91E-20 |
Inactivation of natural flora and E. coli 8739 in a milk protein concentrate-fortified soymilk |
S. Q. LI1, Q. H. Zhang2, T. V. T. Pham3, and Y. Z. Lee3. (1) Department of Food Science, The Ohio State University, 2015 Fyffe Road, Columbus, OH 43210, (2) Department of Food Science & Technology, The Ohio State University, (3) BioFoods Department, Stolle Milk Biologics Inc Pulsed electric field (PEF) pasteurization is a newly developed nonthermal food processing technology. PEF processing of functional food can avoid the detrimental effects of thermal processing. To investigate the feasibility of using PEF in functional food pasteurization and to determine kinetics of inactivation of natural flora and inoculated E. coli 8739 in a milk protein concentrate-fortified soybean milk. OSU-4A PEF unit with co-field flow chambers provided PEF treatments. The soymilk powder fortified with milk protein concentrate was rehydrated with autoclaved water and incubated at 22°C for 24 hrs. Samples before and after PEF treatment were collected and spread-plated PCA and PDA and incubated at 35°C for 4 days and 27°C for 6 days, respectively. E. coli 8739 was incubated in Tryptic Soy Broth at 35±2°C for 10 hrs and harvested by centrifugation at 5000 rpm for 5 min at 23°C. The cells were inoculated into the freshly rehydrated soymilk product at room temperature for further treatment. E. coli 8739 inoculated samples were plated on Violet Red Brilliant Agar plates and incubated at 35±2°C for 2 days. PEF treatment at 35~40kV/cm electric field strength with square waveform resulted in more than 5-log reduction in the natural flora and E. coli 8739 populations. The higher the electric field strength, the higher the inactivation effects by PEF both to the natural flora and to E. coli 8739. When stored at 4°C, the shelf life (microbial counts below 105 cfu/ml) was extended from 6 days for untreated samples to 18 days for PEF-treated samples. No significant change of pH (p>0.05) and color (p>0.05) of the product was observed after PEF treatments. PEF treatment of a milk protein concentrate-fortified soymilk product is effective for inactivation of natural flora and E. coli. PEF does not change the color, pH and other attributes of this low-acid product.
Session 91E, Nonthermal Processing: Nonthermal processing of foods
|