- Email: [email protected]
Experiments on the Freezing of Poultry
EXPERIMENTS ON THE FREEZING OF POULTRY 1951. The influence of various levels of penicillin and streptomycin on rate of growth and feed efficiency in broiler diets. Poultry Sci. 30: 929-930. Scott, H. M., L. D. Matterson and E. P. Singsen, 1947. Nutritional factors influencing growth and efficiency of feed utilization. 1. The effect of the source of carbohydrate. Poultry Sci. 26: 554.
383
Singsen, E. P., H. M. Scott and L. D. Matterson, 1948. The effect of sulfaquinoxaline on growth rate and feed efficiency of chicks. Poultry Sci. 27: 627-628. Stckstad, E. L. R., and T . H. Jukes, 1950. Further observations on the "animal protein factor." Proc. Soc. Exp. Biol. Med. 73: 523-528.
Experiments on the Freezing of Poultry E. S. SNYDER, J. H. L. TRUSCOTT AND E. R. WAYGOOD (Received for publication July 11, 1951)
T
HIS paper reports the results of a series of experiments on the freezing of chicken with an over-all objective of discovering the effects of freezing and storage on palatability. 1. EFFECT OF T I M E AND TEMPERATURE ON PALATABILITY
Materials and General Procedure The poultry used in most of the experiments were one-year-old Barred Plymouth Rock hens from a flock raised at the Poultry Department. These hens were laying and were fat. In addition some birds were used at the fryer stage. Two or three birds constituted an experimental unit and a total of 193 birds was used. The birds were killed and dressed at the Poultry Department from May 7-9, 1946. Each day's kill was refrigerated at 32°F. overnight at the Department of Horticulture and processed there the next day. Birds cooked before freezing were eviscerated in the morning, cooked in the afternoon, cooled overnight at 45°F., and packaged and frozen the next morning. Evisceration was done by splitting along the back bone, followed by thorough washing. After processing, each bird was wrapped in a heat-sealed cellophane envelope and placed in individual cardboard boxes which were over-wrapped with heat
sealed cellophane (M.T.S. 300). Freezing was done after the birds were packaged and each package was placed so that the refrigerated air had contact on all surfaces except where the package was in contact with a slatted shelf. Each bird was tagged, trussed and weighed before packaging. Three storage temperatures were utilized in the Department of Horticulture: 15°, 0° and - 1 0 ° F . The first two temperatures were controlled within a 1° range; the third temperature varied between - 7 and - 10°F. Lots of birds were removed from storage for examination at approximately 4month intervals, the last on July 9, 1947, after about 13 months storage. The birds were weighed immediately after removal from storage and, in representative instances, the ice crystals accumulated in the cellophane envelope were weighed. The weighing of the birds in the cellophane envelopes before freezing and after removal from storage was carried out in order to obtain some indication of moisture loss, but with no intention of a critical study. Observations were made on the incidence of freezer burn. The birds were defrosted overnight at 45°F., without covering, on shelves. Those requiring it, were drawn the next morning and
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
Departments of Poultry Husbandry and Horticulture, Ontario Agricultural College, Guelph, Ontario, Canada
384
E. S. SNYDER, J. H. L. TRUSCOTT AND E. R. WAYGOOD TABLE 1.—Outline of experiments with frozen chickens (Pre-storage treatment, storage temperature and method of defrosting)
No. of birds 9 9 9
Dressed
Drawn
Cooked
Stuffed
f^p"°¥
Storage temp. °F.
Age of bird Fowl Fowl Fowl
Expt. 2—Tests of Stuffing Mixtures 1 X mix 1 X mix 1 X mix 2 X mix 2 X mix 3 X mix 3 X mix 4 X mix 1 X mix 1 X mix 1 X mix 1
-10 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
0 0 0 0 0 0 0 IS -10 IS -10
Fowl Fowl Fowl Fowl Fowl Fowl Fowl Fowl Fowl Fowl Fowl
Expt. 3—Methods of Defrosting2 X Defrost 1 X Defrost 1 X Defrost 2 X Defrost 2 X . Defrost 3 X Defrost 3 X Defrost 4 X Defrost 4
-10 -10 -10 -10 -10 -10 -10 -10
0 0 0 0 0 0 0 0
Fowl Fowl Fowl Fowl Fowl Fowl Fowl Fowl
Expt. 4—Comparison of Fryers and Fowl X -10 X -10
0 0
Fryer Fowl
X X X X X X X X X X X X X X X X X X X
9 9
X X
9
X
Expt. 5—Disjointed Fryers Packaged X
-10
0
Fryer
18
X
Expt. 5—Disjointed Fryers Packaged X
9 9 9 9 9 9 9 9 1
X X . X X X X X X
-10
0
Fryer
Expt. 6—Giblets3—Packaged vs. in situ Freezing -10
0
Fowl
Expt. 7—Rate of Freezing Effects X X X X
-10 -10 IS 15
0 0 0 0
Fowl Fowl Fowl Fowl
Expt. 8—Storage Temperature Effects X -10 X -10 -10 X -10 X
15 15 -10 -10
Fowl Fowl Fowl Fowl
1 --bread, onions, sage, fat and salt. 2—bread, peanuts, raisins, fat and salt. 3—bread, sausage meat and salt. 4—cooked potatoes, onions, sage, fat and salt. 2 Defrosting Method 1—In air at 45°F. (used as standard). 2—In air blast at 70°F. 3—In cold, running water. 4—In the cooking oven. 'Hearts, livers and gizzards. Stuffing Mixture;
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
Expt. 1--Effect of Storage Period on Dressed, Drawn and Cooked Frozen Fowl. X X -10 0 X X -10 0 -10 0 X X
3 3 3 3 3 3 3 3 3 3 3 2 2 2 2 2 2 2 2
Raw
EXPERIMENTS ON THE FREEZING OF POULTRY
I t was found that the fowls were not tender enough when roasted in an open pan. Consequently the subsequent lots, removed from storage, were cooked in loosely covered pans with added water. The electric oven was not available and a gas-fired oven was used with these lots. A professional cook cooked these birds without direction. They were smeared with melted pork fat rendered from pork roasts that day and were cooked at about 350°F. in pans which were covered loosely for about four-fifths of the period. The chef decided when the cooking was sufficient. The birds were cooled overnight at 45°F. and tasted the next morning. Birds cooked before freezing were held overnight at 45°F. after removal from storage. Before 9 a.m. on the day following cooking or defrosting, the birds were laid out, in triplicate, on tables in their various groups. A thigh and the breast of each bird was laid open with a knife and bits of flesh were cut from the open surface for testing. The taste panel consisted of 8-12 men and women, all of whom had a
professional interest in foods but who were not especially experienced in poultry meat tasting. Each panel member was requested to note and describe the taste of individual birds or groups which they considered to be abnormal or different in taste to any other individual or groups of birds. Individual records were made and a subsequent general discussion followed in order to definitely reveal unanimity or difference of opinion. An outline of the various experiments with the frozen birds showing pre-storage treatment, storage temperature, method of defrosting et cetera is given in Table 1. Results and Discussions Freezer burn varied at the 4 month examination from a few inconspicuous spots to many areas each about \ of an inch in diameter. There was no evident relationship between weight loss or amount of ice crystals in the cellophane envelope and the intensity of freezer burn. There appeared to be as much variation in freezer burn within an experimental unit as there was between experiments, and observation of all the birds led to the conclusion that the differences were individual bird differences not caused by experimental factors. Freezer burn had increased slightly by 8 months of storage, but there was little or no further increase at the 13-month examination. There was little evidence of freezer burn in any of the packages containing dissected birds. Evidence of freezer burn disappeared during cooking. Water losses as evidenced by "before and after" weighings of the birds within the cellophane envelopes varied from 1 ounce to less than | ounce at 4 months, with an average of \ ounce per bird. At 8 months the variation was from l i ounces
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
those birds, which had not been cooked prior to freezing, were cooked during the afternoon of the day after removal from storage. The first group was removed for examination on September 25, 1946 (approximately 4 months storage). Cooking, when required, was done in an electrical, manually-operated oven by one of the authors (J.H.L.T.). The birds were smeared liberally with visceral fat (melted in boiling water) and roasted in open pans at a temperature of about 300°F. The spatial variation in oven temperature was about 25°F., and the pans were moved twice during the cooking period. The cooking^ period varied with the weights of the birds and was judged by the tenderness of the birds.
