Effect of a commercial freeze/tempering process on the viability of Cryptosporidium parvum oocysts on lean and fat beef trimmings.

ABSTRACT

Lean and fat beef trimmings (25 cm(-2)) were inoculated with approximately 250,000 Cryptosporidium parvum oocysts, placed in commercial packages (28 kg boxes) and subjected to normal commercial processes i.e. blast frozen (to -20 °C within 60 h), stored (-20 °C, 21 days), tempered (48 h at -3 °C), and held at 0 °C for 10 h. Inoculated areas were then excised, pulsified (30 s in 50 ml PBST), and centrifuged (2500×g, 15 min). The resultant pellet was resuspended in 10 ml water and subjected to immunomagnetic separation and viability dye assay. Following the commercial freeze/tempering process the viability of the oocysts had decreased from 90.6% viable in the working stock suspension to 7.17% and 9.46% viable on lean and fat trimmings, respectively. The results of this study indicate that if C. parvum oocysts were present on beef trimmings their viability would be substantially reduced as a result of the freeze/tempering process.