Rheological, spectral and thermal analyses of gellan/ dextran blends as gelatin substitutes

Microbial polysaccharides can serve as renewable sources of hydrocolloids that have great function as viscosifying, stabilizing, emulsifying or gelling agents which are important to improve texture and stability of food and pharmaceutical products. Similar functions are currently being offered by gelatin however the use of gelatin would give rise to health and religious concerns for particular group of consumers. Plant based polysaccharides have been utilized as gelatin substitute but plant requires longer harvest maturity and susceptible to geographical and seasonal changes. Viscosity and gel rigidity are important parameter to determine adequate food texture for mouth feel properties. Phase separation also could affect consumer perception on food products. The aims of this study are to investigate rheological properties that measure flow behaviour, viscosity and gel rigidity to be compared with gelatin as well as to predict molecular interaction between gellan (G) and dextran (D) in their binary blends (1:1, 1:2, 1:3 ratios) in varying concentration range of 0.5%, 1.5% and 3% (w/v) using spectral and thermal characteristics. For rheological measurements, all samples were subjected to steady shear and dynamic shear viscosity tests using rheometer. Spectral analysis and thermal analysis were performed using Fourier Transform Infrared (FTIR) and Differential Scanning Calorimetry (DSC) respectively. Rheological analyses revealed that during blending, dextran plays a significant role and transforms the solid-like characteristics to liquid-like behaviour of gellan with an increase in dextran concentration of G/D blends. The steady flow behaviour was well characterized by the Herschel-Bulkley model (standard error lower than 10) and G/D blends exhibited similar flow behaviour (shear thinning) as bovine and porcine gelatin at 1.5% and 3% concentration as compared to dilute concentration, 0.5% . For dynamic viscoelastic, G/D blends exhibit similar gel characteristic with both porcine and bovine gelatin at 3% as opposed to 0.5% and 1.5%. From spectral characteristic of the blend, a shift in the major gellan band of carboxylic group at 1414 cm-1 and disappearance of two gellan bands at 1072 cm-1 and 1042 cm-1 as well as dextran band at 1080 cm-1 in glycosidic linkage were observed. DSC thermograms showed a single exothermic peak accompanied by a shifting to higher melting temperature for all blends in comparison of individual polysaccharide. These changes suggest a possible molecular interaction event between gellan and dextran. In conclusion, gellan and dextran blends exhibit desired viscosity for mouth feel properties and favorable molecular interaction depended on the amount of added dextran. This interaction is important to design food and pharmaceutical products with desired textural and stability attributes.

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