The resistance to heat of thermo-resistant streptococci attached to stainless steel in the presence of milk.

Skim milk residues had a significant impact on the sensitivity to heat of a dairy isolate of the thermo-resistant, Streptococcus thermophilus. Cells of S. thermophilus (H) suspended in water or in milk had D values at 60 degrees C of 2.0 and 14 min, respectively. Cells of S. thermophilus (H) attached to stainless steel in the presence of water or milk had D values at 60 degrees C of 2.2 and 8.1 min, respectively. The attached cells in both experiments were heat-treated in the presence of water. The increase in heat resistance could not be fully attributed to individual components (caseinate or whey) in the milk. The potential for thermo-resistant streptococci to survive heat treatment in a dairy manufacturing plant is therefore greater than may be expected for the organism in less complex environments.