Extractions and rheological properties of polysaccharide from okra pulp under mild conditions

This study investigated the extraction of polysaccharide from okra pulp (POP), its chemical components, and rheological properties. The results showed that the optimal extraction temperature, time, and the ration of water to material were 20-30 °C, 30 mins, and 150, respectively, giving a maximum yield of 29.4%. The POP extracted under the mild condition showed different properties. The molecular weight of POP varied from 6436 kDa to 7432 kDa. The GalA/Rha and Gal/Rha in POP suggests the domain of rhamnogalacturonan I with long galactose side chains. The POP presented pseudoplastic shear-thinning behavior, which can be described by the Ostward-DeWaele model. The apparent viscosity of POP decreased with temperature rising from 25 °C to 80 °C. In addition, sucrose, CaCl₂, and NaCl led to the reduction of its apparent viscosity which was more sensitive to Ca²⁺ than to Na⁺ and sucrose. A closed hysteresis loop was obtained when the POP concentration reached to 6 g/L. The POP showed an elastic behavior (G' > G″) at concentration of 6 g/L, while it showed predominantly viscous response (G' < G″) at concentration of 2 and 4 g/L, over a wide range of frequencies (0.1-10 Hz). These results are potentially useful for the application of POP in food processing.