Effects of cooking on anthocyanin concentration and bioactive antioxidant capacity in glutinous and non-glutinous purple rice

Purple rice is a source of bioactive antioxidants for rice consumers. Loss of the major antioxidant compounds after a range of cooking processes was evaluated by measuring the change in anthocyanin concentration (ATC) and antioxidant capacity (DPPH activity) of four non-glutinous and four glutinous genotypes. However, soaking in water prior to cooking generally decreased ATC and DPPH activity more in non-glutinous than in glutinous genotypes. Wet cooking (WC) and soaking before wet cooking (S-WC) led to almost all the ATC and DPPH activity being lost with only slight variation between genotypes. In the glutinous genotype PES, which had the highest raw rice ATC, the highest ATC remained when cooked by the WC method. By contrast, almost no ATC remained after WC and S-WC in the low ATC genotypes such as KDK. Overall, the loss of ATC on cooking was greater in non-glutinous than glutinous genotypes for both WC and S-WC, but the reverse occurred for DPPH activity. Wet cooking using electric rice cooker retained higher ATC than the pressure cooking. Thus, for genotypes with high ATC and antioxidant capacity, the selection of cooking method is critical for retaining and stabilizing rice quality

Easy and rapid detection of iron in rice grain

In this study, we show how a preliminary determination of grain Fe in rice may be made with reaction to Perls’ Prussian blue, a stain for Fe (III). Differential localization of Fe in grain parts was indicated by the intensity of reaction of tissue Fe to the dye. The blue colour reaction was most intense in the embryo, weak in the aleurone layer of the pericarp and invisible in the endosperm. The staining intensity also varied with the region of the embryo, generally being strongest in the scutellum, intermediate in the coleorhiza and weakest in the coleoptile. Variation in the reaction to Perls’ Prussian blue was observed among eleven rice genotypes with varying grain Fe contents. The intensity of the blue colour reaction in the embryo of different rice genotypes was indicative of their grain Fe contents for both brown and white (polished) rice. Those with high grain Fe, >14 mg Fe kg-1, were clearly distinguishable from those with <10 mg Fe kg-1 with Perls’ Prussian blue. We suggest that this simple staining procedure may be used to quickly screen for high Fe contents in large germplasms containing hundreds of rice entries, using reactions in genotypes with known grain contents as standards

Responses of milling quality to nitrogen and water management in modern long grain rice varieties

This study determined how nitrogen (N) fertilizer and water management affect grain yield and milling quality of 9 modern rice varieties with long, slender grain in two field experiments. The effect of N on rice grown in wetland culture was evaluated at 0, 60 and 120 kg N ha-1. In a second experiment the rice in aerobic and wetland culture were compared. The rice in both experiments were grown to maturity and evaluated for yield, head rice yield and chalkiness. Grain yield increased with increasing N application, head rice yield increased with increasing N in 8 varieties, while chalkiness was more than halved in 7 varieties. Grain N also increased with increasing N fertilizer, but high head rice yield in several varieties was associated with relatively low grain N. Under aerobic cultivation, all 9 varieties yielded less than in wetland culture, the head rice yield was lower and chalkiness was higher except in 2 varieties. In both experiments, grain yield was associated positively with head rice yield and negatively with chalkiness. Head rice yield and chalkiness were negatively associated in the water experiment but not in the N experiment. This study has shown that modern high yielding rice varieties generally respond positively to nitrogen fertilizer in better milling quality as well as in yield. Grain chalkiness of the varieties was more stable against variation in the environment than head rice yield

Variation of milling and grain physical quality of dry season Pathum Thani 1 in Thailand

