Date of Award:

5-1-1985

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Biology

Committee Chair(s)

Gary H. Richardson

Committee

Gary H. Richardson

Committee

Fred Post

Committee

Bill Barnett

Abstract

Cheddar cheese was manufactured with a proteinase negative strain of Streptococcus cremoris and from a proteinase positive commercial blend, Cheese curing was measured for one year. Soluble nitrogen as a percent of total nitrogen was analyzed at 30, 60, 90, 180, and 365 days of age. Five expert cheese graders judged the cheese at 15, 60, 90, 180, and 365 days of age. All of the cheese graded in the superior range for the six grading catagories; flavor, body, texture, total cheese grade, curdiness, and cheese flavor intensity. The cheese made with proteinase negative cultures graded best in overall texture and body and lowest in cheese flavor and flavor intensity. It also had significantly higher soluble nitrogen. Soluble protein in the cheese made with the proteinase negative culture was higher than in the two groups of cheese made with proteinase positive culture. No significant difference in yield was found. The manufacture of Cheddar cheese was investigated using proteinase negative cultures at constant elevated cooking temperatures. There was a slight drop in culture activity between 38 and 42 C and a marked drop in activity at 44 C. A constant 39 C cooking temperature with a 2% inoculum resulted in a make time increase of 40 minutes over a conventional cooking temperature procedure. An increase in the inoculum to 4% and a constant cooking temperature of 42 C resulted in a manufacturing time of 3.6 hours, one hour less than with a 2% inoculum and a conventional cooking temperature procedure. Plasmid profiles were obtained for a number of the proteinase positive (Prt+) and proteinase negative (Prt-) strains of S. cremoris. They varied among the strains examined and each strain had an unique profile. Although plasmids of the same size were found throughout the strains, each strain had a different complement of plasmids. A comparison of the proteinase negative isolates with their proteinase positive parent strains revealed that many had lost one observable plasmid, and one strain lost two. A common plasmid was not found that could be associated with the loss of proteinase activity in each strain. Results indicated that possibly a deletion event or cointegrate formation had occured with the Prt- variants.

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