Ameliorative Effects of Rice Bran: Bridging Research Gaps and Emerging Trends
Abstract
Rice bran (RB) contains extraordinary nutritional value and bioactive compounds, which are by-products of rice refining and have attracted significant attention over the past few years. In this review, the potential for augmenting human health and well-being with RB is examined in detail. As per nutritional content of RB, it is a rich source of essential constituents such as dietary fibers, vitamins, and minerals. Moreover, the bioactive composites in RB comprise polyphenols, phytosterols, and antioxidants, which have been comprehensively studied for their therapeutic applications. Scientific indications support the idea that RB can prevent inflammation, diabetes, cardiovascular disease, and other related health problems. This article also covers the new investigation regarding the influence of RB on gut health, mainly its prebiotic properties and altering gut microbiota activities.
1. Introduction
One of the basic foods worldwide, mainly in Asia, is rice (Oryza sativa). In 2019, 490.27 million metric tons of rice were used worldwide [1]. Up to 50% of the calories consumed by people in Asia come from rice [2]. It serves as a primary staple food for over half of the global population, providing them with their daily caloric requirements. Eight hundred seventy million people worldwide suffer from chronic malnutrition; most of them belong to underdeveloped nations where rice is closely associated with food security [3]. Moreover, it has been shown that hunger and noncommunicable diseases often coexist globally [4]. Due to the beneficial components of whole grain rice, epidemiological investigations have demonstrated an association between the low incidence of chronic diseases, including cancer and coronary heart disease, and whole grain rice consumption [5].
Compared to rice produced by commercial cultivars, some traditional landraces gather advanced levels of phytochemicals in their grain [6]. Pigmented rice, recognized for its rich content of beneficial phytochemicals, is characterized by its red, black, purple, or multihued aleurone layer [7]. While many of these colored rice varieties have an extensive history of intermittent farming throughout Africa and Asia, which has been documented in ancient writings [8]. For example, black rice is considered an heirloom variety and is valued as a tribute due to its scarcity in ancient China before dynasties [8]. Due to the accumulation of proanthocyanidins, red rice’s domestication process and genetic origin may be traced back to the wild rice Oryza rufipogon [9], while black rice was most likely introduced to Indica by introgressions from Japonica subspecies [10]. It has been shown that a broad range of micronutrients and polyphenolic chemicals found in pigmented rice have anti-inflammatory, anticancer, antioxidant, and antidiabetic effects [7]. The nutritional profile and sustainable usages of rice bran (RB), a high-value byproduct of rice milling, have been gaining attention [11]. Because of its richness in bioactive composites, RB and RB oil can be an encouraging functional food constituent owning antiobesity, antidiabetic, and gut microbiota–modulating activities [12, 13]. Its bioavailability and functional properties have been further improved by recent innovations in processing technologies, such as extrusion [14]. In accumulation, the antioxidant and cardioprotective capacities of RB oil have led to an investigation of its possible nutraceutical solicitations [15].
Furthermore, in cell-based systems, pigmented rice is regarded as a strong intracellular candidate [16]. Genetics plays a major role in colored rice’s nutritional value. A recent summary of the fundamental genes accountable for pigmented rice’s color was circulated [7]. It is still unclear how the environment influences these dense, nutrient-rich characteristics or how to employ effective post harvest processing techniques that maintain extreme nutritional value for cooking and processing without compromising human health. When rice is grown using organic farming methods, it is also necessary to promote the intake of whole grains of pigmented rice, which has a higher antioxidant potential, without pesticide deposits and heavy metal pollution [17]. Although colored rice offers a rich source of nutrients, different procedures impact the duration of these phytochemicals’ presence in the rice. Furthermore, colored rice has been processed using sophisticated postharvest methods to maximize its nutritional value. It has recently been studied how postharvest processing affects grain quality [18], but its impact on colored rice’s nutritional qualities has not been investigated yet. Due to significant technological advancements over the last 10 years, a wide range of culinary and nonfood products based on colored rice have been developed. This review is aimed at (i) planning the phytochemicals of pigmented rice, comprising micronutrients, proanthocyanidins, phenolic acids, and flavonoids; (ii) investigating the influence of post-harvest procedures and new product developments; and (iii) talking about the implications of these nutritional elements on human health. This presented data is aimed at helping address critical food and nutrition security aspects. According to earlier research, rice milling by-products still include a range of nutrients and bioactive chemicals that have positive health effects [19]. These by-products could be added to or utilized in food products to increase rice production’s output and food sustainability and to scavenge free radicals that cause oxidative stress, rapid cell aging, and damage to the heart and muscles, consuming foods high in antioxidants in moderation [20]. A series of procedures, known as food processing, enables the conversion of unprocessed substances into edible food ingredients. For example, cereal crops produce a lot of residues throughout their transformation process and are rarely eaten as whole grains. The third utmost general cereal in the biosphere, rice, is milled to produce RB as a by-product [21].
1.1. Aim of the Review
The goal of this review is to widely explore the positive impact of RB, including its chemical and nutritional composition, bioactive composites, and corresponding health benefits. The purpose of this study is to highlight the potential of RB as a functional food composite by compiling existing investigations and emphasizing its function in improving human health. A detailed analysis of the bioactive composites present in RB, such as flavonoids, phenolic acids, and polymeric polysaccharides, and their mechanisms of action in disease anticipation and health promotion will also be part of the review. Synthesizing existing evidence and bringing to the foreground the worth of RB in food and medicinal usage are the final goals of this review.
