Date of Award:

1999

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Nutrition, Dietetics, and Food Sciences

Advisor/Chair:

Donald J. McMahon

Abstract

As fat is removed from Mozzarella cheese, the resulting increase in protein content causes the cheese to become tough, thus decreasing the desired physical characteristics of meltability and stretch. Low-fat (6% fat) Mozzarella cheese was manufactured with the addition of several levels of a Lactococcus lactis adjunct culture that was proteinase positive and lactose deficient in an attempt to improve these physical properties. During cheese manufacture , milk was acidified to pH 6.0, then inoculated with Lactobacillus helveticus and Streptococcus thermophilus. Experimental vats were also inoculated with either 0.25, 0.50, or 1.0% of the adjunct culture. Cheeses made with the adjunct culture had increased melt properties at d 1. During the first 14 d of storage, cheeses manufactured with 0.50% and 1.0% adjunct culture melted more readily than the control; by 28 d, the meltability of all cheeses was similar. Breakdown of cheese body was more rapid in the experimental cheeses and was particularly apparent during shredding. The increase in softness was presumed to be the result of increased proteolysis in the cheeses. There were no significant differences in melt viscosity between control and experimental cheeses. Storage time, however, was significant, and between d 14 and d 28, melt viscosity decreased for all cheeses. Protein hydrolysis was measured using SDS-PAGE, but no differences were observed in the disappearance of intact caseins.

In the second part of this study, part-skim (18% fat) Mozzarella cheese was manufactured from milk standardized to a casein-to-fat ratio of 1.2 and inoculated with L. helveticus strain and S. thermophilus strain. Low-fat (6% fat) Mozzarella cheese was manufactured from milk with a casein-to-fat ratio of 4.2 and inoculated with the same starter culture with (or without) addition of the proteinase positive, lactose deficient adjunct culture. The cheese was molded into 1.5-lb blocks and stored at 4°C. Meltability and melt viscosity of the cheese were measured during 28 d storage. Disappearance of αs1-casein and ß-casein was measured using free solution capillary electrophoresis, which separated intact proteins and large peptides. Micellar electrokinetic capillary chromatography was used to study the appearance of small peptides (<30 >kDa) during storage. After 28 d storage, there were significant decreases in the amount of intact αs1-casein remaining after 28 d, but no measurable change in ß-casein in either the part-skim or low-fat cheeses. In part-skim cheese, 71% αs1-casein remained, but in the low-fat cheeses only 20% intact αs1-casein remained after 28 d. If adjunct culture was used in low-fat cheese, then only 14% a 5 1-casein was found after 28 d. A similar increase in proteolysis in the low-fat cheeses was observed based on the amount of small peptides produced. Part of these differences may be a function of increased moisture content of the low-fat cheese, 61% vs 51% in part-skim cheese. During storage, part-skim Mozzarella showed a typical increase in melt with a corresponding decrease in melt viscosity. Melt increased from 10.6 cm at d 1 to 16.9 cm at d 28; melt viscosity at 80°C decreased from 1.0 x 106 cP at d 1 to 2.1 x 105 cP at d 28. There was less change in melt in the low-fat cheese during storage, 8.9 cm at d 1 and 10.9 cm at d 28. Melt viscosity decreased from 4.8 x 105 cP at d 1 to 1.9 x 105cP at d 28. It appears that adding the adjunct culture increased initial meltability of the low-fat cheese by accelerating proteolysis during the first 14 d but caused an increase in viscosity and decrease in melt after 14 d of refrigerated storage.

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