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Studies on Thermostabilization of Shell Eggs
1196
S. BORNSTEIN AND B . LlPSTEIN 285, 1960. Romanoff, A. L., and A. J. Romanoff, 1944. A study of preservation of eggs by flash-heat treatment. Food Res. 9: 358-366. Salton, M. J. R., W. J. Scott and J. R. Vickery, 1951. Studies in the preservation of shell eggs. VI. The effect of pasteurization on bacterial rotting. Austral. J. Appl. Sci. 2: 205-222. Schmidt, F. J., and W. J. Stadelman, 1957. Effects of antibiotics and heat treatment of shell eggs on quality after storage. Poultry Sci. 36: 1023-1026. Scott, W. J., and J. R. Vickery, 1954. Studies in the preservation of shell eggs. VII. The effect of pasteurization on the maintanence of physical quality. Austral. J. Appl. Sci. 5: 89-102. Winter, A. R., P. Shields, L. MacDonald and I. Prudent, 1954. Improving the keeping quality of eggs during marketing by hot oil treatment. Food Technol. 8: 515-518.
Studies on Thermostabilization of Shell Eggs 2. ON THE MODE OF STABILIZING INTERNAL EGG QUALITY* S. BORNSTEIN, B. LIPSTEIN AND U. NAHARI Poultry Division, National and University Institute of Agriculture, Rehovot, Israel (Received for publication December 11, 1961)
ALTHOUGH the literature contains a -*•*• number of reports on thermostabilization of shell eggs (Bornstein and Lipstein, 1962b), none of them attempts to elucidate the mode by which internal egg quality is stabilized. It is commonly believed that similar to "flash" heat treatment, the purpose is to coagulate a thin film of albumen, immediately beneath the shell membranes, which acts as a moisture and gas barrier. According to this hypothesis heat treatment is not unlike oil processing, except that in the latter case the shell is sealed externally while in the former it is sealed internally. Funk (1950), how* Publication of the National and University Institute of Agriculture, Rehovot, Israel. 1961 Series, No. 443-E.
ever, demonstrated that the egg white thinning process is more effectively retarded by thermostabilization than by oil treatment. The purpose of the present paper is to present data which contradict the above hypothesis, that thermostabilization acts by sealing the shell internally. MATERIALS AND METHODS
Stabilizing Internal Egg Quality. Percentage weight loss and Haugh unit values were determined as part of the tests on devitalizing the blastoderm in fertilized eggs, as reported previously (Bornstein and Lipstein, 1962b). Evaporation of Water through Egg Shells. Holes were made in the polar ends of eggs, half of which had been previously heat-treated (immersion for 10 minutes in
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 26, 2015
quality. Missouri Agr. Exp. Sta. Bui. No. 659. Funk, E. M., and J. Forward, 19SS. Producing high quality eggs. Missouri Agr. Exp. Sta. Bui. No. 654. Funk, E. M., J. Forward and M. Lorah, 1954. Minimizing spoilage in shell eggs by thermostabilization. Poultry Sci. 3 3 : 532-538. Goresline, H. E., R. E. Moser, Jr. and K. M. Hayes, 1950. A pilot scale study of shell egg thermostabilization. Food Technol. 4: 426-430. Kilpatrick, L., A. W. Brant and H. L. Shrader, 1958. Equipment and methods for measuring egg quality. U. S. Dep. Agric, A.M.S., No. 246. Lipstein, B., 1960. Unpublished data. Murphy, T. W., and W. S. Sutton, 1947. The pasteurization of shell eggs. Agric. Gaz. N.S.W. 58: 103. Cited by Salton et al. Orel, V., 1959. A contribution of J. E. Purkynje to the evaluation of egg quality (Title translated). Abstract World's Poultry Sci. J. 16:
THERMOSTABILIZATION OF EGGS
