USDA (the US Department of Agriculture) scientists and cooperators have provided knowledge about the chemical composition and potential bioavailability of nutritious compounds in a representative group of five colourful rice varieties.
Though often thought of as white or brown, rice is categorised into seven colour classes, based on bran colour, and darker varieties are thought to have higher amounts of some phytochemical compounds than lighter varieties.
Rice bran, an outer layer of whole grain rice, is a rich source of the phytochemical known as gamma-oryzanol, and of two forms of vitamin E - tocopherols and tocotrienols. These nutritional compounds have been linked to preventing oxidative damage in foods and to having a wide spectrum of biological activities that could be beneficial to human health.
The team used analytical methods to determine the profiles of tocopherols, tocotrienols and gamma-oryzanol in white, light brown, brown, red, and purple bran. They found a wide variation in the concentrations of the two forms of vitamin E and of gamma-oryzanol.
The team also analysed other phytochemicals—specifically phenolics and flavonoids—in the same five colour classes of bran. The study showed that the red and purple rice brans had higher phenolic and flavonoid concentrations than the lighter-coloured rice brans measured. The researchers also identified one purple rice bran variety that was both high in phenolic compounds as well as vitamin E and oryzanols.
The study findings were published in the Journal of Food Science and in Food Chemistry.
