Study On Selection Of Starter For Mixed Milk Cheese And Characteristics During Ripenning

The starter and ripening characteristics of mixed milk cheese were studied in this paper. Thebest lactic acid bacteria for fermented mixed milk cheese were selected. Texture, proteolysis,lipolysis and sensory properties of cheese during ripening were investigated. Fluorescence analysis,ultraviolet spectrophotometry, high performance liquid chroma-tography, kjedahl determination, and gaschromatography/mass spectroscopy were adopt.The key work was as follows:1. Coagulation properties of different strains fermented mixed milk, cow milk and soybeanmilk were researched. The results showed that clotting time of fermented soybean milk by differentstrains was shortest, clotting times of fermented mixed milk and cow milk were similar. And thecoagulation properties of clotting mixed milk and clotting cow milk were better than that of clottingsoybean milk; there was no significant difference between clotting mixed milk and clotting cowmilk on coagulation properties. Str.cremoris was the best strain for fermented mixed milk.2. Fermenting properties indexes of different strains fermented mixed milk, cow milk andsoybean milk, such as cohesiveness, acidity, diacetyl, exopolysaccharide, and pH4.6 WSNconcentrations of clotting milk were detected. It is concluded that different strains has differentfermenting properties with the distinct substrate. The cohesiveness and acidity of fermented cowmilk were higher than those of fermented mixed milk and fermented soybean milk. The diacetyleconcentrations of fermented soybean milk were lower than those of fermented mixed milk andfermented cow milk. The diacetyle concentrations of fermented mixed milk and fermented cowmilk were almost similar and no regularity was detected. The exopolysaccharide Concentrations ofclotting cow milk were higher than those of clotting mixed milk and clotting soybean milkfermented by dirrerent strains except Lb.casei 10210. The pH4.6 WSN concentrations of clottingmixed milk were higher than those of clotting cow milk and clotting soybean milk fermented bydifferent strains except Lb.acidophilus F, Lb.casei 10210. From the statistical results of fermentingproperties indexes of clotting mixed milk fermented by different strains we made the order fromhigh to low was Str.cremoris→Str.salivarius ssp.thermophilus→Lac.delbrueckii ssp.bulgaricus12→Str. salivarius ssp.thermophilus 11→Lac.delbrueckii ssp.bulgaricus→Lb. acidophilus F→Str. lactis→Lb.casei 10210. We selected Str.cremoris as culture for making cheese.3. The catabolism abilities forα-galactooligosaccharides of different strains wereresearched. Theα-galactosidase activity of different strains and the acetic acid concentrations inclotting soybean milk were detected. It was showed that different strains had differentα-galactosidase activities. Theα-galactosidase activities of lactobaciilus were significantly higherthan those of lactococcus.The order ofα-galactosidase activities of iactobacillus from high to low was: Lb.casei 10210 and Lb.acidophilus F→Lac.delbrueckii ssp.bulgaricus→Lac.delbrueckiissp.bulgaricus 12. The acetic acid concentrations of clotting soybean milk fermented bylactobacillus were significantly higher than those of clotting soybean milk fermented bylactococcus, between which there were no remarkable difference. The order of acetic acidconcentrations of clotting soybean milk fermented by lactobacillus from high to low was: Lb. casei10210→Lb. acidophilus F→Lac. delbrueckii ssp. bulgaricus→Lac. delbrueckii ssp. bulgaricus 12.Considering the catabolism abilities forα-galactooligosaccharides and the coagulation properties,and fermenting properties, we selected Lac.delbrueckii ssp. bulgaricus as culture for making cheese.4. The growth curve of mixed culture indicated that the growth amount of mixed culturewas higher than that of Strcremoris alone at the same time, and was slightly lower than that ofLac.delbrueckii ssp.bulgaricus alone. The ability of producing acid was higher than that of singlestrain. There was a good intergrowth between Str.cremoris and Lac.delbrueckii ssp. bulgaricus.5. By two factors and five levels of orthogonal experiments, it was concluded that theoptimal culture ratio Str.cremoris: Lac.delbrueckii ssp.bulgaricus was 1:1; the culture using amountwas 3%.6. Texture, Proteolysis, lipolysis and sensory properties of mixed milk cheese weredetected with different ripening conditions. The textures of mixed milk cheese were observedduring ripening time, the textures were better in cow milk cheese than those of mixed milk cheese.The degrees of proteolysis and lipolysis were different under different ripening conditions. With theripening time going, the proteins hydrolyzed to peptides with different molecular weight, andcontents of oligo-peptide, short-peptide and free fatty acid increased. The degrees of proteolysisand lipolyses of mixed milk cheese were higher than those of cow milk cheese. From the statisticalresults of sensory evaluation of mixed milk cheese with different ripening conditions, we concludedthat the optimal ripening condtion for mixed milk cheese was ripening under 4℃for 30 days.