• Food engineering
• rheology and mixing
• transport processes and modeling

EDUCATION:

1980   BS Chemical Engineering, Michigan State University, E. Lansing, MI
1985   MS Food Science, University of California, Davis, CA
1987   PhD Food Engineering, University of California, Davis, CA

POSITIONS HELD:

Professor and Engineer, Department of Food Science and Technology and Department of Biological and Agricultural Engineering, University of California, Davis, CA 2001-present.
Associate Professor and Associate Engineer 1995-2001
Assistant Professor and Assistant Engineer, 1988-1995.
Visiting scientist. Nestle Research Center, Nestec Ltd., P.O. Box 44, CH-1000 Lausanne 26 Switzerland. Sabbatical leave, 1996 Ñ 1997.

RESEARCH OBJECTIVES - LAY TERMS

The objective of the research program is to apply engineering principles to evaluate and predict food properties to ensure that quality is enhanced through processing and maintained during shelf life. The work focuses on the use of experimental evaluation and mathematical analysis of flow behavior and mass transfer, with an emphasis on mixing, moisture transport, and rheology.

RESEARCH OBJECTIVES - FOR PEERS

Professor McCarthy's research program focuses on rheology, mixing, and mass transfer processes in food and biological materials. She and her research group collaborate with spectroscopists using magnetic resonance imaging (MRI) and ultrasonic Doppler velocimetry (UDV) to characterize rheological properties. The evaluation of Newtonian and nonNewtonian fluids in viscometric pipe flow led to patenting an NMR Imaging Rheometer for shear viscosity behavior. Recent work compared the use of UDV and MRI techniques for in-line shear viscosity measurements. The test fluids were Newtonian and nonNewtonian; results agreed well with one another and with off-line conventional rotational methods (Bohlin CVO). In addition, these techniques (UDV and MRI) can directly evaluate yield stress and slip velocity (non-zero velocity at the pipe wall). For example, slip velocity is frequently important in the pumping of fruit/vegetable concentrations and dairy products. In a current study, slip velocity was measured for yogurt flowing in a 1 cm diameter pipe at temperatures relevant to post fermentation processing. Slip velocity is a strong linear function of wall stress and contributes significantly to the overall volumetric flow rate under all experimental conditions. This monitoring of rheological and flow properties in-line is applicable to improved process control and improved final product quality. The mixing of multiple components to achieve a uniform final product is a critical step in the processing of many products. Less than adequate mixing can result in inferior product performance; over mixing results in increased costs and lower throughput. Mixing studies in the McCarthy laboratory are performed using a wide variety of process equipment, both batch and continuous in nature. Current work utilizes a 30 mm APV twin screw extruder to evaluate the mixing of two starch suspensions within the extruder itself. This work is reported at the 2002 Annual IFT Meeting.

RECENT SIGNIFICANT FINDINGS/ACCOMPLISHMENTS

Product quality is an important attribute that contributes to the enjoyment of healthful and wholesome foods. Engineering principles are an integral part of the processing and preservation techniques that ensure food quality is maintained and enhanced. As an example of the research performed, time dependent internal moisture distributions in lasagna pasta were experimentally evaluated and mathematically modeled as a function of cooking time and holding time. During the holding time, changes in the moisture distribution were followed using a magnetic resonance imaging (MRI) technique. Immediately after cooking the moisture distribution was highly nonuniform within the pasta cross section; moisture content was high on the surface of the pasta and low in the central plane. This gradient equilibrated over time as the moisture redistributed. The moisture redistribution was modeled using a one-dimensional Fickian diffusion equation; values of the diffusion coefficient ranged from 0.8 to 1.6 x 10-7 cm2/s. The intent of this research is to provide physcial properties (e.g., the diffusion coefficient) that can be utilized to improve the formulation and/or processing and handling procedures to ensure high quality (al dente) pasta at the time of consumption.

SELECTED PUBLICATIONS:

• Lee, Y., McCarthy, M.J., McCarthy, K.L. November 2001. Extent of mixing in a two-component batch system measured using MRI. Journal of Food Engineering 50(3):167-174.
• Lee, Y., Bobroff, S. and McCarthy, K.L. March 2002. Rheological characterization of tomato concentrates and the effect on uniformity of processing. Chemical Engineering Communications 189(3):339-351.
• McCarthy K.L., Y. Lee, J. Green and M.J. McCarthy. 2002. Magnetic resonance imaging as a sensor system for multiphase mixing. Applied Magnetic Resonance 22:213-222.
• McCarthy K.L., J.J. Gonzalez and M.J. McCarthy. Change in moisture distribution in lasagna pasta post cooking. Journal of Food Science (in press).
• Choi, Y. J., K.L. McCarthy and M.J. McCarthy. Tomographic techniques for measuring fluid flow properties. Journal of Food Science (in press).