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Spoilage of Washed Eggs
Spoilage of Washed Eggs 1. EFFECT OF SPRAYED VERSUS STATIC WATER UNDER DIFFERENT WASHING TEMPERATURES F. W. LORENZ AND PHOEBE BETTY STARR
Division of Poultry Husbandry, University of California, Davis, California (Received for publication May 19, 1951)
HE adverse effect of washing on the resistance of eggs to spoilage is well known. Nevertheless, washing remains a common practice, and, with the development of various methods of machine washing, is becoming even more widespread. Some machines have made washing easier even than segregating clean from soiled eggs; consequently, many poultrymen wash the entire production of their flocks, paying, at the same time, less than normal attention to the ordinary practices of poultry-house cleanliness. Published reports on egg washing have been so almost uniformly unfavorable that one would have thought additional investigation of the subject to be unprofitable. The subject is complicated, however, by the frequent appearance of new washing devices together with remarkable claims by some manufacturers. It is also complicated by not infrequent and apparently bona fide reports of satisfactory results with packs of washed eggs from individual ranches. There has thus been a tendency in some segments of the poultry industry to discount previous reports on the effects of washing eggs and to blame almost anything except washing for egg spoilage, or at least to place responsibility on certain methods only, holding others to be blameless. Nevertheless, serious losses have been the rule in areas where the practice of egg washing is prevalent. These considerations led to the under-
taking, here, of a project on egg spoilage of which the present paper is a partial report. The purpose of this paper is to discuss the results of several laboratory experiments on washing eggs by various methods and using various types of equipment. In these trials the primary objective was to determine the amount of egg spoilage resulting from different methods of washing during subsequent cold storage. LITERATURE REVIEW
Discussion of the relation of any method of egg washing to spoilage involves consideration of the mechanism of egg infection. This subject has received considerable attention; early work has been reviewed extensively by Hadley and Caldwell (1916), and more recently Haines has made notable contributions (1938a, 1938b, 1939, 1940; also Haines and Moran, 1940). Agreement is fairly general that egg infection with spoilage-producing organisms prior to ovi-position is practically non-existent. Infection occurs through the egg shell and most spoilage is produced by a limited group of organisms commonly found in soil and poultry feces. Most of these are small motile rods. These organisms cannot, apparently, penetrate the dry shell. According to Haines (1938a) they do not penetrate even the wet shell readily unless the cuticle has previously been disturbed. Some results of the present authors (to be published elsewhere) throw
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SPOILAGE OF WASHED EGGS
dustry practice is thus twofold. In the first place, cleaning eggs (by whatever method) may hide previously infected eggs in the pack, and spoilage may result from this cause alone if the eggs are held long enough under conditions conducive to bacterial growth. The second consideration relates to additional infection that may occur during, or as a result of, the washing process. Previous reports on the effects of egg washing are almost uniform in their condemnation of the practice because of the increased numbers of infected and/or frankly spoiled eggs found in washed lots, in spite of variation in results and interpretation. Thus Jenkins, and Pennington (1919) attributed a large proportion of bad eggs in cold storage "to the presence of eggs which at some time previous to storage had had wet shells, because of washing or for some other reason." They concluded: "Attempts therefore to improve the appearance of dirty eggs by washing is a practice which cannot be too strongly condemned." Jenkins et al. (1920) found striking increases in bacterial spoilage during" cold storage in experimentally washed eggs that had been sponged with a damp cloth, washed directly in water, or similarly washed and rinsed in 0.25% sulphuric acid. Unwashed dirty eggs contained more spoiled eggs than did clean eggs, but only about half as many as there were in washed eggs. Bryant and Sharp (1934) by contrast, found bacteria in as many unwashed dirty eggs as in washed eggs. Their bacteriological technique was admittedly not optimum, however, since other measurements were made on the same eggs, and the exceptionally high incidence of yolk infections suggests the possibility that the high values may have been spurious and due to contamination after breakout.
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doubt on the latter conclusion. Admittedly, however, Haines' data are striking. He soaked clean, fresh eggs for an hour in a suspension of Pseudomonas sp. containing 5 X104 cells per ml. and produced no spoilage, whereas similar eggs so treated except that they had previously been soaked for 1 minute in warm water, scrubbed with a brush and soap for l j minutes, rinsed in distilled water and dried with a clean glasscloth, spoiled to the extent of 40% within 14 days at 20°C. The importance of pressure differentials produced by the contraction of the egg contents as it cools is generally recognized. Bacteria, in the presence of moisture, may presumably be aspirated through the pores as the egg cools. Infection of eggs soiled in the nest may thus occur within a very short time after laying. Stuart and McNally (1943) demonstrated Pseudomonas aeruginosa in the albumen of newly laid (still warm) eggs within very few minutes after they had been swabbed with a liquefied gelatin culture of this organism. Whether bacteria can penetrate the shell subsequently {i.e., after the soil has dried and the shell has cooled) is highly questionable unless moisture is again applied. Even the clean shell has a very considerable bacterial flora and yet spoilage of such eggs is very rare. To be sure, the physical presence of a considerable layer of dirt over some part of the shell might change the local moisture relation sufficiently to allow bacterial penetration through the pores. Some data suggesting that this may occasionally occur will be presented elsewhere. In all probability, however, most infection occurs at the time of soiling or very shortly thereafter, unless the egg is later moistened (e.g. by condensation or by washing) under contions favorable to penetration. The problem of egg washing as an in-
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egg temperature during washing resulted in fewer infected eggs than were obtained when internal pressure was decreased during the washing procedure. Grizmek (1936) dry-cleaned eggs and observed good storage quality in both cleaned and control dirty eggs. He concluded that spoilage is a result of washing rather than of original soilage. However, in a comparison of dry cleaning and washing made by Zurek (1938) considerable spoilage was observed in both drycleaned and washed eggs and also in uncleaned dirty eggs but not in clean eggs held untreated as controls. A statement by the Egg Producers Council and the Council for Scientific and Industrial Research of New South Wales (1942) summarized the major results of extensive experiments on washing. They concluded that bacterial rotting of eggs in commerce was almost entirely due to washing. More spoilage was found in eggs washed on various types of machines than in hand-washed eggs, but both methods yielded variable results. The statement stressed the importance of cleanliness in either method, and pointed to "certain types of machines" (not further described) that were responsible for especially severe spoilage. In a further summary discussion of the same investigation Sayers (1943) placed especial emphasis on bacterial contamination of the washing machine itself as a primary cause of egg spoilage. He pointed out that "a machine may appear to be scrupulously clean yet be seriously infected with harmful bacteria." Disinfectant dips after machine cleaning were completely ineffective, but any method of reducing the bacterial contamination of the machine itself such as effective disinfectants, or drying the machines thoroughly between uses, served to reduce spoilage. Experience with a large
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They washed both clean and dirty eggs in lots of 1 to 3 dozen with plain water and with several different chemical agents. None of the compounds used gave less infected eggs than plain water, and at least one (an alkaline detergent) apparently gave more, though the significance of the observed differences between treatments is doubtful and the authors did not stress them. Haines (1938a) presented evidence based on small numbers of hand-washed eggs, that washing under "clean" conditions does not result in bacterial penetration and spoilage, but that washing does render the egg more susceptible to penetration if it is subsequently soaked in a bacterial suspension. On the other hand, Moran (1939) reported that washing by any method increases the number of rots during subsequent handling and storage. He further stated that markedly alkaline washing solutions produce the greatest numbers of rots. Wagner (1936) reported increases in bacterial content and spoilage in eggs washed in various solutions. Specific bacteria present in the wash water were detected in the eggs after 4 weeks storage. Funk (1938) reported that dirty eggs cleaned with sodium hydroxide solutions kept as well in storage as clean unwashed eggs. But in 1948 he presented data which contradicted these findings. In the latter paper extensive evidence was presented condemning all methods of surface cleaning of eggs that are to be stored. These methods included variations of water temperature and disinfectant solutions, dry cleaning, and washing followed by heat treatment. Thermostabilizing following washing did reduce spoilage however. Pritsker (1941), using hatchability as a criterion, presented evidence that increasing internal pressure by increasing
