Experiments on the Spoilage of Tomato Ketchup

To test the antiseptic value of oils in ketchup, experiments were made, using olive oil, cottonseed oil, and oleomargarine in the proportions of 1 part of oil to 1,000, 750, and 500 parts of ketchup, respectively. The ketchup was made in small quantities, 2 gallons for each experiment. After bottling, all except the check bottles were inoculated with Penicillium and kept at kitchen temperature. All spoiled, and neither the quantity nor kind of oil used had any marked effect in preventing spoilage. That the oils affected the development of the mold was evident. The mold developed first at the junction of the ketchup with the bottle forming a ring which spread gradually over the surface developing a somewhat heavy mycelium. This remained white longer than usual, spores forming very gradually, as indicated by the change in color from white to a delicate blue. At the end of three weeks only spots of color appeared on the surface and these were still blue, though in ordinary development the blue color changes to green in two or three days.

Another test was made, using olive oil only, and in the proportions of 1 part of oil to 500, 400, and 300 parts, respectively, of the ketchup. Reduction was made in a steam-jacketed kettle, the oil being added when the ebullition of the ketchup was the strongest, after which the boiling was continued for fifteen minutes. The ketchup was bottled, unsterilized bottles being used, then covered loosely with the metal caps.

The time required for the ketchup to spoil was longer than in the first set, but there was not sufficient difference nor enough uniformity in the time to indicate that the use of oil in ketchup is desirable, even if the change of flavor and odor be not taken into consideration. The average number of days before spoilage for those containing 1 part of oil to 500 parts of ketchup, was thirteen and two-thirds days; one has not yet spoiled (a period of forty-five days), while the first bottle spoiled in four days. Those having 1 part of oil to 400 parts of ketchup had an average life of nine and three-fourths days, the minimum being three days, and the maximum twenty-six days. Those having 1 part to 300 parts of ketchup on an average did not spoil for six and three-fourths days, the minimum being four days, and the maximum eleven days.

The failure of some of the bottles to spoil, though similar in every known respect to those which did spoil, is a feature peculiar to ketchup and is familiar to manufacturers who make careful tests before putting their product on the market. For this reason a rather large number of bottles should be used in a test in order that the results may be approximately accurate and represent general conditions.

STUDY OF PENICILLIUM IN KETCHUP

Penicillium is a plant which is distributed widely and apparently is able to grow wherever organic matter is found, though flourishing best when the material contains acid. It causes loss in canneries, breweries, distilleries, etc., the only use made of it being in the manufacture of Roquefort cheese, the immature cheese being inoculated with the conidia for the effect the mold produces in the maturing process.

DEVELOPMENT

In developing, the mold forms a white felt-like mass, covering the medium on which it is growing; then as development proceeds, it changes to bluish-green, and finally to a darker, duller color. The change in color is accompanied by a change in structure, the surface becoming powdery in appearance, a slight current of air being sufficient to dislodge a cloud of fine dust. This fine dust is formed of small, spherical bodies, the spores or conidia (from the Greek meaning dust). These need no resting period, but are able to develop at once. When the conidia lodge on a moist substance they swell to a much greater size and then send out a tube from some part of their surface. The tube lengthens and septa form, dividing the tube into sections, or cells. At the same time branches are sent out, which again form other branches. The original conidium sends out a second branch shortly after the first one, and usually from the opposite side, and may even send out a third one. The formation of the septa and the subbranching goes on in all, so that in a short time the branches mat together and form a felt-like cover.

REPRODUCTION

After a shorter or longer period of development, dependent on the conditions, branches are sent perpendicularly from the substratum, and into the air. These branches cease their growth in length, sending out branches near the tip, which take the same general direction as the original branch. Each of these subbranches is called a sterigma (from the Greek word meaning support). In vigorous development the sterigmata may form secondary branches, the whole forming a tassel-like arrangement. The tip of a sterigma enlarges, a septum forms around the enlargement, cutting it off from the sterigma, and forming a conidium. The sterigma develops to the original length and another conidium is formed, the operation being repeated many times, thus forming a chain of spores. As the other sterigmata are also forming conidia in the same manner, a series of these chains is formed close together. After the cessation of conidial development, the filament below the sterigmata is disorganized, setting free the conidia. The filament and head together are called the conidiophore (Greek, dust-bearer).

