Effect of Enzymes on Serum and Particle Properties of Carrot Cell Suspensions

Abstract

Rheological properties of cell wall suspensions strongly depend on particle size and particle-particle interactions. In the present study, an experimental method was developed to study the effect of particle elasticity and electrostatic interactions on the rheological properties of cell suspensions. Enzymes were used to selectively depolymerize the pectin (backbone) and proteins in suspensions. The enzymatic treatments affected the physical properties, thus a hypothesis for the structure-function relationship of these biopolymers was formulated. The enzymatic treatment directly affected particle properties, resulting in looser cell walls as visualized by cryo-SEM. The effect of the enzymatic treatment on the storage modulus was measured as a function of total solid content (below critical packing fraction). Furthermore, experiments were performed in the presence of varying concentrations of sodium chloride in order to change the Debye screening length. Such method assisted in decoupling the electrostatic effects from particle elasticity. In addition, particle properties were measured directly by applying a compressive strain on the particles and measuring the normal force. By fitting the normal stress relaxation with a Maxwell model, particle properties such as time scale of relaxation and elasticity were obtained. It is suggested that for carrot suspensions, pectins on the cell walls could contribute to the particle hardness. The pectins on carrot cell walls are responsible for electrostatic interactions between particles.