SPOILAGE OF WASHED EGGS
Pino (1950) reported that eggs so washed maintain an internal quality equal to that of untreated eggs kept under the same storage conditions. MATERIALS AND METHODS
Machine A has rubber rollers that turn the eggs end-over-end against rubber backboards until they are clean, at which time they are manually removed. The eggs may be wetted either by a tank of static water into which the rollers dip or by water sprayed over the eggs as they turn. Cleaned eggs are racked on a CarPro lifter and dried in a stream of heated air. Machine B has towel-covered screwtype rollers and towel-covered backboards. Eggs are carried along one roller, wetted in the same manner as Machine A, and carried back by a dry roller in a stream of heated air. The Rutgers method was tested as described above and also with a solution dirtied with chicken droppings to simulate conditions after a considerable number of eggs had been dipped. After spraying, the baskets of eggs were dried overnight in an egg room at 15°C. Each test consisted of washing 5 cases of heavy dirties and a half case of clean eggs. The clean eggs were all from the flock of a nearby producer, selected from current production for these tests. The heavy dirties were selected by candlers at a nearby receiving station from current deliveries. Between each test the machine was cleaned as thoroughly as possible by scrubbing it with hot water and detergent, and rinsing with hot water. The clean eggs were always washed first on the "clean" machine; the heavy dirties were washed immediately after. Three dozen from each case of the latter were taken at random and set aside for storage, so
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number of trials apparently led to considerable pessimism, however, that any method could (or would) be applied to any machine of which he had experience, that would yield a satisfactory pack. Johns and Berard (1946) again found no increase in numbers of infected eggs among those that were experimentally hand-washed. They did observe, however, an increased average bacterial count in the contents of such eggs. They stressed the importance of soil organisms as compared with intestinal organisms in producing spoilage, and produced additional spoilage by applying mud to shells already soiled with feces. This observation and its implication of ground soil as the important source of egg contamination may help to explain some discrepancies in data previously reported. More recently, Davidson et al. (1950) stored current receipt eggs that had been ranch-washed by different methods, buffed, or delivered uncleaned. Washed eggs contained 4.3% sour eggs (as determined by breaking out) while unwashed clean eggs contained 0.9%. None of the washing practices used on the various farms "resulted in the elimination of egg souring or in reducing this loss to the level attained by storing naturally clean eggs." Miller et al. (1950) demonstrated the spoilage-producing effect of a high bacterial count in the wash water, and the ineffectiveness of disinfectant rinses after washing. They also presented evidence that oil processing washed eggs reduced the number of black rots but not of green or mixed rots. Black (1949) described the so-called "Rutgers method" of washing, which consists of twice dipping baskets of eggs momentarily into a hot (65-71°C.) solution of anionic detergent, then spraying them with hot clean water and setting them in a cool place to drain and dry.
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F. W. LORENZ AND PHOEBE BETTY STARR
* There is some disagreement over the classification and terminology of different types of egg spoilage and the related bacteriology. This subject will be reviewed more extensively elsewhere, but for the present consideration should at least be given use of the term "sour." This term was used by Pennington et al. (1914) to designate a type of spoilage that
ent stage of the same condition in which the albumen was fluorescent but in which abnormal odors had not yet developed. Non-fluorescent spoilage included black, red and mixed rot and sour* eggs. Under the term mold are recorded a wide variety of conditions, including moldy air cells, black and red spots and rings inside the shell, and mycelia-filled hemispherical lumps of cohered albumen, with or without some greater or lesser degree of disintegration of the egg contents. Eggs were not recorded as moldy, however, unless there was positive gross evidence of penetration of mold through the shell. Fluorescent spots or patches on the shell membrane were not infrequently observed in eggs that showed no other obvious signs of infection. Fluorescent pseudomonads could usually be isolated from such patches, and sometimes, but only rarely from the non-fluorescent albumen of these eggs. Consequently, such spots are considered to be the first gross evidence of penetration of Pseudomonas organisms and thus of fluorescent spoilage that would have occurred later had the egg been held longer. produced a pungent odor and sometimes a turbidity of the white and a weakened yolk membrane, but no other readily detectable alteration of the egg, and attributed by them to a predominately coliform infection. Common usage, however, has also applied the term to a type of spoilage that is characterized by fluorescent albumen, and odors which have been variously described as sour, fishy, cheesey, fruity, or cabbage-water. Some of these eggs may have crusted yolks, liquefied, stringy albumen and/or pink spots on the yolk or inside the shell. This latter type of spoilage is due to infection of the egg with Pseuiomonas organisms and is probably identical with or very similar to egg spoilage that has previously been variously called grass eggs, eggs with green whites or green rot, but these terms are not entirely descriptive and have been used for other, entirely different egg abnormalities. To avoid further confusion this type of spoilage will be designated here as fluorescent-sour, or simply as fluorescent spoilage.
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that the sample stored for each test was a half case of washed clean eggs and a half case of washed heavy dirties. For each two tests (one day's normal operation) an additional half case of clean eggs was held unwashed and a half case of heavy dirties was selected at random from the 10 cases handled that day and also held unwashed. These two half cases served as controls for that day's experiments. The top, middle and bottom layers of each half-case sample were oil processed by dipping momentarily in a commercial processing oil at room temperature. The other two layers were left natural. All eggs were stored for 6 months in a commercial cold-storage warehouse at -0.5°C. and 85-88% relative humidity. After removal from storage and tempering to allow condensed moisture to evaporate, all eggs were candled, and twelve eggs from a pre-designated position in each layer were set aside at room temperature (20-26°C.) for two weeks. The remainder of the eggs were broken out at once. The eggs were broken into petri dishes and examined for gross appearance and odor. Immediately thereafter the egg contents and inner surfaces of the shells were examined under ultra-violet light for fluorescence. Spoilage, when present, was classified as fluorescent and non-fluorescent types and spoilage due to mold. Some mixed infections of mold and fluorescent pigment producing bacteria were recognized. The fluorescent spoilage included a type of sour* egg and an incipi-
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SPOILAGE OF WASHED EGGS TABLE 1.—Effect of washing eggs on subsequent spoilage after 6 months cold storage Pooled results from bath and spray at 3 temperatures; 3/5 oil processed, 2/5 natural eggs in each group; sound eggs only Original condition
No No Yes Yes
Fluorescent spoilage Shell spots only
Spoiled eggs
With mold
Mold
Total bacterial spoilage
Total mold
Total microbial loss
No.
%
%
%
%
%
%
%
%
531 499 595 567
0 0 0 0.35
0.56 2.20 2.35 4.59
0.19 1.20 0.17 2.29
0 0.20 0 0
0 2.40 0.17 0.18
0.19 1.40 0.17 2.65
0 2.60 0.17 0.18
0.19 4.00 0.34 2.83
apparent from inspection of these tables. First are the detrimental effects both of dirt originally on the shell and of washing on the resistance of eggs to microbial invasion. Clean unwashed eggs had the lowest microbial loss in every category listed in Tables 1 and 2. These effects are at least partially independent since washing increased the spoilage both of clean and of dirty eggs. Washing and original soilage were important both for bacterial and for mold invasion, but with the latter an additional factor—the continued presence of dirt on the shell—apparently came into play. Washing the heavy dirties reduced the number of moldy eggs almost to the level of the washed clean eggs. The effect of holding eggs at room temperature (compare Tables 1 and 2) was
Eggs with checked and sound shells are considered separately. The interpretation of spoilage of the former eggs is complicated because of the difficulty of determining whether infection was made easier by pre-existing breaks in the shell or whether the break may have resulted from the infection. All checks that could be found were removed during the washing procedure, but some were doubtless missed, others could have developed during subsequent handling. RESULTS Trials with machine A were designed to compare sprayed vs. static water and various water temperatures. Spoilage of the sound shelled eggs washed in machine A is recorded in Tables 1 and 2. Certain generalizations are immediately TABLE 2.—Effect
of washing eggs on subsequent spoilage after 6 months in storage plus 2 weeks at room temperature Pooled results from bath and spray at 3 temperatures; 3/5 oil processed, 2/5 natural eggs in each group; sound eggs only Original condition
Clean Dirty Clean Dirty
Fluorescent spoilage Mold
Total bacterial spoilage
Total mold
Total microbial loss
%
%
%
%
%
0 3.47 0.34 1.69
0 15.61 2.03 1.01
0.55 12.72 5.76 19.93
0 19.18 2.37 2.70
0.55 28.40 7.79 20.94
NonEggs fluoresin Washed cent sample spoilage
Shell spots only
Spoiled eggs
With mold
No.
