Low methoxyl pectin gelation under alkaline conditions and its rheological properties: Using NaOH as a pH regulator

Abstract

In this study, NaOH solution was used to adjust the pH of low methoxyl pectin (LMP) dispersions (1%, w/v), and LMP gels were prepared in a wide pH range (3.5–9.5). Then, the effects of pH on LMP gelation mechanism were explored and the rheological properties of the gels were investigated. The results suggested that when the pH was increased from 3.5 to 8.5, the gel strength and gelling rate were increased, due to an increased amount of dissociated carboxylic groups. When the pH was increased to 9.5, however, the decreasing molecular weight of the pectin, caused by β-elimination, resulted in the decrease of the gel strength and gelling rate. Moreover, the incorporation of Ca2+ into the pectin reduced not only the thermal decomposition rate of the pectin but also its crystalline degree. Compared to the other gels, the gel at pH 8.5 had the most compact microstructure and the highest thermal stability, which were indicated by Environmental Scanning Electron Microscope (ESEM) and TG/DTG analyses, respectively. Overall, the investigation for the first time demonstrated the effects of a wide pH range on LMP gelation, especially under alkaline conditions. It may provide an insight into the application of LMP to food and biomedical fields.