Research On The Dry-rendering And Wet-rendering Of Lard And The Its Deacidification Process

Lard is a kind of animal fat that made up of adipose tissue extracted from healthy pig by dry-refining or wet-refining. As its rich resources, high nutritional value, easy absorbing, unique flavor, wide-range in application, etc., it has been loved by customers in China for a long time. The high temperature refining process of lard easily produce adverse effect on its quality. So rational development and utilization of lard become a very important issue. Three different parts of pig fat, pork suet, fat lining and intestinal fat were took as raw material in this thesis. Oil extraction rate of different parts of pig fat and the quality changes of lard under the different rendering methods and conditions were explored. Then the pork intestinal fat was deacidified by alkaline deacidification method and solvent extraction deacidification method. Orthogonal tests were designed on the basis of single factor experiments, the optimum technological conditions were gained after comprehensive consideration of the effect of deacidification process on the acid value and refining rate.The main results showed as follows:1.It is concluded that the oil-extracting rate of pork suet was the fastest by comparing three different parts of pig fat. Wet-rendering was appropriate to pork suet, and dry-rendering was appropriate to fat lining. It taked shorter time to process pork intestinal fat by dry-rendering, but bigger oil extraction rate could be got by wet-rendering. So the selection of rendering method of pork intestinal fat should be comprehensively combined with lard quality.2.Rendering conditions had great influence on the acid value and peroxide value of three kinds of lard. Suitable rendering conditions of pork suet was wet-rendering temperature 110℃, pressure 0.06MPa. Appropriate rendering conditions of fat lining was dry-rendering temperature 100℃. Processing intestinal fat by wet-rendering was suitable. But the acid value of intestinal fat rendered by two kinds of methods was much higher than national standards. After comprehensive comparison of lard oil quality rendered from three different parts of the pig fat, the acid value and peroxide value of pork suet was the lowest between them, but the acid value and peroxide value of pork intestinal fat was the highest.3.The effect of sodium hydroxide concentration, excess alkali amount, the time and the initial temperature of alkali deacidification on the acid value and refining rate of pork intestinal fat were researched when alkali deacidification process of pork intestinal fat was optimized. Orthogonal test was designed to get the optimum processing parameters of the alkaline deacidification. The optimum processing formula was sodium hydroxide concentration 21%, excess alkali amount 0.1%, the time of alkali refining 70min, the initial temperature of alkali refining 45℃.4.Taking 95% ethanol as the extraction solvent, the effect of extraction time, extraction temperature, extraction times and ratio of oil to alcohol on the acid value and yeild of pork intestinal fat were researched when solvent extraction deacidification process of pork intestinal fat was optimized. Orthogonal test was designed to get the optimum processing parameters of the solvent extraction deacidification. The optimal process condition was extraction temperature 45℃, extraction times 4 times, ratio of oil to alcohol 1:1.5, extraction time lOmin.