Physicochemical And Functional Characterization Of Pectin Extracts From Different Okra Genotypes
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Date
2018-04
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KNUST
Abstract
Okra (Abelmoschus spp.) is a plant of the Malvaceae family cultivated for its immature pods. The pectin content is responsible for the slimy texture of okra extracts and is of major technological interest for food, non-food and medicinal applications. A preliminary study on isolation of pectins from eight different okra types obtained from different geographical zones in Ghana revealed that the okra pods had considerable pectin yield and different physicochemical properties which can be exploited for their potential applications. Six different okra (Abelmoschus spp) genotypes were then cultivated under the same environmental conditions and their genetic diversity determined using fragment length analysis (FLA) of ten simple sequence repeat (SSR) markers. Pectins were extracted from the pods of the different okra genotypes using 0.1 M phosphate buffer (pH 6). Physicochemical, functional and rheological characteristics of the pectins were evaluated using FT-IR and NMR spectroscopy, Size-exclusion chromatography (SEC) and dilute solution viscometry. Neutral sugars composition was evaluated using GC-MS. Emulsifying properties of the pectins were determined by analyzing the interfacial protein and pectin concentrations, emulsion rheology, particle size distribution, zeta potential and the emulsion morphology using fluorescence microscopy. Genotypic studies confirmed unique genotypes for each okra sample used with each SSR markers detecting an average of 4.1 alleles. Physicochemical results showed that okra genotypes had pectin yields between 11–14 %. Resultant pectins were all low methoxyl pectin with varied degree of methylation (17–25 %), total carbohydrate (66.2–87.5 %), protein (3.3–7.1 %), sugar composition, degree of acetylation (20– 40 %), GalA content (43–63 %) and weightaverage molar mass (700–1700 x 103 g mol-1). FT-IR and NMR spectroscopy showed structural similarities between the pectins from the different genotypes. Intrinsic viscosity of the okra pectins ranged from 2.91 to 5.10 dL g-1. Huggins constant values calculated for okra pectins ranged from 0.3 to 0.7 revealing flexible chain conformation. Coil overlap plots revealed three concentration regimes with two critical concentrations. Stability of emulsions to creaming varied from 0.8 to 16.9 % and surface coverage of pectins (0.6 – 3.6 mg m-2) were relatively higher than that of the proteins (0.3-1.0 mg m-2). The okra pectins demonstrated good emulsifying abilities with initial surface weighted mean diameter (d3,2) ranging between 1.3 and 3.7 μm. Emulsion destabilization occurred in all samples after five days of storage and the viscosity of samples remained constant with aging. The differences between genetic variations have potential applications in the food industry as emulsifying agents.
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A Thesis submitted to the Department of Food Science and Technology, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY IN FOOD SCIENCE AND TECHNOLOGY