Isolation, characterization and Functional Properties of Okra Pectin

Pectin was isolated by aqueous extraction at pH 6.0 or 2.0 from okra (Abelmoschus esculentus L.) pods. An isolation protocol was designed to extract pectin and study the influence of the extraction pH on its chemical composition, macromolecular and functional properties. The extraction protocols resulted in the isolation of pectin of high purity as evidenced by their high total carbohydrate (70.0 – 82%) and low protein (4.3 – 6.3%) contents. Samples contained between 47-57% galacturonic acid, had broad molecular weight distributions, a low degree of methylation (40 and 25 %) and high degree of acetylation (52 and 38 %). Neutral sugar analysis showed that pectin extracted at pH 6.0 contained more neutral sugars, particularly, galactose, rhamnose and arabinose than that extracted at pH 2.0 indicating variations in fine structure. In addition, molecular parameters of the isolated pectins, such as intrinsic viscosity (2.8 – 4.4 dL g-1), critical concentration (0.15 – 0.45 dL g-1) and coil overlap parameter (0.66 –1.51), showed that extraction conditions resulted in pectin with different chain macromolecular characteristics. Following extraction, the functional properties of okra pectin were investigated in high and low moisture systems and also in colloidal dispersions. It has been shown that okra polysaccharides are non-gelling pectins and their inability to form ordered structures was attributed to the high degree of acetylation and branching of the side-chains. The pH sensitivity of okra pectins has been further demonstrated in high solid systems, where the mechanical relaxation of LM-pectin in the presence of co-solute has been altered by pH. It has been shown that high pH values result in extended chain conformation and early vitrification events. In contrast, viscoelastic functions of polyelectrolyte decreased and resulted in delayed vitrification events at low pH. The next step of present work was focused on potential utilization of okra polysaccharides in fabrication of oil-in-water emulsions for food and pharmaceutical applications. The emulsifying properties of crude okra extracts and okra isolates (rich in pectin) have been investigated under different conditions (e.g., oil volume fraction, biopolymer concentration, pH values, energy input methods) in order to produce fine emulsions with long-term stability. It has been shown that pH of extraction has a pronounced effect on the interfacial activity of both crude extract and pectin isolates. Extracts or isolates obtained at high pH demonstrated higher emulsifying capacity than those extracted at low pH. In general, okra pectin isolates were more efficient in emulsion stabilisation than crude extracts by producing emulsions of smaller droplet sizes. Moreover, emulsifying capacity of okra pectin was affected by the pH and stable emulsions were produced only at low pH values (pH 2.0 or 3.0). It has been shown that okra pectin-stabilized emulsions evolve under the effects of Ostwald ripening and coalescence during the long-term storage. The present work shows the potential of okra pectins as emulsifiers under acidic conditions and serves as the basis for the development of such systems in encapsulation technology of bioactive components.