Penicillium forms spores sexually, but the conditions for their formation are unknown. Brefeld obtained them by growing the mold on damp bread placed between two glass plates, and excluding the air. Lindner obtained carpospores on a wort gelatin culture in a petri dish, from which the air was excluded. The writer has tried various methods for obtaining carpospores, but so far without success. Moist chambers were used with various media, excluding the air. The development of the mold is seemingly dependent on the amount of air in the chamber at the time of sealing. After the air is exhausted, the conidiophores assume fantastic forms, developing only one or a few sterigmata, and on these one or few conidia. In other cases the conidiophores are fascicled, in no cases, however, forming the conidia as luxuriantly as when air is supplied. The hyphæ become clear, much vacuolated, and develop more septa, and some of the cells become much enlarged. An enlarged cell will often contain two or three septa, thus forming cells that are not larger than disks. In cultures from which the air was excluded from the start, no development took place. In test-tube cultures sealed with paraffin after twenty-four hours, the mold developed on the surface of the gelatin, forming a felted white mass, but no conidia nor carpospores were formed.

GROWTH IN KETCHUP

The form of Penicillium which was used in the experiments was isolated from ketchup in which it grew luxuriantly. When conidia are first formed on the ketchup, they are a delicate blue in color; they then become bluish green, then green, and finally olive. The development of the color of mold growing on ketchup is practically the same as when grown in wort, tomato bouillon, pea bouillon, or gelatin made with these solutions as a basis. In ketchup containing sodium benzoate, the blue color appearing first remains for a long time, and in old cultures the mold is a dull drab, not olive, as in normal development.

In ordinary ketchup made without a preservative, the mold forms a heavy, wrinkled mycelium, showing a large development of conidia. In the bottles of ketchup, the mold pushes down into the ketchup, becoming entirely submerged, a clear liquid covering the mold and separating it from the ketchup. This occurred in more than one hundred bottles. No secondary mycelium formed on the surface of the liquid, a method of development which frequently occurs in ordinary media when a mass of mold is submerged.

An exception to this was shown in ketchup which had developed the mold in the laboratory. The bottles were then put in the refrigerator for two weeks. During this time scarcely any development took place; but after they were again placed in the laboratory, the mycelium pushed down into the ketchup and a new, very thin mycelium developed on the surface. The filaments when seen under the microscope were swollen, had irregular outlines, and a comparatively smaller number of septa, and were filled with a coarsely granular protoplasm. The ends were blunt and misshapen and the sterigmata were irregular, tending more toward a fasciculated arrangement, and forming fewer conidia. The filaments from the vinegar and acetic acid media had the same appearance as those developed on ketchup, but had a smoother outline.

TEMPERATURE TESTS

The limits for the germination of Penicillium, as given by W. J. Sykes,5 are 2° to 43 °C. (35° to 110° F.), and the most favorable temperature 22° to 26 °C. (72° to 79° F.). This author states also that according to Pasteur the dry spores retained their vitality at 108 °C. (226° F.), but that they were soon killed when immersed in boiling water. Klöcker6 quotes Pasteur as saying that the conidia are killed if exposed to a temperature of 127° to 132 °C. for half an hour, but that they retain life at 119° to 121 °C.

A series of tests was made to determine the thermal death point of the moist and dry conidia of the Penicillium used in the experiments, a young, vigorous development on ketchup being used. The flasks were kept under observation for a month after the tests were made, as in many cases a development does not occur in the usual time. The high temperatures applied for longer periods of time were tried first, but both temperature and time were reduced as results from the series were obtained. Only the conditions obtaining in the final tests are given in the table. It was found that the Penicillium used did not have the high resistance supposed.

