A model of non‐isothermal degradation of nutrients, pigments and enzymes

Abstract

Published isothermal degradation curves for chlorophyll A and thiamine in the range 100-150 • C and the inactivation curves of polyphenol oxidase (PPO) in the range 50-80 • C could be described by the model C(t)/C 0 = exp[−b(T )t n ] where C(t) and C 0 are the momentary and initial concentrations, respectively, b(T ) a temperature dependent 'rate parameter' and n, a constant. This suggested that the temporal degradation/inactivation events of all three had a Weibull distribution with a practically constant shape factor. The temperature dependence of the 'rate parameter' could be described by the logwhere T c is a marker of the temperature level where the degradation/inactivation occurs at a significant rate and k the steepness of the b(T ) increase once this temperature range has been exceeded. These two models were combined to produce a non-isothermal degradation/inactivation model, similar to one recently developed for microbial inactivation. It is based on the assumption that the local slope of the non-isothermal decay curve, ie the momentary decay rate, is the slope of the isothermal curve at the momentary temperature at a time that corresponds to the momentary concentration of the still intact or active molecules. This model, in the form of a differential equation, was solved numerically to produce degradation/inactivation curves under temperature profiles that included heating and cooling and oscillating temperatures. Such simulations can be used to assess the impact of planned commercial heat processes on the stability of compounds of nutritional and quality concerns and the efficacy of methods to inactivate enzymes. Simulated decay curves on which a random noise was superimposed were used to demonstrate that the degradation/inactivation parameters, k and T c , can be calculated directly from non-isothermal decay curves, provided that the validity of the Weibullian and log logistic models and the constancy of the shape factor n could be assumed.

Kinetic Stability Modelling of Keratinolytic Protease P45: Influence of Temperature and Metal Ions

“…varied between 0.007 and 0.107. These values are comparable [13,15,21,36]. Hence, among the mathematical models evaluated, the first order was accepted as the best equation to describe the inactivation of protease P45 in the conditions employed.…”

“…Distinct isoenzymes [14] A (6) successfully to compare kinetics of inactivation models of several bioactive proteins [13,20,21]. Calculation of # 2 is done by the equation:…”

Modelling heat-disinfestation of dried fruits on “biological model” larvae Ephestia kuehniella (Zeller)

“…The Weibull model has often been used in modeling time to failure in reliability (electronic and mechanical systems) and quality control work in engineering (Smith, 1991). Due to its flexibility, the distribution has also been applied in the field of life data analysis (Fleming, 2001; van Boekel, 2002) for death in biomedical organisms, ecological organisms, microorganisms (Aragao, Corradini, Normand, & Peleg, 2007;Mafart, Couvert, Gaillard, & Leguerinel, 2002) and enzymes and in nutrient degradation (Corradini & Peleg, 2004). While the conventional first-order model implicitly assumes that larvae populations are homogeneous from the point of view of their heat resistance, in this work we assumed that at a given temperature the time of heat exposure, which caused the death of a larvae, is variable from one individual to another and that the dispersion of individual heat resistance is governed by a Weibull distribution.…”

Kinetic and thermodynamic study of thermal inactivation of the antimicrobial peptide P34 in milk

“…At lower processing temperatures, the results suggest that there was not enough dissociation of MFGM and consequently low exposition of the peptide P34 to the fat content of the globules. The onset of thermal degradation of many food compounds and many enzymes usually starts only when a certain temperature level is reached (Corradini & Peleg, 2004). The fat globules in milk seem to play a defensive action on peptide P34 against heat treatments at temperatures lower than 110°C.…”