Effect of milling on proximate composition, γ-oryzanol, vitamin B1, polyphenolic, and bioaccessibility of phenolic of brown rice

The effect of milling treatment on the nutrients of brown rice and the release of polyphenols during in vitro digestion were studied in this paper. As the milling degree increased, the protein, fat, and total dietary fiber content of brown rice decreased and the total starch content increased, the changes in fat and dietary fiber contents were more significant. The contents of gamma-oryzanol, vitamin B-1, total phenolic, and total flavonoids all decreased to varying degrees with different milling times. The contents of 11 phenolic acids in brown rice were significantly reduced (p < .05). Additionally, the results of simulated digestion in vitro showed that the content of phenolic in gastric juice and intestinal juice all decreased with the increasing milling degree. The phenolic in brown rice are mainly released during gastric digestion, and the total phenolic in gastric juice and intestinal juice are 1.79-2.04 times and 2.24-2.71 times of those before digestion, respectively. These results suggest that it is indispensable to advocate reducing milling degrees to improve the edible value of rice. It will also provide data support and theoretical guidance for promoting moderate rice processing, reducing grain loss, and developing whole grain in China. Practical applications In this paper, the changes in main nutrients (total starch, protein, fat, dietary fiber) and bioactive substances (gamma-oryzanol, vitamin B-1, total phenolic and profile of phenolic, total flavonoids) of brown rice with different milling degrees produced by the actual process in the factory were analyzed, and the effect of milling on the bioaccessibility of phenols in brown rice through simulated digestion experiments in vitro was also investigated. The results of this paper suggest that it is indispensable to advocate reducing milling degrees to improve the edible value of rice. It will also provide data support and theoretical guidance for promoting moderate rice processing, reducing grain loss, and developing whole grain in China.

Automated summary

This study investigated the effect of milling treatment on the nutrients of brown rice and the release of polyphenols during in vitro digestion. The results showed that as the milling degree increased, the protein, fat, and total dietary fiber content of brown rice decreased, while the total starch content increased. The content of various bioactive substances, such as gamma-oryzanol, vitamin B-1, total phenolic, and total flavonoids, also decreased with different milling times. Furthermore, the simulated digestion experiments showed that the content of phenolic in gastric juice and intestinal juice decreased with increasing milling degree. It was found that the phenolic in brown rice are mainly released during gastric digestion, and the total phenolic in gastric juice and intestinal juice are significantly higher than those before digestion. These findings emphasize the importance of reducing milling degrees to improve the edible value of rice and provide guidance for promoting moderate rice processing and developing whole grain in China.