.2–5.9, and the enzyme digestibilities of steamed polished rice grains were 0.9–12.6 °Brix. Amylose content and RVA parameters (viscosity, breakdown, and setback) correlated significantly with enzyme digestibility of steamed rice grains. Multiple regression formulas were constructed to predict digestibility of steamed rice grain as a function of the molecular characteristics of the starch. When both amylose content and the short/long chain amylopectin ratio were used as predictor variables, they accounted for >80% of the observed variance in digestibility of steamed rice grains. Multiple regression revealed that the more digestible rice samples had starch with a lower amylose content and more short‐chain amylopectin. Reassociation of amylose‐lipid complex and recrystallization of amylopectin in the stored steamed rice grains was monitored by differential scanning calorimetry (DSC), and the observed retrogradation properties were related to the structural characteristics of starch and to the enzyme digestibility of steamed rice grains.

Late-maturing cooking riceSensyurakuhas excellent properties, equivalent to sake rice, for high-quality sake brewing

“…amylose/ amylopectin content and side-chain structure of amylopectin. 4,13,14,20) Thus, the previous reports indicate a strong correlation between the RVA parameters and brewing properties (water absorption and enzyme digestibility). Further, the side-chain of amylopectin in late-maturing YAM tends to be shorter than that in early-maturing GOM, and one of the reasons of this phenomenon is thought to be caused by the low temperature during the ripening period.…”

“…3(A)), including peak viscosity (PV), breakdown (BD), set back (SB), and pasting temperature (PT: start of gelatinization), in the heat-induced gelatinization of rice flour were measured using Rapid Visco Analyzer (RVA; Model RVA-4500, Newport Scientific, Australia) according to the method of Aramaki et al 13) and Okuda et al 14) : distilled water was added to 2.8 g (10%, w/w, dry weight basis) of rice flour to make the total weight to 28 g. Each suspension was equilibrated at 50°C for 1 min, heated at a rate of 5°C/min to 95°C, maintained at 95°C for 5 min, cooled to 50°C at a rate of 5°C/min, and then maintained at that temperature for 6 min. A constantly rotating paddle (160 rpm) was used.…”

“…3(A)), including peak viscosity (PV), breakdown (BD), set back (SB), and pasting temperature (PT: start of gelatinization), in the heatinduced gelatinization of rice flour determined using a RVA. 13,14) The reported correlations are as follow 13) : the crude protein content of rice is correlated negatively with PV and BD, and positively with PT. Water absorption of rice is correlated positively with PV and BD.…”

Effects of Milling Ratio on Properties of Endosperm Starches and Rice Flours from Milled Japanese Rice Grains

“…11,16) FI and FIIb FIIa values for the 70% milled rice samples closely correlate with starch retrogradation and enzyme digestibility of the steamed rice grains. 9,11) The observed FI and FIIb FIIa values were relatively constant within the same cultivar from brown rice to a 30% milling ratio, although some differences were found among the three cultivars (Table 1). This indicates that even if the milling ratio is different, the starch structural properties may not affect starch retrogradation or possibly enzyme digestibility of steamed rice grains of the same cultivar.…”

“…8,9) Amylopectin chain length distribution and retrogradation properties have also been observed to affect enzyme digestibility of steamed rice grains. 9 11) In the present study, the physicochemical and structural properties of endosperm starches and rice flours prepared from milled Japanese rice grains of various milling ratios were examined in order to clarify the relationship between milling ratio and starch properties of milled rice grains.…”