Abstract #T195

# T195
Casein and exopolysaccharide degrading activities of Bacillus strains isolated from the dairy environment.
Dipakkumar Mehta*1, Hasmukh Patel1, Ashraf Hassan2, Brandon Nelson2, 1South Dakota State University, Brookings, SD, 2Daisy Brand, Garland, TX.

Milk proteins and exopolysaccharides (EPS) play an important role in texture formation and stabilization of yogurt. Many Bacillus strains have the ability to breakdown proteins and degrade polysaccharides. To our knowledge, the ability of the Bacillus spp. to degrade EPS from starter cultures has not been tested. The objective of this study was to quantify proteolytic and the EPS-degrading activity of Bacillus strains. Twenty-five Bacillus strains isolated from the pasteurizer balance tank of a dairy company were pre-screened for their proteolytic ability using skim-milk agar (SMA) at 42°C. The strains that showed proteolytic activities were inoculated individually at 103 cfu/mL in heated (90°C for 10 min) rehydrated nonfat dry milk (11% w/v) which was then incubated at 42°C for 48h. The evidences of proteolytic activity were quantified by SDS-PAGE and measuring the non-casein nitrogen (NCN). To study EPS degradation, 2 Bacillus strains that were able to degrade a wide range of polysaccharides in a previous study were selected. The reduction in viscosity of a whey protein concentrate (WPC) solution (10% w/v) fermented with yogurt cultures producing high, medium, or low EPS in the presence of the test Bacillus strains (103 cfu/mL) indicated positive results. The viscosity of the fermented media was measured using the Stress-Tech rheometer at 42°C and a shear rate of 100 s−1. Out of the 25 Bacillus strains, 20 stains showed proteolytic activities on SMA. Of these 20 strains, 8 strains showed significant (P < 0.05) 30–50% degradation of caseins (predominantly β- and κ-CN) as determined by SDS-PAGE and 4 fold increase in NCN contents. Highly proteolytic strains also caused sweet curdling in skim milk. Used Two Bacillus strains showed 20–30% reduction in viscosity was observed in the WPC medium containing the low EPS producing culture whereas only 8–10% decrease in viscosity was found in the medium fermented with the high EPS-producing culture. The results of the present study showed the potential of Bacillus strains to degrade EPS and reduce viscosity of the fermented dairy products. It also provided useful information on the prevalence of highly proteolytic Bacillus strains in a relatively large number of isolates from a dairy plant.

Key Words: Bacillus, protein, EPS