When rennet type cottage curd was made from cheese milk pasteurized at 143°F. for 30 min. the heat labile serum proteins remained with the whey and represented a loss of approximately 15% of the total cheese milk protein. However, when higher heat treatments than pasteurization were applied, up to 65% of the serum proteins of cheese milk were denatured, rendered coagulable with the caseins and incorporated into the cottage curd. Similar results were obtained by blending high- and low- heat cheese milk. Composition and flavor quality of cards containing increased amounts of serum protein were closely comparable to curds made from conventional pasteurized cheese milk. The yield of curd was increased. As the heat treatment of cheese milk was increased from 143 to 180°F., the denaturation of serum protein in drained whey increased from 0.0 to 60.01%, the percent of whey solids decreased 7.1%, pH at the A-C endpoint increased from 4.72 to 5.10, and time from setting to cutting decreased from 4.75 to 2.50 hr. When the percent of high-heat milk in blended cheese milks was increased from 20 to 95%, the percent of denatured serum protein in drained whey increased from 4.8 to 37.2%, the percent of whey solids decreased from 1.1 to 5.3%. pH at the A-C endpoint increased from 4.70 to 5.05, and time from setting to cutting decreased from 5.50 to 2.50 hr. High quality curd comparable to the control was made from cheese milks receiving heat treatments up to 170° F. for 30 min. and from blonde containing up to 95% high·heat milk. Heat treatments over 170°F. slightly lowered the quality score of curd. Pounds of curd per lb. of cheese milk protein was found to be the best procedure for calculating and expressing yield. When curd was made from cheese milk heated at 170°F. and from blends containing 85% high·heat milk, the curd yield was increased 16.22 and 9.61% above the control, respectively. / Master of Science

Sales of cottage cheese have been on the decline since 1972. Several factors have contributed towards this decline, including limited shelf-life. Cottage cheese shelf-life is estimated to be 10-21 days, in standard, non-barrier containers held at refrigeration temperatures. Shelf-life is shortened when aerobic, psychrotrophic microorganisms grow at refrigeration temperatures, producing changes which are undesirable. Previous studies have demonstrated that modified atmosphere packaging (MAP) is able to maintain cottage cheese quality and extend shelf-life over air packaging. The objectives of our study were to evaluate the ability of MAP to maintain cottage cheese quality, while establishing the proper atmosphere to be used. Further, we wanted to determine the potential for discoloration and development of undesirable acid flavors in cottage cheese by elevated CO₂ levels. Direct-set cottage cheese was packaged in barrier containers and flushed with 100% CO₂, 75% CO₂:25% N₂, 100% N₂, and air, and stored at 4°C for 28 days. Product quality was assessed by sensory evaluation. Microbiological and chemical tests were conducted to obtain a better understanding of the effects of MAP on cottage cheese. Results obtained demonstrated that there was no change during storage for headspace gas composition. Psychrotrophic and lactic acid bacteria increased for air treated samples. Counts for MAP cottage cheese remained unchanged. In contradiction to previous studies, elevated CO₂ levels did not cause product discoloration. Acidity increased over storage life; however, the increase in acidity was not perceived organoleptically. These results contradicted previous studies which demonstrated that elevated CO₂ levels imparted a sharp acid flavor to the food product. Lactic acid did not contribute towards increased acidity. Sensory evaluation demonstrated that air treatment was inadequate in maintaining product quality past day 19. Cottage cheese packaged under 100% CO₂ was judged most acceptable, followed by 75% CO₂ - 25% N₂, and 100% N₂ treatments. / Master of Science