Characteristics Of Rice Bran And Its Stabilization
Rice is the most consumed staple cereal food in large part of the world, especially in Asia. More than 100 countries, it is grown and there are around 18,000 varieties of rice for around 25% of the world’s grain production. The important rice producing continents are Asia, Africa and America. Rice bran is obtained by milling of rice paddy yields 70% of endosperm as the main product and by - products consisting of 20% rice husk, 8% rice bran and 2% rice germ. Rice bran is originally used as animals feeds, however, now there is a chance of producing oil from it. The main countries in rice bran oil production are India and Thailand.
Rice bran is highly contains in proteins, fiber, lipid and anti-oxidant; also it contains anti-nutritional factors, like the inhibitor of the tripsins and the lectin. The bran contains less soluble fiber and low cholesterol and other characteristics of health that they improving. Although the nutritional and nutritive potential of the bran have been recognized, the consumption of rice bran in human foods has limited to itself a very small quantity due to rapid rancidity of the bran. Stabilization process will inactivate enzyme, which causes the rancidity and anti-nutritive factors. As the bran degrade due to the presence of lipase enzymes, the flavor of bran also will change to initiate rancidity, smelly, and sour. Physicochemical properties are very important to know how rice bran will behave during food processing. These physiochemical properties are very important to know that how will behave during the food processing.
Although rice bran has beneficial compounds, which has health-enhancing properties, due to its rough texture and low concentration of the bioactive compounds, limit its application and incorporation into food products for the preparation of preserving foods. Stabilization processes become a prior condition to arrest the lipase enzyme in rice bran. These efforts are directed to the destruction or the inhibition of the lipase – the enzyme that causes the development of the free fatty acids (FFA). This does to reduce the losses of oil that are directly proportional to the content of FFA. Stabilized rice bran has a longer shelf life than non-stabilized rice bran, because it undergoes some processes that inactivate enzymes that would otherwise degrade the rice bran, turning it rancid.
Stabilization, which does not affect the nutritional value of the bran. In this study, chemical stabilization technique using lime juice and vinegar will be applied using rice bran from Klong Yong sub-district Nakhon Pathom, Thailand. Solid-state fermentation (SSF) is the fermentation process, which includes solid matrix and is carried out in absence or near absence of free water; however, the substance must have enough moisture to support growth and metabolism of the microorganisms. The solid matrix could be either the source of nutrients or simply a support by the proper nutrients that allow the development of the microorganisms. In current study, SSF will be optimized with response surface methodology, Box-Behnken Design (BBD) and used to enhance value-added bioactive compounds from rice bran.
Microwave-assisted extraction (MAE) is a novel extraction method, which means the environmental-friendly method. And it also has more performance than conventional methods. It takes shorter time and give higher yield than traditional methods. Therefore, it is also called green technology.
Rice bran
The bran of the rice is where approximately 85% of the nutritional power of the rice kernel is stored. The bran portion of rice is extremely nutrient dense.
Rice bran, or Oryza sativa, is a waste of paddy milling process in producing polished white rice as shown in figure 2.2, this illustrates that the paddy is applied by the dehusking process to separate paddy husk and brown rice. And then polishing process will be applied to the brown rice to distinguish between white rice and rice bran. People normally consume is white rice and the rice bran is normally a waste or feed to the animals. However, rice bran contains 12 to 15% protein and its main components; protein, carbohydrates, fats, fiber, and also rich in nutrients with different types of vitamins, mineral and antioxidants.
Stabilization of rice bran
Until recently, rice bran as a source of value-added food product was under-utilized due to lipase enzyme which is endogenously present or produced as a result of microbial activity which is activated during the milling process. These lipases hydrolyze the oil into glycerol and free fatty acids which give the product a rancid smell and bitter taste that renders the bran unsuitable for consumption. Under normal milling conditions rice bran will degrade in approximately six hours into an unpalatable material making it unsuitable as human food. Because of the problem with rancidity, most rice bran is used as a high protein feed additive for animals or as fertilizer or fuel. Since oxidative changes affect the oil quality adversely and are not very rapid in their manifestation, stabilization becomes a pre-requisite. These efforts are aimed at destruction or inhibition of lipase – the enzyme that causes development of free fatty acid (FFA). This is done so as to reduce oil losses which are directly proportional to the FFA content. Properly processed extrusion- stabilized rice bran from rough rice can be safely stored for up to one year at ≤22°C in gas-permeable packaging. But the maximum safe storage life for par-boiled rice bran is estimated at less than 3-4 months.
The methods employed to stabilize the bran (prevention of rancidity by lipase action) are based on reducing the moisture content, or altering the temperature or pH to destroy the activity of lipase. These include processes involving heat treatment, cold storage or low temperature storage, chemical treatment, control of relative humidity during storage and simultaneous milling and extraction and microwave heating. Hydrochloric acid treatment has been successfully used to stabilize rice bran. When rice bran is subjected to a short-term, high-temperature treatment immediately after milling, the lipase activity is destroyed, thereby stabilizing the bran. Rice bran stabilization methods and conditions are shown in table 2.5 below. SRB is naturally processed to inactivate enzyme that cause rancidity to ensure oxidative stability. SRB is all natural with no-chemical additives.
