Comparative Physico-Chemical Characterization of the Mucilages of Two Cactus Pears (Opuntia Spp.) Obtained from Mekelle, Northern Ethiopia

Cactus is a plant that naturally grows in tropical and semi-tropical regions of the world. The composition of this mucilage is believed to differ from species to species. Hence, comparative study was carried out on mucilages of Opuntia ficus-indica (OFI) and Opuntia stricta (OS) as regard to their physico-chemical properties and acute toxicity levels. The study indicated that solubility of the dry mucilages were comparable and increased as raise in temperature. However, at all temperature levels the swelling powers were significantly higher in mucilage of OS than that of OFI. At 100% RH the moisture sorption property of OFI (95.4%) was higher than that of OS (76.9%). The pH values of both mucilages at 12% dispersions were found to be 5.57 and 5.87 for OFI and OS, respectively. The conductivity at the same concentration, 12% (w/v), of OFI was 13.12 mS/cm while that of OS was 9.31 mS/cm. The apparent viscosities at 12% (w/v) were 9017 mPas and 10,060 mPas for OFI and OS, respectively. The apparent viscosities of the dispersions decreased with increase in shear rates which rendered the dispersions a pseudoplastic flow. The surface tension of the aqueous dispersions of OFI (28.71 mN/M) decreased significantly as compared to that of OS (39.7 mN/M). The results of the study proved that the mucilage of OS was superior to OFI mucilage for use as food and pharmaceutical excipients. Moreover, both mucilages exhibited low acute toxicity levels.