%
%
%
179 173 295 296
0.55 3.46 4.75 16.22
3.35 6.34 2.37 6.08
0 5.78 0.68 2.03
No No Yes Yes.
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Clean Dirty Clean Dirty
NonEggs fluoresin Washed cent sample spoilage
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F. W. LORENZ AND PHOEBE BETTY STARR
TABLE 3.—Effect of method of applying washwater on egg spoilage (Machine A—Data for 40° and 60°C. Data combined from Tables 1 and 2) Method of application of wash water Static Sprayed
N
"
ggs
693 711
Total bacterial spoilage 5.34 1.41
°J\
,
Total microbial ioss
1.59 0.70
6.20 1.97
T mola
TABLE 4.—Effect of wash-water temperature on egg spoilage (Machine A with static water—Combined data from Tables 1 and 2) Water temperatures °C. 60 40 20
No. eggs 350 343 351
Total bacterial spoilage
%
2.57 8.16 12.82
Total Total mold microbial loss
%
%
2.00 1.17 0.28
3.43 9.04 13.11
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to magnify the spoilage in every category. In unwashed clean eggs the additional spoilage was very slight, but in the other groups it was striking, demonstrating that what appears to be relatively minor damage as eggs come out of cold storage may be very much more serious by the time the eggs reach the ultimate consumer. Of interest is the shift in preponderant type of spoilage during the period at room temperature. Immediately after cold storage 91.3% of the bacterial spoilage was of the fluorescent type, but in the held eggs 77.5% was non-fluorescent. Meanwhile, the fluorescent spoilage was nevertheless more than doubling in frequency (or if mixed infections are included, increasing more than fourfold). The number of mixed infections is also of interest. Several times as many eggs were invaded by both mold and fluorescent bacteria as would be expected from the total number invaded by each. This relation points either to especial susceptibility of certain eggs to infection in general, or else to a symbiotic effect of the two classes of organisms on their mutual ability to invade. The disadvantage of static as compared with sprayed water in this trial is strikingly shown in Table 3. Using combined data from originally clean and dirty washed eggs, both immediately after removal from cold storage and after 2 subsequent weeks at room temperature, the bacterial spoilage was nearly 4 times as
great and mold loss over twice as great after use of static as of sprayed water. The effect of water temperature is best shown by similarly comparing use of static water at the 3 temperatures tested (Table 4). Water at 40°C. produced over 3 times as much bacterial loss, and at 20°C, 5 times as much as did 60°C. water Mold loss was apparently affected in the opposite direction but not enough to change the trend in total microbial loss. The same trends were observed in eggs washed with sprayed water, though not so strikingly since total infection was less. Although the data in Tables 3 and 4 show clearly the effects of these variables, they fail to point out the extremes of spoilage that were obtained. Dirty eggs washed in cold, static water were spoiled to the extent of 7.9% immediately after cold storage, and to the extraordinary extent of 53.4% after an additional 2 weeks at room temperature. On the other hand, dirty eggs washed in a 60°C. spray had no spoilage immediately and only a single spoiled egg after the additional storage period. These extremes are not emphasized, however, because later trials to be reported elsewhere throw doubt on their significance, and because of the reverse trend of mold incidence with temperature which complicates the possible application. Machine B was tested with sprayed water at 20°C. only, and all eggs were examined immediately after removal from
SPOILAGE OF WASHED EGGS
211
temperature after removal from cold storage, contained any bacterial spoilage, but an appreciable number of rots, not due to mold, were present in each of the washed lots. About twice as much bacterial spoilage was found in the eggs washed in the dirtied solution as in the clean solution.
cold storage. The total bacterial loss was 1.16% which was little different from the results (0.86%) obtained with machine A under the same conditions, so that in this trial, at least, the two machines had no important differences in their effects on spoilage. The test of the Rutgers method failed in one respect to follow the recommended procedure. According to Black (1949) the eggs should be washed by this method the day they are laid: however the use of commercial heavy dirties in the present
EFFECT OF OIL PROCESSING
TABLE 5.—Effect of oil processing on spoilage (grouped data—all eggs)
Storage condition
Postwashing treatment
NonEggs fluoresin cent sample spoilage
Fluorescent spoilage Shell spots only
Spoiled eggs
With mold
Mold
Total bacterial spoilage
Total mold
Total microbial loss
No.'
%
%
%
%
%
%
%
%
6 Months cold storage
Oiled
2,123
0.23
2.38
1.04
0.06
0.64
1.33
0.70
1.97
Natural
1,425
0
1.64
0.69
0
0.26
0.69
0.26
0.95
Same plus 2 weeks room temperature
Oiled
780
9.33
5.10
2.46
2.11
3.17
13.90
5.28
17.07
Natural
519
4.53
3.47
1.07
0
1.07
5.60
1.07
6.67
test precluded compliance with this practice. As a result, removal of obvious dirt was not as complete as it might have been otherwise and some eggs were stored with small amounts of dirt still adhering to the shells. Unfortunately, also, the warehouse was shut down while these eggs were in storage and they had to be transferred to another establishment. Doubtless some sweating occurred in spite of efforts to minimize it, and in any event, mold loss was more prevalent in these eggs, both washed and controls, than in any other lots studied. In spite of the complication of mold, however, increased bacterial spoilage in the eggs washed by this method was evident. None of the lots of unwashed eggs, except the dirty eggs held at room
nal condition or treatment, are grouped according to whether or not they were oiled before being placed in storage. Both bacterial and mold spoilage were greatly increased by coating the shells with oil. Spoilage in the oiled and unoiled eggs was roughly proportional regardless of the treatment or of their original condition, suggesting that the effect of the oil coating is a true potentiation of microbial growth rather than an additional source of infection. The contradiction between these results and the conclusion of Miller et al. (1950) may be more apparent than real, since our results were determined after 6 months of cold storage and Miller's data were obtained only 2 to 5 weeks at room temperature after the eggs were
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The effect of oil processing on subsequent spoilage is summarized in Table 5 where all sound eggs, regardless of origi-
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F. W. LORENZ AND PHOEBE BETTY STARR
SPOILAGE IN CHECKED EGGS
Spoilage in the checked eggs examined immediately out of cold storage is recorded in Table 6. Remarkably, none of the clean eggs, unwashed or washed on machines A or B, were spoiled. Dirty eggs, washed and unwashed, all had strikingly greater spoilage than did the sound eggs. TABLE 6.—Spoilage in checked eggs ( D a t a for eggs after 6 m o n t h s cold storage only)
Clean eggs—washed and unwashed 21 Dirty eggs—not washed 55 Dirty eggs—washed 51
0 5.46 13.73
0 12.73 0
0 16.37 13.73
About 4 times as many checks were found among the dirty as among the clean eggs. Whether this was due to a difference in shell strength of the two lots of eggs, or to easier identification of checks in the clean eggs when sampling or to other factors is not known. The possibility is left open that checking may have been secondary to spoilage in some instances at least, but the total amount of spoilage is not nearly enough to account for all of the discrepancy. The checked eggs held at room temperature were few, since eggs of this nature were avoided when making up the samples. The spoilage pattern was very similar, however. None of the 8 originally clean eggs were spoiled, and a third of the 15 originally dirty eggs had one type of spoilage or another. CANDLING CHARACTERISTICS OF WASHED EGGS
No attempt was made to assign grades to the eggs in these studies, but certain observations were made on each egg before the candle. The only consistently significant effect noted (other than spoilage) was an increase in the number of tremulous air cells in machine washed eggs, an effect probably of the motion of the eggs on the rollers. Some 50.7% of these eggs had tremulous air cells as compared with 7.6% and 5.2% respectively in unwashed eggs and eggs washed by the Rutgers method. The yolk shadow was apparently unaffected by washing and there was little or no effect on shrinkage. To be sure one groups—the unprocessed eggs washed on machine A—had more excessively enlarged air cells than did other groups but this observation was not confirmed in a collateral study made with the same machine. Groups of eggs washed with 20 to 44°C. water were stored for 55 days at 15°C. together with equivalent groups of unwashed eggs. These
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washed. Furthermore, black rot, the type of spoilage against which Miller reported protection by oil processing, was infrequent in the present studies. The non-fluorescent spoilage that was increased here by oil processing was mostly of the type commonly called mixed rot, and Miller's data also showed increases in this type of spoilage as a result of oil processing. These data have an important bearing upon current practices. Little can be done, perhaps, about eggs intended for cold storage since oil processing has become an apparently indispensable part of egg storage, but these results do bring into question the common practice of oilprocessing washed eggs intended for the fresh egg market. Unfortunately a specific test simulating conditions in fresh-egg marketing has not been included in the present study, but it should be remembered that at least one type of spoilage apparently potentiated by oil is a type that develops readily at warm temperatures and is not uncommonly found in socalled fresh eggs. That oil might increase spoilage under these conditions thus seems quite likely.
