Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Sciences

Committee Chair(s)

Gary H. Richardson


Gary H. Richardson


Anthon Enrstrom


Rodney Brown


Jeffrey Kondo


Fred Post


Rex Hurst


The effects of whey-based and milk-based starter media, and low concentrations (0.02% each) of citrate, phosphate and calcium upon various milk coagulation properties were measured. Samples inoculated with milk-based starter medium had shorter coagulation times, faster rate of curd formation, and greater final curd firmness than those inoculated with externally neutralized whey-based starter. Starter medium treatment was statistically interacted with calcium for coagulation time and rate of curd formation. Citrate addition caused longer coagulation times, slower rates of curd formation, and weaker final coagula. Citrate interacted with calcium and phosphate for several of the parameters measured. Addition of phosphate did not affect any of the measured parameters but was involved in several significant two-factor interactions as was calcium addition.

Effects of the above treatments on nitrogen loss were investigated. Cheddar curd manufacture was simulated in laboratory batches using 100 ± 0.01 g samples of 10% reconstituted nonfat dry milk. Less nonprotein nitrogen was lost to whey from whey-base inoculated samples than from milk-base inoculated samples. Phosphate addition had no significant effect. A three-factor interaction between starter medium, citrate, and calcium for curd total nitrogen retention, showed that in the absence of calcium, citrate addition increases protein nitrogen recovery for whey-base inoculated samples, and slightly decreases it for milk-base inoculated samples. In the presence of calcium, citrate addition slightly increases protein nitrogen recovery for whey-base inoculated samples and greatly increases it for the milk-base inoculated samples.

Cheddar curd manufacture was simulated to compare the effects of proteinase negative mutant cultures with their wild type parents on protein breakdown and loss. With three of the four strains tested, milk coagulated faster and coagula required cutting 5 to 8 min sooner when proteinase negative cultures were used. Use of proteinase negative cultures resulted in greater loss of total nitrogen to whey in all but one strain, and a lower increase of nonprotein nitrogen when compared to the use of proteinase positive cultures. Increased yield of curd total nitrogen of 0.37% was found for UC3 10 proteinase negative and calculated to be economically advantageous.