Extraction of low methoxylated pectin from pea hulls via RSM

Abstract

Nowadays, low methoxylated pectin (LMP) is generated in a multi-step process from high methoxylated pectin using fruit by-products as a raw material. In this study, we prove that LMP may be directly extracted from pea hulls. Extraction was conducted according to a central composite design (CCD) and evaluated via response surface methodology (RSM). The influence of different parameters (pH, temperature, time) on yield and composition of the extracted pectic polysaccharides (PPS) was investigated using nitric acid and citric acid as extraction media. Citric acid yielded higher amounts of PPS (3.5–9.8%) compared to nitric acid (1.4–8.0%). However, there is a conflict of aims between a high yield and the purity of the extracted PPS. Composition analysis suggests that under ‘mild’ extraction conditions (pH 2, 70 °C) PPS consist of homogalacturonan, xylogalacturonan and rhamnogalacturonan with arabinose and galactose side chains (RG-I). With increasing temperature (90°), yield is maximised due to an increased solubilisation of cell wall polysaccharides. Under “harsh” conditions (pH 1, 90 °C) the purity of PPS increases in terms of a relatively higher content of uronic acids, but yield decreases. This is attributed to a cleavage of non-GalA components and an ongoing depolymerisation of the pectic galacturonan. PPS extracted under these conditions is characterised by a low degree of acetylation (4%) and a relatively high protein content (7%).