Abstract: The physicochemical and rheological characteristics of pectic polysaccharides from okra wine pomace were studied. The results showed that the intrinsic viscosity [η] of the pectic polysaccharides from okra and from okra wine pomace were 41.12 and 4.66 dL/g, and the viscosity average molecular masses were 1.466 × 106 and 2.470 × 105 g/mol, respectively. The intrinsic viscosity of the pectic polysaccharide from okra wine pomace was lower than that of the pectic polysaccharide from okra, while Huggies constants were slightly different between the two samples, which were 0.59 and 0.55, respectively, indicating that both have good molecular chain flexibility. The results of flow sweep experiments showed that the pectic polysaccharide from okra wine pomace was a non-Newtonian pseudoplastic fluid that had a shear thinning behavior. The flow curve was fitted to the Cross mode and on the basis of this model combined with the double logarithmic curve, we obtained a critical concentration c*, about 4 g/dL, and the molecular space occupied was about 20 in the pectic polysaccharide from okra wine pomace, while there was no critical concentration c* for the pectic polysaccharide from okra. The results of oscillation amplitude experiments showed that the linear viscoelastic region appeared within the strain range of 2%–10%. Furthermore, the pectic polysaccharide from okra wine pomace was a weak gel without obvious gelling point in the experimental temperature range. The results of oscillation frequency experiments showed that the storage modulus of the pectic polysaccharide solution from okra was greater than its loss modulus, suggesting that its elasticity was more dominant than its viscosity; the loss modulus of the pectic polysaccharide solution from okra wine pomace was greater than its storage modulus, showing that it was more prone to viscosity characteristics. Cox Merz model fitting showed that the complex viscosity of the pectic polysaccharide from okra wine pomace at low shear rate was greater than its steady shear viscosity, indicating that a new structure may be formed between its molecules, which was more sensitive to steady shear. The degrees of esterification of the pectic polysaccharides from okra wine pomace and from okra were 74.45% and 55.817%, respectively, and both of them were high-ester pectins. Monosaccharide composition analysis showed that the two pectin polysaccharides consisted of mannose, glucose, rhamnose (Rha), galacturonic acid (GalA), glucuronic acid, galactose (Gal) and arabinose (Ara), altogether accounting for 52.3% and 54.7% of pectin polysaccharides, respectively, indicating that both were acidic heteropolysaccharides. Based on the monosaccharide composition data, the proportions of rhamnogalacturonan I (RG I) in the pectin polysaccharides from okra wine pomace and from okra were 46.74% and 90.00%, respectively, the proportions of homogalacturonan (HG) were 16.76% and 2.21% respectively, and the ratios of (Ara + Gal)/Rha were 3.29 and 2.54, respectively. We speculated that the length or number of side chains of RG I in the pectin polysaccharide from okra wine pomace were larger than that in the pectin polysaccharide from okra. The results of this study can provide a theoretical guidance for the application of pectin polysaccharides from okra wine pomace.

Key words: okra; wine pomace; pectic polysaccharides; rheological characterization