1.2. Research Gaps
Even as RB is attaining popularity as a functional food, numerous questions remain unanswered. First, little is known about the bioavailability and bioaccessibility of its bioactive composites, which are critical features in evaluating how good they are for human health. Two, it is not yet recognized exactly how RB brings its health welfare predominantly at the molecular level. In addition, instead of pointing at the synergistic effects of RB as a whole, most studies emphasize its separate constituents, for example, lipids or phenolic composites. In accumulation, there are too few long-term medical trials to substantiate the health benefits of consuming RB. Filling in these gaps will help us better grasp the potential of RB and how simple it will be to incorporate it into nutrition and therapy.
2. RB
The outer husk of rice grains formed during the rice milling process is called RB. It is rich in phytochemical compounds such as phenolic compounds, vitamins, flavonoids, steroidal compounds, and polymeric carbohydrates. RB is highly economically valuable due to these phytochemicals (Figure 1) [22]. However, many of the people are ignorant of RB’s advantages. Additionally, RB is used to make animal feed, medications, and bran oil, which is its primary application. According to Latha and Nasirullah [23], RB should include roughly 23% saturated fatty acids, 44% oleic acid, and 30% linoleic acid. Figure 1 shows the parts of the rice plant.
3. Chemical Composition of RB
Protein, crude fiber, lipids, carbohydrates, phenolic compounds, oryzanols, polyunsaturated fatty acids (PUFAs), and monounsaturated fatty acids are all found in rice fiber [24]. Conferring to Heredia-Olea et al. [25], RB’s nutritional value comprises carbs, lipids, protein, fiber, moisture, and minerals in that order. RB has a moisture content of 4.3%. It contains 17.50, 13.10, 7.85, 21.17, 2.17, 23.34, 52.33, and 4.92 g of protein, fat, crude fiber, insoluble dietary fiber, soluble dietary fiber, total dietary fiber, carbs, and ash content per 100 g, respectively. According to Park et al. [26], the energy content is 398.00 Kcal/100 g. The types of rice, the environment, and the methods rummage-sale to process the rice all distress the constituents of RB. RB, a nutrient-dense by-product, encompasses vitamins, minerals, dietary fiber, amino acids, and antioxidants (Figure 2) [28]. RB has a rich nutritional profile, which makes it useful for creating bread, ice cream, pasta, noodles, cornflakes, and low-trans-fat shortening [29]. Owing to their superior quality, rice bran proteins (RBPs) have probable solicitations in the food and pharmaceutical segments. Figure 2 shows the food applications of RBP.
4. Nutritional Components of RB
About 6% of the bulk of rice is made up of RB, a by-product of rice milling. It frequently comprises rice germ, seed coatings, aleurone layers, and brown rice shells. RB is high in phytic acid, polysaccharides, protein, dietary fiber, and vitamins [30]. Y-oryzanol is one of them; it has anti-inflammatory, anticancer, antidiabetic, and antioxidant properties. It can also decrease cholesterol and enhance plasma lipid patterns [31]. Consuming dietary fiber can improve digestive function. Furthermore, RB contains roughly 90% insoluble dietary fiber, of which 22% is hemicellulose. The most prevalent hemicelluloses are arabinoxylans, which have been shown in research to have advantages in immunoregulatory function and decreased glycemic reaction in the body. Additionally, RB has a sizable quantity of dietary fiber, which may have prebiotic functions [32]. RB is rich in nutrients, with 41.3% being carbohydrates, 13.0% being proteins, 17.9% being lipids, 6.5% being fibers, 10.0% being minerals, and 11.2% being moisture. As a result, bran is a useful addition to food formulations, enhancing and augmenting the nutritional content up to the recommended daily intake (RDI) for various age groups [33]. Brown RB has a total mineral concentration of 10.4% and meets Anvisa’s RDI for its mineral profile. Despite having an amino acid profile restricted by some essential amino acids (such as lysine and threonine), rice proteins are unique among cereals since they are hypoallergenic [34]. By combining it with other protein sources (such as quinoa and peas) to source the preventive amino acid, this restraint can be upgraded by Codex Alimentarius. With its 10% protein content, RB could be a valuable addition to meals with a distinct amino acid profile [35]. Membrane RB oil contains significant lipids; unsaponifiable lipids comprise about 4%, associated with 1%–2% in other vegetable oils [36]. For calcium, phosphorous, iron, and zinc, the mineral contents of steadied and probiotic preserved RB were 52.10 and 49.90, 1185.20 and 1186.50, 28.10 and 30.05, and 6.02 and 5.89 mg/100 g, correspondingly. In mineral composition, the phosphorus is the major, 90% of which is phytate phosphorus. Silicon is the major component of rice hull. By calculations, the bran germ polish components contain 78% rice kernel thiamine, 57% riboflavin, and 63% niacin. Consequently, RB’s mineral, fatty acids and amino acid compositions indicate its potential to meet the dietary needs of diverse populations, aligning with the RDI s set by national and international regulatory standards (Table 1).
| Nutrients | Rice bran (%) | White rice (%) | Brown rice (%) | Reference |
|---|---|---|---|---|
| Carbohydrates (g/100 g) | 35–60 | 82–89 | 77–80 | Carcea [37] |
| Energy (Kcal) | 3650 | 334 | 341 | Carcea [37] |
| Protein (g/100 g) | 11.3–14.9 | 4.5–10.5 | 4.3–18.2 | Juliano and Tuaño [38] |
| Lipids (g/100 g) | 15–19.7 | 0.3–0.5 | 1.6–2.8 | Pereira et al. [39] |
| Dietary fiber (g/100 g) | 19.0–29.0 | 0.7–2.7 | 2.9–4.4 | Champagne [40] |
| Ash (g/100 g) | 6.6–9.9 | 0.3–0.8 | 1.0–1.5 | Juliano and Tuaño [38] |
| Moisture (%) | 10–15 | 10–14 | 10–14 | Devi et al. [41] |
The macronutrient composition and bioactive compounds of RB are adequately discussed in the article. But to make it more understandable and support these claims, Table 1 compares the nutritional composition of brown rice, white rice, and RB in detail. In comparison to brown and white rice, RB contains a significant amount of more protein (11.3–14.9 g/100 g), fat (15–19.7 g/100 g), and dietary fiber content (19.0–9.0 g/100 g) [38, 40]. Apart from providing functional advantages, RB includes a greater content of ash level (6.6–9.9 g/100 g), which provides evidence of its higher mineral intensity [41]. Due to its higher fat content, RB is far more calorific (3650 kcal) than milled rice [37]. By incorporating this table into the manuscript, the justification for the superior nutritional advantage of RB would be made stronger, and readers would have a concrete point of reference for comparison. Based on pertinent chromatographic and spectroscopic data from studies referenced [22, 42], the bioactive constituents (e.g., γ-oryzanol, tocotrienols, and phenolic acids) of RB that are to be credited for the nutritional advantages of RB will be elaborated on further in the following sections. Table 1 depicts the nutritional composition of RB, white rice, and brown rice.
