Date of Award:

1995

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:

Donald J. McMahon

Abstract

The hot wire method, with pH and temperature sensors, was evaluated to determine its usefulness and application for cheese production automation. Coagulation of milk substrate was measured with the hot wire instrument and by four other methods: Formagraph, Brookfield®, vixcometer, Omnispec™ bioactivity monitor, and Sommer and Matsen rolling bottle method. The hot wire, using the time at maximum slope, detected coagulation before methods that measure resistance to shear, and after methods that measure light reflectance. Coagulation time was not significantly different from the industry standard rolling bottle method used by Sommer and Matsen. the hot wire instrument was also used to distinguish samples that formed curd at different rates. This was accomplished by measuring the rate of temperature change of the hot wire probe during curd formation. Milk samples of varying protein, fat, and calcium concentrations were prepared to determine if the instrument could be used to predict a consistent curd cut-point. The pH level was also adjusted, and rennet additions were varied.

Coagulation was monitored simultaneously with the hot wire system and a Formagraph. All five factors (pH, calcium, fat, protein, and rennet) had significant effects on cut time estimations (CT20) on the Formagraph. Linear correlations (R2) ranging from .74 to .94 were obtained using stepwise regressions when comparing hot wire and compositional data with the Formagraph.

A Formagraph was used to measure effects of calcium, pH, and rennet changes on the coagulation properties of late lactation milk. Calcium, pH, and rennet treatments significantly affected the coagulation parameters measured by the Formagraph. However, response among the poor coagulating samples to treatments to improve coagulation was sample dependent. General composition and SDS-PAGE fractionation data could not be used as an indicator of poor or good coagulability of samples.

The hot wire method worked well for monitoring coagulation time and curd firming rate, but did not measure maximum curd firmness well. Curd firming rates determined from the hot wire data are acceptable for estimation of a curd cut time. Added benefits of the hot wire method for monitoring cheese manufacture are that stirring, coagulation, and healing of curd can also be measured. Therefore, the rates of change of important parameters, such as pH, temperature, and coagulation during critical processing steps, can easily be determined by a computer and displayed, printed out, or saved for future evaluation.

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