ARS | Publication request: HEAT RESISTANCE OF E. COLI IN APPLE CIDER DURING REFRIGERATED STORAGE TIME

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 3, 2006
Publication Date: June 27, 2006
Citation: Jin, Z.T., Zhang, H.Q., Boyd, G., Geveke, D.J. 2006. Heat resistance of e. coli in apple cider during refrigerated storage time. IFT Annual Meeting, June 24-28, 2006, Orlando, FL. Pager No. 054A-37.

Technical Abstract: The FDA recommends apple cider to be pasteurized after outbreaks of E. coli O157:H7 contamination. In juice production, freshly pressed cider usually is stored or held in a refrigerated tank from 0 to 24h before thermal pasteurization. Studies have shown that an acidic environment may enhance the thermal resistance of microorganisms. The objective of this study was to conduct thermal inactivation tests to investigate the possible change in heat resistance of E. coli as affected by storage/holding time prior to pasteurization. E. coli ATCC 23716 was inoculated into apple cider (pH 3.57). The inoculated cider was stored at refrigerated temperature for 0, 2, 4, 6, and 24h. One mL of sample was placed inside a TDT can. The TDT can was submerged in a water bath at 56C. At timed intervals of 0 to 4 min, duplicate cans were removed from the water bath and immersed in an ice-water bath. Heat-treated samples were plated on tryptic soy agar and incubated at 37C for 24 h. The log numbers of the survivors at each time were used to determine D values. The D values of E. coli in cider at 56C for 0h, 2h, 4h, 6h, and 24h were 0.91 min, 0.90 min, 0.92 min, 1.03 min, and 1.39 min, respectively. A statistical analysis revealed that there was no significant difference of D values at 0h, 2h, and 4h. However, the D values significantly increased at 6h and 24h. This study shows that acid adaptation enhances the ability of E. coli to survive in a subsequent heat pasteurization, and suggests raw juices should be pasteurized within 4h or a more aggressive thermal process would be needed to achieve comparable microbial kill. This study provides useful data for juice-processing plants to design production procedures to ensure sufficient reduction of possible contaminant microorganisms.