The strings used to tie the plastic bags were also tied to a higher shelf in the incubator, in order to exert a light pull upward, thus creating an "air-cell" in the plastic eggs. The plastic wall above this "air-cell" was perforated a few times (constant for each trial) by a sewing needle, to simulate shell pores and enable gaseous exchange. At the end of the incubation period the "plastic" eggs were weighed again and their contents poured carefully onto a glass surface for the determinations of pH (paper strips sensitive to a 0.3 value), yolk index (Funk, 1948) and Haugh units (Kilpatrick etal, 1958). The main problems encountered were mold and Pseudomonas infections during the incubation period at 32°C; these were kept at a minimum by first soaking the plastic bags, and also washing the eggs beforehand, in a phenol solution and then rinsing them with sterile distilled water. RESULTS AND DISCUSSION Stabilizing Internal Egg Quality. The results of thermostabilization on weight loss and thick white deterioration during a 8day storage period at 32°C. are summarized in Table 1. Ten temperature-time combinations resulted in Haugh unit values of 47 and above, while the remainder dropped to 42 and below. However, since 6 of these 10 combinations produce, or are liable to produce, either perceptible opacity or coagulated spots in the albumen (Barott and McNally, 1943; and Bornstein and Lipstein, 1962b), and since one result is questionable (Haugh unit value of 48.6, based only on 10 eggs), the recommended treatments are : 15 minutes immersion in water at 55°C. or 8-10 minutes at 58°C. These practical recommendations agree with many listed in Table 1 of the previous report (Bornstein and Lipstein, 1962b). In some cases the differences are due to the main
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 26, 2015
water at S8°C), and their contents blown out. One hole was then plugged with hot paraffin, and through the other the egg was filled with regular tap water by means of a 20 cc. syringe equipped with a large needle. When full, this hole, too, was similarly closed, the egg was weighed to the nearest 0.25 gram, and then placed for 14 or 16 days in an incubator at 32°C. (at natural humidity). Final weighings were made at the end of this period, and evaporation through the shell was expressed as percent weight loss. Ionic Diffusion through Egg Shells. As in the above experiment, the normal contents of eggs, half of which had been thermostabilized previously, were replaced by distilled water. After preliminary tests to determine optimal time, the water-filled eggs were immersed into a 1.0 percent solution of NaCl for 10 minutes. They were then removed, dried with a towel, and their contents removed quantitatively into beakers. The concentration of diffused NaCl was determined as described by Kolthoff and Stenger (1947). Storing Egg Contents in Plastic Bags. The purpose of this experiment was to determine the direct effect, if any, of thermostabilization on egg contents, without the possibly confounding influence of the shell and its membranes. Eggs, half of which had been previously heat-treated at 58°C. for 10 minutes, were weighed, broken open, and their contents carefully transferred to plastic bags, larger than the necessary volume, without disturbing the different parts of the egg interior. These bags were placed into evaporating dishes (in order to regain some of the curvature of the normal eggs) and tied hermetically so as to leave just a small "air cell" above the fluid egg contents. These "plastic" eggs were weighed again and then transferred to an incubator, in which they were kept for 8 days at 32°C. and at natural humidity.
1197
1198
S. BORNSTEIN, B. LIPSTEIN AND U. NAHARI
TABLE 1.—Effect of hot-water treatment on Haugh unit values and weight loss after storage at 32°C. for 8 days Total No. of eggs
3 1 1 1 1 2 1 2 2 1 2 4 4 1 2 2 1
40 10 10 10 10 20 20 30 20 10 20 50 50 20 30 30 10
Temp, of Length of Average f Average t water treatment Haugh weight (°C.) (min.) units loss (%)
— 50 50 55 55 55 58 58 58 60 60 60 60 62 62 65 65
40.9 35.1 41.4 39.5 42.4 47.3 51.9 52.0 52.1 48.6 41.6 53.2 57.3 41.2 47.6 51.2 58.4
10 20 8 10 15 8 10 12 3 5 8 10 3 5 3 5
3.4 4.7 4.9 6.0 6.4 4.6 5.2 4.5 5.7 5.2 5.2 5.0 4.5 ' 2.7 3.9 4.5 4.1
* Lots of 10 or 20 eggs were tested on different dates. t Weighted average.
