Influence of Growth of Coliforms on Flavor Acceptability of Commercially Processed Milk Samples

Abstract

Commercially processed whole milk samples were surveyed during the last 3 yr to evaluate flavor acceptability during storage to sell-by dates. Growth of coliforms influenced flavor acceptability. Samples with 150 or greater colony-forming units per milliliter by the violet red bile agar method after 10 day storage at 6.7°C had unacceptable flavor scores by trained panels in 50, 70, and 72% of three surveys in 1979, 1980, and 1981. The preliminary incubation violet red bile agar method was evaluated as a procedure for predicting shelf-life of milk samples by detecting coliforms soon after processing. Unsatisfactory flavor scores in 35 commercially processed samples found positive for coliforms by the preliminary incubation were 0, 11, 57, and 91% at 1, 7, 10, and 14 days. The preliminary incubation count on freshly processed milks was related to unacceptable flavor scores: 8, 33, 55, and 69% of the samples with unacceptable flavor scores after 10 days had counts of 0, 1–10, 11–100, and greater than 100 colony forming units/ml. Samples positive for coliforms had higher standard plate counts and rapid psychrotrophic counts than coliform-negative samples. Pyruvate content, lipolysis, and proteolysis were greater also in samples positive for coliforms. Growth of coliforms may influence growth of psychrotrophic pseudomonads in commercial milk samples.