Doctoral Dissertations

Date of Award

8-1972

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Food Science and Technology

Major Professor

Grayce E. Goertz

Committee Members

Mary Jo Hitchcock, Ada Marie Campbell, Peter Cowling, Jimmie Collins, Bernadine Meyer

Abstract

Thermal conductivity, in association with characteristics of the thermodynamic medium at the food surface, establishes heat flow at the food boundary and reflects the transient properties meat has undergone during temperature change. The purpose of this research was to design and build an apparatus to measure thermal conductivity and to study some of the transient properties of ground pectoral turkey muscles.

Ground turkey pectoral muscles were heated in 9 increments from 77 to 185°F and held at end point temperature for 0 to 15 minutes. Thermal conductivity was calculated directly from data or indirectly by solving for diffusivity and then calculating for thermal conductivity. Water-holding capacity (expressible moisture index, total moisture, cooking loss), protein solubility (protein extractability), and change in pH were studied to determine the possible relation between thermal conductivity and protein denaturation.

The thermal conductivity values were expressed in terms of cal/sec cm °F or Btu/hr ft °F. With both methods of calculation, thermal conductivity values were significantly affected (P < 0.05) by end point temperature at the 0 minute but not at the 15 minute holding time even though holding times per se had no significant effect.

Several approaches and modes of calculation of the thermal properties suggested that conductivity values were influenced by a number of factors. Protein denaturation was postulated as a factor contributing to inconsistencies in thermal values. Significant (P < 0.01) effect of temperature upon cooking loss, total moisture, and expressible moisture suggested protein denaturation. The water-holding capacity expressed by these determinations tended to decrease with increasing temperature. These changes were greatest in the end point temperature range of 104 to 158°F. Protein solubility decreased with increase in end point temperature from 77 to 131 to 185°F. A protein fraction extracted with phosphate buffer (I = 0.05, pH 7.6) decreased in solubility 30 percent and 60 percent from an initial end point at 77 to 131 to 185°F, respectively. The pH was significantly (P < 0.01) affected by temperature. With all parameters, no difference was found between holding times.

It can be postulated that the denaturation phenomenon in the current experiment influenced conductivity values by the changes in structure and composition of the muscle system as well as by the energy consumption involved in conformational changes of the protein. However, specific relationships were not defined.

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