purpose of the authors, pasteurization of spoilage bacteria rather than stabilization of albumen quality. Figure 1 combines some of the results of the above table together with those of 68
1
1 _ \51
*> 60 -
{
1
° Live embryo • Devitalized embryo 35-58 Haugh units
5.8
64 — -
1
—
41 o
49 0
-
\ * o \
-
53 •
57 •
\52
52
39
§: 55
0
5.2
-
42 ^ " " - - - - ^ . t f 0
-«__
-
-
52 ~ 48
1 5
35
41
0
o
1 10
1 15
1
20
Treatment minutes FIG. 1. Effect of thermostabilization on the blastoderm ai:d on albumen quality.
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 26, 2015
No. of tests*
Table 2 of the previous report (Bornstein and Lipstein, 1962b). There is a striking similarity in conditions causing both embryo inactivation and albumen stabilization due to hot water treatment: those treatments which devitalized embryos also preserved albumen quality at 47 to 58 Haugh unit values, while those which failed allowed the latter values to decline to 35 to 42. The one exception to this generalization is the result obtained from 3 minutes immersion at 60°C; this was based only on 10 eggs and probably represents chance variation. The close correlation of the two types of data seems to indicate that albumen stabilization, parallel to embryo devitalization, may be the result of direct heat effect on the albumen. Fig. 1 also demonstrates that albumen stabilization is improved either by prolonging the treatment or by raising its temperature.
1199
THERMOSTABILIZATION OF EGGS
TABLE 2.—Effect of thermostabilization on evaporation of water through egg shells (%) Storage of 16 days at 32°C. Date' 8/8/60 8/9 8/10 mearf 1 2 3
Control
10 m at 5 J£
3.76(5)2 3.56(5) 6.17(3) 5.78(3) 4.52(5) 5.08(5) 4.61(13)4.88(13)
Storage of 14 days at 32°C. W
^
a
t
Date
Control
8/22 8/23 8/24 mean*
4.06(7) 4.11(8) 4.55(7) 4.60(9) 4.76(8) 4.27(9) 4.47(22)4.34(26)
Date of placing eggs in incubator. In parentheses—number of eggs. Weighted average.
weighted averages of both groups of eggs— irrespective of length of storage—are identical, namely 4.52%. These results clearly contradict the existence of a seal in thermostabilized eggs, which supposedly adheres to the inside of the shell membranes and constitutes a barrier for water vapor. Ionic Diffusion through Shells. While the purpose of the previous experiment had been to demonstrate the presence or absence of an internal shell-seal by means of water evaporation from the inside to the outside, the present experiment attempted to demonstrate this by means of diffusion from the outside to the inside of eggs. The results, presented in Table 3, do not show any slower diffusion through shells of heat-treated eggs than through shells of control eggs, but rather a non-significant trend towards the opposite direction. The latter may have been due to dissolution of the cuticle and part of the pore substance by the hot-water treatment. Again no trace was found of an effective barrier adhering to the inside of shells of heat-treated eggs. Storing Egg Contents in Plastic Bags. After the above experiments had failed to demonstrate the existence of an internal shell seal, it seemed appropriate to investigate the possibility of a direct heat effect, due to thermostabilization, on the liquid interior of eggs—in the absence of a surrounding shell. The replacement of natural egg shells by plastic bags was so successful
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 26, 2015
