Optimization Of Preparation Technology And Functional Properties Of Food Grade Casein By Acid Precipitation Method

Casein is a dairy product produced by fresh cow milk through a series of processes such as centrifugation,defatting,acid precipitation and drying.Casein is an important food additive and chemical raw material,contains eight kinds of essential amino acids,and contains a variety of biologically active peptides,which has a high value.With the rapid development of my country's food industry and the improvement of consumption levels,the demand and quality requirements for food-grade casein continue to increase,the existing market is in short supply,and the prospect is very broad.This experiment takes fresh milk as the research object,adopts acid precipitation method(malic acid,citric acid,hydrochloric acid)prepare food-grade casein from milk,and optimizes the process conditions by response surface methodology and orthogonal test.The effect of different processing conditions on the functional properties of casein was determined.Besides improving the yield of casein,the functional properties of casein by different processing conditions were also determined.Meanwhile,it provides experimental basis for the preparation of food-grade casein with fresh milk.The main results were as follows:1.The results show that the best sterilization condition of skim milk was 63?,30 min,under this sterilization condition,the yield of casein was 2.26g/100 ml,casein protein content was 90.3%,casein content(proportion of total protein)was 95.6%;The optimum conditions for acid precipitation conditions were: malic acid concentration was10.38g/100 ml,acid precipitation temperature was 33?,stirring speed was 12r/s.The casein content of casein was 97.8% under this condition;The optimum conditions for washing conditions were:the temperature of the washing water was 65 ?,the number of washing times was 3,the amount of washing water is 40% of skim milk.Under this condition,the ash content of casein is 1.2%;The optimum conditions for drying conditions were:drying temperature was 50?,drying time was 3.5h.Under this condition,the moisture content of casein was 7.65%,and the color sensory score was90.6 point.2.The results show that casein has the highest foaming property,foaming stability,water holding capacity,solubility and viscosity when the sterilization condition of skim milk was 63? for 30 min.When the sterilization condition of skim milk is 80-85? for 20 s,the emulsification and emulsification stability of casein is the largest;The casein extracted with malic acid has greater foaming,emulsifying,water holding and solubility properties than casein prepared with citric acid and hydrochloric acid.The foaming stability,emulsification stability,and viscosity of casein prepared by hydrochloric acid are greater than those prepared by citric acid and malic acid;The emulsification and emulsification stability of casein increase first and then decrease with the increase of acid concentration,acid precipitation temperature,washing water temperature and drying temperature;The foaming and foaming stability of casein increases first and then decreases as the acid concentration,acid precipitation temperature and drying temperature increase.However,the increase in the temperature of the washing water causes the foaming property to increase first and then decrease,and the foam stability decreases first and then increases;The water holding capacity of casein increases first and then decreases with the increase of acid concentration,acid precipitation temperature and washing water temperature,while the increase of drying temperature causes the water holding capacity to gradually decrease;The solubility of casein increases first and then decreases with the increase of acid concentration,acid precipitation temperature and washing water temperature,while the increase of drying temperature causes its solubility to gradually decrease;The viscosity of casein decreases first and then rises with the increase of acid concentration,and gradually increases with the increase of acid precipitation temperature and drying temperature.The temperature of washing water has no significant effect on the viscosity of casein.These functional properties of casein are related to the molecular structure and size of casein,ion content,p H,and calcium ion content in micelles.