Ming-Hsuan Chen

Addressing the dilemmas of measuring amylose in rice.

ABSTRACT Amylose content is a parameter that correlates with the cooking behavior of rice. It is measured at the earliest possible stages of rice improvement programs to enable breeders to build the foundations of appropriate grain quality during cultivar development. Amylose is usually quantified by absorbance of the amylose-iodine complex. The International Network for Quality Rice (INQR) conducted a survey to determine ways that amylose is measured, reproducibility between laboratories, and sources of variation. Each laboratory measured the amylose content of a set of 17 cultivars of rice. The study shows that five different versions of the iodine binding method are in use. The data show that repeatability was high within laboratories but reproducibility between laboratories was low. The major sources of variability were the way the standard curve was constructed and the iodine binding capacity of the potato amylose used to produce the standard. Reproducibility is much lower between laboratories using ...

Effects of hydrothermal processes on antioxidants in brown, purple and red bran whole grain rice (Oryza sativa L.).

The impacts of parboiling and wet-cooking, alone and in combination, on the concentrations of lipophilic antioxidants (vitamin E and γ-oryzanol), soluble (including proanthocyanidins and anthocyanins) and cell wall-bound phenolics, and antioxidant capacities in whole grain rice from six cultivars having different bran colours were investigated. Parboiling rough and brown rice increased the concentrations of lipophilic antioxidants in whole grain rice but decreased the concentrations of total phenolics and antioxidant capacities found in the soluble fraction. After hydrothermal processing of purple bran rice, the retention of extractable anthocyanins was low, but was high for simple phenolics. For proanthocyanidins found in red bran rice, the extractable oligomers with a degree of polymerization (DP) less than 4, increased up to 6-fold; while for oligomers with DP⩾4 and polymers, there was a significant decrease that was positively correlated with the DP and the temperature of the processing methods. The presence of hulls helped to retain water-soluble antioxidants during parboiling.

Development of three allele-specific codominant rice Waxy gene PCR markers suitable for marker-assisted selection of amylose content and paste viscosity

Four Waxy haplotypes, previously identified as each having a different combination of three single nucleotide polymorphisms (SNPs) in the Waxy gene, were highly correlated with apparent amylose content and pasting properties, which are important grain quality traits for predicting cooked rice (Oryza sativa L.) texture and processing properties (Chen et al. in J Cereal Sci 47:536–545, 2008a; Chen et al. in J Cereal Sci 48:781–788, 2008b). Three allele-specific PCR markers were developed to genotype the three aforementioned functional SNPs in a single PCR amplification. Each marker contained two allele-specific primers and one common primer. For each marker, the two allele-specific primers differed by one base at the 3′-end to provide discrimination of SNP alleles, and were labeled with unique fluorescence probes. An additional mismatched base, the third base from the 3′-end, was inserted in some allele-specific primers to increase selectivity. The amplification step of the PCR thermal cycling program was initially set for 20× touch-down cycles with the annealing temperature of the first cycle approximately 6°C above the thermal melting temperature of all three primers at a touch-down rate of −0.3°C per cycle, and followed by 25× regular thermal cycles with the annealing temperature at their thermal melting temperature. The allelic genotypes for each SNP were distinguished from each other by both their differential primer-allele fluorescences and their amplification product lengths. The simplicity of these assays makes it easy to utilize these markers as part of a marker-assisted selection strategy in rice breeding programs selecting for these important grain quality traits.

Concentrations of oligomers and polymers of proanthocyanidins in red and purple rice bran and their relationships to total phenolics, flavonoids, antioxidant capacity and whole grain color

Proanthocyanidins, a flavonoids subgroup, are proposed to have chronic disease modulation properties. With the eventual goal of enhancing rice phytonutrient concentrations, we investigated the genotypic variation of the concentrations of individual oligomers and polymers of proanthocyanidins in red and purple rice brans. A 4.3-fold variation in total proanthocyanidins (sum of oligomers and polymers) in the extractable fraction was found and the concentration was highly correlated with total phenolics, total flavonoids and antiradical capacity. Variation in the proportion of oligomers and polymers existed, with monomers to trimers, 4-6mers, 7-10mers and polymers accounting for 7, 18, 26.5 and 48.7%, respectively, of the total. The redness value a(∗) of whole grain rice measured in CIE L(∗)a(∗)b(∗) color space was negatively and positively correlated with extractable and non-extractable proanthocyanidins, respectively. The variation found indicates it is possible to select rice with bran containing high levels of total proanthocyanidins and specific degree of polymerization profiles.

