The bioactivity and gelling properties of a carbohydrate-rich algal extract obtained from locally harvested Ascophyllum nodosum seaweed using a chemical-free approach were investigated for its potential interest in food applications. Physicochemical characterisation and compositional analysis of the extract, using FTIR, biochemical methods and monosaccharide analysis, confirmed the presence of alginates and fucoidans, although the main polysaccharide present in it was laminarin. Significant amounts of phenolic compounds (~9 mg phloroglucinol/100 mg sample) were also detected. As a result, the extract exhibited good antioxidant activity. It also showed promising prebiotic potential, promoting the growth of beneficial Lactobacillus sp. and Bifidobacteria sp. when compared with commercial prebiotics, but not that of pathogenic bacteria such as E. coli or P. aeruginosa. The gelling properties of the raw extract were explored to optimize hydrogel bead formation by external gelation in CaCl2 solutions. This was enhanced at neutral to alkaline pHs and high extract and CaCl2 concentrations. The mechanical strength, nano- and microstructure of the hydrogel beads prepared under optimised conditions were determined using compression tests, synchrotron small- and wide-angle X-ray scattering (SAXS/WAXS) and scanning electron microscopy (SEM). It was concluded that the raw algal extract at neutral pH had potential for use as a gelling agent, although further enrichment with alginate improved the mechanical properties of the obtained gels. The advantages and disadvantages of applying the non-purified algal extract in comparison with purified carbohydrates are discussed.
Keywords: AAE, ascorbic acid equivalents; ATR, attenuated total reflectance; Algae; BSA, bovine serum albumin; FOS, fructooligosaccharides; FTIR, Fourier transfrom infrared spectroscopy; G, α-L-guluronic acid; GOS, galactooligosaccharides; Hydrogel; M, β-D-mannuronic acid; NCF, protein conversion factor; OD, optical density; PGE, phloroglucinol equivalents; Polysaccharide; SAXS; SAXS, small-angle X-ray scattering; SEM, scanning electron microscopy; Seaweed; TE, Trolox equivalents; WAXS, wide-angle X-ray scattering.
© 2021 The Authors.