Extrusion of rice bran – the best way to obtain high-effective animal feedTuesday, 09 June 2015 10:49
About rice bran
Utilizing commodities and by-products to their fullest extent is a successful strategy to increase overall food production in all parts the world. Rice and rice products are the chief source of energy for 40% of the world’s people, Rice bran is a major cereal by-product available for animal feeding in many parts of the world, especially in Asia. Rice bran is produced from the rice milling process that makes white rice for human consumption; it is the outer layer of the rice kernel after the hull is removed. The bran constitutes nearly 7%-8.5% of the total grain. Rice bran is the most nutritious part of the rice grain. It has good balance of protein, fat, carbohydrates, fiber, vitamins and minerals.
The composition of rice bran varies based on the source and the milling process. On average, rice bran has approximately 3.2 kcal/gram, contains 8% moisture, and 20% to 30% total dietary fiber, mostly insoluble. It also acts as an excellent source of B vitamins and minerals and contains minerals such as iron, potassium, calcium, chlorine, magnesium, and manganese. The protein content of rice bran ranges from 12% to 20%, depending on pre-treatment. The nutritional value of rice bran protein is relatively high because of the high lysine content, one of the essential amino acids with a protein efficiency ratio (PER) of 1.6. Major carbohydrates in rice bran are hemicellulose (8.7%-11.4%), cellulose (9%-12.8%), starch (5%-15%), and ß-glucan (1%). Comprised of 16% to 22% fat, the fatty acid composition of rice bran is roughly 19% saturates (primarily palmitic), 41% monounsaturates (primarily oleic acid), and 36% polyunsaturates (primarily linoleic acid). Rice bran contains large amounts of omega-3 fatty acids and gamma oryzanol. Omega-3 fatty acids are called essential fatty acids as they are required in the animal’s diet and are responsible for many basic cellular functions. Gamma oryzanol is only found in rice bran, and has been found to have powerful antioxidant properties. Rice bran is also a rich source of biotin and other B vitamins.
The greatest restriction to use rice bran is its highly unstable state during storage leading to rancidity, and presence of heal labile anti-nutritional factors. Lipase is naturally present in rice bran and is responsible for breaking down fatty acids and causing rancidity, which reduces the nutritional value of rice bran and makes it unpalatable. Due to high oil content and lipolytic enzymes, rice bran is easily oxidized during storage at room temperature. Feeding rancid rice bran reduced growth performance in chicks and in pigs. Free fatty acid content in rice bran is used as an indirect indicator to evaluate the efficiency of lipase inactivation. It is considered that there are no significant fall in digestibility until the free fatty acid reaches 50%. Also rice bran contains some antinutritional factors, i.e., trypsin inhibitor and haemaglutinin-lectin, which reduce feed intake and depress poultry performance.
Extrusion – the best method to process rice bran
Extrusion cooking proved to be the most effective process in stabilizing rice bran by inactivating the lipase, destroying the bacteria and stabilizing the free acid and so reducing the rancidity and increasing the storage life. The extrusion process destroys the enzyme immediately after milling and therefore stabilizes the oil content and preserves the nutritional value of the rice bran. The increase in free fatty acid level of extruded rice bran is significantly lower than that of raw or pelleted rice bran during storage. Also antinutritional factors such as trypsin inhibitors are destroyed by extrusion cooking. This provides a high-quality product that needs no chemical preservatives and has a one-year shelf life.
Feeding stabilized rice bran made greater gains in chicks and better digestibility of nutrients in chicks and pigs than raw rice bran. While using in broiler starter and finisher rations at various levels replacing maize, for six weeks rice bran processed by extrusion cooking has better performance of broiler chicks comparing with roasting and pelleted bran. Rice bran can be used up to 20 percent in ration without any adverse effect on broiler chicks mortality and organ weights. Non-significant differences are observed in broiler performances when fed rations with raw and pelleted rice bran. So pelleting is not effective to improve nutrient digestibility of raw bran. Chicks fed rations with extrusion cooked rice bran result in significantly better growth performance than other treatments. Extruded rice bran can be used up to 30 percent in ration without any significant effect on performance, mortality and organs weight of chicks. Chicks fed rations with rice bran treated with antioxidant up to 250 ppm have non-significant effect on broiler performance.
Better performance is observed when extruded rice bran stored for four months is given to chicks instead of raw bran, while extruded rice bran gives significantly better performance even after storage for 8 and 12 months. And no difference is observed between raw and roasted rice bran stored for four months. Treatments of rice bran by different levels of antioxidant had no effect on digestibility of fat and fiber when incorporated in broiler feed. Interaction of storage, processing and levels is significant for fat digestibility.
Processing of rice bran by extrusion cooking significantly increases fat digestibility, even used at higher levels in broiler feeds. Extruded rice bran stored for a year and used up to 30 percent in feed results in significantly higher fat digestibility in feeds as compared to feeds contained roasted or raw bran.