Editorial for the Special Issue, “Quality Assay, Processing and Bio-Function of Rice Products”

Rice is one of the most important cereals in the world alongside wheat and maize [...

Characteristics of Physicochemical Properties of Chalky Grains of <i>Japonica</i> Rice Generated by High Temperature during Ripening

Global warming has caused devastating damage to starch biosynthesis, which has led to the increase in chalky grains of rice. This study was conducted to characterize the qualities of chalky rice grains and to develop the estimation formulae for their quality damage degree. We evaluated the chalkiness of 40 Japonica rice samples harvested in 2019, in Japan. Seven samples with a high ratio of chalky rice grains were selected and divided into two groups (whole grain and chalky grain). As a results of the various physicochemical measurements, it was shown that the surface layer hardness (H1) of cooked rice grains from chalky grains was significantly lower, and their overall hardness was significantly lower than those from the whole grains. In addition, α- and β-amylase activities, and sugar contents of the chalky rice grains were significantly higher than those of the whole rice grains. The developed estimation formula for the degree of retrogradation of H1 based on the α-amylase activities and pasting properties, showed correlation coefficients of 0.84 and 0.81 in the calibration and validation tests, respectively. This result presents the formula that could be used to estimate and to characterize the cooking properties of the rice samples ripened under high temperature

Evaluation of Hardness and Retrogradation of Cooked Rice Based on Its Pasting Properties Using a Novel RVA Testing

With rice being one of the most important crops worldwide, rapid and objective quality evaluation methods based on physicochemical measurements of rice are necessary. We compared the pasting properties of various rice samples using three different heating and cooling programs (maximum temperatures were 93, 120, and 140 °C, respectively) in a newly developed high-temperature-type Rapid Visco Analyzer (RVA, RVA 4800). Furthermore, we investigated the relationship between the different pasting properties measured by the three programs, with starch microstructure measured by iodine scanning analysis, the physical properties of the cooked rice measured by a Tensipresser after 2 h at 25 °C or after 24 h at 6 °C, and prolamin ratio measured by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The consistency value (final viscosity–minimum viscosity) yielded by a new program of maintenance for 2 min at 120 °C using RVA 4800 had a higher positive correlation with retrograded surface hardness H1(R) (r = 0.92), retrograded overall hardness H2(R) (r = 0.90), and the absorbance at λmax (Aλmax) of cooked rice (r = 0.88) and resistant starch (r = 0.80) than those by the conventional program at 93 °C. We developed estimation formulae for H1(R) for various kinds of rice, of which the determination coefficient was 0.86. It led to an easy and rapid assay method for the cooking properties of the various rice samples

Development of formulae for estimating amylose content, amylopectin chain length distribution, and resistant starch content based on the iodine absorption curve of rice starch

<div><p>Not only amylose but also amylopectin greatly affects the gelatinization properties of rice starch and the quality of cooked rice grains. We here characterized the starches of 32 rice cultivars and evaluated the relationship between their iodine absorption curve, apparent amylose content (AAC), pasting property, resistant starch (RS) content, and chain length distribution of amylopectin. We found that the iodine absorption curve differed among the various sample rice cultivars. Using the wavelength at which absorbance becomes maximum on iodine staining of starch (λmax), we propose a novel index, “new λmax” (AAC/(λmax of sample rice starches–λmax of glutinous rice starch)). We developed the novel estimation formulae for AAC, RS contents, and amylopectin fractions with the use of λmax and “new λmax.” These formulae would lead to the improved method for estimating starch properties using an easy and rapid iodine colorimetric method.</p></div

Development of formulae for estimating amylose content and resistant starch content based on the pasting properties measured by RVA of <i>Japonica</i> polished rice and starch

