Abstract:

With the purpose of understanding the existence of Staphylococcus aureus during cold chain circulation, the
total number of viable cells and the number of non-injured cells as well as sublethal rate under －18 ℃ storage, freeze-thaw
cycle and a simulated cold chain were determined in the present study. As shown by our results, when S. aureus ATCC6538
was frozen and stored at －18 ℃, the total number of viable cells revealed a gradual reduction along with an increase in
sublethal rate, but the number of viable cells declined at a markedly lower rate after 56 d of storage, suggesting a potent
freezing stress resistance of cells with sublethal injury. In contrast, an obvious increase in total number of viable and noninjured
cells together with a decrease in sublethal rate was observed, when S. aureus cells were subjected to 0.5 h freeze-thaw
treatment. Under the condition of temperature fluctuation-induced food cold chain, although the total viable cell number
decreased during the circulation process, the non-injured cell number fluctuated with temperature. It could be concluded
from the present study that the sublethal state was an intermediate transition state of S. aureus during inactivation, and could
be rapidly recovered under a suitable temperature. Moreover, the recovery of sublethal cells due to inevitable temperature
fluctuation during cold chain circulation, along with the regulation capability of sublethal injured cells against freezing stress
might have a close relationship with frequent detection of S. aureus in quick-frozen food.

Key words: freezing stress, S. aureus, quick-frozen food, sublethal injury