385
386
E. S. SNYDER, J. H. L. TRUSCOTT AND E. R. WAYGOOD TABLE 2.—Weight losses from birds stored 13 months
Bird
Dressed Dressed Dressed Dressed Drawn Drawn Drawn Cooked Cooked Cooked Stuffed & Stuffed & Stuffed & Stuffed & Stuffed &
Cooked Cooked Cooked Cooked Cooked
Gross
Gross
"out" weight
"in" weight lb. 4 4 4 5 3 3 4 2 2 2 3 3 3 4 4
oz. 4 64 9 14 12 124 3 3 11 14 1 3 8 0
to I ounce, with an average of about 1 ounce. The weight losses at 13 months were similar to those at 8 months (Table 2). The weight of ice crystals within the envelope was noted in a few instances at the first two observations, but several weighings of ice crystals were made at the 13-month examination. They are shown in Table 2. Weight losses from packages containing the parts of two birds averaged about 2 ounces. The weight of ice crystals within the envelope was not associated with the amount of freezer burn, for there were several instances of the larger amounts of crystals associated with very minor burn. It would appear that the amount of ice crystals from raw birds was an individual bird factor. The largest amounts of crystals were associated with stuffed cooked birds.
i
lb. 4 4 4 5 3 3 3 2 2 2 3 3 3 3 4
oz. 3| 64 8f 13f Hi 12J 12i 124 104 131 0 z
2
74 154 i 2
Ice crystal weight
Total loss
gm. 9 9 9 9 9 2 4 4 4 4 20 15 47 10 10
gm. 16 9 9 16 16 9 11 18 18 11 48 29 54 24 10
Taste Panel Observations
test, but there was no indication that any experimental procedure had influenced the flavour. The three fresh-killed birds used as controls, represented as great a flavour range as was noted in the frozen birds. At the 8-month test, the degree of difference between birds had decreased, while at the 13-month test there was a remarkable uniformity in all of the frozen birds. Again, fresh-killed birds exhibited individual flavour characteristics. At the 13-month test the panel was asked to note especially the group of birds held at 15°F. in comparison with those held at — 10°F., without knowing the identity of either group. There was uniformity of opinion that the — 10°F. stored birds were slightly better flavoured than those held at + 15°F. The panel could not distinguish between birds stored at 0°F. and — 10°F., or between birds frozen in a blast of air at — 10°F. and those frozen in still air at 15°F.
The panel members were in complete agreement on the following points: (1) That there was a very considerable individual bird difference in the flesh flavour characteristics at the 4-month
Under the conditions of the experiment, all of the birds retained excellent flavour condition during 13 months storage, and they reached a state of remarkable uniformity of flavour.
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
1A9 1A7 1A8 7C2 7D2 1B8 1B9 1C8 1C9 1C7 2C3 2E3 2G3 2A3 2L3
Pre-storage process
EXPERIMENTS ON THE FREEZING or POULTRY
The bread-onion-sage stuffing was characterized by a gradual but almost complete elimination of the sage flavour, and a decided reduction in onion flavour at 3 months. The onion flavour was strong and somewhat off-flavoured at 4 months. This commonly used stuffing mixture was rated palatable at all three examinations. Chemical determination of the course of fat oxidation (see Part 2) indicated that there was an increase in the amount of oxidation of internal fat, the effect being most marked in the fat which had been in contact with the stuffing mixtures. No determinations were made on the stuffing mixtures and it was in these stuffings that the taste panel noted the initial development of a flavour described as rancidity, and noted its subsequent elimination as the storage term progressed. No off-flavour was detected in the flesh of the stuffed birds. Thus the degree of oxidation indicated by chemical tests, was not detected by any member of the panel. (3) Young birds (fryers) stored as well as older birds (fowl), and dissected fryers stored in excellent condition for 13 months. The only point of disagreement within the taste panel concerned frozen livers. Livers removed before freezing were washed and packaged in cellophane bags, placed in waxed cardboard boxes and
overwrapped with cellophane. (These packages were designed for frozen fruit.) They were frozen at — 10°F. and stored at 0°F. They were tested in comparison with livers frozen in situ at — 10°F. and stored at 0°F. Some members of the panel preferred the in situ livers and some the packaged livers. There was a great variation in the fattiness and flavour of individual livers. Frozen gizzards, livers and hearts were indistinguishable from fresh ones. Birds defrosted in air at 45°F., in air at 70°F.; in cold, running tap water; and in the cooking oven were indistinguishable when cooked, in the opinion of the taste panel. Summary Barred Plymouth Rock hens, 1 year old, fat and in good laying condition, were dressed, then frozen either dressed, drawn or stuffed. The drawn and the stuffed birds were frozen, both raw and cooked, at — 10°F. and 15°F. in individual packages. Four stuffing mixtures included, between them, the more common ingredients used for such purposes: bread crumbs, nuts, raisins, onion, sage, salt, fat, sausage meat, and cooked potatoes. Whole and dismembered fryers were also frozen both raw and cooked, for comparison with the flesh of older birds. There was no indication of palatability deterioration in the flesh of any bird during 13 months of storage at either 0°F. or 15°F. Individual bird flavours became less marked as storage time progressed, until at the end of 13 months there was a conspicuous uniformity of flavour. Pork sausage meat and nuts in stuffings exhibited marked off-flavour at 4 months, less at 8 months, and with the nut stuffing, no off-flavour at 13 months. The sausage meat was still not palatable at 13 months but it was decidedly improved as compared to the 4-month examination.
