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COOKINGCooking is excellent preparation for most oilseeds and necessary for those too soft to withstand the pressure generated within a screw pressEFFECTS OF COOKING PROCESS ON THE PHYSICAL AND CHEMICAL PROPERTIES OF OIL SEEDS:1. The oil droplets in the oil seed are ultramicroscopic in size. Because of the increase in temperature they come together and form larger droplets to flow from the seed2. Heating of the seeds causes the protein to denature and as a consequence, the emulsion to break and the oil to separate from the solid surface of the seed3. Cooking of the seed gives the seed mass the proper plasticity for efficient pressing4. Insolubulization of phosphatides and other impurities5. Destruction of molds and bacteria6. Increase of the fluidity of the oil through increase in temperature7. In the case of cottonseed, detoxification of gossypol or related substances8. Cooking also ruptures oil cells, thereby releasing the oil into a more fluid state9. Cooking inactives troublesome enzymes that adversely affect oil and meal qualityEXTRUSION PREPARATIONCooking by extrusionDETOXIFICATIONSeveral toxin are troublesome in oil seeds;Cotton seed contain three toxins, CB-1A being the most difficult to inactive Seed like peanuts, cotton seed that are permitted to mold can contain alfatoxin, a metabolic waste product of several Aspergili moldsEXTRACTION1. RenderingWetprocess, Dry process, Slurry, Digestive process2. Mechanical ExtractionScrew press, Hydraulic press (full pressing, pre-pressing, cold pressing)3. Solvent ExtractionContinuous process, Batch processProcessing Options:Oilseeds can be processed using one or more of a number of stages, depending on the nature of the seed, the capacity of the plant and the intended marketSeeds which contain relatively little oil < 20 % (soybeans), are almost processed by solvent extraction . (residual oil content in meal 0,5-1%)Seeds with a higher oil content are processed in two stages. A-pre press to reduce the oil content to around 18-20% and the press cake is then treated with hexane to produce a meal with 0,7-1,5% oilCold pressing may also be used when a particular oil quality is required. However extraction rates are generally significantly poorer than with conventional processingRENDERING OF ANIMAL MATERIALSFatty anima tissues, free from muscle and bone, usually contain 70-90% fat, the balance being water and connective tissueConnective tissue is high in protein, hence the dried solids from rendering (tankage), like the solids in the raw material is small- low temperature, done at temp below the boiling point of water- high temp, or steam rendering, done under pressure in closed vesselsDRY RENDERINGDR is a simler method of fat extraction. It differs from wet rendering in that the explusion of fat is accompanied by dehydration of the fat and solid residue so that both are of low moisture at the end of the operationSLURRY RENDERINGThe raw material is coarsely ground, mixed with finished fat, and is then fine ground to form a pumpable slurry of approximately 68% fat, 10% solid, and 22% moisture.The slurry is pumped through an evaporator under vacuum for moisture removal, then through a centrifuge for fat removalThe solid residue at approximately 35% fat is pressed to 10% fat in screw pressesDIGESTIVE RENDERINGConsiderable attention has been given to wet rendering of animal fats with the assistance of added chemicals or enzymes that promote the separation of fat by hydrolyzing and dissolving the connective tissue.Best result were obtained whwn the fat was digested at 85-95 C for 45 min to 1 h with a 1,75% sodium hydroxide. Solution . After digestion, the fat was seperated from the aqueous liquid (which contained a small amount of undigested solids) by cntrifuging. The fat was thn washed, first with 2-5 % salt solution, and then with water.The process for the recovery of lard or other animal fat involves digestion of the fatty stock with a proteolytic enzyme of vegetable origin, for example , 0,005-0,020% papain at a pH of 6,0-7,5, followed by heating to 60-85°C to separate the fat.
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