SPOILAGE OF WASHED EGGS
eggs were weighed individually to 0.01 gram at the beginning and end of the stfcfcage period. The average weight loss of 288 washed eggs was 1.014 grams while the same number of unwashed eggs lost 1.015 grams indicating no effect of washing on weight loss whatsoever.
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produced more spoilage than fresh-running sprayed water, and cold water produced more than warm water. 4. Spoilage was greater in oil-processed eggs than in eggs stored unprocessed. 5. Machine washing, on the machines used in this investigation, produced a high percentage of tremulous air cells.
DISCUSSION
CONCLUSIONS
1. Originally soiled eggs spoiled more frequently than originally clean eggs. Bacterial spoilage was increased by washing regardless of original condition, but mold spoilage was greatest when eggs were stored with dirt on the shell. 2. Nearly all of the bacterial spoilage found immediately after removal of eggs from cold storage was of the fluorescent type, but after an additional 2 weeks at room temperature non-fluorescent types became predominant. 3. Static water in washing machines
ACKNOWLEDGMENTS
The authors wish to acknolwedge the technical assistance of Dorothy E. Foos and Carolyn M. Cobble. Our thanks are due to the Poultry Producers of Central California for a gift of the eggs used in this investigation, for arranging for loan of the egg-washing machines and for the courtesy of their cold storage facilities. REFERENCES Black, L. M., 1949. How to wash eggs properly. Rutgers University, New Jersey Agr. Ext. Leaflet No. 35. Bryant, R. L., and P. F. Sharp, 1934. Effect of washing on the keeping quality of hen's eggs. J. Agr. Research 48: 67-89. Davidson, J. A., L. E. Dawson and C. C. Sheppard, 1950. The occurrence of sour eggs in stored eggs. Michigan Agr. Expt. Sta. Quart. Bull. 32: 526-534. Egg Producers Council and Council for Scientific and Industrial Research, 1942. Rotting in eggs. Agricultural Gazette (N.S. Wales) 53: 393-394, 397. Funk, E. M., 1938. Improving the keeping quality and the market value of eggs by proper cleaning. Missouri Agr. Expt. Sta. Bull. No. 394. Funk, E. M., 1948. Experiments in cleaning soiled eggs for storage. Missouri Agr. Expt. Sta. Bull. No. 426. Grzimek, B., 1936. Versuch mit der mecbanischen Reinigung von Schmutzeiern. Tierarztliche Rundschau 42: 407-408. Hadley, P. B., and D. W. Caldwell, 1916. The bacterial infection of fresh eggs. Rhode Island Agr. Expt. Sta. Bull. 164. Haines, R. B., 1938a, Bacterial flora of hen eggs, with a description of a new species of Proteus and Pseudomonas causing rots in eggs. J. Hygiene, 38:338-355. Haines, R. B., 1938b. The bacteriology of the hen's eggs. Great Britain Dept. Scientific and In-
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The data presented here are consistent with previously reported conclusions on the effects of pressure differentials and of wash-water contamination on egg infection. They thus add confirmation to present understanding of the mechanisms of egg spoilage. They do not, however, offer an acceptable method of washing eggs in commercial practice. Even the single combination of conditions that yielded minimum spoilage should be considered, at present, only a laboratory result, and not the basis of field recommendations—-partly because of the impossibility of assessing the level of infection that may already be present in dirty eggs prior to washing, and partly because supplementary data described in Paper 2 of this series shows that additional variables encountered in the field may profoundly modify or even reverse whatever conclusions may be reached under laboratory restrictions.
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FELLOWS OF THE POULTRY SCIENCE ASSOCIATION Report Food Investigation Board for the year 1938:43. Pennington, M. E., M. K. Jenkins, E. Q. St. ^ | h n and W. B. Hicks, 1914. A bacteriological and chemical study of commercial eggs in the producing districts of the central west. U.S.D.A. Bulletin #51. Pino, J. A., 1950. Effect of washing with a hot detergent solution on keeping quality and hatchability of eggs. Poultry Sci. 29: 888-894. Pritsker, I. Y., 1941. Researches on the hatching qualities of eggs. II. Disinfection of egg shells under increased pressure within the egg. Poultry Sci. 20: 102-103. Sayers, C. W., 1943. Rotting in eggs. Agricultural Gazette (N.S. Wales), 54: 292-296. Stuart, L. S., and E. H. McNally, 1943. Bacteriological studies on the egg shell. U. S. Egg and Poultry Magazine 49: 28-31, 45-47. Wagner, J., 1936. Der Einfluss des Waschens auf die Haltbarkeit des Huhnereies. Zeitschrift fur Fleisch-Milchygiene 46: 422-423'. Zurek, F., 1938. Vergleichende Untersuchungen uber Reinigung von Schmutzeiern mit bersonderer Berucksichtigung der mechanischen Reinigung. Zeitschrift fur Fleisch-Milchygiene 48: 147-150.
Fellows of the Poultry Science Association
T
HE constitution of the Poultry Science Association provides that, from the active members there shall be chosen a body of Fellows not to exceed five percent of the active membership. The title "Fellow" shall be granted for professional distinction only, and be bestowed as provided in the sub-sections. (a) Nominations for Fellows may be made by any active member of the Association. They shall be made in writing and submitted to the Secretary in advance of the annual meeting. A special committee shall be appointed by the Executive Committee to consider such nominations and make recommendations to the Executive
Committee. It shall require an unanimous vote of the Executive Committee present to elect a Fellow. (b) It shall be provided, however, that until all the vacant Fellows are filled, not more than five may be appointed at any one annual meeting. (c) A suitably inscribed scroll shall be presented to all "Fellows." The Fellowship list is as follows: 1933—J. E. Rice, Cornell University, Ithaca, N. Y. W. R. Graham, Ontario Agricultural College, Guelph, Canada. 1934—H. Atwood, West Virginia Experiment Station, Morgantown. (deceased) J. G. Halpin, University of Wisconsin, Madison.