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
(2) A finding of considerable interest concerned rancidity or bitterness in two of the stuffing mixtures. It resembled the rancid flavour which develops in fat. The stuffing containing peanuts was inedible when cooked after 4-months storage. That containing pork sausage meat was decidedly unpalatable after the same period. A distinct improvement in the flavour of both stuffings was noted after 8-months storage, and, after 13-months storage, the nut stuffing was normal and the sausage meat stuffing was greatly improved in flavour.
387
388
E. S. SNYDER, J. H. L. TRUSCOTT AND E. R. WAYGOOD
2. PEROXIDE OXYGEN FORMATION I N STORED POULTRY FATS
TABLE 3.—Effect of method of drying and nitrogen treatment in analytical procedure
Introduction
Analytical Procedure s. Preparation of the Sample for Analysis. id The extraction procedure of Cook and w White (1939) was followed with a few emodifications. The visceral fat was re;ri . moved from the bird, placed in a petri n. dish, and stored at — 10°F. until frozen. The frozen fat was chopped finely with aa ts stainless steel knife, mixed with 50% of its id weight of anhydrous sodium sulphate, and le placed in a fat-free Soxhlet thimble. The in thimble and contents were then placed in ;d a wide mouth Erlenmeyer flask, covered 5with petroleum ether (Benzine, B. P. 3560°C.), and allowed to stand overnight in in as a darkened room at 40°F. The extract was id then filtered into an evaporating dish and id placed on a steam bath until the ether had
Ml. 0.002N Sodium thiosulphate per gram fat
Dried in vacuo at 104°F. plus nitrogen treatment
4.03 4.15
Dried in dessicator at - 10°F. plus nitrogen treatment
4.00 4.20
Dried in vacuo at 104°F. minus nitrogen treatment
4.10 4.20
completely evaporated. At first the samples were dried in vacuo at 104°F., but later this procedure was omitted since no significant error was introduced (Table 3). The extracted fat was then placed in a desiccator at — 10°F., to await analysis. Peroxide Oxygen Determination. A modification of the determination of French, Olcott and Mattill (1935) based on the iodometric procedure of Lea (1931) was used. The oxygen formed by the decomposition of the peroxide oxygen in the fat liberates iodine from potassium iodide, and the iodine liberated is estimated by titration with standard sodium thiosulphate, using starch as the indicator. The following procedure was tested against both methods and gave similar results, Approximately 1 gram of fat was placed in a tared glass vial and weighed accurately. The vial and contents were then dropped into a 125 ml. Erlenmeyer flask. Fifteen ml. of acetic acid-chloroform mixture (2:1 by volume), and approximately 1 gm. of powdered potassium iodide, were added. The flask was then fitted with a holed rubber stopper and immediately plunged into a boiling water bath and shaken continuously for 1 minute. The nitrogen treatment at this stage to exclude atmospheric oxygen was found to be unnecessary providing no time was wasted in carrying out the procedures after the addition of potassium iodide
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
It is difficult, if not impossible, to detect the degree of chemical changes occurring in stored fats until the so-called "induction period" is completed and the offflavours or rancidity become evident. It is generally agreed that rancidity is associated with the oxidative and hydrolytic chemical changes occurring in stored fat, and that peroxide oxygen and free fatty acid formation are a measure of these chemical changes (Lea, 1929; White, . 1941). Cook and White (1939) found that . the free fatty acid content of poultry fat after storage is usually low and shows no relation to storage conditions but, on the other hand, peroxide oxygen formation . was susceptible to storage environment. j* Therefore it was deemed advisable to follow the peroxide oxygen formation of the • fats of the poultry stored as outlined in Part 1, and, if possible, to substantiate the organoleptic tests carried on at the same time.
Treatment
389
EXPERIMENTS ON THE FREEZING OF POULTRY
Results The effect of the method of drying the sample prior to analysis and omission of the nitrogen treatment employed by previous workers (Cook and White, 1939; French et al., 1935; and Lea, 1931) was studied on a sample of fat which was showing some peroxide oxygen formation. The results are shown in Table 3, and indicate that both the drying treatment in vacuo and subsequent nitrogen treatment to exclude atmospheric oxygen were superfluous. Formation of Peroxide Oxygen in Fat Held at Room Temperature. A large sample of fat was obtained from chickens during the initial cooking process. Part of the fat was extracted in the usual manner and both samples were placed in a large flatbottomed dish and allowed to stand on the laboratory table with access to air. Organoleptic and peroxide oxygen tests were conducted at frequent intervals. Unfortunately the extracted fat was lost accidentally and tests on this sample had to be discontinued. The results are shown in Table 4.
TABLE 4.—Peroxide oxygen formation in extracted and unextracted fat held at room temperature (Fat seeped from chickens during cooking) Ml. 0.002N sodium thiosulphate per gram fat Time (days)
Unextracted fat
Extracted fat
Flavour
0
6
10
17
27
3.11 3.10 3.09
3.24 3.30
5.30 5.40 5.40
8.5b 8.70
17.1 13.4 16.5
—
2.86 2.92
4.40 3.90 4.80
—
—
Sweet
Sweet
Sweet
Sweet
Off
Initially the fat showed some peroxide oxygen content, presumably due to the heat treatment experienced. Peroxide oxygen formation was negligible in the first 6 days in the unextracted fat, but thereafter increased until the 27 th day when an offflavour was noticed. This sample contained a quantity of extraneous material which could affect the peroxide oxygen formation and also produce the off-flavour which was not likened to rancidity in itstrue sense. Unfortunately the figures for extracted fat do not show this stage, but it can be seen that the extraneous material accounted for approximately 20% of the peroxide oxygen formation in the earlier stages. These results, while not giving any indication of the amount of peroxide oxygen coincident with rancidity, serve to show its rapid development at room temperature, when exposed to atmospheric oxygen. Peroxide Oxygen Formation in Stored Fat. The majority of the tests were concerned with the chickens stored under the conditions of Experiment 1, Part 1. However, other tests were made and the results are assembled in Table 5. The fat from freshly killed chickens was tested at each 4-month interval, but none showed any peroxide oxygen formation. The only stored fat of those tested which showed no peroxide oxygen formation over the 13-
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
(Table 3). The flask was then cooled under running water, with the index finger placed over the hole in the stopper to prevent access of air to the mixture. After cooling to room temperature, 50 ml. of air-free distilled water and 3 drops of starch indicator were added. The mixture was then titrated with 0.002N sodium thiosulphate. If iodine is liberated from potassium iodide, a blue color appears and the endpoint of the titration is a change in colour from blue to white. Generally, tests were made first on an unweighed sample of fat and, if negative, the quantitative determination was unnecessary. The results are expressed in the usual manner as ml. 0.002N sodium thiosulphate per gram of fat.
