Kefiran films plasticized with sugars and polyols: water vapor barrier and mechanical properties in relation to their microstructure analyzed by ATR/FT-IR spectroscopy

Kefiran, an exopolysaccharide produced by microorganisms present in kefir grains, is a glucogalactan that has several health promoting properties. In the present work the effect of different sugars (glucose, galactose, sucrose) and polyols (glycerol and sorbitol) as plasticizers on kefiran film properties was evaluated. Kefiran films were brittle and rigid and all the tested plasticizers improved film properties. They were all transparent with low opacity. Unplasticized kefiran films X-ray diffraction patterns were similar to those of plasticized ones, showing an amorphous-crystalline structure with low crystallinity degree. All films presented low aw values (below 0.5) conferring protection properties against microorganism growth. The lowest permeability value was obtained with glucose as plasticizer whereas the best mechanical properties were obtained with glycerol addition. The relative high intensities of the bands assigned to water molecules stretching and bending modes in ATR/FT-IR average spectra of glycerol–kefiran films were correlated with their relative high water content compared to the other plasticized films. The analysis of the bands due to C–H stretching modes showed that glucose and glycerol could be reducing the interaction between the adjacent chains in the kefiran polymer. It would demonstrate the importance of the analysis of kefiran, plasticizers and water molecules interactions when films properties are studied.