Abstract
The aim of this study was to prepare sodium alginates (SAs) with different molecular weight and G/M ratio, and characterize their rheological behaviors and emulsifying properties. The result of Fourier transform infrared (FTIR) showed that the chemical bonds among the β-d-mannuronic acid- (M-), α-l-guluronic acid- (G-), and MG-sequential blocks in the SA chains were not changed significantly by acid treatment. Meanwhile, the molecular weight and G/M ratio of the SA exhibited drastic variation after acid modification. The result of rheological analysis suggesting that the apparent viscosity of SA reduced from 30 to 16.4 mPa.s with the increase of shear rate, reveals that SA solution belongs to pseudoplastic liquid. Also, the apparent viscosity of acid-modified SA solution dropped rapidly with the decrease of the molecular weight. The properties of emulsions stabilized by SA, SA-Ms, and commercial SAs were evaluated via the interface tensiometry and determination of the zeta potential, droplet size, creaming index (CI), and Turbiscan stability index (TSI). Compared with the SA-stabilized emulsion, the interfacial tension of the emulsion stabilized by SA-M increased with the decrease of the molecular weight reduced at the similar M/G ratio. The decrease in zeta potential and the increase in TSI of the emulsion were observed with the decrease of molecular weight, indicating that molecular weight plays an important role on the emulsifying ability of SA. In addition, the SA with low G/M ratio can form emulsions with stable and fine droplets.
Highlights
Sodium alginate (SA) is an important natural polysaccharide which is made up of (1-4)-linked β-d-mannuronic acid (M) and α-l-guluronic acid (G) monomers
The SA-Ms with low molecular weight failed to bind to Coconut milk isolate protein (CMIP) like high molecular weight ones, indicating that molecular weight has an important influence on the application of SA as an emulsifier
SAs with different molecular weight and G/M ratio were prepared by acid modification and their rheological behaviors and emulsifying properties were characterized
Summary
Sodium alginate (SA) is an important natural polysaccharide which is made up of (1-4)-linked β-d-mannuronic acid (M) and α-l-guluronic acid (G) monomers. According to the sequence of structure units (M and G), there are three block structures: M-, G-, and MG-sequential block structures [1]. The G-block is stiffer and more extended in chain configuration than the M-block due to a higher degree of hindered rotation around the glycosidic linkages [2]. Molecules 2019, 24, 4374 groups of SA and calcium to form hydrogels and a wall material of microcapsule to control the release of drug in pharmaceutical industry [5,6]. Alginate and its modified forms serve as a water-soluble dietary fiber because they do not contribute significant nourishment or calories as they pass through the human digestive system. Alginates are used as functional foods in the adjuvant treatment of obesity and diabetes
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