Effects of pH and temperature on the structure, rheological and gel-forming properties of sugar beet pectins

Abstract

Sugar beet pectin (SBP) was modified by alkaline at both 25 °C and 3 °C to produce gel-type pectins. The structure, rheological and gelation properties of series modified SBPs were then assessed. The results showed that low temperature effectively inhibited the β-elimination of SBP during alkali treatment, and the average molecular weight (Mw) and galacturonic acid (GalA) content of the resulting SBP were much higher than that of the alkali-treated SBP at 25 °C. Due to the low degree of methylation (DM) (≦ 21.2) and degree of acetylation (DA) (≦ 14.6), SBP treated under pH 11 and 12 at 3 °C could successfully form stable elastic gels, and these gels were further confirmed to be frequency-independent through rheological analysis. The SEM and TG/DTG results showed that the corresponding gel of SBP treated under pH 12 at 3 °C for 120 min had the most uniform micro-network structure and the best thermal stability. This work for the first time demonstrated the effect of a wide pH range on the chemical structure, rheological and physical gelation properties of SBP, especially under alkaline conditions at a low temperature (3 °C). Findings from this work suggest that alkali treatment at low-temperature allows SBP to have the potential to become a gel-type commercial pectin.