Prickly pear nopals pectin from Opuntia ficus-indica physico-chemical study in dilute and semi-dilute solutions

The water soluble fraction of peeled prickly pear nopals called native sample (NS) has been characterised mainly by SEC/MALLS analysis. Two main components have been identified: one with high average molar mass (M-w of 13 x 10(6) g mol(-1)) called the high weight sample (HWS), the other being a low M-w fraction (LWS). After extensive ultra filtration of NS, isolated HWS acid LWS are obtained. From sugar composition analysis, HWS has been found to be a pure polysaccharide, without protein of the pectin family. Moreover, HWS contains a low amount of charged sugar. The conformation of HWS has been discussed using molar masses, gyration radii and viscometry results and LWS has been evidenced as a protein. Rheological behaviour is reported to give an initial understanding of the system's behaviour. The effect of the degree and purification and added monovalent and divalent salts were investigated, The low charge density of the polymer backbone resulted in interesting viscosity stability even in the presence of salts. (C) 2001 Elsevier Science Ltd. All rights reserved.