摘要 : Composite evening and morning milk was obtained from a farm known to produce milk of very good microbiological quality and was designated milk A. For comparative purposes, raw milk representative of the general quality of milk sup... 展开 Composite evening and morning milk was obtained from a farm known to produce milk of very good microbiological quality and was designated milk A. For comparative purposes, raw milk representative of the general quality of milk supplied to the milk processing industry was obtained from a large central bulk-collection depot and was designated milk B. Three replicate production runs were carried out for each type of milk. In order to simulate conditions within large commercial bulk raw milk storage silos, 3 pilot-scale 50-litre capacity storage units were assembled. An aseptic sampling port and a CO2-gas sparging system with an outlet tube was fitted to each unit. One unit was flushed with CO2 to give a final concentration of 30 mmol CO2/litre, and asecond unit was flushed to give a final concentration of 45 mmol CO2/litre. The third unit received no added gas and was used as a control. All units were maintained at 6?.5鳦 throughout each run. After flushing the appropriate bulk milk sample at a flow rate of 1 litre CO2/min for a known period of time, the concentration of dissolved CO2 in the milk was determined. Duplicate 5-ml aliquots of gas-sparged milk were aseptically withdrawn and transferred into rubber-sealed 20 ml roll-tube bottles. One ml M H2SO4 was then injected through the seal into the subsample. After shaking to release dissolved gas, the CO2 concentration in the headspace was measured using gas chromatography. When milk A was incubated for 7 days, no organoleptic deterioration wasevident either in the control or the treated samples. When milk B was assessed, incubation was terminated after 6 days due to overt spoilage in all 3 replicate experiments. The categories of microorganism enumerated were coliforms, psychrotrophs, lipolytic and proteolytic bacteria, Pseudomonas and Lactobacillus. With milk A, either level of carbonation limited proliferation of coliforms up to day 5, whereas in milk B, growth took place sooner and at a higher rate, although it was still slower than thatobserved in the controls. 收起