October 6, 2008

Fat Processing

Fat Processing
Plant Oils
The oils are usually removed from plant tissues by three methods. In the first method, cells containing oil are ruptured by heat and mechanical methods. In the past, cottonseeds free of lint were hulled, then flaked between rollers, and cooked with lived steam prior to hydraulic pressing to separate the oil. A second method, called screw pressing, involves heating the flakes or cracked meats, followed by passage through closed-fitting cages of screws to press out the oil. The third method involves solvent extraction using petroleum hydrocarbons at 60 – 70 degree Celsius. This method, which is a continuous one, has a capacity of processing of hundreds of tons of oil per day. The by-products of these methods are proteins, which are used in animal feeds.

Animal Fats
Animal fats are separated from fatty tissues by wet or dry rendering. In wet rendering, the fatty tissue is heated under steam pressure, thus rupturing the cells and liberating the fat. In dry rendering, the fatty tissue is heated in jacketed drums with agitation until the fats is released. Presently, centrifuges are used to separates the fat from water and protein.

Hydrogenation of unsaturated fats and oils increase their melting point and hardness, this process often used in the production of shortenings, which are generally defined as plastic materials made wholly from fats and oils. Hardness can be controlled by varying the ratio of solid to liquid glycerides. The shortenings are made by blending the desired oils and/or fats, deodorizing the mixture, chilling, and finally packaging.

When fats and oils are heated in the presence of certain catalysts, the fatty acids attached to glycerol rearrange in a process called interesterification. While vegetable oils are randomly distributed, animal fats generally are not. For example, at a level of 0.4% tin in standard hydroxide added to fat at 140 degree Celsius, then heated to 225 degree Celsius for 90 min in a vacuum, the distribution pattern of fatty acids will become random. In similar process, the melting point of soybean oil can be increased from -7 degree to +5.5 degree Celsius and its softening form -13 degree to -0.5 degree Celsius.

Interesterification is used in the industry to produced standard oils, which may be blended with others for use in the margarine and cooking fat trade. During interesterification, if the temperature is lowered, a certain amount of the higher melting triglycerides crystallize out. This has a dramatic effect on the remaining portion of liquid oil and alters the course of esterification. This is called directed interesterification.
Fat Processing

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