A preliminary report of the effects of pressure in the pre---servation of milk was published as Bulletin 56 of this Experiment Station. The work therein reported was continued until hope of preventing certain slow changes in the milk had to be -abandoned. The changes were due to enzymes which the pressure could not destroy. The writers are now studying the effect of pressure on enzymes and have shown that the .activity of some milk enzymes is not destroyed by a pressure of 100,000 pounds per square inch, at room temperature for seven days, nor by the same pressure applied for an hour each day for more than a week. Cultures of bacteria have not been obtainable from any samples of milk so treated.It is not always necessary to apply such pressures so long or to repeat them so often in order to obtain sterile samples.A single application probably destroys all non sporeforming bacteria and all spore formers in the; vegetative stage certainly no non sporeformers hereinafter mentioned except B. prodigiosus have survived such a pressure for half a minute.The destruction of bacteria in a sample of old milk is usually a most striking demonstration of the effect of pressure. An original count of thirty or forty millions per cc. may be cut down to a few hundred, or a few dozen, by an application of 100,000 pounds for ten minutes.Such sweeping reductions in the bacterial content of milk are believed to be quite as desirable as the ori'^inally contemplated preservation of milk in salable condition. It should be observed that the good effect of pressure is not entirely a matter of the number of bacteria destroyed ; for milk is not ordinaril}^suspected and has never been convicted of being the frequent carrier of sporeforming pathogenic organisms, while lion sporeforming pathogenic bacteria known to thrive in W. Va. Agr'l. Experiment Station [Bul. 146] [Oct., 1!)14| Efk.xt of I'hessure on MicKo-oi^cANisMs Fig. 2. -Tin and glass containers for cultures.milk (See B. diphthcriae and B. typhosus) are among the organisms that are the easiest to destroy b}' pressure.The changes taking place in compressed samples of milk, fruit juices, etc., are, of course, but a measure of what can be accomplished by the organisms and enzymes surviving the pressure, during such time as they can survive the media.Milk and vegetables are very suitable media for many different organisms, including sporeformers, against which a single application of pressure is useless. In the case of ripe fruits, the yeasts and other organisms having most to do with decomposition are very susceptible to pressure, while other organisms not so susceptible do not long survive the acid media. W. Va. Agk'l. Experiment Station [Bul. 146] FRUIT JUICES UNDER PRESSURE.The equipment and method of procedure were essentially the same as were used in the work on milk and may be described briefly as follows. A collapsible block tin tube, Fig. 2, A, was filled with the fruit juice, closed with a metal screw cap and placed in a lead tube (packing) which was filled with water, cl...
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