Epidemiological studies suggested that the low incidence of certain chronic diseases in rice-consuming regions of the world might be associated with the antioxidant compound contents of rice. The molecules with antioxidant activity contained in rice include phenolic acids, flavonoids, anthocyanins, proanthocyanidins, tocopherols, tocotrienols, γ-oryzanol, and phytic acid. This review provides information on the contents of these compounds in rice using a food composition database built from compiling data from 316 papers. The database provides access to information that would have otherwise remained hidden in the literature. For example, among the four types of rice ranked by color, black rice varieties emerged as those exhibiting the highest antioxidant activities, followed by purple, red, and brown rice varieties. Furthermore, insoluble compounds appear to constitute the major fraction of phenolic acids and proanthocyanidins in rice, but not of flavonoids and anthocyanins. It is clear that to maximize the intake of antioxidant compounds, rice should be preferentially consumed in the form of bran or as whole grain. With respect to breeding, japonica rice varieties were found to be richer in antioxidant compounds compared with indica rice varieties. Overall, rice grain fractions appear to be rich sources of antioxidant compounds. However, on a whole grain basis and with the exception of γ-oryzanol and anthocyanins, the contents of antioxidants in other cereals appear to be higher than those in rice.

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Rice antioxidants: phenolic acids, flavonoids, anthocyanins, proanthocyanidins, tocopherols, tocotrienols, γ-oryzanol, and phytic acid

Background Rice is a staple food and an important source of proteins in many regions worldwide. Its protein component is generally regarded as hypoallergenic, and a number of studies have highlighted the nutritional and health benefits associated with consumption of rice proteins. In recent years, the processing of plant proteins has drawn scientific and industrial interest, and rice protein-enriched ingredients have become commercially available. Scope and Approach The aim of this study was to provide a critical review of the state of the art regarding the composition, extraction methods, functional properties and applications of rice proteins. Key Findings and Conclusions Rice is composed of four protein fractions, namely albumin (water-soluble), globulin (salt-soluble), glutelin (alkali-soluble), which represents the dominant protein in brown and milled rice, and prolamin (alcohol-soluble), a minor protein in all rice milling fractions. Different methods to extract proteins from rice, including alkaline, enzymatic and physical methods, have been, and continue to be, evaluated for their efficacy, and some have been applied industrially. However, only a limited amount of studies have described the functional properties of rice proteins and how these can be improved by means of enzymatic hydrolysis. Applications of intact rice proteins are limited due to their poor solubility in water. However, hydrolysed rice proteins are used in the formulation of hypoallergenic infant formulas and may potentially be used in a variety of food systems due to their improved functionality. Despite the advances in the characterisation of rice proteins, a greater understanding of their physicochemical properties and how to modify their functionality is required in order to expand their range of food applications.

The composition, extraction, functionality and applications of rice proteins: A review

Rice bran protein has been found to be of high quality and of importance for food and pharmaceutical applications. It is a plant protein that can be derived from rice bran, an abundant and cheap agricultural byproduct. The protein content in rice bran is about 10-15% and it consists of 37% water-soluble, 31% salt-soluble, 2% alcohol-soluble, and 27% alkali-soluble storage proteins. Its unique property as being hypoallergenic and having anti-cancer activity makes it a superior cereal protein that may find a wide range of applications. There were already reports on the extraction of rice bran protein several decades ago. However, as of now, commercial rice bran protein is still unavailable in the market. This review is aimed at providing valuable discussions on rice bran protein, that is, storage protein, its various properties, and extraction methods for the development of an effective processing scheme. Also, an update on the current processing methods is also included.

A Review on Rice Bran Protein: Its Properties and Extraction Methods

How the sourdough may affect the functional features of leavened baked goods.

A pool of selected lactic acid bacteria was used for the sourdough fermentation of various cereal flours with the aim of synthesizing antioxidant peptides. The radical-scavenging activity of water/salt-soluble extracts (WSE) from sourdoughs was significantly (P < 0.05) higher than that of chemically acidified doughs. The highest activity was found for whole wheat, spelt, rye, and kamut sourdoughs. Almost the same results were found for the inhibition of linoleic acid autoxidation. WSE were subjected to reverse-phase fast protein liquid chromatography. Thirty-seven fractions were collected and assayed in vitro. The most active fractions were resistant to further hydrolysis by digestive enzymes. Twenty-five peptides of 8 to 57 amino acid residues were identified by nano-liquid chromatography-electrospray ionization-tandem mass spectrometry. Almost all of the sequences shared compositional features which are typical of antioxidant peptides. All of the purified fractions showed ex vivo antioxidant activity on mouse fibroblasts artificially subjected to oxidative stress. This study demonstrates the capacity of sourdough lactic acid bacteria to release peptides with antioxidant activity through the proteolysis of native cereal proteins.

Selected lactic acid bacteria synthesize antioxidant peptides during sourdough fermentation of cereal flours

Rice bran protein fraction (RBPF)—albumin, globulin, glutelin and prolamin were hydrolyzed with proteases M, N, P, S and pepsin under their optimal conditions for 24 h. Hydrolysates of various hydrolysis periods were collected and subjected to peptide mapping and the antioxidative activity measured by the 2,2-Azino-bis-3-ethylbenzothiazoline-6-sulfonic Acid (ABTS) method. Protease M hydrolysates showed high degree of hydrolysis (DH), but low antioxidative activity. On the contrary, pepsin hydrolysates showed low DH with high activity. Albumin and globulin hydrolysates had higher DH values, but lower values for glutelin and prolamin. The globulin hydrolysate (Opep2) from 2 h-pepsin hydrolysis was separated by using three consecutive purification steps with RP-HPLC. Nineteen antioxidative peptides were isolated and their amino acid sequences were determined by a gas-phase protein sequencer and MALDI-TOF mass spectrometry. These peptides were composed of 6–30 amino acid residues with molecular masses ranging from 670–3,611 Da. Tyr-Leu-Ala-Gly-Met-Asn had the highest antioxidative activity among them.

Junko Yamashita

Papers

Purification and characterization of antioxidative peptides derived from rice bran protein hydrolysates

Changes of functional components and antioxidative activity in the process of fermentation of soybeans