<div><p>We searched for the easy and simple method to measure the novel indicators which reflect not only AAC, but also (RS) based on pasting properties using RVA. Novel indexes such as SB/Con and Max/Fin (Maximum viscosity/Minimum viscosity) ratios had a very high correlation with proportion of intermediate and long chains of amylopectin; Fb₁₊₂₊₃ (DP ≧ 13). In <i>Japonica</i> polished rice, estimation formulae for AAC and RS content were developed using novel indexes based on pasting properties by RVA, and these equations showed determination coefficients of 0.89 and 0.80 for calibration and 0.71 and 0.75 for validation test. We developed the estimation formulae for AAC and RS content for <i>Japonica</i> starch samples. These equations showed determination coefficients of 0.86 and 1.00 for calibration and 0.76 and 0.83 for validation test, which showed that these equations can be applied to the unknown rice samples.</p></div

2-<i>O</i>-α-D-Glucosylglycerol Phosphorylase from <i>Bacillus selenitireducens</i> MLS10 Possessing Hydrolytic Activity on β-D-Glucose 1-Phosphate

<div><p>The glycoside hydrolase family (GH) 65 is a family of inverting phosphorylases that act on α-glucosides. A GH65 protein (Bsel_2816) from <i>Bacillus selenitireducens</i> MLS10 exhibited inorganic phosphate (Pi)-dependent hydrolysis of kojibiose at the rate of 0.43 s⁻¹. No carbohydrate acted as acceptor for the reverse phosphorolysis using β-d-glucose 1-phosphate (βGlc1<i>P</i>) as donor. During the search for a suitable acceptor, we found that Bsel_2816 possessed hydrolytic activity on βGlc1<i>P</i> with a <i>k</i>_cat of 2.8 s⁻¹; moreover, such significant hydrolytic activity on sugar 1-phosphate had not been reported for any inverting phosphorylase. The H₂¹⁸O incorporation experiment and the anomeric analysis during the hydrolysis of βGlc1<i>P</i> revealed that the hydrolysis was due to the glucosyl-transferring reaction to a water molecule and not a phosphatase-type reaction. Glycerol was found to be the best acceptor to generate 2-<i>O</i>-α-d-glucosylglycerol (GG) at the rate of 180 s⁻¹. Bsel_2816 phosphorolyzed GG through sequential Bi-Bi mechanism with a <i>k</i>_cat of 95 s⁻¹. We propose 2-<i>O</i>-α-d-glucopyranosylglycerol: phosphate β-d-glucosyltransferase as the systematic name and 2-<i>O</i>-α-d-glucosylglycerol phosphorylase as the short name for Bsel_2816. This is the first report describing a phosphorylase that utilizes polyols, and not carbohydrates, as suitable acceptor substrates.</p></div

Possibility for Prevention of Type 2 Diabetes Mellitus and Dementia Using Three Kinds of Brown Rice Blends after High-Pressure Treatment

As it has been reported that type 2 diabetes mellitus increases the risk of Alzheimer&rsquo;s disease, we investigated how to prevent type 2 diabetes and dementia using biofunctional boiled rice. We adopted unpolished super-hard rice (SHBR) for diabetes and wax-free unpolished black rice (WFBBR) for dementia and blended those with ordinary non-polished rice (KBR) (blending ratio 4:4:2), adding 2.5% waxy black rice bran (WBB) and 0.3% rice oil after high-pressure treatment (HPT) (WFBSK) to improve its palatability. This boiled rice is rich in dietary fiber, anthocyanin, free ferulic acid and &beta;-secretase inhibitory activity. A randomized, parallel-group comparison study was conducted for 12 weeks with 24 subjects, using Cognitrax to evaluate their cognitive function primarily. Furthermore, as the secondary purpose, we performed a single-dose test for postprandial blood glucose and insulin secretion at the end of the human intervention test. After 12 weeks, consumers of the WFBSK rice exhibited significant improvement in language memory by cognitive test battery compared with those who consumed the control white rice (p &lt; 0.05). Moreover, subjects who consumed the WFBSK rice had lower insulin secretion levels than those who consumed the control polished rice (p &lt; 0.05)