12 January - 20 June 2016

Effect of degree of milling on phenolic profiles and cellular antioxidant activity on whole brown rice

21 May 2015

The use of whole brown rice is increasing in popularity, and it along with lightly milled rice has been used to produce whole grains-related products.  There is increasing evidence to suggest that the consumption of whole grains is associated with the prevention of chronic diseases such as cancer and cardiovascular disease attributed in part to phtyochemicals such as tocopherols, tocotrienols, vitamin B and phenolic compounds.  Whole brown rice is an important source of two types of phenolic compounds that are beneficial to overall health.  

The aims of the study conducted at the Guangdong Academy of Agricultural Sciences were (1) to determine the total phenolic content, total flavonoid content, and phenolic composition of brown rice with different degrees of milling (DOM), (2) to investigate the effect of DOM on the percentage composition of free and bound fractions to total phenolics and (3) to evaluate the antioxidant activity of brown rice with DOMs.    

Two types of brown rice were successfully milled to obtain rice with four different degrees of milling.  Free and bound phenolics were extracted from the powdered rice samples and then analysed for total phenolic content, total flavonoic content, phenolic composition and cellular antioxidant activity. The results showed that increasing the degree of milling significantly reduced the level of phenolics in the brown rice.   Furthermore, the percentage contribution of bound forms to total phenolics and flavonoids also decreased with increased degree of milling.  

In summary, the researchers’ results indicated that an increase in milling led to the loss of phytochemicals beneficial to health, that the levels of nine phenolic compounds decreased and that the cellular antioxidant activity was also decreased.  Milling is a traditional method for rice processing, and serves to improve the stability and sensory quality of rice during storage.  The research indicates that degree of milling should be carefully controlled for acceptable sensory quality and retention of phytochemicals during brown rice milling, and provides important evidence in support of health benefits of consuming brown rice, particularly lightly milled rice.

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