Abstract #404

# 404
Potential role of Bacillus strains isolated from the dairy environment as defect-causing organisms in yogurt.
Dipakkumar Mehta*1, Ashraf Hassan2, Brandon Nelson2, Hasmukh Patel1, 1South Dakota State University, Brookings, SD, 2Daisy Brand, Garland, TX.

Bacillus spp. can cause spoilage of milk and dairy products due to their ability to produce heat resistant enzymes and spores. Milk proteins, fat, and stabilizers (such as gelatin, amylopectin (AP), xanthan, and pectin) play an important role in structure formation and stability of yogurt. Possible sources of Bacillus spp. in these products include raw milk, ingredients such as dairy powders, and processing equipment. The objective of this study was to test the proteolytic, lipolytic, and phospholipase activities as well as stabilizer-degrading characteristics of 25 Bacillus strains isolated from the dairy environment. Proteolysis, lipolysis, and phospholipase activity were tested using skim-milk agar, spirit blue agar, and lecithin agar, respectively. A basic agar medium containing AP, xanthan, or pectin and gelatin agar were used to study the stabilizer-degradation activities of the various Bacillus strains. All experiments were conducted in triplicate at 42°C and under mesophilic conditions. Many of the tested Bacillus strains were highly proteolytic and could degrade various stabilizers (AP, pectin, xanthan and gelatin). It was found that the majority (92%) of Bacillus strains were able to degrade AP while only 20% showed lipolytic activities. All proteolytic strains showed gelatin degradation activities. The xanthan, phospholipid, and pectin degradation activities were found in 68%, 40% and 24% Bacillus strains, respectively. Generally, Bacillus spp. exhibited higher activities at 42°C than at mesophilic temperatures. Based on these results, it can be concluded that the order of susceptibility of the different tested components to Bacillus strains was AP > protein = gelatin > xanthan > phospholipids > pectin > fat, suggesting their ability to induce texture defects in yogurt.

Key Words: Bacillus, yogurt, stabilizer