A total of 450 Gram-negative psychrotrophs were isolated from raw milk, cream and yoghurt samples in Egypt. They were identified and used to investigate the effect of temperature and time on their lipolytic and proteplytic activities on Spirit Blue Agar and Standard Caseinate Agar media, respectively. Under 6, 17 and 30 ℃ the lipolytic and proteplytic isolates have almost equal percentages in the total number of isolates. Under low temperature the isolates that can show their proteolytic activities are very few. It is suggested that the efficient control of low storage temperature could control the proteolytic activities. Lipolytic activities seemed to be produced earlier and considerably higher percentage of the isolates can begin their activities under low temperature after short time. Therefore, special attention should be given to lipolytic Gram-negative psychrotrophs.

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　Pseudomonas fluorescens was isolated from raw milk. It was found to be a high incidence, active lipase producing psychrotrophic organism. Its lipolytic activity on Spirit Blue Agar media varied with the incubation time and temperature. It appeared after 12 h at 6 ℃, while at 30℃ it was stronger after 6 h. Its extracellular lipase showed maximum activity at 2 % tributyrin. Lipase enzyme exhibited optimum temperature of 40℃ and it still had some of its activity at 5℃. It had some stability at 65℃ for 5 min, 105℃ for 5 sec and 115℃ for 5 sec. The enzyme could escape some industrial heat treatments that commonly used in dairy practices. The optimum pH was 8. It showed 63. 63 % of its maximum activity at pH 6.6 (pH of milk). It had a slight stability over a pH range 8-9.

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