Kefiran edible films plasticized with sugars and polyols.

PIERMARIA J,, BOSCH A, PINOTTI A., YANTORNO O, GARCÍA M. A.; ABRAHAM A. G.

San Miguel de Tucumán,

Simposio; III Simposio Internacional de Bacterias Lácticas. II Encuentro Red BAL,; 2009

Cerela -AAM

Exopolysaccharides producing lactic acid bacteria have recently gained attention in food research due to functional properties and for its biological activities that can offer healthy promoting capabilities. Kefiran, the heteropolysaccharide produced by Lactobacillus kefiranofaciens in kefir grains, is able to form edible transparent but brittle films. Mechanical properties of biopolymer films are commonly improved by the addition of plasticizers as glycerol which gives better mechanical properties to kefiran films in an optimal relation of 25g per 100g of polyasaccharide. The objective of the present work was to analyse unplasticized kefiran films and films obtained with different plasticizers such as sugars (glucose, galactose or sucrose) or polyols (glycerol or sorbitol) at the same relationship (25 g per 100 g of kefiran) in order to analyse their effect on films properties. The physicochemical characteristics of the films were studied by measuring thickness, humidity, water activity and transparency. The microstructural characterization was carried out by scanning electron microscopy and crystalline degree. Furthermore, water vapor permeability (WVP) and the mechanical properties of films were determined. To get a better insight into the molecular characterisation of these films, an ATR-FTIR analysis was performed. All films were transparent (1.88 ± 0.23UA/mm to 3.30 ± 0.98UA/mm) and extremely thin (21.6 ± 2.4mm and 30.5 ± 2.6mm). The humidity of films without plasticizer was 15.07%. The incorporation of galactose, glucose, sucrose or sorbitol did not alter the moisture content significantly while glycerol increased this parameter to 20.42%. Water activity values were found in the range 0.445 to 0.497. All films had a smooth surface, no holes were observed in transversal SEM preparation, and X-ray diffraction patterns showed an amorphous structure (crystalline grades less than 3.1%). WVP values of plasticized films were lower than those obtained for unplasticized films. Glucose was the plasticizer which gave the lowest permeability values (3.056.10‑11g/m.s.Pa). All plasticizers studied improved mechanical properties since they decreased elastic modulus and tensile strength and increased the elongation values of films. Elongation of films with galactose, glucose, sucrose and sorbitol was 50% meanwhile films plasticized with glycerol increased this value to 150%. In conclusion glucose yielded the best results from the water vapour barrier properties viewpoint while glycerol allowed obtaining films with the best mechanical properties. Nevertheless, all the plasticizers studied in this work produced transparent kefiran films which may find application on food product industries.