Structure and properties of the polysaccharides from pea hulls—II. Modification of the composition and physico-chemical properties of pea hulls by chemical extraction of the constituent polysaccharides

• Published in: Carbohydrate polymers Vol. 26; no. 2; pp. 121 - 128
• Main Authors: Weightman, R.M., Renard, C.M.G.C., Gallant, D.J., Thibault, J.-F.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 1995; Elsevier Science
• Subjects: Applied sciences; Biological and medical sciences; composition; Exact sciences and technology; Food industries; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology; hulls; microscopy; monosaccharides; Natural polymers; particle size distribution; physicochemical properties; Physicochemistry of polymers; Pisum sativum; polysaccharides; Starch and polysaccharides; structure; swelling; Particle size; Pod; Experimental study; Solvent extraction; Pea; Chemical modification; Cation exchange capacity; Chemical treatment; Distribution; Oside polymer; Chemical composition; Dietary fiber; Water holding capacity; Polysaccharide; Physicochemical properties
• ISSN: 0144-8617; 1879-1344
• DOI: 10.1016/0144-8617(94)00102-Y

Fibres, prepared from pea hulls as the alcohol insoluble residue (AIR), were modified by two sequences of chemical treatments. In one, chelating agent (CDTA), acid (HCl) then increasing concentrations of alkali (0·05, 1 and 4
m KOH), removed firstly the pectins, and then the xylans, whereas in the second (alkali alone: 0·05, 1 and 4
m KOH) only significant quantities of xylans were extracted. The AIR was rich in total polysaccharides and was characterised by low water holding capacity (WHC; 3·2 ml/g), low swelling capacity (SC; 5·2ml/g), and high cation exchange capacity (CEC; 0·52 meq/g)/. The fibre preparations CSPR, HSPR and OHSPR-I, recovered after CDTA, HCl and 0·05
m KOH, gave an augmentation in WHC and SC, respectively to 5·8 and 8·3 ml/g in CSPR and 6·6 and 12·6 ml/g in OHSPR-I, while the CEC decreased (to 0·18 meq/g in OHSPR-I) in proportion to extraction of pectins. After depectination, extraction with 1 and 4
m alkali caused a breakdown in cell wall structure of the preparations, followed by changes in average particle size, and microscopic examination of the pea hull particles. As the structure broke down, a concomitant decrease in the hydration properties was measured in these fibre preparations. In contrast, the residues produced by extracting the AIR with 0·05, 1 and 4
m alkali, respectively, showed a marked increase in hydration capacities and also in CEC. This phenomenon was due to the fact that almost no pectin was extracted by alkali-only treatment. Examination of the residues by light microscopy confirmed that significant breakdown of particles only occurred after depectination and extraction with alkali. These results show that chemical treatments which extract specific classes of polymers can provide fibre preparations with increased hydration properties and with either increased or decreased CEC.