Study On The Stability Of Acidified Fruit Milk And Casein System In Acidic Condition

The stability of acidified fruit milk affected by the factors such as material quality, the milk content, the system acidity, additive categories, the process and parameters of machining and so on, it is a difficulty problem in new dairy products development. To improve the stability, the critical point is settling the stability of casein in acidic condition.To produce the acidified fruit milk, the raw materials were the whole fat ultra high temperature (UHT) milk and concentrated apple juice, and the technological regulations were followed, the protein content was 1.5%, the juice content was 50%, pH was 4.10 in the product, which were defined by organoleptic rating. The directions of stabilizer were defined by single factor test and orthogonal chart: Carboxymethylcellulose 0.2%, Propylene glycol alginate 0.175%, High-ester pectin 0.14%, Sodium tripolyphosphate 0.08%, and Sodium citrate 0.04%. After sterilized under 90℃ for 10 min, the product could storage at least 30 days at 4℃ conditions.Casein was extracted from pasteurized whole fat milk to manufacture the casein system, it studied the effect of high-ester pectin upon casein under acidic condition, the result showed that casein system added with high-ester pectin in acidic condition could be stable and the stability was affected by the dosage of high-ester pectin,pH,degree of esterification(DE),chelating agents and sugar dosage in the system. The relationship was linearity between dosage of high-ester pectin and content of casein, when the content of casein changed from 0.6% to 1.5%, the linearity equation was y=0.3333x+0.2458, when the pH of system less than 3.60, the system geled resulted from the gelation characteristic of the high-ester pectin. Analyzed from the photoes of casein and high-ester pectin by atomic force microscope, it founded that the reason casein was stable caused by high-ester pectin, which coated on the casein micells and prevented their depositions. Casein was stable in the acidic condition when isoelectic point less than 4.60, and we thought that the isoelectic migrated. When casein and high-ester pectin were in the system, the quantity of isoelectric migration was 0.47, When casein, high-ester pectin and sodium tripolyphosphate were existed in the same system, the quantity of isoelectric migration was 0.88.