Results of Table 1 indicate rather variable percent weight loss, which appears to be completely independent of the various treatments. With few exceptions weight loss ranged between 3.9 to 5.2 percent, regardless of thermostabilization. A large variability in weight loss from egg to egg in all lots was reported also by Scott and Vickery (1954). They, as well as Schmidt and Stadelman (1957), found little, or no, effect of thermostabilization on weight losses during storage. Goresline et al. (1950), on the other hand, reported marked moisture retention by stabilized eggs. In the latter case, however, eggs were immersed in hot oil, and oil alone, without heat-stabilization, could have reduced their weight loss. Thus only Bose and Stewart (1948) claimed a decrease in percentage weight loss during storage due to heat treatment. The absence of a clear-cut effect of thermostabilization on weight loss during storage raises doubts as to the existence of a thin film of coagulated albumen immediately beneath the shell membranes and to its sealing properties. Evaporation of Water through Egg Shells. Even if a decided moisture retention (or reduced weight loss) had been found in the above trials, this alone would not have sufficed to prove the existence of an internal seal of coagulated albumen. Reduced evaporation could have been the result of an increased viscosity of the albumen due to thermostabilization, as reported by several investigators, and reviewed by Funk (1955). In order to further clarify this point, the egg interior was replaced with water and the differential rate of weight loss was determined. The data obtained in this trial are presented in Table 2. There was no difference in the rate of evaporation through shells of eggs previously heat-treated as compared to shells of untreated controls. In fact, the
1200
S. BOENSTEIN, B . LlPSTEIN AND U . NAHARr
TABLE 3.—Effect of thermostabilization on ionic diffusion through egg shells
Trial no.*
Control
10 min. at 58°C.
No. of % NaCl eggs inside eggf
No. of % NaCl eggs inside egg
4 6 7 4 6 6
0.0087 0.0064 0.0071 0.0087 0.0100 0.0073
4 3 5 4 5 4
0.0095 0.0075 0.0099 0.0095 0.0090 0.0075
33
0.0078
25
0.0089
* Performed on different dates. t After immersion in a 1% solution of NaCl for 10 minutes. | Weighted average.
that in preliminary trials, and under standard conditions of incubation, we were able to obtain normal appearing embryos up to the 7th day of incubation. The death of embryos on the 7th day may have been due to improper gaseous exchange, to lack of calcium, or other disturbances. According to Table 4, there is no difference between thermostabilized and control eggs stored in the above fashion with regard to percent weight loss, to pH, and to yolk index. However, there is a significant difference in Haugh unit values. This difference is very similar to that obtained by Schmidt and Stadelman (1957) after storage for 5 weeks at 9.5°C. (Haugh unit TABLE 4.—Effect
of thermostabilization on the broken-out contents of eggs whtch had been transferred to plastic bags and stored for 8 days at 32''C* 10 minutes at 58°C.
Control Trial No.
Weight loss (%)
pH
Yolk index
Haugh units
Weight loss (%)
pH
Yolk index
Haugh units
1 2 3 4 5
7.7 8.2 4.8 3.9 5.6
9.6 9.6 9.6 9.6 9.5
0.20 0.21 0.24 0.21 0.23
42.3 43.3 44.4 38.8 42.3
7.5 8.1 5.0 4.6 5.3
9.6 9.6 9.6 9.5 9.5
0.23 0.22 0.26 0.24 0.23
73.4 67.3 73.8 69.0 54.2
Average!
5.9
9.6
0.22
42.1
5.8
9.6
0.24
67.9
* Every figure represents the mean of 4 to 6 eggs. f Weighted average of 5 lots totalling 26 eggs.