The tests were made in small flat-bottomed 10-cc flasks, tomato bouillon being used for the tests on moist conidia. The bouillon was used so as to have the conidia in a nutritive medium after the test was made, without transferring. The time for those at 100 °C. was estimated from the time of ebullition. At the end of the specified time, the flasks were cooled promptly under running water. As the flat bottoms gave comparatively large surface, the heating and the cooling could be effected in a short time. For the tests below 100 °C. a vessel of water was heated to the desired temperature, and the flasks were immersed in it and shaken constantly. The dry conidia were placed in test tubes which were immersed in boiling water for the desired time and cooled under running water, after which 10 cc of sterilized tomato bouillon was added. After determining the death point in this manner and finding it to be much lower than had been supposed, it was decided to make the test again, but using ketchup as the medium. Ten grams of ketchup were sterilized, then inoculated from a vigorous growth of mold, and tested with a set in which the tomato bouillon was used. For those below 100 °C. the two flasks which were to receive the same temperature were held in the vessel of water at the same time, so that as nearly as possible the treatment would be identical. The following results were obtained:

Thermal death point of moist and dry conidia of Penicillium.

The moist heat was very effective in destroying the vitality of the conidia of Penicillium, the death point being 27 °C. higher than the maximum temperature for germination as given by Sykes. The heating was more effective in destroying germs when applied to bouillon than to ketchup, no development taking place for any temperature above 65 °C., even when applied for a short time.

In the ketchup the lower temperatures for the longer periods of time were more effective in checking the development, even though they did not destroy the vitality. In the ketchup, with the exception of Nos. 9 and 10, the colonies started invariably along the sides of the flasks. The greater access of air to those on the sides would account for this. The conidia on the sides of flasks Nos. 9 and 10 must have been destroyed, as no development took place in either case except in the center of the surface.

The dry conidia were destroyed at 100 °C. when heated for thirty-five minutes; they did not reach a normal development in any case, even when heated for only ten minutes, many of the conidia being destroyed by this treatment. Where development failed to take place, the conidia were stained with a water solution of eosin, so as to be sure that the effect was death, and not an arrested development.

The results of the tests do not agree with those obtained in factory practice, where the ketchup is cooked at 100 °C. for at least forty minutes and sometimes for fifty or fifty-five minutes, depending on the consistency of the pulp.

HISTOLOGICAL STRUCTURE OF KETCHUP

In ketchup are found parts of all the various tissues of the tomato broken into fine pieces by the action of the cyclone. Although the sieves take out the seeds, skins, and any large pieces, particles of the various tissues are present in size sufficient for identification. Among the distinctive features are the red crystalline bodies in the parenchyma, which serve to a certain extent to distinguish the parenchyma from that of other plants which might be used for adulteration, and serve also to differentiate the natural from the artificially colored ketchup. Some of the red dye used colors all protoplasm indiscriminately, even that of the fungi present, and as a colored ketchup is usually poor stuff, containing many fungi, the mold filaments, yeast cells, and bacteria receive their share of the color. Other red dye used is in the form of fine powder, which does not go into solution, but is distributed as irregular particles which are distinct from the red crystalline bodies.

Good ketchup made from whole tomatoes has a clean appearance readily distinguishable under the microscope; but the poor ketchup has usually a superabundance of fungi present, fully developed colonies of mold, many forms of conidia, besides yeast-like cells, and different forms of bacteria. All of these may be dead, but neither preservatives nor dosage of odorous spices can disguise their presence. In some of the ketchup examined, which was put up in attractive form and labeled as being made from the whole tomatoes, and which had the appearance and odor of good ketchup, the microscope showed the presence of such quantities of fungi as to leave no doubt that the tomatoes were spoiled when cooked. It is presumable that some of the dealers placing this sort of stuff on the market do not know its condition themselves, and either buy their pulp from other factories or trust its manufacture to employees whose only care is that the ketchup shall have a bright color and shall “keep.” Some of the mould filaments and conidia are distorted in the same way as those of the Penicillium are when grown in ketchup to which sodium benzoate has been added.

The ketchup made from sound tomatoes and manufactured in a cleanly manner has practically no fungi present. The ketchup that was used in these experiments was made at different times during the season and was of this character, no bottle examined showing mold filaments when first opened.

