Isolation and characterisation of cell wall polysaccharides from legume by-products: Okara (soymilk residue), pea pod and broad bean pod

Cell wall material (CWM) from three legume by-products: okara (O), pea pod (PP) and broad bean pod (BBP) were isolated. CWM was sequentially extracted with a chelating agent to obtain S1, and with dilute alkali (S2), 1 M alkali (S3), 4 M alkali (S4) and NaClO2/acetic acid (S5) to leave a cellulose-rich residue (RES). The S1 fraction was different in each by-product (O: 7.2%; PP: 5.5%; BBP: 29.4 %). S2 (O: 7.4%; PP: 3.2%; BBP: 8.1%) and S5 (O: 9.8%; PP: 5.6%; BBP: 10.8%) were low in pea pod and similar in okara and broad bean pod. S1, S2 and S5 were characterised as pectin-rich fractions, whereas S3 and S4 were hemicellulose-rich fractions. There was a high percentage of S3 in pea pod (O: 8.9%; PP: 11.5%; BBP: 6.8%) and S4 in okara (O: 17.8%; PP: 7.1% BBP: 5.7%). RES was the fraction with the highest percentage of cellulose, and the remainder was pectin and hemicellulose material (O: 48.9%; PP: 67.1%; BBP; 39.2%). In addition, the swelling and water retention capacity of these by-products indicates their potential application as a texturing additive.