In a project sponsored by US Poultry & Egg Association, Dr Paul Dawson of the Food Nutrition and Packaging Sciences Department at Clemson University investigated the effect of surface (crust) freezing on the survival of Escherichia coli and Salmonella Typhimurium on fresh chicken breast as well as the effect of surface freezing on native spoilage bacteria.

Pathogens were inoculated onto meat, allowed to attach, then live cells were recovered after exposure to surface freezing and compared to inoculated bacteria on meat that was only refrigerated or completely frozen. In addition, since bacteria in the processing environment are likely to have been previously exposed to low temperatures, one half of the samples were inoculated with bacteria that had been cold-shocked or exposed to cold temperatures prior to inoculation.

Dr Dawson found no significant differences in the reduction of cold-shocked or non-cold-shocked bacteria on products that were crust or completely frozen, with or without skin. The average reduction for E. coli was 0.15 log₁₀CFU per mL of rinse and for S. Typhimurium, 0.10 log₁₀CFU per mL of rinse. Therefore, none of the final reductions was greater than the desired target (1 log).

Data showed minimal initial reduction of these pathogens due to crust freezing. Crust freezing (20 min, -85°C) on the quality of raw chicken breasts, with or without skin, during aerobic, refrigerated storage for up to 18 days was assessed by means of the International Commission on Illumination (CIE) colour parameters L*, a* and b*; tenderness; and total aerobic (APC) and yeasts and moulds counts (YMC).

Microbial load increased over time and exceeded 8.0 log₁₀CFU per ml, which occurred before 12 days of storage.

Under experimental conditions used, Dr Dawson reports that crust freezing did not affect colour or tenderness of raw chicken breasts, with or without skin, and did not significantly increase microbiological shelf life compared to non-crust frozen meat held under the same refrigeration conditions.