An empirical kinetic expression for modelling the viscometric data of enzymatic pectin degradation and measurement of enzyme activity

Although pectolytic enzymes have been used in biotechnology for a long time (mainly in fruit processing), the measurement and expression of their pect olytic activity has not been satisfactorily solved. The only rational metho d based on the chemical determination of the end-groups formed during the p rogress of the reaction is laborious and is not satisfactory for the practi cal uses of this class of enzymes. We propose a simple empirical kinetic expression for the reduction in visco sity when a pectin solution (or a pectin-containing raw material) is subjec ted to the action of pectolytic enzymes. It is written Yt = Yo - a.t/(b + t ), where Yt is the measured viscosity at any time, Yo is the initial viscos ity and a and b are parameters the physical sense of which will be discusse d in this paper. This model has been proven to efficiently to: 1) fit the whole progress curve, including the early and late phases and, f urther, to determine two relevant pieces of information about the enzyme/su bstrate couple-namely, the initial velocity of the process and the residual viscosity at the final plateau region. 2) measure and express the activity of the enzyme solution used, oil the pe rtinent basis (for applications of pectinases in biotechnology) of a physic al property of the reaction medium. The model was validated with data obtained in a variety of experimental sit uations, ranging from the use of a semi-purified enzyme solution acting on a semi-purified pectin in a dilute solution, to the liquefaction of a fruit puree. A "viscometric unit" of pectolytic activity is proposed, after the observed proportionality between enzyme concentration and one of the parameters of the model. Our approach, based on the kinetic modelling of change in viscosity, using an empirical equation, presents advantages over recently published methods, also based on viscometric measurements.