{Continued on page 220)
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dustrial Research, Annual Report Food Investigation Board for the year 1937: 35-38. Haines, R. B., 1939. Microbiology in the preservation of the hen's egg. Great Britain Dept. Scientific and Industrial Research Annual Report Food Investigation Board, 47: Special Report, 1-65. Haines, R. B., 1940. Preservation of eggs. Chemistry & Industry 59: 391-396. Haines, R. B., and T. Moran, 1940. Porosity of, and bacterial invasion through, the shell of hen's egg. J. Hygiene 40: 453-461. Jenkins, M. K., and M. E. Pennington, 1919. Commercial preservation of eggs by cold storage. USDA Bull. No. 775. Jenkins, M. K., J. S. Hepburn, C. Swan and C. M. Sherwood, 1920. Effects of cold storage on shell eggs. Ice and Refrigeration 58: 140-J47. Johns, C. K., and H. L. Berard, 1946. Effect of certain methods of handling upon the bacterial content of dirty eggs. Sci. Agric. 26:11-15. Miller, M. W., V. Joukovsky and A. Kraght, 1950. Experiments relating to the spoilage of washed eggs. Poultry Sci. 29: 27-33. Moran, T., 1939. Washing of eggs. Great Britain Dept. Scientific and Industrial Research Annual
Division of Poultry Husbandry, University of California, Davis, California (Received for publication May 19, 1951)
HE adverse effect of washing on the resistance of eggs to spoilage is well known. Nevertheless, washing remains a common practice, and, with the development of various methods of machine washing, is becoming even more widespread. Some machines have made washing easier even than segregating clean from soiled eggs; consequently, many poultrymen wash the entire production of their flocks, paying, at the same time, less than normal attention to the ordinary practices of poultry-house cleanliness. Published reports on egg washing have been so almost uniformly unfavorable that one would have thought additional investigation of the subject to be unprofitable. The subject is complicated, however, by the frequent appearance of new washing devices together with remarkable claims by some manufacturers. It is also complicated by not infrequent and apparently bona fide reports of satisfactory results with packs of washed eggs from individual ranches. There has thus been a tendency in some segments of the poultry industry to discount previous reports on the effects of washing eggs and to blame almost anything except washing for egg spoilage, or at least to place responsibility on certain methods only, holding others to be blameless. Nevertheless, serious losses have been the rule in areas where the practice of egg washing is prevalent. These considerations led to the under-
taking, here, of a project on egg spoilage of which the present paper is a partial report. The purpose of this paper is to discuss the results of several laboratory experiments on washing eggs by various methods and using various types of equipment. In these trials the primary objective was to determine the amount of egg spoilage resulting from different methods of washing during subsequent cold storage. LITERATURE REVIEW
Discussion of the relation of any method of egg washing to spoilage involves consideration of the mechanism of egg infection. This subject has received considerable attention; early work has been reviewed extensively by Hadley and Caldwell (1916), and more recently Haines has made notable contributions (1938a, 1938b, 1939, 1940; also Haines and Moran, 1940). Agreement is fairly general that egg infection with spoilage-producing organisms prior to ovi-position is practically non-existent. Infection occurs through the egg shell and most spoilage is produced by a limited group of organisms commonly found in soil and poultry feces. Most of these are small motile rods. These organisms cannot, apparently, penetrate the dry shell. According to Haines (1938a) they do not penetrate even the wet shell readily unless the cuticle has previously been disturbed. Some results of the present authors (to be published elsewhere) throw
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T
SPOILAGE OF WASHED EGGS
dustry practice is thus twofold. In the first place, cleaning eggs (by whatever method) may hide previously infected eggs in the pack, and spoilage may result from this cause alone if the eggs are held long enough under conditions conducive to bacterial growth. The second consideration relates to additional infection that may occur during, or as a result of, the washing process. Previous reports on the effects of egg washing are almost uniform in their condemnation of the practice because of the increased numbers of infected and/or frankly spoiled eggs found in washed lots, in spite of variation in results and interpretation. Thus Jenkins, and Pennington (1919) attributed a large proportion of bad eggs in cold storage "to the presence of eggs which at some time previous to storage had had wet shells, because of washing or for some other reason." They concluded: "Attempts therefore to improve the appearance of dirty eggs by washing is a practice which cannot be too strongly condemned." Jenkins et al. (1920) found striking increases in bacterial spoilage during" cold storage in experimentally washed eggs that had been sponged with a damp cloth, washed directly in water, or similarly washed and rinsed in 0.25% sulphuric acid. Unwashed dirty eggs contained more spoiled eggs than did clean eggs, but only about half as many as there were in washed eggs. Bryant and Sharp (1934) by contrast, found bacteria in as many unwashed dirty eggs as in washed eggs. Their bacteriological technique was admittedly not optimum, however, since other measurements were made on the same eggs, and the exceptionally high incidence of yolk infections suggests the possibility that the high values may have been spurious and due to contamination after breakout.
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doubt on the latter conclusion. Admittedly, however, Haines' data are striking. He soaked clean, fresh eggs for an hour in a suspension of Pseudomonas sp. containing 5 X104 cells per ml. and produced no spoilage, whereas similar eggs so treated except that they had previously been soaked for 1 minute in warm water, scrubbed with a brush and soap for l j minutes, rinsed in distilled water and dried with a clean glasscloth, spoiled to the extent of 40% within 14 days at 20°C. The importance of pressure differentials produced by the contraction of the egg contents as it cools is generally recognized. Bacteria, in the presence of moisture, may presumably be aspirated through the pores as the egg cools. Infection of eggs soiled in the nest may thus occur within a very short time after laying. Stuart and McNally (1943) demonstrated Pseudomonas aeruginosa in the albumen of newly laid (still warm) eggs within very few minutes after they had been swabbed with a liquefied gelatin culture of this organism. Whether bacteria can penetrate the shell subsequently {i.e., after the soil has dried and the shell has cooled) is highly questionable unless moisture is again applied. Even the clean shell has a very considerable bacterial flora and yet spoilage of such eggs is very rare. To be sure, the physical presence of a considerable layer of dirt over some part of the shell might change the local moisture relation sufficiently to allow bacterial penetration through the pores. Some data suggesting that this may occasionally occur will be presented elsewhere. In all probability, however, most infection occurs at the time of soiling or very shortly thereafter, unless the egg is later moistened (e.g. by condensation or by washing) under contions favorable to penetration. The problem of egg washing as an in-
205
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F. W. LORENZ AND PHOEBE BETTY STARR
egg temperature during washing resulted in fewer infected eggs than were obtained when internal pressure was decreased during the washing procedure. Grizmek (1936) dry-cleaned eggs and observed good storage quality in both cleaned and control dirty eggs. He concluded that spoilage is a result of washing rather than of original soilage. However, in a comparison of dry cleaning and washing made by Zurek (1938) considerable spoilage was observed in both drycleaned and washed eggs and also in uncleaned dirty eggs but not in clean eggs held untreated as controls. A statement by the Egg Producers Council and the Council for Scientific and Industrial Research of New South Wales (1942) summarized the major results of extensive experiments on washing. They concluded that bacterial rotting of eggs in commerce was almost entirely due to washing. More spoilage was found in eggs washed on various types of machines than in hand-washed eggs, but both methods yielded variable results. The statement stressed the importance of cleanliness in either method, and pointed to "certain types of machines" (not further described) that were responsible for especially severe spoilage. In a further summary discussion of the same investigation Sayers (1943) placed especial emphasis on bacterial contamination of the washing machine itself as a primary cause of egg spoilage. He pointed out that "a machine may appear to be scrupulously clean yet be seriously infected with harmful bacteria." Disinfectant dips after machine cleaning were completely ineffective, but any method of reducing the bacterial contamination of the machine itself such as effective disinfectants, or drying the machines thoroughly between uses, served to reduce spoilage. Experience with a large
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They washed both clean and dirty eggs in lots of 1 to 3 dozen with plain water and with several different chemical agents. None of the compounds used gave less infected eggs than plain water, and at least one (an alkaline detergent) apparently gave more, though the significance of the observed differences between treatments is doubtful and the authors did not stress them. Haines (1938a) presented evidence based on small numbers of hand-washed eggs, that washing under "clean" conditions does not result in bacterial penetration and spoilage, but that washing does render the egg more susceptible to penetration if it is subsequently soaked in a bacterial suspension. On the other hand, Moran (1939) reported that washing by any method increases the number of rots during subsequent handling and storage. He further stated that markedly alkaline washing solutions produce the greatest numbers of rots. Wagner (1936) reported increases in bacterial content and spoilage in eggs washed in various solutions. Specific bacteria present in the wash water were detected in the eggs after 4 weeks storage. Funk (1938) reported that dirty eggs cleaned with sodium hydroxide solutions kept as well in storage as clean unwashed eggs. But in 1948 he presented data which contradicted these findings. In the latter paper extensive evidence was presented condemning all methods of surface cleaning of eggs that are to be stored. These methods included variations of water temperature and disinfectant solutions, dry cleaning, and washing followed by heat treatment. Thermostabilizing following washing did reduce spoilage however. Pritsker (1941), using hatchability as a criterion, presented evidence that increasing internal pressure by increasing
