Date of Award:

1984

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Nutrition and Food Sciences

Advisor/Chair:

Dr. Gary H. Richardson

Abstract

A rugged and sensitive instrument "Vatimer" was developed to evaluate the coagulation properties of milk in cheese vats. Microvolt signals from the instrument varied with standing-wave motion of milk, forces arising from coagulation, curd firming, curd syneresis and also clean-in-place spray forces. Curd firmness at cutting varied three to four fold in commercial Cheddar cheesemaking operations.

The Formagraph instrument was used to select individual cow milk samples with good and poor chymosin-coagulation characteristics from the Utah State University Holstein herd. Blending 50% good-, and 50% poor-coagulating samples did not improve average coagulation properties of poor samples. Higher chymosin concentration caused curd disintegration in poor samples. It was not necessary to add more than .02 rennin units per milliliter of milk, or .02% CaC1 2 to produce adequate curd firmness 30 min after chymosin addition if milk pH was reduced to at least 6.4 before coagulation.

Hydroxyapatite chromatography and polyacrylamide gel electrophoresis of whole casein from milk samples with good and poor chymosin-coagulation characteristics showed abnormally high contents of y - and para-K-caseins and lower K- and 8 -casein concentrations in poor-coagulating samples. Poor samples showed higher deterioration in curd firmness than the good samples on chymosin coagulation after storage of milk samples at 4°C for 24, 48, and 72 h with and without added .02% CaCl2. Prolonged storage for 30 days at -1°C caused 7.6% and 68.2% losses in curd firmness for good and poor samples respectively.

Cheddar cheese was made in 9 liter laboratory cheese vats with various proportions of blended, and coagulation modified poor-, and good chymosin-coagulating milk. One hundred percent poor-coagulating milk produced cheese with significantly higher moisture, lower yield, and very bitter flavor.

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