MICROSCOPIC EXAMINATION OF SOME COMMERCIAL BRANDS

In examining ketchup the color, odor, amount of discoloration, presence of foreign tissue, foreign coloring matter, oil, and fungi were determined. If no preservative was mentioned, some of the ketchup was put in petri dishes and inoculated with Penicillium to determine whether growth could take place. The following examinations are reported, as they represent some of the best known brands on the market:

No. 9.– Opened September 2, 1907; age unknown; pint bottle; no preservative mentioned; not spoiled July 6 of following year. This ketchup was guaranteed to be made from fresh, ripe, tomatoes by a new process. The color is an unnatural red, has not faded, and the odor is good. The microscope showed the presence of much refuse, and large quantities of fungi, whole colonies of molds, the filaments distorted, many yeast cells, and bacteria. The red color was not confined to the red crystalline bodies, as is the case in ripe tomatoes, but the whole of the protoplasm of the cells, including the nucleus and nucleolus was red, as were also most of the mold filaments and yeast, indicating the presence of considerable artificial coloring matter. The structure indicated that the stock had been manufactured from “trimmings,” and further, that they were not fresh when used, but had fermented. There was no oil present. The “new process” is a success in keeping ketchup, as no preservative is mentioned. The price was 20 cents.

No. 112.– Another bottle of the same brand of ketchup; examined in April, 1908; presumably manufactured in 1907; one-twelfth of 1 per cent of sodium benzoate declared on label; a bright red; guaranteed to be from fresh ripe tomatoes and uncolored. The microscope showed no dyeing of the tissues, few fungi, and no extraneous matter. The price was 20 cents.

No. 17.– Opened September 28, 1907; age unknown; a pint bottle; sodium benzoate declared on supplemental label, no amount being stated; reddish brown color, badly discolored on top; greasy odor; not spoiled July 6, 1908; refuse present; large amount of oil; many fungi; the mold filaments enlarged and distorted. The price was 15 cents.

No. 109.– Another bottle of the same brand examined in April, 1908; presumably manufactured the preceding year; had one-tenth of 1 per cent of sodium benzoate; not spoiled July 6, 1908; reddish brown color, discolored near top; greasy odor. This was practically the same as the first bottle examined, had fewer mold filaments, but many bacteria.

No. 18.– Opened September 28, 1907; age unknown; pint bottle; no preservative mentioned; not spoiled July 6, 1908. A neck label stated that it is made from sound ripe tomatoes and uncolored. Color reddish brown; greasy odor; many oil globules; too many mold filaments and bacteria for sound tomatoes. Price 20 cents.

No. 113.– Another bottle of the same brand examined in April, 1908; said to have been manufactured in 1908; no preservative mentioned; not spoiled after standing open for seventy days; same as No. 18 in color and odor; oil and many fungi again present.

No. 10.– Opened September 2, 1907; age unknown; half-pint bottle; no preservative mentioned; not spoiled July 6, 1908. A neck label 2 inches in height guaranteed the highest quality; an extra label lower down on the neck stated the product to be the natural color, and made from fresh, ripe tomatoes; the regular label carried the brand, manufacturer’s name, etc. Color brown; sweetish odor; colonies of mold; distorted filaments; many bacteria; a few small oil globules. Price 25 cents.

No. 106.– Same brand; pint bottle; examined in April, 1908; said to be manufactured in 1907; color red, discolored near surface; 2-inch neck label in addition to regular label; no preservative mentioned; did not spoil in seventy days; oil globules; particles of red, amorphous matter; whole colonies of mold, as well as fragments of filaments; teeming with bacteria.

No. 77.– Different brand, but same manufacturer as Nos. 10 and 106; age unknown; pint bottle; one-twelfth of 1 per cent of sodium benzoate declared; opened December 1; placed in incubator at 95° F. for a month; not spoiled July 6; color reddish brown; greasy odor; oil globules, many mold filaments, and bacteria present. Price 20 cents.