390
E. S. SNYDER, J. H. L. TRUSCOTT AND E. R. WAYGOOD
T A B L E 5.—Effect of storage time and treatment on peroxide oxygen formation in fat of stored poultry Storage temp. °F. Sample No.
Frozen at
Stored at
M l . 0.002N sodium thiosulphate per gm. fat Time (months) 0
4
8
13
0
0
0
0
0.68 0.80
0
0
9.25 8.54
— —
3.07 2.50
—
-10
0
1A cooked
-10
0
IB
-10
0
I B cooked
-10
0
IC
-10
0
0
—
10.50 11.21
19.30 21.20
2A
-10
0
0
—
—
32.10 29.50
2B 2C 7A 7C 8A 8C 'resh fat
-10 -10 -10 +15 -10 -10
0 0 0 0 +15 -10
0 0
0
0
'at stored*
— — 0
—
0
0 0 0 0 0
0
0
0
—
—
2.06 1.88
1A—dressed, not drawn. IB—Drawn before storage. IC— drawn before storage. IC—drawn and cooked before storage. 2A—stuffed and cooked before storage, type 1 dressing. 2B stuffed, not cooked before storage, type 1 dressing. 2C—stuffed and.cooked before storage, type 2 dressing. 7A—not drawu, frozen at —10°F. 7C—not drawn, frozen Cat +15°F. 8A—not drawn, frozen at —10°F., stored at +15 F. 8C—not drawn, frozen at — 10°F., stored at — 10°F. *The fat was stored in wax paper at 0°F.
month storage period was that in fowl, dressed but not drawn (Table 5, 1A). The maximum peroxide oxygen formation was found in the fat of fowl stuffed and cooked before storage (Table 5, 2A). In general, the greatest development was associated with the fat from birds cooked prior to storage. Those fats not cooked before storage but analyzed after having been cooked at the 8-month period, showed a small titration value. Initially and after 4 months in storage, peroxide oxygen formation was nil in all samples tested, and these included samples of fat from birds stored at 15°F. and - 1 0 ° F . (Table 5, 8A and 8C). Presumably, the freezing temperature has little effect on its formation after 4 months (Table 5, 7A and 7C). None of the fats analyzed throughout the experiment had any offflavours, rancidity, or tallowiness. Fat re-
Discussion and Conclusions The results show that the process of cooking has a definite effect on the formation of peroxide oxygen in poultry fats. The partially extracted fat which seaped from freshly cooked birds showed some peroxide oxygen formation and it seems probable that this heat treatment is a greater factor in its formation than frozen storage temperatures. Birds drawn prior to storage showed more susceptibility to oxidation changes than those not drawn. This may be due to both a disturbance of the fatty tissue and easier accessibility of oxygen to such tissues. Organoleptic tests conducted on stored fats indicated no off-flavours and, therefore, it is still impossible to. state the amount of peroxide oxygen formation associated with rancidity. Lea (1933) found that bacon fat became rancid when the titration value reached 8-10 ml. These results confirm his presumption that much higher values are required before rancidity can be detected in poultry fats (Lea, 1934) Cook and White (1939) found that little or no peroxide oxygen was formed in the fat of birds stored in temperatures ranging from —13.5° to — 7.5°F., and even after 25 months of storage the maximum titration value observed was 8 ml. Figures obtained in our work indicate that this temperature range can be raised to 15°F. for a 4-month period with no peroxide oxygen formation, but values considerably higher than theirs were observed in the fat of birds which had been stuffed with various mixtures, over a 13-month period. It is true perhaps that the oxidative changes are not a function of temperature below 15°F.
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
1A
moved from birds at the beginning of the experiment (May 1946), and stored in waxed paper at 0°F. for 13 months, showed some peroxide oxygen formation.
THYROPEOTEIN AND PRODUCTION
It is concluded that poultry fats are particularly resistant to the chemical changes associated with oxidative rancidity and that these may proceed to relatively high values without noticeable effect of the sweetness of the fat! REFERENCES
Lea, C. H., 1929. Rancidity in edible fats. Dept. Sci. Ind. Res., F.I.B.: 30-31. Lea, C. H., 1931. Effect of light on the oxidation of fats. Proc. Roy. Soc. B, 108: 175-189. Lea, C. H., 1933. Chemical changes in the fat of frozen and chilled meat. V. The effect of smoking and the influence of atmospheric humidity on the keeping properties of bacon. J. Soc. Chem. Ind. 52:57-63T. Lea, C. H., 1934. Cold storage of poultry. II. Chemical changes in the fat of gas-stored chickens. J. Soc. Chem. Ind. 53: 347-349T. White, W. H., 1941. Methods for the investigation of rancidity, their interrelation, and application to bacon fat. Can. J. Res. 19: 278-293.
Effect of Thyroprotein on Egg Production, Egg Weight and Body Weight of Chickens During Summer MOHAMED M . OLOUFA College of Agriculture, Cairo University, Egypt (Received for publication September 11, 1952)
I
N Egypt, egg production is the lowest during July and August, which are the hottest months of the year. Reineke and Turner (1945), Turner et al. (1945b) and Turner (1948a) found that thyroxine secretion started to decline in May at a time when egg production began to decrease. They concluded that the seasonal cycle of egg production was due in part to a reduced secretion of thyroxine during summer. While Turner et al. (1945a, b, 1946 and 1947) found that egg production was maintained at a higher level than the control by feeding thyroprotein during the hot months of the year, Wilson (1949) stated that thyroprotein did not prevent the decline in egg production due to high ambient temperature. On the other hand, Hutt and Gowe (1948), Godfrey (1949) and Berg and Bearse (1951) found that feeding thyroprotein caused a depression in the rate of lay during summer. With the exception of Blaxter et al. (1949) who stated that egg weight de-
clined during hyperthyroidism, feeding thyroprotein was without effect on the weight of eggs (Turner et al., 1945a; Hoffman and Wheeler, 1948; Turner, 1948b; and Berg and Bearse, 1951). Gutteridge and Novikoff (1947), Hoffman and Wheeler (1948) and Berg and Bearse (1951) found that feeding thyroprotein resulted in an improvement in egg shell strength. Investigators also agree that thyroprotein caused a loss in body weight (Turner et al., 1945a, 1946; Hoffman and Wheeler, 1948; and Berg and Bearse, 1951). The purpose of the present investigation was to study the effect of feeding thyroprotein during July and August on egg production, egg weight, egg shell thickness and body weight of Egyptian chickens. EXPERIMENTAL
A total of 204 Egyptian hens were used on the farm of the Animal Husbandry Department, College of Agriculture, Cairo University. They were in their first, second or third laying season. The hens were
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
Cook, W. H., and W. H. White, 1939. Frozen storage of poultry. III. Peroxide oxygen and free fatty acid formation. Food Res. 4: 433-440. French, R. B., H. S. Olcott and H. A. Mattill, 1935. Antioxidants and the antioxidation of fats. III. Ind. Eng. Chem. (Anal. Ed.) 27: 724-728.
