Preparation Of Milk Ingredinets In The Form Of Antimicrobial Peptides Powder Derived From Bovine Casein

Bovine casein accounts for about78.8%of milk protein, which consists of α-casein,β-casein, γ-casein and κ-casein. Besides nutritional function, Bovine casein also containsabundant biological activity sequences, which if be hydrolyzed by certain protease, canrelease active fragments. Those fragments can be processed into the base stock of functionalmilk drink, which can take pressure off the import pressure, and also solve the digestionproblem of raw milk. Therefore, the development and research of milk ingredients is the trendof the development and inevitable choice for quite a long time.In order to prepare better antibacterial milk Ingredients, fresh milk were used as thematerials to extract casein, and a protease was chosen to hydrolyze bovine casein from neutralprotease, alcalase, trypsin and papain by the indexes of inhibition zone against escherichiacoli, salmonella and staphylococcus aureus. Then, the optimum hydrolysis conditions wereobtained by single-factor tests and orthogonal tests. Later, for providing the basis aboutpreparation of antibacterial milk Ingredients, hydrolyzates that bovine casein was hydrolyzedunder the optimum hydrolysis conditions were isolated and purified by macroporousabsorption resin and gel filtration chromatography. The antimicrobial activities of theseparated component were studied by the indexes of inhibition zone, MIC and MBC againstthree kinds of bacterias, and the following the results were obtained:(1)Bovine casein was hydrolyzed by neutral protease, alcalase, trypsin and papain inmuch time, and antibacterial rest results of their hydrolyzates show that hydrolyzates ofpapain had stronger antimicrobial effect against escherichia coli, salmonella andstaphylococcus aureus than the other three hydrolyzates. therefore, this test decided to selectpapain as optimal protease to hydrolyze bovine casein.(2)The optimum hydrolysis conditions are hydrolysis temperature of50℃, hydrolysistime of4.5h,enzyme amount of4500U/g, pH of5.5, and hydrolyzates before and after heattreatment were studied by the indexes of inhibition zone against three kinds of bacterias, andits result showed that they do not exist significant differences, therefore, hot stability ofbovine casein hydrolyzates are good. (3)Macroporous absorption resin was used to separate casein hydrolyzates into fourcomponents, and the75%alcohol elution components showed stronger antibacterial effect, itsinhibition zone against escherichia coli, salmonella and staphylococcus aureus were15.5mm,15.3mm and14.0mm; MIC were2.600mg/mL,2.930mg/mL and2.600mg/mL; MBC were5.210mg/mL,10.410mg/mL and5.210mg/mL.(4)The75%alcohol elution components was purified into four fractions by gelfiltration chromatography. Fractions A showed stronger antibacterial effect againstescherichia coli and salmonella, its inhibition zone against escherichia coli and salmonellawere20.3mm and17.3mm; MIC were0.121mg/mL and0.242mg/mL; MBC were0.484mg/mL and0.967mg/mL. Fractions B showed stronger antibacterial effect againststaphylococcus aureus, its inhibition zone against staphylococcus aureus were18.3mm, MICis0.084mg/mL; MBC is0.336mg/mL.Then,two antimicrobial milk Ingredients weresuccessfully prepared with fractions A and fractions B by freeze drying, and their antibacterialactivities were well.