Antibacterial Effect Of Carbon Dioxide In Raw Milk And Application In Extending The Shelf-Life Of Cottage Cheese

As the natural component in raw milk, carbon dioxide is a sort of natural and safe bacterial inhibitor, furthermore, the cost of carbon dioxide is low and it is easy to manipulate in production. The flavor of cottage cheese is easy to be accepted for consumers in china because its flavor is weak and sour, furthermore, cottage cheese has some other characters, for example, its production period is short, its fund turnover is quick and its yield efficiency is high. Cottage cheese is the first choice when China popularizes its cheese industry. Cottage cheese is a sort of fresh cheese and its packaging is cold, so the shelf life of cottage cheese is short. The purpose of this study is applying carbon dioxide to extend the shelf life of cottage cheese. First, the bacteriostasis effect of carbon dioxide to main putrefying bacteria in raw milk was studied. On this bases, making cottage cheese with acidifying raw milk, and then we studied the effect of adding carbon dioxide on the shelf life of cottage cheese by comparing microbial number of control cheese and carbon dioxide treated cheese during storage. We compared the making process, component, component recovery rate and yield of cottage cheese. At last, we optimized making process of cottage cheese added with carbon dioxide to get high quality and high yield cottage cheese when applying carbon dioxide to extend the shelf life of cottage cheese.1. The bacteriostasis effect of carbon dioxide to main putrefying bacteria in raw milk by Gompertz mathematical model was studied. The results indicated that at 0, 4, and 7℃, the higher the concentration of carbon dioxide is, the greater bacteriostasis effects on Pseudomonas, Enterobacteriaceae and lactobacillus in raw milk are. The strength of carbon dioxide bacteriostasis effects is Pseudomonas> Enterobacteriaceae> lactobacillus. Dissolving 42.27mmol/L carbon dioxide could extend the shelf life of raw milk to 54h, 48h and 24h respectively, but the control samples are 30h, 24h, and 12h respectively, extending one time nearly.2. The effect of adding carbon dioxide on microbial number in cottage cheese during storage was studied. The results indicated that on the condition of refrigeration and room temperature, the shelf life of control samples are 8 days and 3 days respectively, but the shelf life of carbon dioxide treated samples are 17 days and 6 days respectively, extending the shelf life of cottage cheese 9 days and 3 days respectively. Adding carbon dioxide has inhibitory action to growth of psychrophilic bacteria, yeast fungus and mold. Adding carbon dioxide could rev down the pH change rate of cottage cheese during storage on the condition of refrigeration and room temperature. For the carbon dioxide treated samples, with the extending of storage time, carbon dioxide content in cottage cheese is losing gradually, but the carbon dioxide losing content is smaller relatively.3. By comparing the making time, component, component recovery rate and yield of cottage cheese, the results were got. The making time of carbon dioxide treated samples are shorter than control samples significantly, the difference is about 2.5h. Adding carbon dioxide could reduce solid substance content and solid substance recovery rate of cottage cheese significantly, but the effect of adding carbon dioxide on protein content and protein recovery rate of cottage cheese is not significant. Adding carbon dioxide could reduce yield of cottage cheese significantly.4. For the sake of improving the senses quality of cottage cheese and increasing the yield of cottage cheese, process optimization was studied. First, the single factor experiments for the function and the flavor of milk curd were made. The condition of milk curd were that the adding content of starter culture was 5%, the ratio of Streptococcus cremoris and Streptococcus acidi lactici was 1:4, carbon dioxide acidification pH was 6.1, the adding content of CaCl2 was 0.005%, the adding content of chymosin was 0.01%. On this bases, using carbon dioxide acidification pH, the adding content of CaCl2 and the adding content of chymosin as independent variable, using the senses synthetic score, hardness and yield of cottage cheese as response, applying Box-Behnken model, response surface process optimization experiments were made. The process optimization parameter were that carbon dioxide acidification pH was 6.15⁶.28, the adding content of CaCl2 was 0.0021%⁰.0061% and the adding content of chymosin was 0.0067%⁰.0108%. The effect of carbon dioxide acidification pH on the senses synthetic score, hardness and yield of cottage cheese is the most significantly, the effects of the adding content of CaCl₂ and chymosin are not significant relatively. On this condition that making cottage cheese added with carbon dioxide, the senses quality was better, the hardness was more suitable and the yield was higher, furthermore, chymosin usage amount would reduce about 50%, and this would reduce the manufacture cost.