Elaboration and characterization of maleated sodium alginate derivative from west Algerian algae biomass with enhanced antioxidant potential

Abstract

The present study aimed to characterize Cystoseira stricta sodium alginate and its maleated derivative for potential use in food preservation. The alginate was extracted from the brown alga Cystoseira stricta, harvested from west Algerian coast (35°49′N/0°01′W). The sodium alginate was grafted with maleic anhydride to obtain maleated sodium alginate. The native and grafted sodium alginate were analyzed using FTIR, XRD, SEM, DSC, TGA, X-ray, and EDX. Their antioxidant potential was evaluated using DPPH scavenging activity. Additionally, a nanoemulsion based on maleated sodium alginate and date seed oil was synthezised and applied as an edible functional coating for delaying strawberries’ spoilage. The extraction of sodium alginate resulted in good yield (37.52%) with a β-D-mannuronic acid /α-L-guluronic acid (M/G) ratio of 0.80. The grafting of sodium alginate with maleic anhydride has been successfully executed and confirmed by infrared analysis and DSC. The degree of substitution was estimated to 93%. The crystallinity becomes greater according to x-ray diffraction data. Thermal analysis indicated that maleated sodium alginate was more thermally stable. The SEM/EDX analyses revealed well defined morphological characteristics and high chemical purity of native and modified sample. The maleated sodium alginate exhibits higher antioxidant activity than native sodium alginate. It was found the maleation cannot improve only the antioxidant ability but also the product esthetic. The prepared nanostructured system demonstrated dispersion stability with a zeta potential of −29.9, as determined by DLS. When applied as an edible coating, it effectively protected and enhanced the shelf-life of fresh strawberries at ambient temperature.