4.1. Protein
Because rice has more lysine than other cereals, rice protein comprising that found in the endosperm and bran is favored. According to Fabian and Ju [43], RB contains roughly 10%–16% extremely nutritious protein. Except for prolamin, RBP is made up primarily of necessary amino acids and is constituted of albumin, globulin, prolamin, and glutelin [44]. Han et al. [45] discovered that the nutritious and organic properties of RBP were similar to those of animal and vegetable proteins, such as whey protein, casein, soy protein, and rice endosperm protein (REP). Furthermore, rice proteins have a strong potential for use as components in gluten-free goods and baby formulae due to their proven hypoallergenic properties [46]. Various technologies, such as enzymatic, physical, chemical, and other technologies, are used to excerpt protein from rice and RB.
Nevertheless, due to the high cost and inefficiency of the currently known extraction techniques, the abstraction of RBP on a marketable scale is restricted [47]. Thus, developing an effective and novel technique to excerpt protein from RB can offer a low-cost, high-quality source of protein for food consumption and may open up new value-added prospects for RB. The biological value and composition of protein’s amino acid content are the primary determinants of its quality. In addition, for a protein to be considered high quality, it should not only be easy to digest and absorb. Still, it should comprise all vital amino acids for bodily functions. Research has identified the biological value and composition of amino acids in RBP. In a study, stabilized RB underwent procedures such as dry heat, microwave, or parboiling to produce BRP isolates with a stable amino acid profile. The organic value and actual digestibility of RBP isolates varied from 78.57 to 88.23 and 76.0% to 86.11%, respectively.
Furthermore, following a 45-day feeding trial with RBP isolates, the rats’ organ-to-body weight ratio and serum biochemical profile showed regular metabolic activity and no negative possessions. Additionally, the biological value and nutritional quality of RBP isolates differed based on the RB stabilization action (Figure 3) [48]. RBP’s nutritional quality was assessed and contrasted with that of vegetable and animal proteins, such as casein, whey protein isolate (WPI), REP, and soy protein isolate (SPI), in a different study. The RPB isolate has an 89.8% pepsin digestibility and 74.93% protein content. In addition, the RBP demonstrated similar results to those of animal proteins in rats’ experiments, including a 2.39 protein effectiveness ratio, 3.77 disposable protein ratios, 70.7 net protein applications, and 72.6 organic values. Moreover, the RBP established true digestibility of 94.8%, which was analogous to casein and much higher than that of REP (90.8%), SPI (91.7%), and WPI (92.8%). Furthermore, it was discovered that most of the necessary amino acids are included in RBP fractions, such as albumin, globulin, prolamin, and glutelin, except prolamin. Leucine, methionine, valine, phenylalanine, and histidine are among the amino acids shown to be more abundant in RBP concentrate than in SPI. Recently, the nutritional response of RBP fractions, such as albumins, albumin–globulins, and alkali-mined protein, was assessed in male Wistar rats that were starved and normally fed. According to Kalpanadevi et al. [49], the findings indicated that RBP might be endorsed as a substitute for plant-based protein to help with protein deficiency. Consequently, RBP was recommended as a healthy element in food arrangements due to its stable amino acid content, high biological worth, and protection. Figure 3 shows the composition of RB.