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 26, 2015
score of 64 in thermostabilized eggs as compared to 41 in untreated eggs). The results of Table 4 are not directly comparable with those of Table 1 because of a difference in the source of eggs used. The marked differences in percentage weight loss between the trials (but not between the two groups within one trial) may have resulted from changing conditions of natural relative humidity, or may be due to the experimental technique: in trials 1 and 2 the plastic wall over the "aircell" was punctured by 10 small holes per egg, while in trial 3 the number of holes per egg was 3, and 6 for the last two trials. According to Table 1 the typical weight loss of shell eggs during 8 days at 32°C. ranged from about 4.1% to 5.2%; hence the weight loss of the first two trials was exaggerated by the excessive number of holes in the plastic "shell." The lack of effect of thermostabilization on weight loss was dealt with in a previous paragraph. Table 4 shows that neither pH nor yolk index were affected by thermostabilization. The latter's ineffectiveness with regard to pH has been mentioned by Bose and Stewart (1948) and Goresline et al. (1950). Except for Bose and Stewart (1948), most investigations (Funk, 1950; Goresline et al., 1950; Carlin and Foth, 1952; and Scott and Vickery, 1954), including the
THEEMOSTABILIZATION OF EGGS
SUMMARY Stabilization of albumen quality is best accomplished by immersing eggs for IS minutes in water at 55°C. or for 8-10 minutes at S8°C. These optimal conditions coincide with those of our previous report for devitalizing the blastoderm of fertilized eggs. This thermostabilization has no effect on weight loss of eggs during storage. Experiments with blown-out eggs filled with water have demonstrated that thermostabilization of eggs had no effect on the rate of water evaporation or of diffusion of NaCl, thus raising doubts as to the creation of an internal shell seal by this heat treatment. By storing egg contents in plastic bags,
in the absence of their natural shells, it was shown that the effect of thermostabilization is a direct heat-effect on the albumen, with no apparent result on the yolk. REFERENCES Barott, H. G., and E. H. McNally, 1943. Heat treating shell eggs. U. S. Egg Poultry Mag. 49: 320-322. Bornstein, S., and B. Lipstein, 1962a. Some characteristics of measures employed for determining the interior quality of eggs. To be pubished. Bornstein, S., and B. Lipstein, 1962b. A study of thermostabilization of shell eggs. 1. Devitalizing fertilized eggs. Poultry Sci. 4 1 : 1192-1196. Bose, S., and G. F. Stewart, 1948. Comparative and complementary effects of heat treating and oiling shell eggs on their keeping quality. Poultry Sci. 27: 228-233. Carlin, A. F., and J. Foth, 1952. Interior quality and functional properties of oiled and thermostabilized shell eggs before and after commercial storage. Food Technol. 6: 443-450. Feeney, R. E., J. M. Weaver, J. R. Jones and M. B. Rhodes, 1956. Studies of the kinetics and mechanisms of yolk deterioration in shell eggs. Poultry Sci. 35: 1061-1066. Funk, E. M., 1948. The relation of the yolk index determined in natural position to the yolk index as determined after separating the yolk from the albumen. Poultry Sci. 27: 367. Funk, E. M., 1950. Maintenance of quality in shell eggs by thermostabilization. Missouri Agr. Exp. Sta. Res. Bull. 467. Funk, E. M., 1955. Treating shell eggs to maintain quality. Missouri Agr. Exp. Sta. Bull. 659. Goresline, H. E., R. E. Moser, Jr and K. M. Hayes, 1950. A pilot scale study of shell egg thermostabilization. Food Technol. 4 : 426-430. Kilpatrick, L., A. W. Brant and H. L. Shrader, 1958. Equipment and methods for measuring egg quality. U. S. Dep. Agric, A.M.S., No. 246. Kolthoff, I. M., and V. A. Stenger, 1947. Volumetric Analysis. Vol. II. Interscience Publishers, Inc., New York. Schmidt, F. J., and W. J. Stadelman, 1957. Effects of antibiotics and heat treatment of shell eggs on quality after storage. Poultry Sci. 36: 1023-1026. Scott, W. J., and J. R. Vickery, 1954. Studies in the preservation of shell eggs. VII. The effect of pasteurization on the maintenance of physical quality. Austral. J. Appl. Sci. 5: 89-102.