Pathum Thani 1 (PTT1) is a photoperiod-insensitive, aromatic Thai rice variety that is grown year-round. The rice from some locations is often priced lower than others due to sub-standard grain quality. This study sought to determine the limiting grain quality characteristic(s) in dry season PTT1 and their distribution across Thailand’s irrigated rice regions. To do so, we evaluated the milling and physical quality of milled rice grain of dry season PTT1 from 24 provinces in 5 regions in Thailand. Sixty-seven paddy rice samples were collected and evaluated for head rice yield, chalkiness, whiteness, and translucency. Head rice yield varied by region, with the highest (48.1%) found in samples from the Central region, compared to 34.5-39.7% elsewhere. Head rice chalkiness was the physical quality that varied more widely among the provinces within each region than among regions, with chalkiness at a level that would adversely affect price in more than one-half of the samples. Contrary to the general perception that chalky grain is less resistant in milling, head rice yield actually increased with total chalkiness, expressed as % chalky grain by weight. The total chalkiness correlated negatively with translucency, while the head rice chalkiness correlated positively with whiteness. Grain chalkiness was identified as the grain quality attribute of PTT1 rice that varied with location; this directly affected the price of milled rice grain, as well as indirectly through its relationship with head rice yield and visual appearance of the milled rice grai

Simultaneous Quantification of Anthocyanins and Phenolic Acids in Pigmented Rice (Oryza sativa) using UPLC-PDA/ESI-Q-TOF

Anthocyanins and phenolic acids are the major antioxidants in purple rice. The method conditions were specified and not coved for both anthocyanins and phenolic acids. The objective of this study was to adopt the UPLC coupled with ESI-MS method for determination of the major anthocyanins and phenolic acids under the same condition in purple, red and white rice varieties. A UPLC-PDA/ESI-Q-TOF method was optimized with a high linearity for all analyzed compounds with regression coefficients greater than 0.99. Repeatability was good with the relative standard deviation values generally less than 5.5%. The limit of detection and quantification ranged from 1.9-36.6 and 5.0-123.1 mu g kg(-1), respectively. Spike recoveries were between 81-116%. Mass spectroscopy was used to confirm identity in the positive ion mode for all analyzed compounds Cyanidin-3-glucoside and ferulic acid were the most abundant anthocyanins and phenolic acids, respectively. Bound ferulic acid was higher in purple rice than in red and white rice flours. This developed procedure can be used to facilitate the rapid screening of rice seed banks for anthocyanins and phenolic acids of interest for rice pre-breeding

Grain zinc and yield responses of two rice varieties to zinc biofortification and water management

Zinc (Zn) biofortification can improve grain yield and nutritional quality in rice, but its effectiveness is subject to agronomic practices and other factors. In a previous study, the application of Zn to soil enhanced grain Zn in lowland rice in well-drained and waterlogged soil, whereas grain Zn in upland rice increased only in well-drained soil. This new study explores the hypothesis that the application of foliar Zn can enhance grain Zn in upland and lowland rice grown under waterlogged and well-drained conditions. Two rice varieties, CNT1 (wetland rice) and KH CMU (upland rice) were grown in containers in waterlogged or well-drained soil with three Zn treatments (no Zn, soil Zn and foliar Zn). For the soil Zn treatment, 50 kg ZnSO4 ha−1 was applied to the soil before transplanting. For the foliar treatment, 0.5% ZnSO4 (equivalent to 900 L ha−1) was applied at booting and repeated at flowering and milky growth stages. Grain yield in CNT1 was 15.9% higher in the waterlogged than in the well-drained plants, but the water regime had no effect on grain yield in KH CMU. Grain Zn concentration in CNT1 increased from 19.5% to 32.6% above the no Zn control when plants were applied with soil or foliar Zn. In KH CMU, there was an interaction between the water regime and Zn treatment. Application of foliar Zn increased grain Zn by 44.6% in well-drained and 14.7% in waterlogged soil. The results indicate strong interaction effects between variety, water regime and Zn fertilizer application on Zn biofortification in rice. Thus, the selection of rice varieties and growing conditions should be considered in order for producers to achieve desirable outcomes from high grain Zn concentrations

Effects of Foliar Application of Zinc on Grain Yield and Zinc Concentration of Rice in Farmers’ Fields

Three field experiments were conducted on farms in Chiang Mai, Thailand in 2015 to evaluate the effects of: (i) foliar application of Zn on the grain yield and grain Zn concentration of rice and (ii) using Zn-enriched seeds in the next cropping on growth and yield. Zn was applied by foliar spraying 0.5% ZnSO 4 at three different growth stages: booting, flowering, and early milk stages. Foliar spraying of Zn improved the grain Zn concentration by 41% in one field, and an average of 30% across the three fields. The foliar- sprayed Zn did not, however, affect the grain yield in any of the fields. The Zn-enriched seeds also did not affect the grain yield of the plants in the farmers’ fields in the next cropping, probably because of the high amount of soluble Zn already in the experimental fields. Clearly, the foliar application of Zn significantly increased grain Zn concentration, but had no effect on grain yiel