4.2. Fat
RB constitutes 5%–10% of the whole grain. It contains crude protein (11%–13%), oil (20%), and dietary fibers (22.9%) such as hemicelluloses, arabinogalactan, arabinoxylan, xyloglucan, and raffinose, as well as vitamin E, minerals, and γ-oryzanol. RB oil is a transparent, light-yellow oil with a faint nutty aroma and is odorless [50]. Because of its fatty acid composition and other ingredients, RBO is regarded as a “healthy oil” by the Chinese Cereals and Oils Association, the American Heart Association, the World Health Organization, the Indian Council of Medical Research, and the National Institute of Nutrition (India). According to Lai et al. [51], RBO is considered one of the healthiest edible oils since it has a balanced amount of saturated (SFA: 20% palmitic acid), monounsaturated (MUFA: 42% oleic acid), and PUFAs: 32% linoleic acid), with an average ratio of 0.6:1.1:1.0. The usual breakdown of crude RBO is as follows: 0.8% glycolipids, 1%–2% phospholipids (PL), 2%–3% diacylglycerols (DAG), 1%–2% monoacylglycerols (MAG), 2%–6% FFA, 3%–4% wax, and 4% unsaponifiable fraction. The unsaponified fraction is rich in c-oryzanol, phytosterols, polyphenols, squalene, and tocopherols and tocotrienols. In RBO, enzymatic hydrolysis is connected to FFA, MAG, and DAG. Compared to other vegetable oils, crude RBO often has greater concentrations of non-TAGs, most of which are meant to be eliminated throughout refining. According to the existence of tocopherols, γ-oryzanol, and tocotrienols, RBO is superior to conventional cooking oils in several ways, including oxidative stability and other health advantages. One group of RPO’s nonsaponifiable lipids is γ-oryzanol. According to Rogers et al. [52], it is a blend of phytosterols and ferulic acid esters of triterpene alcohols. Krishna et al. [53] investigated the impact of various processing phases on the availability of γ-oryzanol. The findings demonstrated that while alkali treatment removed up to 94% of the γ-oryzanol from the original crude RBO, degumming and dewaxing of crude RBO removed just 1% and 6% of the γ-oryzanol. They also determined that the original amounts of γ-oryzanol in physical and alkali-refined RBOs were 1.10%–1.74% and 0.19%–0.20%, respectively. According to Pestana-Bauer et al. [54], there was 12.4 g/kg of γ-oryzanol in crude RBO but only 0.49 g/kg in purified RBO. Since RBO contains significant concentrations of the cardioprotective γ-oryzanol, it is known as the “heart-friendly” oil. In addition, RBO contains plant sterols such as β-sitosterol, campesterol, isofucosterol, and stigmasterol, which are naturally occurring antioxidants, as well as vitamin E (tocopherols and tocotrienols) [55]. RBO was reported to have a total phenolic content of no more than 2 mg/100 g [56]. When HPLC identified phenolic acids, ferulic acid was found, while Janu et al. recognized cinnamic and sinapic acid (2014). Tocopherols and tocotrienols are abundant in RBO and have antioxidative properties. It was discovered that adding RBO to milk effectively decreased WMP oxidation without noticeably altering its flavor. Yogurt was fortified by Abbas et al. [57] by adding a strain of Bifidobacterium and RBO, and the results indicated that the yogurt had a satisfactory viscosity and possible health benefits.
4.3. Carbohydrates
The carbohydrates in RB come in various forms, including starch, cellulose, hemicellulose, polysaccharides, and certain sugars. In addition to water-soluble phytochemicals, RB contains water-soluble polysaccharides such as oligosaccharides, hemicelluloses, and nonstarchy polysaccharides. A particular conformational shape seen in plant polysaccharides stimulates the synthesis of anti-inflammatory cytokines while suppressing the production of proinflammatory cytokines [58]. They also function as immunomodulators through interactions with T cells, monocytes, macrophages, polymorphonuclear lymphocytes, and innate and cell-mediated immunity [26].
5. Bioactive Profile of RB
5.1. Phenolic Compounds
Phenolic molecules with at least one hydroxyl group and one or more aromatic rings are classified as secondary metabolites. These phenolic chemicals are essential to many metabolic pathways in diverse ways. These are part of the antioxidant pathways that counteract the effects of oxidative stress. In addition to their antioxidant properties, they also have anti-inflammatory, anticarcinogenic, and antimutagenic properties. The findings highlight the importance of phenolic compounds in the anticipation and treatment of disease [59]. An extract of RB has been reported to contain many phenolic components. According to Ooi et al. [60], RB arabinoxylan compounds modulate the fabrication of numerous cytokines, comprising tumor necrosis factor-alpha (TNF-α), interleukins (IL-12 and IL-2), and interferons (IFN-γ and IFN-λ), which have anticancer uses. This explains why RB has a variety of therapeutic and dietary uses [61].
5.2. Flavonoid Compounds
Plants naturally produce secondary metabolites called flavonoids. They are regarded as a collection of compounds having various phenolic structures. These substances are well-known for improving human health. These find extensive use in various sectors, including the pharmaceutical, cosmetic, nutraceutical, and medical industries [62]. The fact that RB is thought to be a rich source of numerous flavonoid composites increases its medicinal value. RB contains luteolin, myricetin, quercetin, apigenin, and catechin, among other common flavonoid components [63].
Additionally, they have a diversity of biological actions, comprising anti-inflammatory, antiallergic, antiviral, and antithrombotic properties, suggesting RB’s beneficial role in the treatment of a range of illnesses [64]. In plants, flavonoids have a range of uses as well. There are reports that they have a role in the process of flower coloration. Additionally, they shield the plants from UV rays [65]. According to Pourcel et al. [66], flavonoids help shield plants from biotic and abiotic stresses.
5.3. Polymeric Carbohydrates
Our body uses carbohydrates as its primary energy source, which may be found in almost every dietary item, including grains, fruits, vegetables, and milk. Carbohydrate concentrations, however, differ among foods. Additionally, polymeric carbohydrates are present in RB. According to Choi et al. [67], roughly 17.92 g of digestible carbs are in 100 g of RB. The various types of rice also affect its composition. Hemicellulose, glucans, and arabinoxylan are communal polymeric carbohydrates in RB (Table 2) [22].
