The Effect of Hydrogen Ion Concentration on the Bacterial Content of Gelatin

Abstract

Summary A study of 34 samples of gelatin failed to reveal any relation between the reaction and the bacterial count. The bacterial counts ranged from less than 5 bacteria per gram to 20,000, and the reactions expressed as pH were between 4.8 and 6.6. The keeping quality test failed to check with the relative bacterial counts since some of the samples with the highest counts failed to liquefy in twenty-one days at room temperature, and some of the apparently sterile samples developed liquefaction in as short a time as nine days. A study of the effect of the reaction on bacterial growth revealed that the high acidity of some of the samples had a marked deterring action on the rate of growth of the microorganisms. Although the high acidity of some of the gelatins exerted a marked retarding effect on the development of microorganisms, in no case did the reaction completely inhibit growth where a mixed microorganic population was added. Under practical conditions, gelatin produced in an insanitary plant where no effort is made to prevent contamination, especially during the drying process, the resulting contamination would likely be composed of a wide variety of microorganisms, comparable perhaps to the heterogeneous mixture used in artificially contaminating the gelatins in this experiment. The results obtained indicate that if such contamination were to take place while the gelatin was in the drying alleys, very little growth would be likely to result in those gelatins having a high acidity. In other words, the resulting microbial numbers would approximate the extent of contamination since little or no growth would have taken place. On the other hand, if a gelatin with a nearly neutral reaction were subjected to the same contamination, growth of the organisms during the drying process would likely result. A numerical estimate of the microorganisms in this instance would lead to a misinterpretation of the relative sanitary conditions under which the two gelatins were produced. Undoubtedly many of the organisms present in the finished product die before the gelatin reaches the consumer as a result of the unfavorable environmental conditions, of which high acidity is only one. In other words, the bacterial analysis, under any conditions, is likely to present a picture of the conditions surrounding production of the gelatin which has been modified by the effect of environmental factors on the microbial flora of the finished product. Even though some of the more sensitive organisms originally present in gelatin may have been destroyed, and the growth of other microorganisms deterred by adjustment of the pH, it is believed that gelatin which has been carelessly produced will have a relatively high bacterial count. However, intelligent interpretation of any bacterial count, whether it be on gelatin or any other product, depends on a thorough understanding of, and adequate allowances for, all the factors which may tend to increase or decrease the number of bacteria. The results of this investigation indicate that in interpreting a low bacterial count of gelatin, one of the factors to be taken into consideration is the reaction. This, however, does not render the bacterial count of gelatin useless. The purchaser of gelatin can eliminate from consideration many samples of gelatin because of the undesirable conditions which their high bacterial counts reveal. He cannot, however, be absolutely certain that gelatin with a low bacterial count is per se beyond reproach from the standpoint of sanitary quality. This interpretation never should be made on the basis of a bacterial analysis of any product. A bacterial count on gelatin or any other product only indicates a conclusion and never proves it, unless that conclusion is corroborated by an inspection of the source of supply. A low bacterial count indicates that at least an effort has been made on the part of the manufacturer to prevent excessive contamination of his product and to destroy those bacteria which do gain entrance. If the acidity is high, it is likely that the low bacterial count may be due in part to the death of organisms incapable of surviving the environment, and to the increased efficiency of bacterial destruction by heat in high acid media. Nevertheless, if gelatin has a low bacterial count it indicates, even though it does not prove, that the conditions under which the gelatin was produced did not permit of excessive contamination or else more of the resultant heterogeneous microbial flora would have survived. A low bacterial count is, therefore, believed to be a fairly good index to gelatin of good sanitary quality, although the factors affecting bacterial destruction and growth, such as the acidity, must be taken into consideration.