391
383
Singsen, E. P., H. M. Scott and L. D. Matterson, 1948. The effect of sulfaquinoxaline on growth rate and feed efficiency of chicks. Poultry Sci. 27: 627-628. Stckstad, E. L. R., and T . H. Jukes, 1950. Further observations on the "animal protein factor." Proc. Soc. Exp. Biol. Med. 73: 523-528.
Experiments on the Freezing of Poultry E. S. SNYDER, J. H. L. TRUSCOTT AND E. R. WAYGOOD (Received for publication July 11, 1951)
T
HIS paper reports the results of a series of experiments on the freezing of chicken with an over-all objective of discovering the effects of freezing and storage on palatability. 1. EFFECT OF T I M E AND TEMPERATURE ON PALATABILITY
Materials and General Procedure The poultry used in most of the experiments were one-year-old Barred Plymouth Rock hens from a flock raised at the Poultry Department. These hens were laying and were fat. In addition some birds were used at the fryer stage. Two or three birds constituted an experimental unit and a total of 193 birds was used. The birds were killed and dressed at the Poultry Department from May 7-9, 1946. Each day's kill was refrigerated at 32°F. overnight at the Department of Horticulture and processed there the next day. Birds cooked before freezing were eviscerated in the morning, cooked in the afternoon, cooled overnight at 45°F., and packaged and frozen the next morning. Evisceration was done by splitting along the back bone, followed by thorough washing. After processing, each bird was wrapped in a heat-sealed cellophane envelope and placed in individual cardboard boxes which were over-wrapped with heat
sealed cellophane (M.T.S. 300). Freezing was done after the birds were packaged and each package was placed so that the refrigerated air had contact on all surfaces except where the package was in contact with a slatted shelf. Each bird was tagged, trussed and weighed before packaging. Three storage temperatures were utilized in the Department of Horticulture: 15°, 0° and - 1 0 ° F . The first two temperatures were controlled within a 1° range; the third temperature varied between - 7 and - 10°F. Lots of birds were removed from storage for examination at approximately 4month intervals, the last on July 9, 1947, after about 13 months storage. The birds were weighed immediately after removal from storage and, in representative instances, the ice crystals accumulated in the cellophane envelope were weighed. The weighing of the birds in the cellophane envelopes before freezing and after removal from storage was carried out in order to obtain some indication of moisture loss, but with no intention of a critical study. Observations were made on the incidence of freezer burn. The birds were defrosted overnight at 45°F., without covering, on shelves. Those requiring it, were drawn the next morning and
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
Departments of Poultry Husbandry and Horticulture, Ontario Agricultural College, Guelph, Ontario, Canada
384
E. S. SNYDER, J. H. L. TRUSCOTT AND E. R. WAYGOOD TABLE 1.—Outline of experiments with frozen chickens (Pre-storage treatment, storage temperature and method of defrosting)
No. of birds 9 9 9
Dressed
Drawn
Cooked
Stuffed
f^p"°¥
Storage temp. °F.
Age of bird Fowl Fowl Fowl
Expt. 2—Tests of Stuffing Mixtures 1 X mix 1 X mix 1 X mix 2 X mix 2 X mix 3 X mix 3 X mix 4 X mix 1 X mix 1 X mix 1 X mix 1
-10 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
0 0 0 0 0 0 0 IS -10 IS -10
Fowl Fowl Fowl Fowl Fowl Fowl Fowl Fowl Fowl Fowl Fowl
Expt. 3—Methods of Defrosting2 X Defrost 1 X Defrost 1 X Defrost 2 X Defrost 2 X . Defrost 3 X Defrost 3 X Defrost 4 X Defrost 4
-10 -10 -10 -10 -10 -10 -10 -10
0 0 0 0 0 0 0 0
Fowl Fowl Fowl Fowl Fowl Fowl Fowl Fowl
Expt. 4—Comparison of Fryers and Fowl X -10 X -10
0 0
Fryer Fowl
X X X X X X X X X X X X X X X X X X X
9 9
X X
9
X
Expt. 5—Disjointed Fryers Packaged X
-10
0
Fryer
18
X
Expt. 5—Disjointed Fryers Packaged X
9 9 9 9 9 9 9 9 1
X X . X X X X X X
-10
0
Fryer
Expt. 6—Giblets3—Packaged vs. in situ Freezing -10
0
Fowl
Expt. 7—Rate of Freezing Effects X X X X
-10 -10 IS 15
0 0 0 0
Fowl Fowl Fowl Fowl
Expt. 8—Storage Temperature Effects X -10 X -10 -10 X -10 X
15 15 -10 -10
Fowl Fowl Fowl Fowl
1 --bread, onions, sage, fat and salt. 2—bread, peanuts, raisins, fat and salt. 3—bread, sausage meat and salt. 4—cooked potatoes, onions, sage, fat and salt. 2 Defrosting Method 1—In air at 45°F. (used as standard). 2—In air blast at 70°F. 3—In cold, running water. 4—In the cooking oven. 'Hearts, livers and gizzards. Stuffing Mixture;
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
Expt. 1--Effect of Storage Period on Dressed, Drawn and Cooked Frozen Fowl. X X -10 0 X X -10 0 -10 0 X X
3 3 3 3 3 3 3 3 3 3 3 2 2 2 2 2 2 2 2
Raw
EXPERIMENTS ON THE FREEZING OF POULTRY
I t was found that the fowls were not tender enough when roasted in an open pan. Consequently the subsequent lots, removed from storage, were cooked in loosely covered pans with added water. The electric oven was not available and a gas-fired oven was used with these lots. A professional cook cooked these birds without direction. They were smeared with melted pork fat rendered from pork roasts that day and were cooked at about 350°F. in pans which were covered loosely for about four-fifths of the period. The chef decided when the cooking was sufficient. The birds were cooled overnight at 45°F. and tasted the next morning. Birds cooked before freezing were held overnight at 45°F. after removal from storage. Before 9 a.m. on the day following cooking or defrosting, the birds were laid out, in triplicate, on tables in their various groups. A thigh and the breast of each bird was laid open with a knife and bits of flesh were cut from the open surface for testing. The taste panel consisted of 8-12 men and women, all of whom had a
professional interest in foods but who were not especially experienced in poultry meat tasting. Each panel member was requested to note and describe the taste of individual birds or groups which they considered to be abnormal or different in taste to any other individual or groups of birds. Individual records were made and a subsequent general discussion followed in order to definitely reveal unanimity or difference of opinion. An outline of the various experiments with the frozen birds showing pre-storage treatment, storage temperature, method of defrosting et cetera is given in Table 1. Results and Discussions Freezer burn varied at the 4 month examination from a few inconspicuous spots to many areas each about \ of an inch in diameter. There was no evident relationship between weight loss or amount of ice crystals in the cellophane envelope and the intensity of freezer burn. There appeared to be as much variation in freezer burn within an experimental unit as there was between experiments, and observation of all the birds led to the conclusion that the differences were individual bird differences not caused by experimental factors. Freezer burn had increased slightly by 8 months of storage, but there was little or no further increase at the 13-month examination. There was little evidence of freezer burn in any of the packages containing dissected birds. Evidence of freezer burn disappeared during cooking. Water losses as evidenced by "before and after" weighings of the birds within the cellophane envelopes varied from 1 ounce to less than | ounce at 4 months, with an average of \ ounce per bird. At 8 months the variation was from l i ounces
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
those birds, which had not been cooked prior to freezing, were cooked during the afternoon of the day after removal from storage. The first group was removed for examination on September 25, 1946 (approximately 4 months storage). Cooking, when required, was done in an electrical, manually-operated oven by one of the authors (J.H.L.T.). The birds were smeared liberally with visceral fat (melted in boiling water) and roasted in open pans at a temperature of about 300°F. The spatial variation in oven temperature was about 25°F., and the pans were moved twice during the cooking period. The cooking^ period varied with the weights of the birds and was judged by the tenderness of the birds.
