Comparison of rapid tests for assessing UHT milk sterility.

Samples of UHT milk were contaminated at two levels (10(2) and 10(4) cfu/ml) with 52 bacterial strains associated with spoilage. Samples were assayed, using various tests, to determine efficiency in detecting non-sterility after an incubation period shorter than that advised in standard procedures. The tests performed were colony count, titratable acidity and pH modification, organoleptic assessment, stability towards ethanol (68, 80 and 88% v/v), resazurin and nitrate reduction. After 3 d incubation at 30 degrees C every case was detected by the resazurin test with a good statistical probability (P = 0 x 999). Reliability was not so high in all other tests, even after 14 d incubation.