Rice bran is the outer brown layer of the rice grain. A paddy grain’s basic components include fiber, lipids, amino acids as well as a variety of vitamins and minerals. This nutritionally rich bran is obtained as a by-product of the rice milling process. The oil extracted from this bran is called rice bran oil (RBO) .
Depending on the method of extraction, rice bran has an oil content ranging from 10% to 23%. Rice bran oil contains 22% of saturated fatty acid (SFA), 43% of monounsaturated fatty acid (MUFA), 35% polyunsaturated fatty acid (PUFA), and other bioactive components present in the unsaponifiable fraction of RBO. RBO is a rich source of bioactive compounds, especially γ-oryzanol which is rarely found in other edible oils. However, the RBO refining process affects the amount of bioactive compounds [1, 2].
The Properties of Rice Bran Oil
Anti-lipidemic effect and Lower Blood Sugar
The fatty acid composition of RBO surprisingly is enabled to reduce body total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and apolipoprotein B (ApoB) .
The anti-lipidemic effect of RBO has been observed by its PUFA because the PUFA is claimed to have anti-obese, antidiabetic, and antihypertensive properties. The bioactive compound γ-oryzanol have a similar antilipidemic effect but there is no significant difference between a low and high dose of γ-oryzanol for atherosclerotic condition. Due to the synergistic effects of γ-oryzanol and other micronutrients like tocopherol, tocotrienol, and phytosterols including campesterol, stigmasterol, and beta-sitosterol, RBO can alleviate atherosclerotic diseases .
The positive effect of RBO on diabetics and hyperlipidemia depends on the available bioactive components γ-oryzanol and tocotrienol. Diabetes, whether it is type I or type II, insulin independent or dependent, causes impaired glucose metabolism as well as undesirable oxidative stress at the cellular and molecular levels. Studies have shown that the bioactive components of RBO lower blood sugar and oxidative stress, which may indicate that the compounds themselves or their metabolites modulate cellular or molecular biomarkers related to diabetes. Adiponectin, which is released by adipocytes, controls the upstream signal of glucose metabolism. In obese people, adiponectin levels dropped while glucose and lipogenesis levels rose in insulin-sensitive tissues such the liver and muscles. The adiponectin modulates the signal transduction of glucose utilization by translocation of glucose transporters (GLUT-2 and GLUT-4) to the cell surface and activation of the insulin receptor. A study showed that glucose level and lipogenesis are reduced by γ-oryzanol supplement because of its ability to increase adiponectin in obese patients. The bioactive component of RBO, γ-oryzanol induces the adipocyte to increase adiponectin secretion, which in turn increases the phosphorylation of AMP-activated protein kinase (P-AMPK) and inhibits gluconeogenesis and lipogenesis pathways in the liver. Additionally, RBO increases insulin secretion from pancreatic beta islet cells and decreases oxidative stress in these cells, which in turn increases the consumption of glucose in liver and muscle cells .
A study was conducted to find out how RBO affected the blood lipid profiles and insulin resistance in type 2 diabetes patients. When compared to the placebo group, the RBO group’s fasting and two-hour postprandial blood glucose levels significantly increased. Additionally, a 5-week dietary intervention that included RBO consumption resulted in a significant decrease in the concentration of LDL-C and total serum cholesterol .
Oxidative stress results in a deleterious process that culminates in the damage of cell structures, including membranes and lipids, as well as proteins and DNA. Both enzymatic and non-enzymatic processes frequently generate reactive oxygen species (ROS). The major reactions catalyzed by enzymes that generate ROS include those involving NADPH oxidase, nitric oxide synthase (NOS), xanthine oxidase, arachidonic acid, and metabolic enzymes such as the cytochrome P450 enzymes, cyclooxygenase, and lipoxygenase. ROS are produced non-enzymatically by the mitochondrial respiratory chain. Singlet oxygen (1O2), superoxide anion (O2•−), hydroxyl radical (OH•), hydrogen peroxide (H2O2) and organic peroxides are the major ROS generated in the human body. In addition, reactive nitrogen species (RNS), such as nitric oxide (NO), nitrite (NO2−); carbon monoxide (CO); hydrogen sulfide (H2S) and its anion HS− are molecules that influence oxidative balance .
Several reactive compounds are produced by oxidative imbalance and are scavenged by γ-oryzanol or its metabolites. The consumption of high-fat diets (HFD) has been shown to induce the formation of free radicals and ROS, resulting in lipid peroxidation and oxidative stress. In mice given an HFD diet, γ-oryzanol and fatty acid suppressed lipid peroxidation .
One of the biggest problems facing the globe today is an aging population. Ageing is regarded as a significant risk factor for neurological illnesses including Alzheimer’s disease (AD), and Parkinson’s disease (PD). Currently approved medications only attenuate but do not relieve the symptoms. Therefore, new research methods are focusing on strategies to prevent certain diseases through long-term dietary intervention. There is evidence that dietary components such as polyphenols, omega-3 fatty acids, and vitamin E can prevent mitochondrial dysfunction. Mitochondrial dysfunction appears to play a significant role in the progression of age-related illnesses. The progression in age is a major factor responsible for the development of symptoms of Alzheimer’s disease. In the pathophysiology of AD, there are no identified pathogenic processes. The function of mitochondria in synaptic transmission is one of the key pathogenetic processes. Mitochondria play an important role in the regulation of synaptic signaling. Whenever there is an increase in amyloid plaques the increased oxidative stress leads to mitochondrial dysfunctions and ultimately cognitive dysfunctions. According to certain studies, rice bran exerts its neuroprotective properties by controlling mitochondrial biogenesis. Consequently, using rice bran to treat Alzheimer’s disease symptoms may be beneficial .
Immune System Modulation
Immune system modulation, also known as immunomodulation, is the process that involves the use of therapy to modify the immune response, often to prevent tissue damage resulting from an excessive response. The immune system is controlled both by direct interaction of several types of cells (lymphoid cells: B and T lymphocytes, T helper (Th) cells, natural killer (NK) cells; myeloid cells: neutrophils, basophils, monocytes, macrophages) and secreted molecules (immunoglobulins, cytokines: interleukins, colony-stimulating factors, growth factors, interferons, etc.) by them. RBO modulates the immune system by enhancing B-lymphocyte proliferation and TH1-type cytokines such as IL-2 or TNF-α. The antiallergenic characteristics of RBO were suggested by a decrease in TH2 cytokine IL-4 and immunoglobulin E (IgE) levels. However, it has been discovered that γ-oryzanol has the capacity to significantly increase immunological activity through cellular processes .
RBO is gaining popularity in Asia and other countries due to balanced fatty acid profile and γ-oryzanol, which is a natural antioxidant present in the crude oil . Both the RBO itself and therapeutically bioactive components are secure and effective in ameliorating lifestyle-related diseases. RBO appears to be a highly promising oil to reduce the growing incidence of non-communicable disease for 21st century’ s ailment. However, more research is needed to confirm the beneficial effects of RBO .
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- Behl T, Kumar S, Sehgal A, Singh S, Kumari S, Brisc M, et al. Rice bran, an off-shoot to newer therapeutics in neurological disorders. Biomedicine Pharmacotherapy. [Internet]. 2021 [cited 2022 May 27]; 140: 1-12. Available form: https://www.sciencedirect.com/science/article/pii/S0753332221005783?via%3Dihub