CONICET | Buscador de Institutos y Recursos Humanos

Gelation of caseinate emulsions by homogeneous acidification produce hydro-gels containing oil drops, that can be used in different food and medical applications. The hydrogels find also applications in the preparation of plastic films with potential application in food packaging or drug delivery. The rheological and mechanical properties of the materials (hydrogels or films) determine its further applications in the different fields. These properties are very dependent on the micro and nanostructure of the material, which are very much influenced by formulation. The presence of sucrose as a soluble additive in the emulsion, affects the gelation process and very likely the microstructure of the resulting hydrogel. Among other properties, the retention of oil inside the hydrogel and the macroscopic aspect are also affected by sucrose. Hydrogels containing sucrose can retain the oil, while without sucrose the oil is expelled from the hydrogel. It is possible that the framework of the hydro-gels is determined by the connectivity of the construction units, which are aggregates of sodium caseinate or micelles [1]. Previous studies by SAXS demonstrated that during gelation the size of the aggregates increases indicating that gelation is consequence of the aggregation of the construction units. In the presence of sucrose, the size of the construction units is notably smaller [1]. When the units are in the nanometric scale, the interactions between the caseinate molecules that lead to gelation are different from the ones of microemulsions. The gel framework (and rheological properties) should also be different. Preliminary results from our group indicate that nano-hydrogels displayed a more homogeneous distribution of oil. Nanosystems are more stable with respect to syneresis (loss of oil) and more transparent. Synchrotron X-ray imaging is a powerful technique that provides direct information about the distribution of pores and/or particles in a continuous matrix [2]. In the particular case of hydrogels, where water is distributed in a framework formed by a polymer or particle net, the elimination of water by lyophilization allows determining the microstructure of the solid network (aerogel). The aim of this project was to describe the porosity of aerogels formulated with different concentrations of sodium caseinate and sucrose. Micro and nano gels were prepared stabilizing emulsions or nanoemulsions with 3 or 4 wt.% sodium caseinate. The effect of sucrose was checked on the 4 wt.% micro and nanoemulsions. Selected concentrations were: 2, 4, 6 and 8. The results showed that porosity diminished when protein or sucrose concentration increased. Images of gels with 3 wt.% of sodium caseinate (less amount of protein) showed more voids than gels with 4 wt.% of sodium caseinate. No sucrose crystals were present in images indicating that sugar form part of protein structure. Protein network looked thicker with 6 or 8 wt.% sucrose concentration more likely because sucrose interacted with sodium caseinate and formed part of connectivity units. The experiments performed added evidence to confirm the effect of sucrose and droplets size on the microstructure of the gels. A better understanding of the relationship between the microstructure and the mechanical and rheological properties of these materials was obtained. This knowledge will allow a better fitting to the applications for which they were developed. [1] J.M. Montes de Oca-Ávalos, C. Huck Iriart, R.J. Candal and M.L. Herrera, Food Bioprocess Technol. 9, 981 (2016).[2] D. Wildenschild and A.P. Sheppard, Advances in Water Resources 51, 217 (2013).Acknowledgements: This work was supported by the National Agency for the Promotion of Science and Technology (ANPCyT) through project PICT 2013-0897 and the Synchrotron Light National Laboratory (LNLS, Campinas, Brazil) through project IMX-20160535.

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