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 26, 2015
present study, showed no beneficial effect of thermostabilization on maintaining yolk index during storage. On the other hand, it has been reported that the basic causes for the deteriorative mechanisms of yolk and thick egg white are very similar or identical (Feeney et al., 1956), and that the rate of deterioration of their respective quality is rather parallel for eggs held at 32 °C. (Bornstein and Lipstein, 1962a). These findings raise doubts as to the effectiveness of thermostabilization in causing an internal carbon dioxide barrier. The present experiments with water evaporation and ionic diffusion have proved the absence of such a barrier or seal, and the storage experiments in plastic bags have demonstrated that the stabilizing effect is present also in the absence of egg shells and their membranes, and is restricted to the albumen. The obvious conclusion apears to be, therefore, that thermostabilization is the result of a direct heat effect on the albumen, similar to the direct heat effect on the blastoderm of fertilized eggs (Bornstein and Lipstein, 1962b). The data of Figure 1 represent, therefore, an identical mode of action by heat-treatment.
1201
S. BORNSTEIN AND B . LlPSTEIN 285, 1960. Romanoff, A. L., and A. J. Romanoff, 1944. A study of preservation of eggs by flash-heat treatment. Food Res. 9: 358-366. Salton, M. J. R., W. J. Scott and J. R. Vickery, 1951. Studies in the preservation of shell eggs. VI. The effect of pasteurization on bacterial rotting. Austral. J. Appl. Sci. 2: 205-222. Schmidt, F. J., and W. J. Stadelman, 1957. Effects of antibiotics and heat treatment of shell eggs on quality after storage. Poultry Sci. 36: 1023-1026. Scott, W. J., and J. R. Vickery, 1954. Studies in the preservation of shell eggs. VII. The effect of pasteurization on the maintanence of physical quality. Austral. J. Appl. Sci. 5: 89-102. Winter, A. R., P. Shields, L. MacDonald and I. Prudent, 1954. Improving the keeping quality of eggs during marketing by hot oil treatment. Food Technol. 8: 515-518.
Studies on Thermostabilization of Shell Eggs 2. ON THE MODE OF STABILIZING INTERNAL EGG QUALITY* S. BORNSTEIN, B. LIPSTEIN AND U. NAHARI Poultry Division, National and University Institute of Agriculture, Rehovot, Israel (Received for publication December 11, 1961)
ALTHOUGH the literature contains a -*•*• number of reports on thermostabilization of shell eggs (Bornstein and Lipstein, 1962b), none of them attempts to elucidate the mode by which internal egg quality is stabilized. It is commonly believed that similar to "flash" heat treatment, the purpose is to coagulate a thin film of albumen, immediately beneath the shell membranes, which acts as a moisture and gas barrier. According to this hypothesis heat treatment is not unlike oil processing, except that in the latter case the shell is sealed externally while in the former it is sealed internally. Funk (1950), how* Publication of the National and University Institute of Agriculture, Rehovot, Israel. 1961 Series, No. 443-E.
