Impact of process parameters (temperature & pH) and salts on kinetics and rheological properties of Hibiscus sabdariffa L. leave puree

Abstract

Thermal kinetics of Hibiscus sabdariffa L. leaves puree (HSLP) were measured to determine the energy of kinetic degradation of chlorophyll a (Chl a) & chlorophyll b (Chl b) of puree at pH (1.4 to 5.8) and temperature (343 K to 363 K). Degradation curves were fitted using first-order reaction kinetic models & the activation energy (Ea) for Chl a & Chl b was found to be 44.623±0.18, 39.158±0.25 & 35.775±0.11 kJ mol^-1 and 6.086±0.14, 5.174±0.24 & 4.328±0.20 kJ mol^-1 at pH 1.43, 3.8 & 5.8, respectively. Every single rheological estimation was done at different shear rates, temperatures, pH, & in the presence of various salts for the product development, quality control, and engineering applications. Rheological data fitted with the Herschel-Buckley model revealed that puree exhibit non-Newtonian, shear-thinning behavior at all tested concentrations and temperatures. The viscosity reached a maximum value at pH 5.8 and it decreased at lower pH values. Salts caused a reduction in viscosity. Comparatively, NaCl had a more pronounced effect than CaCl₂ at a similar concentration.