Influences of combined enzyme-ultrasonic extraction on the physicochemical characteristics and properties of okra polysaccharides

This study obtained two novel polysaccharides from okra by enzyme-assisted and combined enzyme-ultrasonic methods while comparing with previously established hot-water, ultrasonic methods, for their food application potentials. Structural characteristics and physicochemical properties were evaluated and their relationships with functional properties and biological activities including viscosity, emulsifying abilities, antioxidant and antimicrobial activities were observed. All okra polysaccharides (OKPs) showed similar structural features as revealed by H-1 NMR, in accordance with FT-IR spectroscopy. The result of monosaccharide composition confirmed isolated OKPs as acidic heteropolysaccharides consisting of galactose, glucose, rhamnose, arabinose, galacturonic and glucuronic acid, in the varying molar percentages of 33.8-38.6%, 12.4-17.9%, 13.7-17.5%, 3.0-9.9%, 19.0-21.2%, and 6.7-8.3%, respectively. All OKPs were broadly polydispersed with molecular weights (M-w) ranging between 129 and 193 x 10(3) g mol(-1), polysaccharide content ranging from 43.95 to 70.75%, a high degree of acetylation (20.81-37.88%) and low methyl-esterification (26.9-38.95%). Combined enzyme-ultrasonic extracted polysaccharide (CEUP) exhibited superior properties such as solubility, emulsifying capacity, high antioxidant activity and showed more potency in Escherichia coli and Listeria monocytogenes inhibition, extending its versatility in food applications. Principal component analysis (PCA) revealed CEUP to possess unique characteristics different from other samples, substantiating the significance of combined extraction technology over single techniques. Overall, the present study suggests OKP extracted by enzyme-ultrasonic technology as a potential new source of food hydrocolloid with novel functional and biological properties adoptable in the food industry as coating material and food ingredients.