Inhibition of Psychrotrophic Bacterial Growth in Refrigerated Milk by Addition of Carbon Dioxide

Treatment of refrigerated milk with 20 to 30 mM CO₂ was evaluated as a method for extending storage-life by inhibiting growth of psychrotrophic bacteria. Generation times for each of five psychrotrophic pseudomonads were significantly longer when grown at 7°C in sterile milk treated with CO₂ than when the same bacteria were grown in ungassed sterile milk. When raw milks were stored at 7°C and treated with CO₂, the time required for aerobic plate counts to increase 10-fold was at least 24 h longer than in the same milks left untreated. Numbers of coliforms, psychrotrophs, and anaerobes (facultative and obligate) were significantly lower in raw milks treated with CO₂ than in untreated milks incubated at 7°C for 6 d.