Iron and zinc variation along the grain length of different Thai rice varieties

This study examined the distribution of iron (Fe) and zinc (Zn) along the grain length of seven rice varieties. The experiment was conducted in a completely randomized design with two factors (variety and grain fraction) and three independent replications. Samples of brown and white rice of six common Thai rice varieties and a high Fe and Zn variety, IR68144, were transversely cut into three fractions per grain (basal, middle, and distal) with approximately the same length in each fraction. The concentration of Fe and Zn was determined by the dry ashing method and quantified using atomic absorption spectrometry. The middle grain fraction of brown rice was found to have the lowest Fe and Zn with greater concentration of Fe and Zn in the basal (embryo end) than the other fractions. The rice varieties differed in the amount of Fe and Zn allocated to different fractions of the endosperm (white rice). The potential for loss of Fe and Zn during milling due to their uneven distribution along the grain length will become more significant when higher nutrient concentrations are involved, such as those achieved by biofortification efforts. Micronutrient distribution needs to be taken into consideration to ensure that rice consumers benefit from Fe and Zn biofortification

Anthocyanin and phenolic acid profiles in purple, red and non-pigmented rice during germination

There is a growing interest in using germinated rice in health products based on their antioxidant properties but studies exploring differences in pigmented and non-pigmented rice types are limited. Therefore, anthocyanin and phenolic acid contents and composition were quantified using UPLC over 6 days of germination in three pigmented (two purple and one red) and one non-pigmented rice genotypes. Most of the anthocyanin content in purple rice, mainly cyanidin-3-glucoside and peonidin-3-glucoside, was lost during the imbibition and radicle emergence phase of germination. By contrast, there were only small changes in free and bound phenolic acid fractions over the 6 days of germination in all genotypes. Vanillic and ferulic acids comprised the main components of the free and bound pools, respectively. Vanillic acid contents, but not ferulic acid, were considerably greater in purple rice than in red and non-pigmented rice. Germination rapidly decreased the anthocyanin content in purple rice, but only had a minor effect on the free and bound phenolic acids in purple, red and non-pigmented rice. The increasing content of bound p-coumaric, ferulic and vanillic acids in germinated purple rice may provide an opportunity to develop rice products as functional foods

Identifying rice grains with premium nutritional quality among on-farm germplasm in the highlands of Northern Thailand

Local rice varieties with premium nutritional quality grains are beneficial to consumers, and their genetic traits may be deployed in breeding programmes for many purposes. This study explores grain quality characteristics with health implications of rice germplasm maintained and used by farmers in the highlands of Northern Thailand. Concentrations of iron (Fe), zinc (Zn), phenols and anthocyanin and anti-oxidative capacity were determined in the caryopsis without husk of 77 samples of rice seed collected from farmers. Entries with the highest grain quality characteristics identified were grown together with four standard check varieties at two different elevations in a farmer’s field at Mae Wang District of Chiang Mai province (800 m above mean sea level), as well as in pots at Chiang Mai University (CMU) (330 m above mean sea level). The grain quality characteristics were determined at maturity, separately for 10 individual plants grown at CMU. A wide variation in all the grain quality characteristics was found among samples grown in the farmer’s field. There were approximately twofold differences in the lowest and highest Fe and Zn concentrations, especially high variation in contents of phenols and anthocyanin and anti-oxidative capacity found in grain with purple pericarp. The top entries identified from the farmer’s seed had significantly higher anthocyanin concentration and anti-oxidative capacity than the check varieties when grown together at Mae Wang and CMU, in spite of the strong locality-specific effects on these characteristics. Further variation was found in the grain quality characteristics within each of the selected farmer’s seed samples. Quality improvement could thus be made by either eliminating the poorest performing lines or development of single-seed descent lines from the top-performing plants. The desirable genetic traits can also be used in breeding programme for improvement of grain yield as well as cooking and nutritional quality