385
386
E. S. SNYDER, J. H. L. TRUSCOTT AND E. R. WAYGOOD TABLE 2.—Weight losses from birds stored 13 months
Bird
Dressed Dressed Dressed Dressed Drawn Drawn Drawn Cooked Cooked Cooked Stuffed & Stuffed & Stuffed & Stuffed & Stuffed &
Cooked Cooked Cooked Cooked Cooked
Gross
Gross
"out" weight
"in" weight lb. 4 4 4 5 3 3 4 2 2 2 3 3 3 4 4
oz. 4 64 9 14 12 124 3 3 11 14 1 3 8 0
to I ounce, with an average of about 1 ounce. The weight losses at 13 months were similar to those at 8 months (Table 2). The weight of ice crystals within the envelope was noted in a few instances at the first two observations, but several weighings of ice crystals were made at the 13-month examination. They are shown in Table 2. Weight losses from packages containing the parts of two birds averaged about 2 ounces. The weight of ice crystals within the envelope was not associated with the amount of freezer burn, for there were several instances of the larger amounts of crystals associated with very minor burn. It would appear that the amount of ice crystals from raw birds was an individual bird factor. The largest amounts of crystals were associated with stuffed cooked birds.
i
lb. 4 4 4 5 3 3 3 2 2 2 3 3 3 3 4
oz. 3| 64 8f 13f Hi 12J 12i 124 104 131 0 z
2
74 154 i 2
Ice crystal weight
Total loss
gm. 9 9 9 9 9 2 4 4 4 4 20 15 47 10 10
gm. 16 9 9 16 16 9 11 18 18 11 48 29 54 24 10
Taste Panel Observations
test, but there was no indication that any experimental procedure had influenced the flavour. The three fresh-killed birds used as controls, represented as great a flavour range as was noted in the frozen birds. At the 8-month test, the degree of difference between birds had decreased, while at the 13-month test there was a remarkable uniformity in all of the frozen birds. Again, fresh-killed birds exhibited individual flavour characteristics. At the 13-month test the panel was asked to note especially the group of birds held at 15°F. in comparison with those held at — 10°F., without knowing the identity of either group. There was uniformity of opinion that the — 10°F. stored birds were slightly better flavoured than those held at + 15°F. The panel could not distinguish between birds stored at 0°F. and — 10°F., or between birds frozen in a blast of air at — 10°F. and those frozen in still air at 15°F.
The panel members were in complete agreement on the following points: (1) That there was a very considerable individual bird difference in the flesh flavour characteristics at the 4-month
Under the conditions of the experiment, all of the birds retained excellent flavour condition during 13 months storage, and they reached a state of remarkable uniformity of flavour.
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
1A9 1A7 1A8 7C2 7D2 1B8 1B9 1C8 1C9 1C7 2C3 2E3 2G3 2A3 2L3
Pre-storage process
EXPERIMENTS ON THE FREEZING or POULTRY
The bread-onion-sage stuffing was characterized by a gradual but almost complete elimination of the sage flavour, and a decided reduction in onion flavour at 3 months. The onion flavour was strong and somewhat off-flavoured at 4 months. This commonly used stuffing mixture was rated palatable at all three examinations. Chemical determination of the course of fat oxidation (see Part 2) indicated that there was an increase in the amount of oxidation of internal fat, the effect being most marked in the fat which had been in contact with the stuffing mixtures. No determinations were made on the stuffing mixtures and it was in these stuffings that the taste panel noted the initial development of a flavour described as rancidity, and noted its subsequent elimination as the storage term progressed. No off-flavour was detected in the flesh of the stuffed birds. Thus the degree of oxidation indicated by chemical tests, was not detected by any member of the panel. (3) Young birds (fryers) stored as well as older birds (fowl), and dissected fryers stored in excellent condition for 13 months. The only point of disagreement within the taste panel concerned frozen livers. Livers removed before freezing were washed and packaged in cellophane bags, placed in waxed cardboard boxes and
overwrapped with cellophane. (These packages were designed for frozen fruit.) They were frozen at — 10°F. and stored at 0°F. They were tested in comparison with livers frozen in situ at — 10°F. and stored at 0°F. Some members of the panel preferred the in situ livers and some the packaged livers. There was a great variation in the fattiness and flavour of individual livers. Frozen gizzards, livers and hearts were indistinguishable from fresh ones. Birds defrosted in air at 45°F., in air at 70°F.; in cold, running tap water; and in the cooking oven were indistinguishable when cooked, in the opinion of the taste panel. Summary Barred Plymouth Rock hens, 1 year old, fat and in good laying condition, were dressed, then frozen either dressed, drawn or stuffed. The drawn and the stuffed birds were frozen, both raw and cooked, at — 10°F. and 15°F. in individual packages. Four stuffing mixtures included, between them, the more common ingredients used for such purposes: bread crumbs, nuts, raisins, onion, sage, salt, fat, sausage meat, and cooked potatoes. Whole and dismembered fryers were also frozen both raw and cooked, for comparison with the flesh of older birds. There was no indication of palatability deterioration in the flesh of any bird during 13 months of storage at either 0°F. or 15°F. Individual bird flavours became less marked as storage time progressed, until at the end of 13 months there was a conspicuous uniformity of flavour. Pork sausage meat and nuts in stuffings exhibited marked off-flavour at 4 months, less at 8 months, and with the nut stuffing, no off-flavour at 13 months. The sausage meat was still not palatable at 13 months but it was decidedly improved as compared to the 4-month examination.
