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 accounte...

Structural Characteristics, Properties, and In Vitro Digestibility of Rice

The effects of environmental temperature during the early development of seeds on the structural characteristics of the endosperm starch were investigated using near-isogenic lines of rice plants (Taichung 65, waxy), grown under temperature controlled conditions. High performance gel permeation chromatography (HPLC) demonstrated that Pseudomonas isoamylase-debranched amylopectins of rice plants grown at lower temperature (25 °C) contain increased amounts of short chains and decreased amounts of long chains as compared with amylopectins obtained from rice plants grown at higher temperature (30°C). By high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) of isoamylase-debranched amylopectins it was detected that the amount of unit chains with degree of polymerization (DP) 6 and 11-13, in the amylopectin of rice plants grown at lower temperature (25°C) had significantly increased and the amount of unit chains with DP 8, 22-24 and 29 had significantly decreased, as compared with the amylopectin of rice plants grown at higher temperature (30°C ). It was confirmed that the environmental temperature between 5 and 10 d after pollination strongly influenced the structure characteristics of the endosperm starch of rice plants.

The effect of environmental temperature on distribution of short chains of rice amylopectin

Structural and physicochemical characteristics of endosperm starch from milled rice grains of seven Japanese cultivars used in sake production were examined. Amylose content was 15.2–20.2%, number-average degree of polymerization (DPn) of amylose was 900–1,400, and the ratio of short-to-long chain amylopectin was 2.7–3.5, respectively. The degree of retrogradation of purified starch stored for seven days at 4°C after gelatinization was 20–31%. The degree of retrogradation correlated negatively with the ratio of short-to-long chain amylopectin. The effect of holding time after steaming on enzyme digestibility and starch retrogradation of steamed rice grains was investigated. The longer the holding time after steaming, the greater the extent of retrogradation, and the less the degree of enzymatic digestibility. The decreased rate of enzyme digestibility correlated with amylopectin chain length distribution. Samples with short-chain amylopectin exhibited a slow decrease in enzyme digestibility. It w...

Structural and Retrogradation Properties of Rice Endosperm Starch Affect Enzyme Digestibility of Steamed Milled-Rice Grains Used in Sake Production

This study investigated the effect of postharvest drying conditions on resistant starch (RS) content and quality of rice. Paddy was subjected to hot-air drying at 40, 65, 90, and 115°C, and sun dry...

Influence of postharvest drying conditions on resistant starch content and quality of non-waxy long-grain rice (Oryza sativa L.)

Chain-length distributions of amylopectins by HPAEC-PAD from japonica and indica waxy-rice samples were characterized, and the relationship between the chain-length distributions and pasting properties of rice flour by RVA and the physical properties of cooked rice grains by Tensipresser were studied. In comparison with jaonica and indica types, the pattern of chain-length distribution of indica amylopectin typically differed, and the ratio of degree of polymerization (DP) 6-12, fa short chains of indica type was clearly lower, while the ratio of DP>13, fb1+2+3 long chains was clearly higher. The physical properties of cooked rice grains and powder pasting of the indica type showed clearly as hard type starch. There were differences in the chain-length distribution among japonica waxy-rice starches. The ratios of fb3, DP>37 for japonica waxy amylopectins were positively correlated with RVA paste viscosity parameters, such as minimum viscosity, final viscosity, pasting temperature and setback, and iodine absorbance. Iodine absorbance was negatively correlated with properties of cooked rice grains, such as overall adhered mass, L6. The results showed the possibility that the long chain portion of the amylopectin structure is a factor in regulating its starch physical properties.

Relationship between chain-length distributions of waxy rice amylopectins and physical properties of rice grains

Starches from three waxy rice cultivars (Hakuchoumochi, Hiyokumochi and Koganemochi) showing different physical properties were studied in order to identify the relationship between physical properties and their amylopectin structures. Pastes of Hakuchoumochi, Hiyokumochi and Koganemochi are known as soft, intermediate and hard, respectively. Pasting properties of the soft type starch showed the lowest setback (SB) and the highest breakdown (BD) among the three. The hard type showed the reverse relationship and the middle type showed an intermediate property. To follow these physical properties, partial hydrolysates of starches with debranching enzymes were prepared and the distributions of debranched short side-chains in amylopectin existing mainly in the outer layer of the amylopectin were analyzed by HPAEC-PAD. Hakuchou mochi was composed of plentiful shortish chains and scarce longish chains and suggested to be resistant to retrogradation. Koganemochi had the reverse properties and was suggested to be sensitive to retrogradation. Hiyokumochi was intermediate. From these results, it could be presumed that a feature of chain-length distri bution on the outer layer of the amylopectin molecule influenced the physical properties relating to retrogra dation.

Relationship between Physical Properties and Amylopectin Structure of Waxy Rice Starch

Starches from a variety of Sake-rice (Yamadanishiki, Gohyakumangoku, Miyamanishiki, Kitanishiki and Wakamizu) which are suitable for Sake brewing were investigated by comparing them with Koshihikari starch to recognize their structural properties of amylopectins. The partial hydrolysate (about 15% hy drolysis) of starch with isoamylase was fractionated into three fractions (fr.1, fr.2 and fr.3) by gel permeation chromatography (GPC) with a Toyopearl HW-50S, and then the short-amylose chains derived mainly from the outer portion of the amylopectin collected in the fr.3 were analyzed by a HPAEC-system equipped with a pulsed amperometric detector (HPAEC-PAD). From comparison of the chain-length distributions between Sake-rice starches and that of Koshihikari, it was found that Sake-rice amylopectins were plentiful in longish chains around DP 13-23 and scarce in shortish chains around DP 6-12, suggesting a structural property susceptible to retrogradation. The pasting properties of Sake-rice starches analyzed by Rapid Visco Analyzer (RVA) showed higher pasting temperature (PT), higher setback (SB), and lower breakdown (BD) than Koshi hikari starch, suggesting the outer portions of amylopectin had abundant longish debranched short side chains. These results suggested that rice starches with amylopectins susceptible to retrogradation are adequate for Sake-rice.

Structural Properties of Amylopectins Corresponding to Physical Properties of Rice Starches Appropriate for Sake

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Relationship between Physical Properties and Amylopectin Structure of Waxy Rice Starch

Structural Properties of Amylopectins Corresponding to Physical Properties of Rice Starches Appropriate for Sake