| Bioactive compound | Type/subclass | Function/activity | Extraction method | References |
|---|---|---|---|---|
| Phenolic compounds | Ferulic acid, p-coumaric acid, sinapic acid | Antioxidant, anti-inflammatory, anticancer, and cardioprotective properties | Solvent extraction (ethanol, methanol), ultrasound-assisted extraction | Friedman [22]; Ghasemzadeh et al. [63]; Islam et al. [68] |
| γ-Oryzanol | Reduces cholesterol, antioxidant, and anti-inflammatory effects | Supercritical fluid extraction, solvent extraction | Ali & Devarajan [50]; Lai et al. [51] | |
| Vanillic acid, caffeic acid | Antioxidant, antimicrobial, and neuroprotective effects | Alkaline hydrolysis, solvent extraction | Friedman [22]; Park et al. [26] | |
| Protocatechuic acid | Antioxidant, anti-inflammatory, and hepatoprotective effects | Solvent extraction, microwave-assisted extraction | Ghasemzadeh et al. [63]; Zhang et al. [69] | |
| Chlorogenic acid | Antioxidant, anti-inflammatory, and antidiabetic effects | Solvent extraction, ultrasound-assisted extraction | Friedman [22]; Ghasemzadeh et al. [63] | |
| Naringenin | Antioxidant, anti-inflammatory, and hepatoprotective effects | Ethanol extraction, ultrasound-assisted extraction | Ghasemzadeh et al. [63]; Mathesius [65] | |
| Syringic acid | Antioxidant, anti-inflammatory, and hepatoprotective effects | Solvent extraction, ultrasound-assisted extraction | Ghasemzadeh et al. [63]; Zhang et al. [69] | |
| Gallic acid | Antioxidant, antimicrobial, and anticancer properties | Solvent extraction, microwave-assisted extraction | Friedman [22]; Ghasemzadeh et al. [63] | |
| Flavonoid compounds | Quercetin, kaempferol | Antioxidant, anticancer, and anti-inflammatory properties | Ethanol extraction, ultrasound-assisted extraction | Ghasemzadeh et al. [63]; Mathesius [65] |
| Apigenin, luteolin | Antioxidant, antimicrobial, and cardioprotective effects | Solvent extraction, supercritical fluid extraction | Friedman [22]; Roleira et al. [59] | |
| Anthocyanins (cyanidin, delphinidin) | Antioxidant, anti-inflammatory, and anticancer properties | Acidified ethanol extraction, ultrasound-assisted extraction | Bhat & Riar [64]; Ghasemzadeh et al. [63] | |
| Catechin, epicatechin | Antioxidant, neuroprotective, and antidiabetic effects | Solvent extraction, microwave-assisted extraction | Friedman [22]; Park et al. [26] | |
| Myricetin | Antioxidant, anticancer, and anti-inflammatory properties | Ethanol extraction, ultrasound-assisted extraction | Ghasemzadeh et al. [63]; Mathesius [65] | |
| Rutin | Antioxidant, anti-inflammatory, and cardioprotective effects | Ethanol extraction, ultrasound-assisted extraction | Ghasemzadeh et al. [63]; Mathesius [65] | |
| Polymeric carbohydrates | Arabinoxylan | Prebiotic, immunomodulatory, and antioxidant effects | Alkaline extraction, enzymatic hydrolysis | Ooi et al. [60]; Sapwarobol et al. [2] |
| β-Glucan | Cholesterol-lowering, immune-enhancing, and antioxidant properties | Hot water extraction, enzymatic extraction | Ooi et al. [60]; Park et al. [26] | |
| Cellulose | Improves gut health, dietary fiber, and satiety enhancement | Alkaline extraction, mechanical milling | Friedman [22]; Gul et al. [34] | |
| Hemicellulose | Prebiotic, improves digestion, and supports gut microbiota | Alkaline extraction, enzymatic hydrolysis | Ooi et al. [60]; Sapwarobol et al. [2] | |
| Resistant starch | Prebiotic, improves insulin sensitivity, and supports gut health | Enzymatic extraction, heat-moisture treatment | Ooi et al. [60]; Sapwarobol et al. [2] | |
| Pectin | Antioxidant, anti-inflammatory, and gut health improvement | Acid extraction, enzymatic extraction | Friedman [22]; Gul et al. [34] | |
| Inulin | Prebiotic, improves gut health, and enhances mineral absorption | Hot water extraction, enzymatic extraction | Ooi et al. [60]; Sapwarobol et al. [2] | |
The processing techniques employed these days have significantly impacted the nutrition contained in RB, both regarding their stability as well as their bioactivity. Liao et al. [35] showed that in contrast to conventional thermal processing, hot air-assisted RF heating effectively stabilized RB without inactivating lipases and with the antioxidant activity and the phenolic contents preserved. For protein-fortified meal production, extrusion processing, particularly in twin-screw systems, is critical as it enhances the solubility and digestibility of RBPs, enhancing their technofunctionality [25]. Compared to solvent-based procedures, subcritical water extraction stabilizes and extracts RB oil simultaneously, retaining γ-oryzanol and tocotrienols [70]. Conversely, thermolabile chemicals can be eliminated by refining under high temperatures; for example, tocopherol content in RB oil decreases upon high-temperature deodorization [54]. In a move to retain the bioactive potential of RB as a functional food component, these findings emphasize the need to process RB gently. Table 2 depicts the bioactive compounds in RB, their types, activities, and extraction methods.
6. Health Benefits of RB
Phytochemicals found in RB show promise for improving health. Phytosterol and oryzanol abound in RB oil. Numerous health benefits of oryzanol have been documented, such as growth promotion, hypolipidemia, and hypothalamic stimulation. Oryzanols function as an antioxidant and a blood cholesterol lowering agent, among other biological and physiological benefits. Menopausal problems and nerve imbalances can be treated with it [34]. Large amounts of several chemicals can be found in stabilized RB, which may be able to prevent a variety of chronic illnesses. According to Nagendra Prasad et al. [71], RB is thought to play a significant role as a functional food because of its ability to decrease cholesterol, improve cardiovascular health, and have antitumor capabilities.
RB’s fiber increases the frequency and fecal output, acting as a laxative. Soluble fibers can subordinate postprandial blood glucose stages in usual and diabetic patients. The fiber in RB is made up mostly of insoluble fiber, with only a minor quantity of soluble fiber (7%–13%). RB’s soluble and fiber fractions are used to create nutraceuticals, which are used to treat Type I and Type II diabetes [72]. Additionally, RB comprises lipoic acid. Its antioxidant and antilipogenic potentials can be rummage-sale to treat Parkinson’s and Alzheimer’s disease and avoid diabetic neuropathy and retinopathy (Figure 4) [74]. Nutrition and nutritional status meaningfully influence immune system performance and infection resistance. This suggests that numerous nutrients can control immune function and that the actions of immune cells are influenced by varying dietary intake. RBO has been shown in numerous clinical trials to increase immunological function in patients with depression [26]. Phytosterols, sterolins, ɗ-oryzanol, Omega-3 fatty acids, phytonutrients, and minerals are among the immune system–boosting substances found in RB [26]. Figure 4 shows the health potential of RBP.
