Effects of bacterial exopolysaccharide on rheological properties of acid milk curd and its correlates

Abstract

Exopolysaccharide (EPS) is a general term for the forms of bacterial polysaccharides found outside the cell wall of bacteria. The industrial  microbiologist has become interested in exploiting microbial exopolymer production due to an increasing interest and need for novel  polysaccharides. The use of bacterial EPS in acid milk curd (AMC) production accounts for a quality improvement of the milk curd in terms of stability  during the normal operations of storage and transportation. On the other hand, EPS have been used as prebiotic because of its health-  promoting effects in human beings. The objective of this study was to evaluate the rheological properties (RP) and their statistical correlations in  acid milk curd (AMC) samples added with bacterial EPS. Rheometric properties are suitable parameters to evaluate food quality such as AMC. Some  of the RP normally used in this evaluation include elastic modulus (EM), hardness (HR), breaking energy (BE), viscosity (VIS) and stress. Correlation  between pairs of these parameters are important to understand in order to predict statistically other parameters in case they cannot be easily  determined. Acid milk curd samples were formulated using 10, 15, and 20 % of reconstituted skim milk (RSM), to which 0, 0.2, 0.4, 0.6, 0.8, and 1 %  level of EPS were added, respectively. Samples were pasteurized at 60^o C for 30 min, and at 85^oC for 30s. Afterwards, AMC samples were tempered  to 40°C inoculated with Lactobacillus delbrueckii subsp. bulgaricus B-5b, and incubated at 37°C for 16 h. Results indicated that viscosity  and hardness showed the strongest and highest correlation among all the parameters evaluated (r=0.9272) and it was comparable to that between  viscosity and breaking energy (r=0.8349) and breaking energy and hardness (r=0.7694). However, elastic modulus and viscosity showed a rather low  correlation (r=0.5394) and very low correlation (r=0.1830), respectively, suggesting that estimation of elastic modulus from viscosity values would be  inaccurate. In general, rheometric properties of acid milk curd increased with higher EPS concentrations until 1 % level of EPS addition. Therefore, it  is recommended to use BE and HR values, and BE and VIS values to predict accurate measurements of other RP values.