Extraction and Characterisation of Novel Polysaccharides From the Solanaceae Family

  • Onome Obodo-Ovie

Student thesis: Doctoral Thesis

Abstract

Pectin belongs to a large family of complex heteropolysaccharides, which are found in plant cell walls. Pectin has been used for several years in the food industry as a gelling agent, thickener, and stabiliser. In recent years pectin has also been reported to show some health benefits. The structure of pectin is usually affected by its physiochemical properties which are also linked to the pectin source, extraction conditions, genetic variation, and growing conditions. A conventional acid extraction method was used to extract pectin from the Solanaceae family (eggplant, bell pepper and tomato). A 23 experimental design (two level factorials with three factors: temperature, pH and time) was used to study the relationship between the extraction conditions and the measured polysaccharide properties. The extracted polysaccharides were analysed using high performance anion exchange chromatography (HPAEC), FTIR, NMR, viscometry, and colorimetric techniques. The pectin yields ranged from (3.8 – 11.4 %) for eggplant, (28.6 - 35.5 %) tomato and (11.6 - 20.6%) green bell pepper respectively. The highest yield value for both green bell pepper and tomato was extracted at pH 1 whereas the highest yield for eggplant was extracted at pH 3.

Analysis of the extracts using FTIR further confirmed the presence of polysaccharides. Moreover, there were no observable differences between tomato and green bell pepper spectra. Furthermore, rhamnose, arabinose, galactose and galacturonic acid were present in all three-extracts confirmed the presence of pectin. For all three extracts, galacturonic acid was the most abundant monosaccharide followed by galactose. Based on the values of the galacturonic content, the polysaccharides were classified as pectin like materials. The neutral sugar ratio was calculated and used to provide information about the pectin structure. The degree of esterification of all three pectin extracts regardless of extraction conditions was above 50 % and therefore was classified as high methoxyl pectin. Also, protein and phenolic materials were present in all three extracts and their amounts varied depending on the extraction conditions. However, the phenolic content in eggplant (48.0 - 85.6 mg gallic acid equivalent (GAE)/g pectin) was much higher compared to the other pectin extracts (23 - 50 mg GAE/g pectin). All three-extracts demonstrated good antioxidant and emulsifying properties; however, tomato fruit and eggplant had the highest antioxidant activities. The observations from this work showed that all three-pectin extracts had high molecular weight with eggplant having the highest. In addition, all three extracts could also be used adequately to stabilize oil/water emulsion systems. The Solanaceae family could be used as an alternative source of pectin and extraction conditions could be fine-tunned to produce pectin with desired quality depending on the application.
Date of Award17 Nov 2024
Original languageEnglish
SupervisorGordon Morris (Main Supervisor) & Alan Smith (Co-Supervisor)

Cite this

'