Structure and properties of the polysaccharides from pea hulls. I. Chemical extraction and fractionation of the polysaccharides

• Published in: Carbohydrate polymers 1994, Vol.24 (2), p.139-148
• Main Authors: Weightman, R.M, Renard, C.M.G.C, Thibault, J.F
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; chromatography; extraction; Food industries; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology; hemicellulose; hulls; peas; pectins; Pisum sativum; seeds; sugars; testa
• ISSN: 0144-8617; 1879-1344

Pectins and hemicelluloses were extracted sequentially from the alcohol insoluble residue (AIR) of pea hulls using chemical agents. The AIR was rich in carbohydrates (942 mg g-1), notably cellulosic glucose, and was poorly lignified (6 mg g-1). Approximately 4 and 6% of the AIR could be sequentially extracted using CDTA and HCl (CSP and HSP respectively). After such depectination treatments, 4.6 and 4% of the AIR were extracted by increasing concentrations of KOH (0.05 M (OHSP-I), 1 M (1OH-I) & 4M (40H-I), respectively). By contrast, alkali treatments alone (KOH 0.05 M (OHSP-II), 1 M (1OH-II) & 4M (4OH-II)) extracted 2, 4 and 5% of the AIR, respectively. Hemicelluloses extracted by 1 M and 4 M KOH in both series were further fractionated through precipitation, upon neutralization of the extracts. Precipitates accounted for 82, 60, 74 and 60% of total hemicelluloses in the 1OH-I, 40H-I, 1OH-II & 40H-II extracts respectively, and appeared to be essentially pure, acidic xylans. More variation was seen in the composition of the soluble polymers, which were rich in xylose, glucose and uronic acids. Extracts were fractionated on Sephacryl S500 and DEAE Sepharose CL-6B. In the 'pectic' fractions, high molecular weight arabinans were found in HSP as well as xylose-rich polymers. Concentrated alkalis extracted small amounts of low molecular weight pectic material, but only after prior depectination had been carried out. The final residue accounted for around 61% of the AIR after depectination and alkali treatment, and contained 91% cellulose: after alkali treatment alone, it accounted for about 84% of the AID and was rich in glucose (approximately 70%) and uronic acids (approximately 16%).