Along with antioxidant and anticancer properties, the bioactive peptides made from RB by enzymatic hydrolysis showed immune-modulatory benefits [73]. RB γ-oryzanol is a potent treatment for a variety of gastrointestinal disorders. A significant public health issue is colorectal cancer, which is one of the most terrifying side effects of inflammatory bowel diseases (IBDs), including Crohn’s and ulcerative colitis (UC). It has been experimental that γ-oryzanol from RB inhibits experimental ulcers in rats and gastric secretion (Table 3) [68]. Table 3 depicts the health benefits and mechanistic compounds of RB.
| Benefit | Mechanism/compounds | Study findings | References |
|---|---|---|---|
| Antioxidant activity | Phenolic compounds, flavonoids, γ-oryzanol, tocotrienols | Rice bran extracts exhibit strong free radical scavenging activity, reducing oxidative stress and preventing cellular damage. | Friedman [22]; Ghasemzadeh et al. [63]; Islam et al. [68] |
| Anti-inflammatory effects | Phenolic acids, flavonoids, γ-oryzanol | Rice bran reduces proinflammatory cytokines and markers such as TNF-α and IL-6, alleviating chronic inflammation. | Park et al. [26]; Saji et al. [75] |
| Cardiovascular health | γ-oryzanol, tocotrienols, dietary fiber | Rice bran oil lowers LDL cholesterol, increases HDL cholesterol, and reduces the risk of atherosclerosis and heart disease. | Ali & Devarajan [50]; Al-Okbi et al. [76]; Lai et al. [51] |
| Diabetes management | Dietary fiber, phenolic compounds, γ-oryzanol | Rice bran improves insulin sensitivity, reduces blood glucose levels, and modulates lipid metabolism in diabetic models. | Kubota et al. [77]; Zhang et al. [69]; Pereira et al. [39] |
| Gut health improvement | Dietary fiber, arabinoxylan, phenolic compounds | Rice bran promotes the growth of beneficial gut microbiota, enhances digestion, and reduces gastrointestinal disorders. | Ooi et al. [60]; Sapwarobol et al. [2] |
| Cancer prevention | Phenolic compounds, flavonoids, γ-oryzanol | Rice bran extracts inhibit the proliferation of cancer cells, induce apoptosis, and reduce tumor growth in various cancers, including breast and colon cancer. | Friedman [22]; Roleira et al. [59]; Park et al. [26] |
| Immune system modulation | Arabinoxylan, phenolic compounds | Rice bran enhances immune response by stimulating the activity of natural killer (NK) cells and macrophages. | Ooi et al. [60]; Park et al. [26] |
| Weight management | Dietary fiber, γ-oryzanol | Rice bran supplementation reduces weight gain, modulates lipid metabolism, and improves satiety in high-fat-diet-induced obesity models. | Yang et al. [78]; Zhang et al. [69] |
| Liver health | Phenolic compounds, γ-oryzanol | Rice bran reduces hepatic lipid accumulation, prevents fatty liver disease, and improves liver enzyme profiles. | Al-Okbi et al. [76]; Zhang et al. [69] |
| Skin health | γ-oryzanol, tocotrienols | Rice bran oil protects skin from UV-induced damage, reduces wrinkles, and improves skin elasticity. | Wang [79]; Lai et al. [51] |
| Neuroprotective effects | Phenolic compounds, γ-oryzanol | Rice bran extracts reduce oxidative stress in the brain, improve cognitive function, and protect against neurodegenerative diseases. | Friedman [22]; Park et al. [26] |
| Antimicrobial activity | Phenolic compounds, flavonoids | Rice bran extracts exhibit antimicrobial activity against pathogenic bacteria and fungi, supporting gut and systemic health. | Friedman [22]; Ghasemzadeh et al. [63] |
| Bone health | γ-Oryzanol, phenolic compounds | Rice bran improves bone density and reduces the risk of osteoporosis by modulating bone metabolism. | Lai et al. [51]; Park et al. [26] |
| Renal health | Phenolic compounds, dietary fiber | Rice bran reduces renal oxidative stress and inflammation, improving kidney function in high-fat-diet models. | Siqueira et al. [80]; Kubota et al. [77] |
| Antiaging effects | Phenolic compounds, γ-oryzanol | Rice bran delays cellular aging by reducing oxidative stress and inflammation, promoting longevity. | Friedman [22]; Park et al. [26] |
| Hypertension management | Bioactive peptides (e.g., Leu-Arg-Ala), phenolic compounds | Rice bran supplementation reduces blood pressure and improves vascular health in hypertensive models. | Ogawa et al. [81]; Lai et al. [51] |
| Wound healing | Phenolic compounds, γ-oryzanol | Rice bran extracts promote tissue repair and regeneration, accelerating wound healing. | Friedman [22]; Park et al. [26] |
| Antihyperlipidemic effects | γ-Oryzanol, tocotrienols, dietary fiber | Rice bran reduces total cholesterol, triglycerides, and LDL cholesterol, improving lipid profiles. | Ali & Devarajan [50]; Al-Okbi et al. [76] |
| Improved digestive health | Dietary fiber, arabinoxylan | Rice bran enhances bowel regularity, prevents constipation, and supports a healthy gut microbiome. | Ooi et al. [60]; Sapwarobol et al. [2] |
6.1. Antiobesity Properties
The fiber content, bioactive composites, and healthy fats found in RB make it a prospective candidate to be utilized against obesity. RB’s fiber content keeps you full on fewer calories [13]. Moreover, the γ-oryzanol and tocotrienols found in RB mark lipid metabolism by slowing down the creation of different fat cells and accelerating the rate of oxidation of fats [82]. Separately from regulating hunger and fat deposition, these composites regulate the levels of the hormones leptin and adiponectin [83]. In one investigation by Duansak et al. [82], mice that were persuaded to be obese using a high-fat diet could lose weight, had subordinate fat mass in their bodies, and had improved lipid profiles upon receiving RB extract supplementations. As additional contribution to its purpose of averting obesity, RB’s anti-inflammatory possessions can decrease metabolic syndrome associated chronic low-grade inflammation [13]. Also, as clarified by Sivamaruthi et al. [13], the metabolic condition is also improved by RB, helping in weight regulation even further. Das et al. [84] establish that fermented RB products upsurge beneficial bacteria such as Lactobacillus and Bifidobacterium, which are associated to a decrease in the risk of obesity [85].