No. 107.– Third brand from same manufacturer as preceding; said to be manufactured in 1907; half-pint bottle; one-twelfth of 1 per cent of benzoate of soda declared; layer of oil on surface; sweet odor; reddish-brown color. Oil globules prominent feature microscopically, whole colonies of distorted mold were present, and sample contained many different forms of bacteria. Price 10 cents.

No. 14.– Opened September 2, 1907; age unknown; no preservative mentioned; not spoiled July 6, 1908; half-pint bottle; color red; good odor; few bacteria; free from refuse. Price 25 cents.

No. 108.– Same brand as No. 14; said to be manufactured in 1907; pint bottle; one-tenth of 1 per cent of benzoate of soda declared; color red; good odor; few fungi; clean and free from refuse.

No. 33.– Opened October 24, 1907; age unknown; one-tenth of 1 per cent of benzoate of soda declared; spoiled November 1; pint bottle (14 ounces); sweetish odor; brown color; many molds, yeast and bacteria. Price 10 cents.

No. 114.– Same brand as No. 33; said to be manufactured in 1907; opened in April; not spoiled in seventy days; many molds, yeasts, and bacteria; some green tissue, and filaments of algæ. The price was 10 cents.

SUMMARY

1. The experiments made during the season of 1907 on the manufacture of tomato ketchup without chemical preservatives were conducted under factory conditions and upon a commercial scale. The results prove that such a ketchup can be made and delivered to the consumer in perfect condition; the product in question having already stood ten months, unopened, without showing the slightest indication of spoilage.

2. The product is of excellent consistency, flavor, and color. The formula employed regularly in the factory where the experiment was conducted was used, but other recipes could be adapted without changing the character of special brands. In the manufacture of such a product the following precautions were observed:

(a) Whole, sound, ripe tomatoes and high-grade salt, sugar, vinegar, and spices were used; care and cleanliness were observed at every step of the preparation, and the preservation accomplished by heat in the following manner: The pulp was cooked in a steam kettle for about forty minutes, until the mass was reduced to about one-half its volume. Additional processing after bottling did not appear to be necessary to keep the ketchup before opening, and had no effect in these experiments in delaying spoilage after opening.

(b) Ketchup was bottled directly from the cooker at a temperature of 205° F. in bottles prepared in two ways: (1) Sterilized in a steam chamber at 230° F.; (2) Washed in hot water, rinsed, and heated to 190° F. in a dry heat for at least thirty minutes. Ketchup was also bottled after the usual process of sieving at 165° F. in bottles prepared in a similar manner. The corks for all bottles were sterilized in a paraffin bath at 270° F. The same ketchup which was bottled at 165° F. was also given subsequent processing at 190° F. and 212° F. for twenty and forty minutes. All have kept without spoilage.

3. Some of the condiments have a limited antiseptic value, but can not be depended upon to prevent spoilage in the quantities used for flavoring. While sugar and vinegar can be added in such amounts as to delay the appearance of molds, and cinnamon and cloves can be depended upon to check deterioration to some extent, these condimental substances have only an incidental value for this purpose.

4. The spoilage of ketchup after opening depends more upon the temperature of the place in which it is kept than on any variation in the manner of processing. Fresh ketchup held, after opening, at a temperature of 95° F. kept for five days on an average without any trace of mold appearing; at 72° it kept for six days; at 67° for eight days; about 46° (refrigerator), fourteen days; and at from 30° to 60° for twenty-seven days. These figures represent the time at which the first trace of spoilage occurred in the neck of the bottle – had this been removed the figures would be much increased – and by no means represent the maximum time during which the ketchup could have been used, the maximum figures, even under these conditions of observation, varying from eight to fifty-eight days. The keeping of the ketchup in warm storage at 70° for one hundred and fifty days before opening hastened the average time of spoilage after opening about one day. The advisability of using small containers, to get the best results with a first-class ketchup, is apparent.

5. Sodium benzoate, even when used in the proportion of 0.1 per cent, is not always effective, and has an injurious effect upon the living matter of the molds, shown by the distortion and swelling of the filaments, which are filled with a coarse granular protoplasm containing much fat.