Isolation and Characterization of Exopolysaccharides from Fermented Milks

Kefiran is an exopolysaccharide produced by the microflora of kefir grains during the milk fermentation process. The health-promoting and physicochemical properties of kefiran led to its exploration for a range of applications, mainly in the food industry and biomedical fields [1]. The physicochemical and biological properties of natural exopolysaccharide vary according to both the raw material and extraction method [2]. Cow, buffalo, goat, camel, donkey and sheep milks were used as raw materials for fermentation. Aiming to establish the most appropriate kefiran extraction protocol, three different processes were evaluated, which differ in the temperature and in the presence (or not) of ultrasound. kefiran biopolymers were characterized by Fourier Transform-Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC) and rheological measurements. The samples showed differences in yield, thermal properties, and morphological features depending on both the type of the milk and the extraction method. The results indicated that extraction protocol with heating and constant agitation was able to provide the best thermal resistance, and the highest yield with the greatest recovery for the cow kefiran (4.79%). The kefiran samples were very thermally stable, having a temperature of degradation (Td) in the range from 264 to 354 °C. Regarding the rheological properties, kefiran solutions showed a pseudoplastic behaviour. The resulting morphological and thermal differences could lead to different practical applications of kefirans in the fields of nutrition and pharmacology.