Kinetics of the color change of grape juice was studied using linearly increasing temperature for heating Noble grape juice in a stainless steel reactor. The juice was heated from 60" to 95°C in 9 hr. Kinetic parameters for the color change were determined using Hunter L,a,bvalues, chroma values, and Total Color Difference (TCD) values. The reaction of the color change of grape juice measured by L-and avalues, and Chroma value followed first order kinetics with activation energies of 114.75, 131.80, and 121.21 kJ/mol and frequency factors of 1.30 x 1012, 8.95 x lOI and 1.93 x 1013 set-', respectively. However, the reaction measured by TCD followed zero order kinetics with the activation energy and the frequency factor of 92.81 kJ/mol and 4.80 x lV" mol/l/sec, respectively.

Rates of sedimentation and fat separation were determined for stored UHT treated milk. For each of three thermal treatments used for indirect and direct heating, homogenization pressures were 0, 10.34, or 20.68 MPa. Storage temperatures were 7, 22 and 35°C. Initial sediment deposits were greater for the direct system. Sedimentation increased with increased heat, treatment and/or storage temperature but decreased as homogenization pressure increased. The indirect system had higher activation energies for sedimentation for all homogenization pressures. Fat separation rates tended to increase with increased storage temperature. The direct system tended to produce more sediment and less fat separation than the indirect system for a given thermal treatment.

Product constituent losses in ultra high temperature processing were examined with Arrhenius kinetics. An iteration procedure was utilized to develop time-temperature relationships for tubular heating systems. After introduction of the time-temperature rela-

AJHTRACT For a linearly increasing temperature, a differential kinetic model is presented for the determination of kinetic parameters, i.e. activation energy, frequency factor, and reaction order. The performance of this method is illustrated by using two well known chemical reactions: acid-catalyzed sucrose hydrolysis and hydrolysis of N-acetyl-p-aminophenol in aqueous solution. Both computer generated and experimentally determined data sets were used for sucrose hydrolysis and published data were employed in the N-acetyl-p-aminophenol hydrolysis. The results obtained by this method agree well with isothermal kinetic data, for the first reaction, and nonisothermal data, for the second reaction. This method is faster, and more accurate than previously reported methods.

Costs of handling and loss of functional properties of frozen liquid whole egg (LWE) has stimulated interest in a refrigerated product. To maintain adequate shelf life at refrigeration temperatures a heat treatment more severe than normal pasteurization may be needed. To establish limits for the thermal treatment and to prevent possible damage to the pasteurization system due to coagulation of the product, flow properties of LWE during pasteurization were investigated. Utilizing a cone and plate viscometer. I egg viscosity was determined at shear rates between I 15 and 450 sec.'. Test temperatures varied from 20-75°C and heat treatment durations ranged from 0.5-10 min. Percent protein denaturation for each treatment was also determined and correlated to the flow properties. Above 60°C viscosities were shear rate dependent while below this temperature flow properties were approximately Newtonian. Mathematical expressions were developed for viscosity as a function of time, temperature and shear rate.