The present study aim is to identify a surrogate microorganism that could be used in validation studies for Extended Shelf Life (ESL) chilled... Show moreThe present study aim is to identify a surrogate microorganism that could be used in validation studies for Extended Shelf Life (ESL) chilled juice beverages with Peracetic Acid (PAA) in the processing system. Historically, Bacillus atrophaeus has been the primary surrogate, especially for aseptic systems with PAA; nevertheless this organism may be overly conservative for ESL processing that doesn’t have as high thermal temperature or PAA concentration. A baseline study was conducted to determine PAA resistance for B. atrophaeus spores. After being heat shocked at 82°C (179.6°F) for 13 minutes, 106 colony forming units per milliliters (CFU/mL) spores were spot inoculated and dried on stainless steel coupons. Then submerged in 200 ppm and 500 ppm VigorOx LS-15® PAA concentration, in two minute increments up to ten minute exposure time, at 50°C (122°F). The PAA reaction was halted and remaining spores were plated on Dextrose Tryptone Agar supplemented with yeast extract (DTA+ye), then incubated at 30°C (86°F) for 24 h. B. atrophaeus is PAA resistant and at least three log CFU/mL reduction was achieved for both concentrations at ten min exposure time. The next phase of the study was the selection of 15 different Bacillus species to conduct similar PAA resistance testing (with exposure time reduced to two and four minutes and additional 100 ppm of PAA) in an effort to evaluate which had the largest potential to be studied further. The three selected were B. pumilus, B. licheniformis (A) and B. licheniformis (B), due to high PAA resistance and similarity to B. atrophaeus inactivation. The three microorganisms were then studied against spoilage microorganisms (Aspergillus niger and Saccharomyces cerevisiae) and pathogenic microorganisms (Listeria monocytogenes, Salmonella species, and Escherichia coli O157:H7) at 200 ppm and 500 ppm PAA concentration. It was concluded that B. licheniformis (B) was the best overall surrogate with half log CFU/mL reduction at one minute and 200 ppm, as it was more resistant to PAA than A. niger and Salmonella. At 500 ppm PAA concentration B. atrophaeus continues to be best surrogate. Further studies, including testing to verify the behavior of B. licheniformis, as a surrogate, are recommended. M.S. in Food Processing Engineering, May 2018 Show less
