Rice bran extract (RBE) is a nutritional substance isolated from rice bran. Due to its high content of bioactive components and its good antioxidant capacity, RBE has unique advantages in the food and health fields. Furthermore, the types and contents of bioactive compounds obtained vary depending on the raw materials and preparation methods used. This review systematically discusses the common preparation methods, functional properties and application status of RBE in the context of recent research on it, and points out the shortcomings of the current research. Next, this paper explores the potential application value of RBE in the food and health fields and future research hotspots, in order to provide a theoretical basis for the intensive processing of rice bran.

In order to analyze the differential metabolites between brown rice and white rice and related metabolic pathways, high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS)-based non-targeted metabolomics was used to analyze the metabolites of brown rice and white rice, and multivariate statistical analyses including principal component analysis (PCA), partial least square discriminant analysis (PLS-DA) and cluster analysis were conducted. Based on the significant changes with multiple difference ≥ 1.2 or ≤ 0.8333, P < 0.05 and variable importance in the projection (VIP) ≥1, 460 differential metabolites including 300 up-regulated metabolites and 160 down-regulated metabolites were detected between brown rice and white rice in the positive ion mode, and 579 differential metabolites including 383 up-regulated metabolites and 196 down-regulated metabolites in the negative ion mode. In the positive mode, two metabolic pathways (phenylalanine, tyrosine and tryptophan biosynthesis, and histidine metabolism) with the involvement of four metabolites were determined. In the negative mode, five metabolic pathways (betalain biosynthesis, C₅-branched dibasic acid metabolism, purine metabolism, zeatin biosynthesis and carbon metabolism) with the involvement of 10 metabolites were determined. These results showed that the differential metabolites were mainly up-regulated in brown rice compared with polished rice, and they regulated the contents of amino acids, polyphenols, and fatty acids in rice bran and embryos by affecting metabolic pathways such as amino acid metabolism, carbon metabolism, purine metabolism, zeatin metabolism, and betaine biosynthesis, thereby improving the nutritional quality of rice. This study provides a theoretical basis for the nutritional evaluation of brown rice, and the development of brown rice processing technologies and products.

Germinated brown rice (GBR) is a whole grain containing the intact bran and embryo, concentrating most nutrients and functional active compounds. However, the dense fiber structure of the bran hinders the rate and capacity of water absorption and starch gelatinization during cooking. Therefore, compared with white rice, GBR has poorer cooking and eating quality, and they cannot be cooked at the same time. For this reason, GBR is not widely accepted by consumers. This article reviews the physiological metabolic reactions of GBR and the changes in nutritional components, bioactive substances, and taste quality during germination. It also summarizes and analyzes the current status of research on stress enrichment of γ-aminobutyric acid (GABA) and functional characteristics of GBR. During germination, enzymes promote the enrichment of various bioactive substances, especially GABA, a characteristic component. The enrichment of GABA can be promoted by various stress conditions with changing Ca²⁺, H⁺ or substrate levels. Some pretreatment techniques are available to further improve the taste quality of GBR. GABA works synergistically with other nutrients and active ingredients to endow GBR with a series of biological functions such as anti-hyperlipidemia, anti-hyperglycemia, heart protection, sleep improvement, anti-inflammatory and antioxidant effects.

Fermentation of brown rice can improve its nutritional composition and flavor quality and enhance the bioavailability of bioactive substances, enabling the high-value utilization of brown rice and its processing by-products. Its products have a broad application market. This paper summarizes the effect of fermentation on improving the nutritional and quality characteristics of brown rice. In order to expand the application of microbial fermentation in rice-based foods, the basis for the application of fermentation in various rice products, optimization of the fermentation process, and its impact on product nutritional quality are briefly described. The deficiencies and problems existing in the application of fermented brown rice in the field of foods are discussed. This review highlights that the scientific application of fermentation holds great potential to improve the nutritional quality and comprehensive utilization rate of brown rice. Through this review we hope to provide references for researchers investigating brown rice fermentation and for future market development in the industry.