SPOILAGE OF WASHED EGGS
Pino (1950) reported that eggs so washed maintain an internal quality equal to that of untreated eggs kept under the same storage conditions. MATERIALS AND METHODS
Machine A has rubber rollers that turn the eggs end-over-end against rubber backboards until they are clean, at which time they are manually removed. The eggs may be wetted either by a tank of static water into which the rollers dip or by water sprayed over the eggs as they turn. Cleaned eggs are racked on a CarPro lifter and dried in a stream of heated air. Machine B has towel-covered screwtype rollers and towel-covered backboards. Eggs are carried along one roller, wetted in the same manner as Machine A, and carried back by a dry roller in a stream of heated air. The Rutgers method was tested as described above and also with a solution dirtied with chicken droppings to simulate conditions after a considerable number of eggs had been dipped. After spraying, the baskets of eggs were dried overnight in an egg room at 15°C. Each test consisted of washing 5 cases of heavy dirties and a half case of clean eggs. The clean eggs were all from the flock of a nearby producer, selected from current production for these tests. The heavy dirties were selected by candlers at a nearby receiving station from current deliveries. Between each test the machine was cleaned as thoroughly as possible by scrubbing it with hot water and detergent, and rinsing with hot water. The clean eggs were always washed first on the "clean" machine; the heavy dirties were washed immediately after. Three dozen from each case of the latter were taken at random and set aside for storage, so
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number of trials apparently led to considerable pessimism, however, that any method could (or would) be applied to any machine of which he had experience, that would yield a satisfactory pack. Johns and Berard (1946) again found no increase in numbers of infected eggs among those that were experimentally hand-washed. They did observe, however, an increased average bacterial count in the contents of such eggs. They stressed the importance of soil organisms as compared with intestinal organisms in producing spoilage, and produced additional spoilage by applying mud to shells already soiled with feces. This observation and its implication of ground soil as the important source of egg contamination may help to explain some discrepancies in data previously reported. More recently, Davidson et al. (1950) stored current receipt eggs that had been ranch-washed by different methods, buffed, or delivered uncleaned. Washed eggs contained 4.3% sour eggs (as determined by breaking out) while unwashed clean eggs contained 0.9%. None of the washing practices used on the various farms "resulted in the elimination of egg souring or in reducing this loss to the level attained by storing naturally clean eggs." Miller et al. (1950) demonstrated the spoilage-producing effect of a high bacterial count in the wash water, and the ineffectiveness of disinfectant rinses after washing. They also presented evidence that oil processing washed eggs reduced the number of black rots but not of green or mixed rots. Black (1949) described the so-called "Rutgers method" of washing, which consists of twice dipping baskets of eggs momentarily into a hot (65-71°C.) solution of anionic detergent, then spraying them with hot clean water and setting them in a cool place to drain and dry.
207
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F. W. LORENZ AND PHOEBE BETTY STARR
* There is some disagreement over the classification and terminology of different types of egg spoilage and the related bacteriology. This subject will be reviewed more extensively elsewhere, but for the present consideration should at least be given use of the term "sour." This term was used by Pennington et al. (1914) to designate a type of spoilage that
ent stage of the same condition in which the albumen was fluorescent but in which abnormal odors had not yet developed. Non-fluorescent spoilage included black, red and mixed rot and sour* eggs. Under the term mold are recorded a wide variety of conditions, including moldy air cells, black and red spots and rings inside the shell, and mycelia-filled hemispherical lumps of cohered albumen, with or without some greater or lesser degree of disintegration of the egg contents. Eggs were not recorded as moldy, however, unless there was positive gross evidence of penetration of mold through the shell. Fluorescent spots or patches on the shell membrane were not infrequently observed in eggs that showed no other obvious signs of infection. Fluorescent pseudomonads could usually be isolated from such patches, and sometimes, but only rarely from the non-fluorescent albumen of these eggs. Consequently, such spots are considered to be the first gross evidence of penetration of Pseudomonas organisms and thus of fluorescent spoilage that would have occurred later had the egg been held longer. produced a pungent odor and sometimes a turbidity of the white and a weakened yolk membrane, but no other readily detectable alteration of the egg, and attributed by them to a predominately coliform infection. Common usage, however, has also applied the term to a type of spoilage that is characterized by fluorescent albumen, and odors which have been variously described as sour, fishy, cheesey, fruity, or cabbage-water. Some of these eggs may have crusted yolks, liquefied, stringy albumen and/or pink spots on the yolk or inside the shell. This latter type of spoilage is due to infection of the egg with Pseuiomonas organisms and is probably identical with or very similar to egg spoilage that has previously been variously called grass eggs, eggs with green whites or green rot, but these terms are not entirely descriptive and have been used for other, entirely different egg abnormalities. To avoid further confusion this type of spoilage will be designated here as fluorescent-sour, or simply as fluorescent spoilage.
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that the sample stored for each test was a half case of washed clean eggs and a half case of washed heavy dirties. For each two tests (one day's normal operation) an additional half case of clean eggs was held unwashed and a half case of heavy dirties was selected at random from the 10 cases handled that day and also held unwashed. These two half cases served as controls for that day's experiments. The top, middle and bottom layers of each half-case sample were oil processed by dipping momentarily in a commercial processing oil at room temperature. The other two layers were left natural. All eggs were stored for 6 months in a commercial cold-storage warehouse at -0.5°C. and 85-88% relative humidity. After removal from storage and tempering to allow condensed moisture to evaporate, all eggs were candled, and twelve eggs from a pre-designated position in each layer were set aside at room temperature (20-26°C.) for two weeks. The remainder of the eggs were broken out at once. The eggs were broken into petri dishes and examined for gross appearance and odor. Immediately thereafter the egg contents and inner surfaces of the shells were examined under ultra-violet light for fluorescence. Spoilage, when present, was classified as fluorescent and non-fluorescent types and spoilage due to mold. Some mixed infections of mold and fluorescent pigment producing bacteria were recognized. The fluorescent spoilage included a type of sour* egg and an incipi-
209
SPOILAGE OF WASHED EGGS TABLE 1.—Effect of washing eggs on subsequent spoilage after 6 months cold storage Pooled results from bath and spray at 3 temperatures; 3/5 oil processed, 2/5 natural eggs in each group; sound eggs only Original condition
No No Yes Yes
Fluorescent spoilage Shell spots only
Spoiled eggs
With mold
Mold
Total bacterial spoilage
Total mold
Total microbial loss
No.
%
%
%
%
%
%
%
%
531 499 595 567
0 0 0 0.35
0.56 2.20 2.35 4.59
0.19 1.20 0.17 2.29
0 0.20 0 0
0 2.40 0.17 0.18
0.19 1.40 0.17 2.65
0 2.60 0.17 0.18
0.19 4.00 0.34 2.83
apparent from inspection of these tables. First are the detrimental effects both of dirt originally on the shell and of washing on the resistance of eggs to microbial invasion. Clean unwashed eggs had the lowest microbial loss in every category listed in Tables 1 and 2. These effects are at least partially independent since washing increased the spoilage both of clean and of dirty eggs. Washing and original soilage were important both for bacterial and for mold invasion, but with the latter an additional factor—the continued presence of dirt on the shell—apparently came into play. Washing the heavy dirties reduced the number of moldy eggs almost to the level of the washed clean eggs. The effect of holding eggs at room temperature (compare Tables 1 and 2) was
Eggs with checked and sound shells are considered separately. The interpretation of spoilage of the former eggs is complicated because of the difficulty of determining whether infection was made easier by pre-existing breaks in the shell or whether the break may have resulted from the infection. All checks that could be found were removed during the washing procedure, but some were doubtless missed, others could have developed during subsequent handling. RESULTS Trials with machine A were designed to compare sprayed vs. static water and various water temperatures. Spoilage of the sound shelled eggs washed in machine A is recorded in Tables 1 and 2. Certain generalizations are immediately TABLE 2.—Effect
of washing eggs on subsequent spoilage after 6 months in storage plus 2 weeks at room temperature Pooled results from bath and spray at 3 temperatures; 3/5 oil processed, 2/5 natural eggs in each group; sound eggs only Original condition
Clean Dirty Clean Dirty
Fluorescent spoilage Mold
Total bacterial spoilage
Total mold
Total microbial loss
%
%
%
%
%
0 3.47 0.34 1.69
0 15.61 2.03 1.01
0.55 12.72 5.76 19.93
0 19.18 2.37 2.70
0.55 28.40 7.79 20.94
NonEggs fluoresin Washed cent sample spoilage
Shell spots only
Spoiled eggs
With mold
No.