6.2. Antidiabetic Effects
The antidiabetic possessions of RB, refining glucose metabolism and insulin sensitivity, are encouraging. Blood glucose concentrations are importantly affected by the bioactive composites, comprising ferulic acid, γ-oryzanol, and dietary fibers [12]. As per Sivamaruthi et al. [86], these composites constrain the activity of enzymes that damage carbohydrates, comprising α-amylase and α-glucosidase, thereby lessening the rate of glucose absorption and averting postprandial hyperglycemia [87]. The action of RB extracts on diabetic animal models has been found to augment pancreatic β-cell function and meaningfully decrease fasting blood glucose levels [88]. As per Boue et al. [88], diabetic illnesses can be advanced from the greater insulin secretion and lesser oxidative stress that purple and red RB, in particular, offer because of their greater levels of anthocyanin. Budhwar et al. [12] exposed that the high fiber nature of RB is liable for slowing down glucose release, thus averting spikes in blood sugar. Type 2 diabetics can achieve amended regulation of their blood glucose with routine usage of RB oil or stabilized RB, per clinical trials [86].
6.3. Anticancer Potential
The chemopreventive properties of RB are because of its numerous bioactive composites, such as γ-oryzanol, phytosterols, and polyphenols [89]. These composites avert tumors from growing and spreading by causing cancer cells to die [90]. RB extracts have anti-inflammatory and antioxidant possessions that make them operative against malignancies of the liver, colon, and breast [89]. As per the investigation done by Park et al. [26], RB chemicals can constrain cell proliferation related to cancer cells by regulating pathways such as NF-κB and PI3K/Akt. As per Yu et al. [89], the bioactivity of fermented RB is improved, that is, it has a sophisticated competence to combat cancer. Squalene and tocotrienols, the other two composites found in RB oil, have strong anticancer effects [73]. From epidemiological studies, persons who consume foods with a great content of RB are less susceptible to certain cancers [74]. To classify optimal doses for medicinal solicitations, more clinical trials must be conducted [27].
The antidiabetic, antiobesity, and anticancer activities of RB are mediated by the regulation of key molecular signaling pathways, according to new research. The bioactive compounds present in RB, namely, γ-oryzanol and tocotrienols, can inhibit the NF-κB signaling pathway, which in turn reduces the production of pro-inflammatory cytokines and suppresses cancer cell growth, says Park et al. [26]. Besides, the PI3K/Akt/mTOR signaling pathway is a key controller of glucose metabolism and insulin sensitivity; through the regulation of this pathway, RB extracts facilitate better blood sugar management in diabetics [77, 88]. Through the enhancement of Nrf2-mediated antioxidant responses, fermented RB enhances bioactivity and guards against oxidative stress linked with metabolic disorders and obesity [82]. Moreover, Punia et al. [73] also reported that the squalene and tocotrienols in RB oil induce apoptosis in cancer cells through the activation of p53 and caspase-3, as well as inhibiting the formation of new blood vessels by suppressing VEGF [91]. Additional clinical studies of the molecular interactions of RB are needed to best determine its therapeutic potential as a multitargeted agent, as evidenced by these mechanistic data.
6.4. Gut Microbiota Modulation
The prebiotic nature of RB rouses the growth of helpful bacteria in the gut, such as Lactobacillus and Bifidobacterium [2]. Das et al. [84] stated that the polyphenols and dietary fiber in RB are provoked by stomach bacteria. The consequence is butyrate and other short-chain fatty acids (SCFAs), which improve the reliability of the intestinal barrier and decrease inflammation. Based on investigation, RB supplement consumption is described to improve the richness of gut microbes, which is important for healthy metabolism and the immune system [2]. Inflection of gut microbiota is a fractional mediator of RB’s antiobesity and antidiabetic effects [13]. Additional nutritional interference to improve digestive wellness is stabilized RB, revealed to decrease gut dysbiosis in metabolic illness [27]. Further studies on applying RB as part of custom dietary regimens to exploit gut flora should be undertaken, as proposed by Das et al. [84].
It is important to distinguish between in vitro, animal, and clinical studies when dealing with the hierarchy of indication in rating the health effects of RB. Numerous studies have established that RB chemicals own possible bioactivities, such as antioxidant and anti-inflammatory activities. These studies have been carried out both in animal and in vitro models [22, 82, 88]. For illustration, Duansak et al. [82] discovered that RB extract reserved obesity in mice that had become overweight on a high-fat diet. This suggests that there could be metabolic benefits to this extract. Clinical validation is wanted strongly, though, to translate these findings to human health outcomes. While there are less such trials with humans, human clinical trials have begun to support these assistances. In a placebo-controlled, randomized trial, Ogawa et al. [81] established that a peptide derived from RB has antihypertensive effects, supporting its application as a functional food element. Likewise, Abbas et al. [57] noted that individuals whose diets consisted of probiotic-fermented milk and RB oil had improved lipid profiles. Clinical trials, such as those by Ogawa et al. [81] and Abbas et al. [57], offer an advanced level of evidence for particular health benefits and should therefore be accorded greater highlighting in the review, although preclinical studies deliver valuable mechanistic information.
