Black rice

About: Black rice is a research topic. Over the lifetime, 2548 publications have been published within this topic receiving 20840 citations. The topic is also known as: purple rice.

Physicochemical and antioxidative properties of black, brown and red rice varieties of northern Thailand

Abstract: Rice, the seed of Oryza species, is the major cereal crop in most of the developing countries. Nearly 95% of global rice production is done in Asian countries, and about half of the world’s population consumes it. Some speciality rices are not commonly consumed. Colored rice is one of such variety. In these varieties, high amounts of anthocyanin pigment are deposited in the rice coat to form its black (also known as purple), brown and red colors. Minimum studies are there to explain the properties of these rice varieties of Thailand. Thus, the current study was aimed to assess the physicochemical and antioxidative properties of three rice varieties (Chiang Mai Black rice, Mali Red rice and Suphanburi-1 Brown rice) of different cultivars of northern Thailand. Rice bran extracts of these three cultivars were prepared with different solvents (polar and non-polar) for the evaluation of total phytochemical content and anti-oxidant free-radical-scavenging properties. Chiang Mai Black rice contained higher concentration of phenolic acid, flavonoids, and anthocyanins (Cyanidin 3-glucoside, peonidin 3-glucoside, cyanidin chloride). Chiang Mai Black rice is richer in free-radical-scavenging compounds and activities than the other tested varieties. Polar extractions of rice bran are high in anti-oxidative compounds and activities than non-polar extractions.

Phytochemical constituents, antioxidant activity, and antiproliferative properties of black, red, and brown rice bran.

Abstract: In the recent years, the health benefits of the pigmented rice varieties have reported due to the presence of bioactive compounds. In this study, the phytochemical constituents (total phenolic, flavonoid and anthocyanin content) and individual phenolics and flavonoids of the extracts of sixteen genotypes of pigmented rice bran were evaluated using spectrophotometric and ultra-high performance liquid chromatography method. Antioxidative properties of the free and bound fractions were evaluated using nitric oxide and 1,1-diphenyl-2-picrylhydrazyl scavenging assays. Extracts were evaluated for antiproliferative activity against breast cancer cell lines (MCF-7 and MDA-MB-231) using the MTT assay. Signifficant diferences were observed in the concentrations of phytochemicals and biological activities among different pigmented rice brans. The highest phytochemical content was observed in black rice bran followed by red and brown rice bran. The concentration of free individual flavonoids and phenolic compounds were significantly higher than those of bound compounds except those of ferulic acid and p-coumaric acid. Highest antioxidant activities were observed in black rice bran, followed by red and brown rice bran extracts. Extracts of black rice bran exhibited potent antiproliferative activity, with half maximal inhibitory concentrations (IC50) of 148.6 and 119.2 mg/mL against MCF-7 and MDA-MB-231 cell lines, respectively, compared to the activity of the extracts of red rice bran (175.0 and 151.0 mg/mL, respectively) and brown rice bran (382.3 and 346.1 mg/mL, respectively). Black rice bran contains high levels of phytochemicals, and thus has potent pharmaceutical activity. This highlights opportunities for researcher to breed new genotypes of rice with higher nutritional values, which the food industry can use to develop new products that will compete in expanding functional food markets.

Ohmic heating-assisted extraction of anthocyanins from black rice bran to prepare a natural food colourant

Abstract: Black glutinous rice bran (Oryza sativa L.) is a potential source of the dark purple anthocyanin pigments. This study investigated some quality aspects and bioactive compounds of the colourant powder obtained from rice bran extracted by ohmic heating (OHM) assisted solvent extraction. The moisture content (MC) of the bran was adjusted to 30% and 40%. Four different levels of electric field strengths (E) of 50, 100, 150, and 200 V cm– 1 were applied. The results showed that OHM assisted solvent extraction was a promising method offering both high yield and high concentration of bioactive compounds. The solubility, aw, bulk density, and color values (L*, C*, and h°) of the colorant powder of all treatments were comparable. The colourant powder obtained from the bran extracted using OHM with 30% MC (E=100, 150, and 200 V cm– 1) and 40% MC (E = 50, 100, 150, and V cm– 1) had the highest level of bioactive compounds. Industrial relevance The ohmic heating was a promising technique to assist solvent extraction of anthocyanin pigment from black rice bran. The colourant powder prepared by ohmic heating assisted (CP-OHM) had higher colourant yield, anthocyanin pigments, and bioactive compounds than conventional methods. The present study suggested that ohmic heating could be applied to develop industrial production scale of natural colourants.

Thermal and pH degradation kinetics of anthocyanins in natural food colorant prepared from black rice bran

Abstract: The study of the stability of anthocyanins in food colorant powder is important to predict the quality changes occurring as the food products are processed, to prevent and control the degradation of the anthocyanins. The objectives of this study were to identify anthocyanin components in natural food colorants obtained from black rice bran, and investigate their thermal stability at 60, 80, and 100 °C, pH stability from 2.0 to 5.0 and also their correlation with visual color, L *, C *, and h°. Results showed that only six types of anthocyanins, cyanidin-3-O-glucoside, cyanidin-3-O-rutinoside, delphinidin, cyanidin, pelargonidin and malvidin were present in raw black rice bran (BRB) and black rice bran colorant powder (BCP). The thermal degradation of both the visual color and the anthocyanin content in the BCP followed a first-order kinetic reaction model. The temperature-dependent degradation was adequately fitted to the Arrhenius equation. In terms of the pH stability, increasing pH values resulted in lower activation energies (E a ) and higher half-life (t 1/2 ) values for both color parameters and individual anthocyanins when heating from 60 to 100 °C. Moreover, the degradation rate constant (k) increased with increasing temperature and pH value. The degradation of cyanidin-3-O-glucoside and total anthocyanins showed a strong positive correlation with C *. The changes in visual color may be used as an on-line quality control indicator during thermal processing of food products containing rice bran colorants which have high anthocyanin content.

Simultaneous determination of phenolic acids and flavonoids in rice using solid‐phase extraction and RP‐HPLC with photodiode array detection

Abstract: An analytical method based on an optimized solid-phase extraction procedure and followed by high-performance liquid chromatography (HPLC) separation with diode array detection was developed and validated for the simultaneous determination of phenolic acids (gallic, protocatechuic, 4-hydroxy-benzoic, vanillic, caffeic, syringic, p-coumaric, ferulic, sinapic, and cinnamic acids), flavanols (catechin and epicatechin), flavonols (myricetin, quercetin, kaempferol, quercetin-3-O-glucoside, hyperoside, and rutin), flavones (luteolin and apigenin) and flavanones (naringenin and hesperidin) in rice flour (Oryza sativa L.). Chromatographic separation was carried out on a PerfectSil Target ODS-3 (250 mm × 4.6 mm, 3 μm) column at temperature 25°C using a mobile phase, consisting of 0.5% (v/v) acetic acid in water, methanol, and acetonitrile at a flow rate 1 mL min−1, under gradient elution conditions. Application of optimum extraction conditions, elaborated on both Lichrolut C18 and Oasis HLB cartridges, have led to extraction of phenolic acids and flavonoids from rice flour with mean recoveries 84.3–113.0%. The developed method was validated in terms of linearity, accuracy, precision, stability, and sensitivity. Repeatability (n = 5) and inter-day precision (n = 4) revealed relative standard deviation (RSD) <13%. The optimized method was successfully applied to the analysis of phenolic acids and flavonoids in pigmented (red and black rice) and non-pigmented rice (brown rice) samples.