%
%
%
179 173 295 296
0.55 3.46 4.75 16.22
3.35 6.34 2.37 6.08
0 5.78 0.68 2.03
No No Yes Yes.
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Clean Dirty Clean Dirty
NonEggs fluoresin Washed cent sample spoilage
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F. W. LORENZ AND PHOEBE BETTY STARR
TABLE 3.—Effect of method of applying washwater on egg spoilage (Machine A—Data for 40° and 60°C. Data combined from Tables 1 and 2) Method of application of wash water Static Sprayed
N
"
ggs
693 711
Total bacterial spoilage 5.34 1.41
°J\
,
Total microbial ioss
1.59 0.70
6.20 1.97
T mola
TABLE 4.—Effect of wash-water temperature on egg spoilage (Machine A with static water—Combined data from Tables 1 and 2) Water temperatures °C. 60 40 20
No. eggs 350 343 351
Total bacterial spoilage
%
2.57 8.16 12.82
Total Total mold microbial loss
%
%
2.00 1.17 0.28
3.43 9.04 13.11
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to magnify the spoilage in every category. In unwashed clean eggs the additional spoilage was very slight, but in the other groups it was striking, demonstrating that what appears to be relatively minor damage as eggs come out of cold storage may be very much more serious by the time the eggs reach the ultimate consumer. Of interest is the shift in preponderant type of spoilage during the period at room temperature. Immediately after cold storage 91.3% of the bacterial spoilage was of the fluorescent type, but in the held eggs 77.5% was non-fluorescent. Meanwhile, the fluorescent spoilage was nevertheless more than doubling in frequency (or if mixed infections are included, increasing more than fourfold). The number of mixed infections is also of interest. Several times as many eggs were invaded by both mold and fluorescent bacteria as would be expected from the total number invaded by each. This relation points either to especial susceptibility of certain eggs to infection in general, or else to a symbiotic effect of the two classes of organisms on their mutual ability to invade. The disadvantage of static as compared with sprayed water in this trial is strikingly shown in Table 3. Using combined data from originally clean and dirty washed eggs, both immediately after removal from cold storage and after 2 subsequent weeks at room temperature, the bacterial spoilage was nearly 4 times as
great and mold loss over twice as great after use of static as of sprayed water. The effect of water temperature is best shown by similarly comparing use of static water at the 3 temperatures tested (Table 4). Water at 40°C. produced over 3 times as much bacterial loss, and at 20°C, 5 times as much as did 60°C. water Mold loss was apparently affected in the opposite direction but not enough to change the trend in total microbial loss. The same trends were observed in eggs washed with sprayed water, though not so strikingly since total infection was less. Although the data in Tables 3 and 4 show clearly the effects of these variables, they fail to point out the extremes of spoilage that were obtained. Dirty eggs washed in cold, static water were spoiled to the extent of 7.9% immediately after cold storage, and to the extraordinary extent of 53.4% after an additional 2 weeks at room temperature. On the other hand, dirty eggs washed in a 60°C. spray had no spoilage immediately and only a single spoiled egg after the additional storage period. These extremes are not emphasized, however, because later trials to be reported elsewhere throw doubt on their significance, and because of the reverse trend of mold incidence with temperature which complicates the possible application. Machine B was tested with sprayed water at 20°C. only, and all eggs were examined immediately after removal from
SPOILAGE OF WASHED EGGS
211
temperature after removal from cold storage, contained any bacterial spoilage, but an appreciable number of rots, not due to mold, were present in each of the washed lots. About twice as much bacterial spoilage was found in the eggs washed in the dirtied solution as in the clean solution.
cold storage. The total bacterial loss was 1.16% which was little different from the results (0.86%) obtained with machine A under the same conditions, so that in this trial, at least, the two machines had no important differences in their effects on spoilage. The test of the Rutgers method failed in one respect to follow the recommended procedure. According to Black (1949) the eggs should be washed by this method the day they are laid: however the use of commercial heavy dirties in the present
EFFECT OF OIL PROCESSING
TABLE 5.—Effect of oil processing on spoilage (grouped data—all eggs)
Storage condition
Postwashing treatment
NonEggs fluoresin cent sample spoilage
Fluorescent spoilage Shell spots only
Spoiled eggs
With mold
Mold
Total bacterial spoilage
Total mold
Total microbial loss
No.'
%
%
%
%
%
%
%
%
6 Months cold storage
Oiled
2,123
0.23
2.38
1.04
0.06
0.64
1.33
0.70
1.97
Natural
1,425
0
1.64
0.69
0
0.26
0.69
0.26
0.95
Same plus 2 weeks room temperature
Oiled
780
9.33
5.10
2.46
2.11
3.17
13.90
5.28
17.07
Natural
519
4.53
3.47
1.07
0
1.07
5.60
1.07
6.67
test precluded compliance with this practice. As a result, removal of obvious dirt was not as complete as it might have been otherwise and some eggs were stored with small amounts of dirt still adhering to the shells. Unfortunately, also, the warehouse was shut down while these eggs were in storage and they had to be transferred to another establishment. Doubtless some sweating occurred in spite of efforts to minimize it, and in any event, mold loss was more prevalent in these eggs, both washed and controls, than in any other lots studied. In spite of the complication of mold, however, increased bacterial spoilage in the eggs washed by this method was evident. None of the lots of unwashed eggs, except the dirty eggs held at room
nal condition or treatment, are grouped according to whether or not they were oiled before being placed in storage. Both bacterial and mold spoilage were greatly increased by coating the shells with oil. Spoilage in the oiled and unoiled eggs was roughly proportional regardless of the treatment or of their original condition, suggesting that the effect of the oil coating is a true potentiation of microbial growth rather than an additional source of infection. The contradiction between these results and the conclusion of Miller et al. (1950) may be more apparent than real, since our results were determined after 6 months of cold storage and Miller's data were obtained only 2 to 5 weeks at room temperature after the eggs were
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The effect of oil processing on subsequent spoilage is summarized in Table 5 where all sound eggs, regardless of origi-
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F. W. LORENZ AND PHOEBE BETTY STARR
SPOILAGE IN CHECKED EGGS
Spoilage in the checked eggs examined immediately out of cold storage is recorded in Table 6. Remarkably, none of the clean eggs, unwashed or washed on machines A or B, were spoiled. Dirty eggs, washed and unwashed, all had strikingly greater spoilage than did the sound eggs. TABLE 6.—Spoilage in checked eggs ( D a t a for eggs after 6 m o n t h s cold storage only)
Clean eggs—washed and unwashed 21 Dirty eggs—not washed 55 Dirty eggs—washed 51
0 5.46 13.73
0 12.73 0
0 16.37 13.73
About 4 times as many checks were found among the dirty as among the clean eggs. Whether this was due to a difference in shell strength of the two lots of eggs, or to easier identification of checks in the clean eggs when sampling or to other factors is not known. The possibility is left open that checking may have been secondary to spoilage in some instances at least, but the total amount of spoilage is not nearly enough to account for all of the discrepancy. The checked eggs held at room temperature were few, since eggs of this nature were avoided when making up the samples. The spoilage pattern was very similar, however. None of the 8 originally clean eggs were spoiled, and a third of the 15 originally dirty eggs had one type of spoilage or another. CANDLING CHARACTERISTICS OF WASHED EGGS
No attempt was made to assign grades to the eggs in these studies, but certain observations were made on each egg before the candle. The only consistently significant effect noted (other than spoilage) was an increase in the number of tremulous air cells in machine washed eggs, an effect probably of the motion of the eggs on the rollers. Some 50.7% of these eggs had tremulous air cells as compared with 7.6% and 5.2% respectively in unwashed eggs and eggs washed by the Rutgers method. The yolk shadow was apparently unaffected by washing and there was little or no effect on shrinkage. To be sure one groups—the unprocessed eggs washed on machine A—had more excessively enlarged air cells than did other groups but this observation was not confirmed in a collateral study made with the same machine. Groups of eggs washed with 20 to 44°C. water were stored for 55 days at 15°C. together with equivalent groups of unwashed eggs. These
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washed. Furthermore, black rot, the type of spoilage against which Miller reported protection by oil processing, was infrequent in the present studies. The non-fluorescent spoilage that was increased here by oil processing was mostly of the type commonly called mixed rot, and Miller's data also showed increases in this type of spoilage as a result of oil processing. These data have an important bearing upon current practices. Little can be done, perhaps, about eggs intended for cold storage since oil processing has become an apparently indispensable part of egg storage, but these results do bring into question the common practice of oilprocessing washed eggs intended for the fresh egg market. Unfortunately a specific test simulating conditions in fresh-egg marketing has not been included in the present study, but it should be remembered that at least one type of spoilage apparently potentiated by oil is a type that develops readily at warm temperatures and is not uncommonly found in socalled fresh eggs. That oil might increase spoilage under these conditions thus seems quite likely.