Correlation of Sensory, Cooking, Physical, and Chemical Properties of Whole Grain Rice with Diverse Bran Color

ABSTRACT Whole grain rice is nutrient dense because of the intact bran layer. The literature indicates that there is genetic variability for compounds in the bran layer of whole grain rice with some compounds in high concentrations in varieties with pigmented bran. The purpose of this study was to compare factors that impact sensory characteristics between different classes of rice bran color. Ten varieties, two from each of five bran colors (white, light brown, brown, red, and purple), were evaluated for descriptive flavor and texture, physical characteristics, gelatinization temperature, apparent amylose content, and polyphenols. Rice that has red or purple pigmented bran has higher contents of phenols and flavonoids, and these varieties were strongly correlated with some flavor attributes. The bran/hay/straw attribute correlated with bran weight and bran thickness, and sweet taste negatively correlated with amylose content. The texture attribute of hardness was significantly different among bran colors...

Bran data of total flavonoid and total phenolic contents, oxygen radical absorbance capacity, and profiles of proanthocyanidins and whole grain physical traits of 32 red and purple rice varieties.

Phytochemicals in red and purple bran rice have potential health benefit to humans. We determined the phytochemicals in brans of 32 red and purple global rice varieties. The description of the origin and physical traits of the whole grain (color, length, width, thickness and 100-kernel weight) of this germplasm collection are provided along with data of total flavonoid and total phenolic contents, oxygen radical absorbance capacity and total proanthocyanidin contents. The contents and proportions of individual oligomers, from degree of polymerization of monomers to 14-mers, and polymers in bran of these 32 rice varieties are presented (DOI: http://dx.doi.org/10.1016/j.foodchem.2016.04.004) [1].

Resistant starch: Variation among high amylose rice varieties and its relationship with apparent amylose content, pasting properties and cooking methods

Resistant starch (RS), which is not hydrolyzed in the small intestine, has proposed health benefits. We evaluated 40 high amylose rice varieties for RS content in cooked rice and a 1.9-fold difference was found. Some varieties had more than two-fold greater RS content than a US long-grain intermediate-amylose rice. The high amylose varieties were grouped into four classes according to paste viscosity and gelatinization temperature based on genetic variants of the Waxy and Starch Synthase IIa genes, respectively. RS content was not different between the four paste viscosity-gelatinization temperature classes. Multiple linear regression analysis showed that apparent amylose content and pasting temperature were strong predictors of RS within each class. Two cooking methods, fixed water-to-rice ratio/time and in excess-water/minimum-cook-time, were compared using six rice varieties that were extremes in RS in each of the genetic variant classes, no difference in RS content due to cooking method was observed.

Effects of Cultivars, Organic Cropping Management, and Environment on Antioxidants in Whole Grain Rice

Whole grain rice contains functional antioxidants such as phenolics, flavonoids (including proanthocyanidins), vitamin E homologs (tocopherols and tocotrienols), and γ-oryzanol that have positive effects on human health. These antioxidants are secondary metabolites in plants that can be induced under external stress. The objectives of this study were to quantify the effects of cultivars, crop management method (organic and conventional), and growing environment on the concentrations of these antioxidants in whole grain rice. Cultivars and environment contributed to a higher percentage of variation in the concentrations of these antioxidants than did crop management method. Cultivars accounted for a greater proportion of the variation than environment for all traits except total tocotrienols and γ-oryzanol. Cultivars that are high in concentrations of these antioxidants were identified, but no one cultivar contained the highest concentration of all antioxidants evaluated. These cultivar differences indicat...

Vitamin E Homologs and γ-Oryzanol Levels in Rice (Oryza sativa L.) During Seed Development

Vitamin E homologs (tocopherols and tocotrienols) and γ-oryzanol have gained significant attention because of their proposed health benefits and ability to increase vegetable oil stability. Changes in the levels of these phytochemicals were examined during seed development. Rapid accumulation of tocopherols, tocotrienols, and γ-oryzanol occurred during early seed development. During the middle stage of seed development, the levels of tocopherols decreased sharply, and the levels of tocotrienols either stayed the same or decreased slightly, whereas γ-oryzanol continued to accumulate until maturity. The levels of these compounds remained constant from maturity to 15 days postmaturity. In conclusion, rice grain for nutraceutical and functional food applications should be harvested during its immature stage to obtain the highest amount of tocopherols, whereas the amounts of the other phytochemicals that were studied can be optimized by harvesting grain at maturity.