The effect of high-power ultrasound on the rheological properties of strawberry pulp.

Abstract

This study investigated the effects of high-power ultrasound (HPU, 0-45°C, 242-968W/cm2, 2-16min) on the rheological properties of strawberry pulp. Following the HPU treatment, the strawberry pulp exhibited an increase in apparent viscosity, storage modulus (G'), and loss modulus (G″). The water-soluble pectin (WSP), pectin methylesterase (PME) activity, and free calcium ions (Ca2+) of the strawberry pulp after HPU treatment were investigated to determine a possible reason for this phenomenon. HPU caused a significant decrease in the degree of esterification (DE), molecular weight (Mw), and particle size of strawberry WSP, but no significant changes were evident in the galacturonic acid (GalA) content and the zeta (ζ)-potential (P>0.05), resulting in decrease in the apparent viscosity. Moreover, the largest reduction of PME activity was 22.6% after HPU treatment at 605W/cm2 and 45°C for 16min, indicating that the PME was resistant to the HPU treatments. The free Ca2+ content in the strawberry pulp was significantly decreased after exposure to HPU (P<0.05). The maximal reduction of 52.01% in the free Ca2+ was achieved at 605W/cm2 and 45°C for 16min. The overall results indicated that the high residual activity (RA) of PME after HPU might induce the low esterification of WSP, while HPU promoted the interaction of free Ca2+ and low-methylated pectin, to form the network structure of Ca2+-low-methylated pectin, resulting in an increase in viscosity in the complex strawberry system.