Effect of carbon dioxide under high pressure on the survival of cheese starter cultures

A new processing method that rapidly forms curds and whey from milk has the potential to improve cheesemaking procedures if cheese starter cultures ca n tolerate the processing conditions. The survival of Lactobacillus delbrue ckii ssp. bulgaricus, Lactococcus lactis ssp. lactis, or Streptococcus ther mophilus through this new process was evaluated. Inoculated milk containing 0, 1, or 3.25% fat or Lactobacillus MRS broth or tryptone yeast lactose br oth (depending on microorganism used) was sparged with CO2 to a pressure of 5.52 MPa and held for 5 min at 38 degrees C. Broth contained 7.93 to 8.78 log CFU/ mi before processing and 7.84 to 8.66 log CFU/ml afterward. Before processing, milk inoculated with L. bulgaricus, L. [lactis, or S. thermoph ilus contained 6.81, 7.35, or 6.75 log CFU/ml, respectively. After processi ng, the curds contained 5.68, 7.32, or 6.50 log CFU/g, and the whey had 5.0 5, 6.43, or 6.14 log CFU/ml, respectively. After processing, the pi-Is of c ontrol samples were lower by 0.41 units in broth, 0.53 units in whey, and 0 .89 units in curd. The PPI Of the processed inoculated samples decreased by 0.3 to 0.53 units in broth, 0.32 to 0.37 units in whey, and 0.93 to 0.98 u nits in the curd. Storing curds containing L. lactis at 30 degrees C or con trol curds and curds with L. bulgaricus or S. thermophilus at 37 degrees C for an additional 48 h resulted in pHs of 5.22, 5.41, 4.53, or 4.99, respec tively. This study showed that milk inoculated with cheese starter cultures and treated with CO2 under high pressure to precipitate casein-produced cu rds that contained sufficient numbers of viable starter culture to produce lactic acid, thereby decreasing the pH.