Caracterização estrutural de dois exopolissacarídeos obtidos dos fermentados de leite e extrato de soja por grãos de kefir

Abstract

Studies on Exopolysaccharides (EPSs), polysaccharides produced by microorganisms, have been growing in recent decades due to the similarity with gums used in the industrial sector such as xanthan gums, dextran, gellan, pullulan, yeast glucans and bacterial alginates. These EPSs present a breakthrough for the food industry, since they can be used in food processing as a thickener and/or stabilizer and because they are extremely important in the alternative use of traditional gums. In this context, the objective of this work was to determine the physicochemical properties of pH, Water Activity (Aa), Protein Content (TP) and Reducing Sugars (TAR), thermal behavior and structural composition of the EPS obtained from the obtained fermented of cow's milk and soybean extract by Kefir BioLogicus® Kefir grains microorganism matrix. With the purpose of verifying the homogeneity and determination of the molar mass of the raw EPS, tests were carried out with Chromatogafia of Exclusion by Size of High Efficiency. The structural characterization and the monosaccharide composition were verified by 13C and 1H NMR analysis and GC-MS. EPS of soybean (EPSsj) and EPS of milk (EPSle) presented Aa of 0,21 and 0,26 at 25ºC, respectively. The pH and TP results of the samples were similar, pH = 6,20 and TP~1,5% of the total sample. The result for the analysis of reducing sugars (TAR) was 11,3% for EPSle and 12,21% for EPSsj. The EPSsj presented the largest fraction with 1,17x104g/mol molar mass and EPSle presented in its largest molar mass fraction 2,22x106 g/mol. The EPSsj is mostly composed of glucose molecules formed by linked α-Glcp units (1,4). EPSle is composed of glucose, rhamnose and galactose molecules in the α-glcp- (1→4)-α-ramp-(1→6)-β-galp formation. Characteristic polysaccharide bands were observed in the infrared spectrum. The data of the IVs presented similarity to several other results for other polysaccharides present in the literature. In relation to the thermal behavior of the EPSs, the thermogravimetric curves of the EPSs obtained were similar to those reported in the literature for other EPSs. The degradation temperatures were relatively high with various endo and exothermic events, showing that the EPSs of this study have high thermal stability and could therefore be used as an additive in thermally processed foods.