CHARLES F. SHOEMAKER
Introduction
Two leading agricultural commodities in California are tomatoes and milk. There are a significant number of food products which are derived from the further processing of these commodities. These include tomato paste which is then used to formulate a wide spectrum of tomato based sauces and condiments. Milk also serves as the base for a number of products ranging from cheese to ice cream. In all cases, the further processing of these commodities greatly adds to their value and their economic contributions to California.
Research Objectives - lay terms
In order to maintain and increase the economic value of these commodities in this ever increasing competitive world, their quality attributes need to be preserved during processing operations. These factors include color, flavor, and texture. A major objective of my lab is the study of food texture as it is affected by the interactions of its components and the effect of food processing operations on these interactions. The measure of food texture is a relatively new area which promises to offer a means to monitor and improve the quality and value of processed foods. We are developing new measurement techniques which will provide information on the nature of fundamental chemical interactions of constituents and their effect on the overall texture of foods.
Research Objectives - for peers
The rheological properties of heat induced whey protein gels was studied by dynamic oscillation rheometry at pH 7 and 12% (w/w) protein. For sample temperatures below 60 Degrees Celcius, rheological properties were found to be completely reversible. For sample temperatures above 60 Degrees Celcius the rheological properties of the gels changed irreversibly. For temperatures below this transition region, the interrelated effects of sample temperature and measurement on the absolute value of the shear modulus and relative viscoelasticity were completely correlated.
Similar rheological measurements for rennetted milk gels have found that the cold storage of milk before gel formation weakens gel strength. A working hypothesis is that during cold storage Beta-casein is solubilized from the casein micelles and either interferes with the enzymatic hydrolysis of k-casein or the aggregation of the micelles during the gel formation process. In either case, the results suggest that prolonged cold storage of milk may have a significant effect on gel strength and consequently on cheese quality.
The Helical Screw Rheometer (HSR) was evaluated for rheological measurements of fluid food suspensions. The HSR consists of a helical screw enclosed in a tight fitting cylinder. Viscosity measurements of standard Newtonian fluids using the HSR were found to correlate well to measurements on a rotational rheometer with cone and plate fixtures. Non-Newtonian food suspensions were also measured and analyzed with a power law model. Although the rate indexes n were in reasonable agreement, the consistency coefficients m from the HSR were 13 to 23% lower as compared to results with the cone and plate fixtures on the rotational rheometer. These results suggest that the HSR could be used as an on-line viscometer in processing environments where the measurement of viscosity is often a critical control parameter for product quality.