SPOILAGE OF WASHED EGGS
eggs were weighed individually to 0.01 gram at the beginning and end of the stfcfcage period. The average weight loss of 288 washed eggs was 1.014 grams while the same number of unwashed eggs lost 1.015 grams indicating no effect of washing on weight loss whatsoever.
• .
213
produced more spoilage than fresh-running sprayed water, and cold water produced more than warm water. 4. Spoilage was greater in oil-processed eggs than in eggs stored unprocessed. 5. Machine washing, on the machines used in this investigation, produced a high percentage of tremulous air cells.
DISCUSSION
CONCLUSIONS
1. Originally soiled eggs spoiled more frequently than originally clean eggs. Bacterial spoilage was increased by washing regardless of original condition, but mold spoilage was greatest when eggs were stored with dirt on the shell. 2. Nearly all of the bacterial spoilage found immediately after removal of eggs from cold storage was of the fluorescent type, but after an additional 2 weeks at room temperature non-fluorescent types became predominant. 3. Static water in washing machines
ACKNOWLEDGMENTS
The authors wish to acknolwedge the technical assistance of Dorothy E. Foos and Carolyn M. Cobble. Our thanks are due to the Poultry Producers of Central California for a gift of the eggs used in this investigation, for arranging for loan of the egg-washing machines and for the courtesy of their cold storage facilities. REFERENCES Black, L. M., 1949. How to wash eggs properly. Rutgers University, New Jersey Agr. Ext. Leaflet No. 35. Bryant, R. L., and P. F. Sharp, 1934. Effect of washing on the keeping quality of hen's eggs. J. Agr. Research 48: 67-89. Davidson, J. A., L. E. Dawson and C. C. Sheppard, 1950. The occurrence of sour eggs in stored eggs. Michigan Agr. Expt. Sta. Quart. Bull. 32: 526-534. Egg Producers Council and Council for Scientific and Industrial Research, 1942. Rotting in eggs. Agricultural Gazette (N.S. Wales) 53: 393-394, 397. Funk, E. M., 1938. Improving the keeping quality and the market value of eggs by proper cleaning. Missouri Agr. Expt. Sta. Bull. No. 394. Funk, E. M., 1948. Experiments in cleaning soiled eggs for storage. Missouri Agr. Expt. Sta. Bull. No. 426. Grzimek, B., 1936. Versuch mit der mecbanischen Reinigung von Schmutzeiern. Tierarztliche Rundschau 42: 407-408. Hadley, P. B., and D. W. Caldwell, 1916. The bacterial infection of fresh eggs. Rhode Island Agr. Expt. Sta. Bull. 164. Haines, R. B., 1938a, Bacterial flora of hen eggs, with a description of a new species of Proteus and Pseudomonas causing rots in eggs. J. Hygiene, 38:338-355. Haines, R. B., 1938b. The bacteriology of the hen's eggs. Great Britain Dept. Scientific and In-
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The data presented here are consistent with previously reported conclusions on the effects of pressure differentials and of wash-water contamination on egg infection. They thus add confirmation to present understanding of the mechanisms of egg spoilage. They do not, however, offer an acceptable method of washing eggs in commercial practice. Even the single combination of conditions that yielded minimum spoilage should be considered, at present, only a laboratory result, and not the basis of field recommendations—-partly because of the impossibility of assessing the level of infection that may already be present in dirty eggs prior to washing, and partly because supplementary data described in Paper 2 of this series shows that additional variables encountered in the field may profoundly modify or even reverse whatever conclusions may be reached under laboratory restrictions.
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FELLOWS OF THE POULTRY SCIENCE ASSOCIATION Report Food Investigation Board for the year 1938:43. Pennington, M. E., M. K. Jenkins, E. Q. St. ^ | h n and W. B. Hicks, 1914. A bacteriological and chemical study of commercial eggs in the producing districts of the central west. U.S.D.A. Bulletin #51. Pino, J. A., 1950. Effect of washing with a hot detergent solution on keeping quality and hatchability of eggs. Poultry Sci. 29: 888-894. Pritsker, I. Y., 1941. Researches on the hatching qualities of eggs. II. Disinfection of egg shells under increased pressure within the egg. Poultry Sci. 20: 102-103. Sayers, C. W., 1943. Rotting in eggs. Agricultural Gazette (N.S. Wales), 54: 292-296. Stuart, L. S., and E. H. McNally, 1943. Bacteriological studies on the egg shell. U. S. Egg and Poultry Magazine 49: 28-31, 45-47. Wagner, J., 1936. Der Einfluss des Waschens auf die Haltbarkeit des Huhnereies. Zeitschrift fur Fleisch-Milchygiene 46: 422-423'. Zurek, F., 1938. Vergleichende Untersuchungen uber Reinigung von Schmutzeiern mit bersonderer Berucksichtigung der mechanischen Reinigung. Zeitschrift fur Fleisch-Milchygiene 48: 147-150.
Fellows of the Poultry Science Association
T
HE constitution of the Poultry Science Association provides that, from the active members there shall be chosen a body of Fellows not to exceed five percent of the active membership. The title "Fellow" shall be granted for professional distinction only, and be bestowed as provided in the sub-sections. (a) Nominations for Fellows may be made by any active member of the Association. They shall be made in writing and submitted to the Secretary in advance of the annual meeting. A special committee shall be appointed by the Executive Committee to consider such nominations and make recommendations to the Executive
Committee. It shall require an unanimous vote of the Executive Committee present to elect a Fellow. (b) It shall be provided, however, that until all the vacant Fellows are filled, not more than five may be appointed at any one annual meeting. (c) A suitably inscribed scroll shall be presented to all "Fellows." The Fellowship list is as follows: 1933—J. E. Rice, Cornell University, Ithaca, N. Y. W. R. Graham, Ontario Agricultural College, Guelph, Canada. 1934—H. Atwood, West Virginia Experiment Station, Morgantown. (deceased) J. G. Halpin, University of Wisconsin, Madison.
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dustrial Research, Annual Report Food Investigation Board for the year 1937: 35-38. Haines, R. B., 1939. Microbiology in the preservation of the hen's egg. Great Britain Dept. Scientific and Industrial Research Annual Report Food Investigation Board, 47: Special Report, 1-65. Haines, R. B., 1940. Preservation of eggs. Chemistry & Industry 59: 391-396. Haines, R. B., and T. Moran, 1940. Porosity of, and bacterial invasion through, the shell of hen's egg. J. Hygiene 40: 453-461. Jenkins, M. K., and M. E. Pennington, 1919. Commercial preservation of eggs by cold storage. USDA Bull. No. 775. Jenkins, M. K., J. S. Hepburn, C. Swan and C. M. Sherwood, 1920. Effects of cold storage on shell eggs. Ice and Refrigeration 58: 140-J47. Johns, C. K., and H. L. Berard, 1946. Effect of certain methods of handling upon the bacterial content of dirty eggs. Sci. Agric. 26:11-15. Miller, M. W., V. Joukovsky and A. Kraght, 1950. Experiments relating to the spoilage of washed eggs. Poultry Sci. 29: 27-33. Moran, T., 1939. Washing of eggs. Great Britain Dept. Scientific and Industrial Research Annual