QUANTIFICATION OF THE FREEZE-CONCENTRATION EFFECT ON QUALITY DEGRADATION RATES DURING FROZEN FOOD STORAGE (SHELF-LIFE, MYOGLOBIN, SIMULATION).

摘要

The purpose of this research is to quantify the influence of the freeze-concentration effect on degradation rate acceleration of frozen foods. A prediction approach based on integration of a rate prediction model and a concentration factor prediction model was developed to achieve this quantification. Inputs to the prediction approach include the rate constants, the activation energy, the reaction order, the mass fraction of water in system, the specific volume of solutes in solution and the effective molecular weight of solutes. Apparent reaction rates or rate constants at sub-freezing temperatures are the outputs.;Based on the prediction approach, the addition of inert (with respect to the object reaction) solutes can reduce or eliminate the influence of the freeze-concentration effect on the rate acceleration. The 'adverse temperature range' for storage, within which storage is unjustified from the standpoint of more energy input without better preservation, is widened by low activation energy, high reaction order and low initial solute concentration.;Autoxidation of oxymyoglobin was used as the model reaction to verify the prediction approach. The reaction followed first order kinetics with respect to oxymyoglobin concentration in de-ionized water, in acetate buffer of different concentrations, in the liquid state before freezing and in the unfrozen solution of frozen state. A common activation energy of 118 KJ/mole was obtained for reaction in acetate buffer of various concentrations. The reaction demonstrated a 0.316 power dependency on buffer concentration when the variation in buffer concentration was large. The rate constants for reactions in supercooled solutions and in de-ionized water (frozen) coincide with the extrapolated Arrhenius plots initiated at temperatures above freezing. Increased rate due to freezing was observed for the autoxidation reaction in acetate buffer. The extents of rate acceleration were larger in less buffered systems. Local rate maxima were near -2 or -3 C. The effectiveness of the prediction approach was verified by the agreements between measured and predicted apparent reaction rate constants for this reaction.