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
(2) A finding of considerable interest concerned rancidity or bitterness in two of the stuffing mixtures. It resembled the rancid flavour which develops in fat. The stuffing containing peanuts was inedible when cooked after 4-months storage. That containing pork sausage meat was decidedly unpalatable after the same period. A distinct improvement in the flavour of both stuffings was noted after 8-months storage, and, after 13-months storage, the nut stuffing was normal and the sausage meat stuffing was greatly improved in flavour.
387
388
E. S. SNYDER, J. H. L. TRUSCOTT AND E. R. WAYGOOD
2. PEROXIDE OXYGEN FORMATION I N STORED POULTRY FATS
TABLE 3.—Effect of method of drying and nitrogen treatment in analytical procedure
Introduction
Analytical Procedure s. Preparation of the Sample for Analysis. id The extraction procedure of Cook and w White (1939) was followed with a few emodifications. The visceral fat was re;ri . moved from the bird, placed in a petri n. dish, and stored at — 10°F. until frozen. The frozen fat was chopped finely with aa ts stainless steel knife, mixed with 50% of its id weight of anhydrous sodium sulphate, and le placed in a fat-free Soxhlet thimble. The in thimble and contents were then placed in ;d a wide mouth Erlenmeyer flask, covered 5with petroleum ether (Benzine, B. P. 3560°C.), and allowed to stand overnight in in as a darkened room at 40°F. The extract was id then filtered into an evaporating dish and id placed on a steam bath until the ether had
Ml. 0.002N Sodium thiosulphate per gram fat
Dried in vacuo at 104°F. plus nitrogen treatment
4.03 4.15
Dried in dessicator at - 10°F. plus nitrogen treatment
4.00 4.20
Dried in vacuo at 104°F. minus nitrogen treatment
4.10 4.20
completely evaporated. At first the samples were dried in vacuo at 104°F., but later this procedure was omitted since no significant error was introduced (Table 3). The extracted fat was then placed in a desiccator at — 10°F., to await analysis. Peroxide Oxygen Determination. A modification of the determination of French, Olcott and Mattill (1935) based on the iodometric procedure of Lea (1931) was used. The oxygen formed by the decomposition of the peroxide oxygen in the fat liberates iodine from potassium iodide, and the iodine liberated is estimated by titration with standard sodium thiosulphate, using starch as the indicator. The following procedure was tested against both methods and gave similar results, Approximately 1 gram of fat was placed in a tared glass vial and weighed accurately. The vial and contents were then dropped into a 125 ml. Erlenmeyer flask. Fifteen ml. of acetic acid-chloroform mixture (2:1 by volume), and approximately 1 gm. of powdered potassium iodide, were added. The flask was then fitted with a holed rubber stopper and immediately plunged into a boiling water bath and shaken continuously for 1 minute. The nitrogen treatment at this stage to exclude atmospheric oxygen was found to be unnecessary providing no time was wasted in carrying out the procedures after the addition of potassium iodide
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
It is difficult, if not impossible, to detect the degree of chemical changes occurring in stored fats until the so-called "induction period" is completed and the offflavours or rancidity become evident. It is generally agreed that rancidity is associated with the oxidative and hydrolytic chemical changes occurring in stored fat, and that peroxide oxygen and free fatty acid formation are a measure of these chemical changes (Lea, 1929; White, . 1941). Cook and White (1939) found that . the free fatty acid content of poultry fat after storage is usually low and shows no relation to storage conditions but, on the other hand, peroxide oxygen formation . was susceptible to storage environment. j* Therefore it was deemed advisable to follow the peroxide oxygen formation of the • fats of the poultry stored as outlined in Part 1, and, if possible, to substantiate the organoleptic tests carried on at the same time.
Treatment
389
EXPERIMENTS ON THE FREEZING OF POULTRY
Results The effect of the method of drying the sample prior to analysis and omission of the nitrogen treatment employed by previous workers (Cook and White, 1939; French et al., 1935; and Lea, 1931) was studied on a sample of fat which was showing some peroxide oxygen formation. The results are shown in Table 3, and indicate that both the drying treatment in vacuo and subsequent nitrogen treatment to exclude atmospheric oxygen were superfluous. Formation of Peroxide Oxygen in Fat Held at Room Temperature. A large sample of fat was obtained from chickens during the initial cooking process. Part of the fat was extracted in the usual manner and both samples were placed in a large flatbottomed dish and allowed to stand on the laboratory table with access to air. Organoleptic and peroxide oxygen tests were conducted at frequent intervals. Unfortunately the extracted fat was lost accidentally and tests on this sample had to be discontinued. The results are shown in Table 4.
TABLE 4.—Peroxide oxygen formation in extracted and unextracted fat held at room temperature (Fat seeped from chickens during cooking) Ml. 0.002N sodium thiosulphate per gram fat Time (days)
Unextracted fat
Extracted fat
Flavour
0
6
10
17
27
3.11 3.10 3.09
3.24 3.30
5.30 5.40 5.40
8.5b 8.70
17.1 13.4 16.5
—
2.86 2.92
4.40 3.90 4.80
—
—
Sweet
Sweet
Sweet
Sweet
Off
Initially the fat showed some peroxide oxygen content, presumably due to the heat treatment experienced. Peroxide oxygen formation was negligible in the first 6 days in the unextracted fat, but thereafter increased until the 27 th day when an offflavour was noticed. This sample contained a quantity of extraneous material which could affect the peroxide oxygen formation and also produce the off-flavour which was not likened to rancidity in itstrue sense. Unfortunately the figures for extracted fat do not show this stage, but it can be seen that the extraneous material accounted for approximately 20% of the peroxide oxygen formation in the earlier stages. These results, while not giving any indication of the amount of peroxide oxygen coincident with rancidity, serve to show its rapid development at room temperature, when exposed to atmospheric oxygen. Peroxide Oxygen Formation in Stored Fat. The majority of the tests were concerned with the chickens stored under the conditions of Experiment 1, Part 1. However, other tests were made and the results are assembled in Table 5. The fat from freshly killed chickens was tested at each 4-month interval, but none showed any peroxide oxygen formation. The only stored fat of those tested which showed no peroxide oxygen formation over the 13-
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
(Table 3). The flask was then cooled under running water, with the index finger placed over the hole in the stopper to prevent access of air to the mixture. After cooling to room temperature, 50 ml. of air-free distilled water and 3 drops of starch indicator were added. The mixture was then titrated with 0.002N sodium thiosulphate. If iodine is liberated from potassium iodide, a blue color appears and the endpoint of the titration is a change in colour from blue to white. Generally, tests were made first on an unweighed sample of fat and, if negative, the quantitative determination was unnecessary. The results are expressed in the usual manner as ml. 0.002N sodium thiosulphate per gram of fat.
390
E. S. SNYDER, J. H. L. TRUSCOTT AND E. R. WAYGOOD
T A B L E 5.—Effect of storage time and treatment on peroxide oxygen formation in fat of stored poultry Storage temp. °F. Sample No.
