Antoine Margot

EMPIRICAL KINETIC MODELS FOR TRYPTIC WHEY-PROTEIN HYDROLYSIS

Enzymic hydrolyses of naturally occurring protein sources represent complex reactions at a molecular level because of the specificity pattern of proteases and the composition of the substrates involved. In addition, rather global criteria are in practical use for describing the extent of protein hydrolysis. Therefore, mechanistically based kinetic modelling may not be applicable under these circumstances. For practical purposes it is often sufficient to use a descriptive mathematical model, which leads to a reliable interpolation of the experimental data. Empirical models are proposed for the kinetics of the limited tryptic whey-protein hydrolysis. These models are identified by fitting profiles of the fraction of soluble protein (non-protein nitrogen, NPN) as a function of operating time of discontinously operated stirred-tank reactors. Models with at least four parameters are required in order to describe profiles obtained at temperatures at which strong enzyme inactivation is observed. A simple model of only two parameters based on a kinetics with exponential decrease of the activity with increasing fraction of soluble protein is sufficient to simulate the tryptic digestion of whey-protein in batch reactors under conditions of moderate enzyme inactivation applicable for temperatures lower than 60 degrees C.

Continuous Monitoring of Enzymatic Whey Protein Hydrolysis. Correlation of Base Consumption with Soluble Nitrogen Content

The optimization of enzymatic protein hydrolysis often represents a tedious task due to complicated analytical methods. The simplest system of continuous analysis consists of monitoring the base consumption during a pH-controlled reactor operation. However, there are other criteria commonly used for characterizing the extent of protein hydrolysis, comprising the degree of hydrolysis (DH) and the SN-TCA index, that is the fraction of nitrogen soluble in trichloroacetic acid under well-defined conditions. Taking the SN-TCA index, expressed in terms of the so-called fraction of non-protein nitrogen NPN, as an example, it is shown that these criteria may be correlated with base consumption. The advantages and limitations of this method are discussed.

Development of a continuously operated reactor for the limited hydrolysis of whey protein by trypsin

A continuously operated reactor was developed for the limited hydrolysis of whey protein using soluble trypsin. It consisted of a stirred tank followed by a tubular device. A stirred tank was used because it allowes pH control to be achieved more easily. The tubular reactor was applied in order to achieve a high level of conversion without pH control. The tubular reactor was equipped with static mixers for approximating plugflow behaviour. The behaviour of the reaction system under floating pH in both parts of the reactor was evaluated separately prior to verification of the results in a pilot-plant which consisted of the combination reactor. The operating temperature and pH in the stirred tank were investigated as the main variables of the process.

Conversion-space time profiles of stirred tank reactors continuously fed with reactants and catalyst under conditions of strong catalyst deactivation

Feeding continuously operated stirred tank rectors with reactants and homogeneous catalysts subject to inactivation will usually lead to a limited substrate conversion with increasing space time. However, it is shown that a maximum of conversion may be observed under certain circumstances. Guided by experimental evidence, the theoretical background is discussed for identifying reaction systems for which such conversion maxima at distinct space times may be obtained. The analysis shows that this phenomenon may only be observed if the catalyst undergoes deactivation characterized by a kinetics of less than first order. Therefore, a likely case for experimental verification consists in an enzymic reaction accompanied by proteolytic degradation of the substrate transforming enzyme due to the presence of a protease.

Determination of partition coefficients of labile compounds subject to dissociation extraction: Analysis of partitioning

A novel method for the determination of partition coefficients in aqueous-organic two-phase systems is described. It is applicable for characterizing the distribution of substances undergoing proton dissociation in the aqueous phase. The method is based on titration by means of the organic phase. A linear form of the respective model is given for parameter estimation by linear regression. This strategy is used for the determination of the partition coefficients of some N-unprotected n-alkyl esters of phenylalanine in various aqueous-organic biphasic systems. These esters are of interest for the optical resolution of phenylalanine with chymotrypsin.