7. Public Awareness and Education
Not many individuals are aware of the nutritional and medicinal potential of RB despite its health benefits being well established. RB, as noted by Ahsan et al. [42] and Friedman [22], is rich in bioactive compounds such as tocotrienols, γ-oryzanol, and dietary fiber, which can help ensure heart health, reduce inflammation, and enhance metabolic processes. However, such consumers in regions where RB oil or enriched products are traditionally eaten may not be well aware of these advantages [50]. One solution to this problem would be to initiate targeted awareness campaigns in association with healthcare initiatives and the food industry. For instance, probiotic-enriched food from fermented RB that has proven to enhance gut health and immunity [57] is yet to be utilized in common diets. The functional characteristics of RB can be employed to tackle malnutrition and chronic diseases; public health initiatives should target its introduction into daily diets [34].
8. Environmental and Economic Impact
By reducing agrowaste and delivering value-added products, RB’s usage is extremely favorable from both an economic and environmental perspective. The wasted or underutilized RB, being a by-product of the milling process, contributes to the issue of environmental waste [21]. Das et al. [84] established that it is one of the sustainable methods of enhancing food security and reducing environmental effects by converting it to edible oil, protein isolates, and nutraceuticals. RB oil production has numerous benefits, such as reduced cardiovascular disease and other illnesses, and it is more economical compared to other vegetable oils [51]. Also, ingredients derived from RB can potentially be a major player in the increasing global trend of functional foods [46]. Policymakers and agribusinesses must drive technology that processes RB in order to attain optimal economic and environmental results.
9. Nutritional Enhancement
RB, rich in protein, essential fatty acids, and antioxidants, has yet to be investigated extensively for prospective application in the fortification of food products. RBP isolates are an excellent plant-based equivalent of whey and soy proteins for protein enrichment as they offer the same level of nutritional value, as proven by studies [45, 49]. Based on a study led by da Rocha Lemos Mendes et al. [32], the incorporation of RB into baked foods, snacks, and milk alternatives can improve their fiber and antioxidant activity. Duansak et al. [82] discovered that clinical trials in rats revealed that RB extracts improved metabolic well-being and lowered oxidative stress. Future studies should be aimed at improving extraction and stabilization techniques in order to preserve bioactive components and enhance the palatability of functional foods [43]. Food manufacturers can use the nutritional content of RB to produce new foods that encourage healthier dietary practices and address dietary shortages across the globe.
10. Conclusion and Future Trends
A high-protein, high-fat, and high-carbohydrate by-product of rice milling, RB, comprises bioactive composites such as flavonoids, phenolics, and polymeric polysaccharides. It is a functional food with high health benefits due to its multifaceted chemical and nutritional configuration. Its role in improving overall health has been recognized through research demonstrating its capability to decrease oxidative stress, inflammation, and chronic illness risk. RB is a prospective component in functional foodstuffs and nutraceuticals due to its bioactive composites, chiefly phenolic acids and flavonoids, which support its immunomodulatory, anti-inflammatory, and antioxidant activities. In accumulation, the medicinal worth of RB is also joined by its capability to improve gut health and modify gut flora. Through amalgamation into diets, nutritional deficiencies are treated, and precautionary benefits in contradiction of cardiovascular illness, metabolic syndrome, and assured forms of cancer are attained. Additional studies are desirable to fully consider its mechanisms of action and its optimum usage in human health. All things being equivalent, RB is an underutilized but highly impending crop needed to improve nutrition and health internationally.
To better comprehend the therapeutic prospective of RB bioactive composites, future investigations should focus on explicating their bioavailability and bioaccessibility. Novel bioactive composites and their mechanisms of action can be exposed through advanced analytical approaches such as proteomics and metabolomics. Clinical trials over a prolonged period are also vital to establish the health benefits of RB and articulate dietary recommendations based on sound proof. A better understanding of RB’s health beneficial possessions can be attained if the synergistic action of its constituents is inspected and not independently. Also, groundbreaking processing technologies should be industrialized to improve the RB’s functionality and constancy in food products. This comprises extended shelf life to avert rancidity and optimizing extraction technology for bioactive substances. One of the promising solutions for addressing international health contests is incorporating RB into drugs, functional foods, and supplements. Finally, through the solicitation of RB’s nutritional and medicinal benefits to advance population health, public education campaigns and programs can endorse its incorporation into normal diets. RB can be transformed from an agricultural leftover product into a critical element of therapeutic and precautionary nutrition by meeting these forthcoming directions.
Ethics Statement
This study did not involve humans or animals.
Consent
The authors have nothing to report.
Conflicts of Interest
The authors declare no conflicts of interest.
Author Contributions
The listed authors have contributed equally to the work. All authors have read and agreed to publish the current version of the manuscript. Writing—original draft preparation: Muhammad Tayyab Arshad. Writing—review and editing: Sammra Maqsood. Methodology: Ali Ikram. Validation: Kodjo Théodore Gnedeka.
Funding
No funding was received for this research.
Acknowledgments
The authors gratefully acknowledge the University of Lahore, Pakistan, and the Functional Food and Nutrition Program, Faculty of Agro-Industry, Prince of Songkla University, Hatyai, Songkhla 90110, Thailand.
Open Research
Data Availability Statement
The data that support the findings of this study are available from the corresponding authors upon reasonable request.
