Rheological properties of pomegranate peel suspensions: The effect of fibrous material and low-methoxyl pectin at acidic pH

Abstract

The gel formation behaviour of four tunisian pomegranate peel powders was investigated at pH 3 in the presence of 30% sucrose and 1 g/L CaCl2. All gels show a rapid formation with G’>G″, which reveals a typically gel-like structure. Since the mechanical properties of pomegranate peel gels are governed mainly by soluble pectins and/or insoluble fibrous material, the rheological properties of pectin and fibrous material gels were individually investigated. Results show that all systems displayed a typical solid-like behaviour, however the profiles obtained for the fibrous material gels (35 g/L fibrous material) were quantitatively higher than those obtained for pectins (7 g/L pectin). Thus, the properties of the peel gels seem then to be mostly governed by fibrous material. However, the G′ and G″ moduli obtained for fibrous material and pectin gels were significantly lower than those of peel suspensions. The rheological properties of peel gels would thus result from a strong synergism between fibrous material and pectins. The mechanical treatment was found to have a significant effect on fibrous material gel strength improvement which could be related to a lower sedimentation of suspensions. The particle size distributions revealed a decrease of fibrous material's particle size, and so an increase in surface area and a decrease of suspension's sedimentation. By heating samples at 82 °C for 1 h, trimodal distributions were obtained for peel samples.