Frozen at
Stored at
M l . 0.002N sodium thiosulphate per gm. fat Time (months) 0
4
8
13
0
0
0
0
0.68 0.80
0
0
9.25 8.54
— —
3.07 2.50
—
-10
0
1A cooked
-10
0
IB
-10
0
I B cooked
-10
0
IC
-10
0
0
—
10.50 11.21
19.30 21.20
2A
-10
0
0
—
—
32.10 29.50
2B 2C 7A 7C 8A 8C 'resh fat
-10 -10 -10 +15 -10 -10
0 0 0 0 +15 -10
0 0
0
0
'at stored*
— — 0
—
0
0 0 0 0 0
0
0
0
—
—
2.06 1.88
1A—dressed, not drawn. IB—Drawn before storage. IC— drawn before storage. IC—drawn and cooked before storage. 2A—stuffed and cooked before storage, type 1 dressing. 2B stuffed, not cooked before storage, type 1 dressing. 2C—stuffed and.cooked before storage, type 2 dressing. 7A—not drawu, frozen at —10°F. 7C—not drawn, frozen Cat +15°F. 8A—not drawn, frozen at —10°F., stored at +15 F. 8C—not drawn, frozen at — 10°F., stored at — 10°F. *The fat was stored in wax paper at 0°F.
month storage period was that in fowl, dressed but not drawn (Table 5, 1A). The maximum peroxide oxygen formation was found in the fat of fowl stuffed and cooked before storage (Table 5, 2A). In general, the greatest development was associated with the fat from birds cooked prior to storage. Those fats not cooked before storage but analyzed after having been cooked at the 8-month period, showed a small titration value. Initially and after 4 months in storage, peroxide oxygen formation was nil in all samples tested, and these included samples of fat from birds stored at 15°F. and - 1 0 ° F . (Table 5, 8A and 8C). Presumably, the freezing temperature has little effect on its formation after 4 months (Table 5, 7A and 7C). None of the fats analyzed throughout the experiment had any offflavours, rancidity, or tallowiness. Fat re-
Discussion and Conclusions The results show that the process of cooking has a definite effect on the formation of peroxide oxygen in poultry fats. The partially extracted fat which seaped from freshly cooked birds showed some peroxide oxygen formation and it seems probable that this heat treatment is a greater factor in its formation than frozen storage temperatures. Birds drawn prior to storage showed more susceptibility to oxidation changes than those not drawn. This may be due to both a disturbance of the fatty tissue and easier accessibility of oxygen to such tissues. Organoleptic tests conducted on stored fats indicated no off-flavours and, therefore, it is still impossible to. state the amount of peroxide oxygen formation associated with rancidity. Lea (1933) found that bacon fat became rancid when the titration value reached 8-10 ml. These results confirm his presumption that much higher values are required before rancidity can be detected in poultry fats (Lea, 1934) Cook and White (1939) found that little or no peroxide oxygen was formed in the fat of birds stored in temperatures ranging from —13.5° to — 7.5°F., and even after 25 months of storage the maximum titration value observed was 8 ml. Figures obtained in our work indicate that this temperature range can be raised to 15°F. for a 4-month period with no peroxide oxygen formation, but values considerably higher than theirs were observed in the fat of birds which had been stuffed with various mixtures, over a 13-month period. It is true perhaps that the oxidative changes are not a function of temperature below 15°F.
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
1A
moved from birds at the beginning of the experiment (May 1946), and stored in waxed paper at 0°F. for 13 months, showed some peroxide oxygen formation.
THYROPEOTEIN AND PRODUCTION
It is concluded that poultry fats are particularly resistant to the chemical changes associated with oxidative rancidity and that these may proceed to relatively high values without noticeable effect of the sweetness of the fat! REFERENCES
Lea, C. H., 1929. Rancidity in edible fats. Dept. Sci. Ind. Res., F.I.B.: 30-31. Lea, C. H., 1931. Effect of light on the oxidation of fats. Proc. Roy. Soc. B, 108: 175-189. Lea, C. H., 1933. Chemical changes in the fat of frozen and chilled meat. V. The effect of smoking and the influence of atmospheric humidity on the keeping properties of bacon. J. Soc. Chem. Ind. 52:57-63T. Lea, C. H., 1934. Cold storage of poultry. II. Chemical changes in the fat of gas-stored chickens. J. Soc. Chem. Ind. 53: 347-349T. White, W. H., 1941. Methods for the investigation of rancidity, their interrelation, and application to bacon fat. Can. J. Res. 19: 278-293.
Effect of Thyroprotein on Egg Production, Egg Weight and Body Weight of Chickens During Summer MOHAMED M . OLOUFA College of Agriculture, Cairo University, Egypt (Received for publication September 11, 1952)
I
N Egypt, egg production is the lowest during July and August, which are the hottest months of the year. Reineke and Turner (1945), Turner et al. (1945b) and Turner (1948a) found that thyroxine secretion started to decline in May at a time when egg production began to decrease. They concluded that the seasonal cycle of egg production was due in part to a reduced secretion of thyroxine during summer. While Turner et al. (1945a, b, 1946 and 1947) found that egg production was maintained at a higher level than the control by feeding thyroprotein during the hot months of the year, Wilson (1949) stated that thyroprotein did not prevent the decline in egg production due to high ambient temperature. On the other hand, Hutt and Gowe (1948), Godfrey (1949) and Berg and Bearse (1951) found that feeding thyroprotein caused a depression in the rate of lay during summer. With the exception of Blaxter et al. (1949) who stated that egg weight de-
clined during hyperthyroidism, feeding thyroprotein was without effect on the weight of eggs (Turner et al., 1945a; Hoffman and Wheeler, 1948; Turner, 1948b; and Berg and Bearse, 1951). Gutteridge and Novikoff (1947), Hoffman and Wheeler (1948) and Berg and Bearse (1951) found that feeding thyroprotein resulted in an improvement in egg shell strength. Investigators also agree that thyroprotein caused a loss in body weight (Turner et al., 1945a, 1946; Hoffman and Wheeler, 1948; and Berg and Bearse, 1951). The purpose of the present investigation was to study the effect of feeding thyroprotein during July and August on egg production, egg weight, egg shell thickness and body weight of Egyptian chickens. EXPERIMENTAL
A total of 204 Egyptian hens were used on the farm of the Animal Husbandry Department, College of Agriculture, Cairo University. They were in their first, second or third laying season. The hens were
Downloaded from http://ps.oxfordjournals.org/ at Edinburgh University on June 9, 2015
Cook, W. H., and W. H. White, 1939. Frozen storage of poultry. III. Peroxide oxygen and free fatty acid formation. Food Res. 4: 433-440. French, R. B., H. S. Olcott and H. A. Mattill, 1935. Antioxidants and the antioxidation of fats. III. Ind. Eng. Chem. (Anal. Ed.) 27: 724-728.
391