The kinetics of ascorbic acid loss and nonenzymatic browning in clarified orange juice (serum) were investigated in an anaerobic environment from 70.3 to 97.6"C and from 11.7 to 80.6"Brix. Data were fitted to firstorder kinetic models. Rate constants of ascorbic acid degradation in serum were not different from rate constants in whole juice. Activation energies were -30 kcal/mol and largely independent of solids concentration. Rate constants of browning pigment formation were 30-50% greater in serum. Activation energies were 19-25 kcal/mol and increased slightly with solids concentration.

On the basis of the principles of freezing point depression, equations for the temperature rate of ice formation, apparent specific heat, and enthalpy were derived and expressed in terms of solids content and temperature. A unique characteristic constant for each food system can be determined experimentally from the calorimetric measurements. The new equations differ only slightly with similar equationspreviously developed by Bartlett in 1944 and by Schwartzberg in 1976. Reliability and accuracy of the methods are demonstrated with literature data for meat, fish and fruit juices. Enthalpy and apparent specific heat values for a range of temperature between 20" and -40°C and solids content between 10 and 50% are presented.

Freezing point depression (FPD) methods were applied to estimate the effective molecular weights of pure solutions and liquid foods. Explicit expressions among FPD, molecular weight and concentration were developed. The estimated molecular weights were about 333-356 for skim milk, 347-3.50 for coffee beverage, 164-167 for grape juice and 196-203 for tomato juice. The FPD methods were considered accurate for nonacidic foods but they could underestimate the values for acidic foods.