Third. No real relation exists between the organisms counted and decomposition, for mere numbers are not always coincident with putrefactive activity. A pulp or ketchup may be bad and show less than 30,000,000 bacteria, or it may be good and show 300,000,000. Rotting, or decomposition, may depend more upon the cocci and the organisms which are not counted than upon those which are. The only work done in which microscopical and chemical work were reported on the same samples appears in Circular No. 78, Bureau of Chemistry. This was not done upon samples prepared and kept under control, but for the most part upon commercial pulp and ketchup. The results do not show any close relation between the number of organisms and the lactic acid content which is given as the measure of decomposition.
Fourth. Bacteria are expressed in numbers per cc, yeast and spores in numbers per 1-60 c mm. Since the counting can be done only in the fluid portion, an error occurs proportional to the number of bacteria in or attached to the tissue which cannot be counted.
The error of assuming that numbers of organisms alone are a sufficient index of the wholesomeness of a food product is well illustrated by work on water analysis. The following statement by an authority on the subject is illuminative: “The belief is widespread among the general public that the sanitary character of a water can be estimated pretty directly by the number of bacteria it contains. Taken by itself, however, it must be admitted that the number of colonies which develop when a given sample of water is plated affords no sure basis for judging its potability. A pure spring water containing at the outset less than 100 bacteria per cubic centimeter may come to contain tens of thousands per cubic centimeter within twenty-four to forty-eight hours, after standing in a clean glass flask at a fairly low temperature. There is no reason for supposing that the wholesomeness of the water has been impaired in any degree by this multiplication of bacteria.”[[3]]
[3]. Jordan, E. O. A text-book of General Bacteriology. 1908.
There are certain steps in the process of manufacture which also influence the number of organisms which may be counted. A pulp may vary from an unevaporated tomato juice to a concentration which is represented by an evaporation of a volume of water up to 60 per cent, and ketchup may vary from a thin watery consistency to one which is so heavy that it will scarcely flow from the bottle. It becomes evident that a method which does not sustain some close relation to the amount of tomato present would naturally be deficient as a standard for judging. For example, a tomato juice with an initial count of 10,000,000 if evaporated to one-half its volume will have more than twice the number of organisms estimated in the original. The pulp is composed of both liquid and solids and part of the liquid portion only is driven off by evaporation, leaving in the residue a different proportion to the solids. As the organisms can be counted only in the liquid portion, it is obvious that with concentration, the number will be increased at a much greater ratio than will the reduction of the bulk. A thin pulp with 10,000,000 bacteria may easily be worse than a heavier one with 30,000,000 or 40,000,000, if judged by numbers alone. The same conclusion is necessarily true for ketchup. It clearly refutes the argument that a product having twice as many bacteria as another of the same kind is more than twice as bad. The effect of recommending an arbitrary low limit for bacterial content, irrespective of the consistency of the product, is to cause manufacturers to pack thin pulp and sloppy ketchup, and to discourage the more desirable heavy body. The examination of a very large number of samples shows that the majority of the heavy pulps and ketchup upon the market show much higher counts than the thin ones when the tissues show good stock in both.
It is not possible to concentrate any pulp to the consistency of paste and have it pass under the present method; that is, considering a product to be filthy, putrid or decomposed if the bacteria exceed 25,000,000 per cubic centimeter.
There are some soup and ketchup manufacturers who still follow the draining method for separation and this is generally done to secure a certain quality in the flavor. This kind of pulp always shows a high bacterial count, which is usually ascribed to fermentation. As the draining can be started in about twenty minutes, and is nearly always completed in forty minutes to one hour, there is little time for fermentation, and yet such a pulp may show several times the count of the original whole pulp. The condition is similar to that which takes place in the separation of cream by gravity. Dr. John F. Anderson, U. S. Public Health Service,[[4]] has shown that the bacterial content of gravity cream is about sixteen times that of bottom milk and that this discrepancy may be much wider. One test is given in which the cream showed 386 times as many organisms as the bottom milk. The question logically arises whether, if a pulp which contains 10,000,000 bacteria per cubic centimeter and is considered sound, becomes “filthy, putrid or decomposed” when the same pulp is heavily concentrated and the count becomes 100,000,000, or a cream is bad when it contains 2,000,000, though the whole milk from which it was derived contained only 300,000. There should be a recognized difference in rating a product in which the number of organisms is influenced by concentration, and one in which they have developed. Some very erroneous statements have been made upon increase of bacteria in pulp while standing. Some of these have been based upon the academic proposition that reproduction in bacteria may occur every twenty minutes under perfect conditions of food supply, freedom of movement, and optimum temperature. Such statements are obviously not based on experiments with pulp. Assuming that such a rate of reproduction were possible, a pulp with an initial start of only 5,000,000 would increase to 10,000,000 in twenty minutes; 20,000,000 in forty minutes; 40,000,000 in one hour; 80,000,000 in one hour and twenty minutes; 160,000,000 in one hour and forty minutes; 320,000,000 in two hours; and 2,560,000,000 in three hours. No food product like tomato pulp, cider, or grape juice would be usable in a very short time. To determine the rate of increase of the organisms in tomato pulp, experiments were made, using sound tomatoes. In each experiment, the tomatoes were divided into two lots, one lot used raw, the other steamed, the steaming varying from two minutes’ time, just sufficient to slip the skins, and eight minutes, in which the whole tomato is softened. Samples were taken at hourly intervals for the first six hours, then at intervals of twelve hours, the samples counted by means of the plate and direct methods. For the plates tomato gelatin was used with an acidity of 0.3% and 0.4%, the samples for the direct count were put in cans, sterilized, and counted later. With the lower acidity there were liquifiers which prevented the counting of some plates, so that in the later trials the higher acidity gelatin was used. The count of the molds was not normal, due to the frequent stirrings, which prevented spore formation, besides injuring the hyphae.
[4]. The Journal of Infectious Diseases. 1909. Vol. 6, p. 393.