Bacteriological examination of fresh and cold-storage chickens-Continued.

By M. E. PENNINGTON, In charge, Food Research Laboratory, Philadelphia.

INTRODUCTION.

The results to be set forth in the following pages represent a preliminary study, on the broadest possible lines, of the action of low temperatures on foodstuffs, more especially those rich in protein, such as meat from various animals, poultry, fish, eggs, etc. study would seem to be a necessity to the well-being of the people

Such a

of the United States because of the almost universal use and enormous increase within recent years of cold-stored food products of varied kinds and from many sources.

The progressive cold-storage warehousemen are also eager for scientifically acquired data, that they may improve their product thereby. From the point of view of pure science the field for investigation would seem to be almost limitless and filled to overflowing with information most interesting and valuable to the chemist, bacteriologist, and histologist. The domain of the study is so vast,

and the factors which must be considered in the correlation and interpretation of results are so numerous and far reaching in their effects, that the question has not been "What phase of the problem shall be investigated?", but, rather, "Which question can be deferred with least injury to the interpretation of the results already obtained?”, since all seem to be interdependent and must be taken into account when any individual question is under consideration.

In view of the fact that this field of investigation is almost barren of reported results and because of its diversified interests, it has seemed better to make a general study of the chemical, bacteriological, and histological conditions prevailing in the case of some standard coldstored product rather than to follow any one line of scientific work, though such a procedure would have made possible the addition of many details now waiting to be investigated. Poultry in general, and chickens in particular, have been selected as objects for study, not only because they are of enormous economic value, but, being small, highly organized, and easily obtained they would seem to be eminently suited to the present investigation.

With the extravagant advocacy of the advantages of cold storage, as claimed by some of those commercially interested on the one side, and the increasing prejudice against cold-stored foods in the minds of the laity on the other, this discussion can not deal. Suffice it to say that such contradictory statements led to the macroscopic examination of chickens which, intended for the general market, had been for varying lengths of time in cold storage, a comparison being made with fresh chickens of like breed and age.

The results of such observations would seem to demonstrate that, in appearance, odor, and texture of the flesh, long storage at low temperatures causes a variation from the normal fresh bird, and also that the changes which do occur slowly and requiring long periods are not comparable with those occurring rapidly and at ordinary temperatures. A discussion of the macroscopic changes, particularly those which might be observed by the housewife, has already been published. A logical sequence of such a study is the microscopic examination of the tissues of such chickens, their chemical analysis, and a

a Yearbook of the U. S. Department of Agriculture, 1907.

determination of their bacterial content, on which may depend their fitness for food. The work reported will, therefore, be classified as chemical, bacteriological, and histological; the technique employed and the results obtained for these phases of the subject will be given. under their respective headings; and the general discussion of the results, with, as far as is possible at this time, a correlation of the data relating to the changes, will be brought together in a final chapter.

CHEMICAL STUDIES.

RÉSUMÉ OF THE LITERATURE ON THE CHEMICAL COMPOSITION OF

POULTRY.

An examination of the literature relating to the chemical composition of poultry in general, and of chickens in particular, reveals a paucity of analytical data. Such analyses as are given usually relate to the gross composition of the birds, comprising the amount of water, nitrogen, fat, nitrogen-free extractives, and ash.

König has brought together in tabular form analyses made by Stutzer, Moleschott, König, Krauch and Allendorff, and Atwater and Woods, aggregating seven in all. As mean percentage values for the flesh of chickens König gives the following:

In connection with a study of the meat supply in Tennessee, C. E. Wait reports analyses of 20 chickens purchased in the open market in that State.

Atwater and Bryant in their summary of the chemical composition of American food materials, give average data for analyses of chicken and other domestic poultry and of the gizzard, heart, etc.

Atwater later reported a number of additional analyses of poultry. He examined, as a nutrition study, the carcasses of representatives of most classes of edible, domesticated birds. His analyses treat not only of the meat, but also of the giblets, the entire fowl, and the meat and giblets together, the latter being the truly edible portion. Only the analyses of the meat are available for comparison with the results obtained in this laboratory and the average data

a Chemie der menschlichen Nahrungs- und Genussmittel, 1903.

Calculated by difference.

cU. S. Dept. Agr., Office of Experiment Stations, Bul. 53.

d U. S. Dept. Agr., Office of Experiment Stations, Bul. 28,

e

The Composition of Poultry, Storrs Agricultural Experiment Station, 15th Annual Report, 1903.

are quoted. On one chicken separate analyses of light and dark meat were made, as will be observed in the table. There has been no attempt, however, to separate or determine the various kinds of nitrogenous bodies which go to make up the sum total of the protein. For further details those interested are referred to the original of Atwater's valuable communication.

Zaitscheck gives an analysis of the fat of two chickens, one of which has been fed on corn and the other on corn and milk. His results are as follows:

Analysis of fat from corn fed, and milk and corn fed chickens (Zaitscheck).

Zaitscheck concludes that the food has influenced the composition of the fat, the fowl on the corn and milk ration showing values nearer those of butter fat than the results found for the chicken fed on corn alone an observation, which, if borne out by further experimentation, is of considerable physiologic interest.

As is to be expected from the small number of analyses recorded, a lack of harmony in technique, and in the use of fowls of unknown age, breed, and previous history, there is a wide variation in results. That the analyses of the flesh of animals so highly organized as are chickens should have an exact and fixed composition is scarcely to be expected, even when breed, food, age, and the length of time between killing and examining are the same. That very wide differences do occur when such factors as have been mentioned are not taken into account is not only reasonable, but has been demonstrated by certain analyses given later in this report.

SELECTION OF MATERIAL FOR STŮDY.

Since the work which has been undertaken is a comparison of the flesh of chickens kept by the aid of low temperatures for varying lengths of time, it is necessary that there should first be an acquaintance with the composition of fresh fowls of known history and of the breeds commonly found in the markets. The species most frequently kept for food purposes in the Middle States are the Plymouth Rock (white and barred), White Wyandotte, Rhode Island Red, and Leghorn. The last-named species is especially valuable for egg production. The birds are too small and the breast muscles are not sufficiently well developed to render them as desirable for market purposes as are the other breeds, but because of their laying qualities they are fairly plentiful, and young cocks and old hens are therefore killed off and sold for food.

As the cold-stored fowls which are to be discussed were taken from regular market stock and are, almost exclusively, of the Plymouth Rock variety, or its crossbreeds, the discussion of the composition of fresh chickens will be limited accordingly.

The birds kept for standards of comparison were fed chiefly on Indian corn, milk, and clean table scraps. They were regularly and abundantly fed, were supplied with pure water, and their runs were placed in an orchard having a southern exposure, this environment insuring rapid growth and tender flesh. For 24 hours previous to killing all food was withheld, but water in plenty was provided. They were killed by puncturing the spinal cord by way of the mouth, and were bled well, dry picked, and the animal heat was quickly extracted. They were kept for from 18 to 24 hours at the temperature of an ordinary refrigerator before the analysis was begun, that being the period required for a frozen chicken to thaw in a house refrigerator. All were undrawn.