ever, demonstrated that the egg white thinning process is more effectively retarded by thermostabilization than by oil treatment. The purpose of the present paper is to present data which contradict the above hypothesis, that thermostabilization acts by sealing the shell internally. MATERIALS AND METHODS
Stabilizing Internal Egg Quality. Percentage weight loss and Haugh unit values were determined as part of the tests on devitalizing the blastoderm in fertilized eggs, as reported previously (Bornstein and Lipstein, 1962b). Evaporation of Water through Egg Shells. Holes were made in the polar ends of eggs, half of which had been previously heat-treated (immersion for 10 minutes in
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 26, 2015
quality. Missouri Agr. Exp. Sta. Bui. No. 659. Funk, E. M., and J. Forward, 19SS. Producing high quality eggs. Missouri Agr. Exp. Sta. Bui. No. 654. Funk, E. M., J. Forward and M. Lorah, 1954. Minimizing spoilage in shell eggs by thermostabilization. Poultry Sci. 3 3 : 532-538. Goresline, H. E., R. E. Moser, Jr. and K. M. Hayes, 1950. A pilot scale study of shell egg thermostabilization. Food Technol. 4: 426-430. Kilpatrick, L., A. W. Brant and H. L. Shrader, 1958. Equipment and methods for measuring egg quality. U. S. Dep. Agric, A.M.S., No. 246. Lipstein, B., 1960. Unpublished data. Murphy, T. W., and W. S. Sutton, 1947. The pasteurization of shell eggs. Agric. Gaz. N.S.W. 58: 103. Cited by Salton et al. Orel, V., 1959. A contribution of J. E. Purkynje to the evaluation of egg quality (Title translated). Abstract World's Poultry Sci. J. 16:
THERMOSTABILIZATION OF EGGS
The strings used to tie the plastic bags were also tied to a higher shelf in the incubator, in order to exert a light pull upward, thus creating an "air-cell" in the plastic eggs. The plastic wall above this "air-cell" was perforated a few times (constant for each trial) by a sewing needle, to simulate shell pores and enable gaseous exchange. At the end of the incubation period the "plastic" eggs were weighed again and their contents poured carefully onto a glass surface for the determinations of pH (paper strips sensitive to a 0.3 value), yolk index (Funk, 1948) and Haugh units (Kilpatrick etal, 1958). The main problems encountered were mold and Pseudomonas infections during the incubation period at 32°C; these were kept at a minimum by first soaking the plastic bags, and also washing the eggs beforehand, in a phenol solution and then rinsing them with sterile distilled water. RESULTS AND DISCUSSION Stabilizing Internal Egg Quality. The results of thermostabilization on weight loss and thick white deterioration during a 8day storage period at 32°C. are summarized in Table 1. Ten temperature-time combinations resulted in Haugh unit values of 47 and above, while the remainder dropped to 42 and below. However, since 6 of these 10 combinations produce, or are liable to produce, either perceptible opacity or coagulated spots in the albumen (Barott and McNally, 1943; and Bornstein and Lipstein, 1962b), and since one result is questionable (Haugh unit value of 48.6, based only on 10 eggs), the recommended treatments are : 15 minutes immersion in water at 55°C. or 8-10 minutes at 58°C. These practical recommendations agree with many listed in Table 1 of the previous report (Bornstein and Lipstein, 1962b). In some cases the differences are due to the main
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 26, 2015
water at S8°C), and their contents blown out. One hole was then plugged with hot paraffin, and through the other the egg was filled with regular tap water by means of a 20 cc. syringe equipped with a large needle. When full, this hole, too, was similarly closed, the egg was weighed to the nearest 0.25 gram, and then placed for 14 or 16 days in an incubator at 32°C. (at natural humidity). Final weighings were made at the end of this period, and evaporation through the shell was expressed as percent weight loss. Ionic Diffusion through Egg Shells. As in the above experiment, the normal contents of eggs, half of which had been thermostabilized previously, were replaced by distilled water. After preliminary tests to determine optimal time, the water-filled eggs were immersed into a 1.0 percent solution of NaCl for 10 minutes. They were then removed, dried with a towel, and their contents removed quantitatively into beakers. The concentration of diffused NaCl was determined as described by Kolthoff and Stenger (1947). Storing Egg Contents in Plastic Bags. The purpose of this experiment was to determine the direct effect, if any, of thermostabilization on egg contents, without the possibly confounding influence of the shell and its membranes. Eggs, half of which had been previously heat-treated at 58°C. for 10 minutes, were weighed, broken open, and their contents carefully transferred to plastic bags, larger than the necessary volume, without disturbing the different parts of the egg interior. These bags were placed into evaporating dishes (in order to regain some of the curvature of the normal eggs) and tied hermetically so as to leave just a small "air cell" above the fluid egg contents. These "plastic" eggs were weighed again and then transferred to an incubator, in which they were kept for 8 days at 32°C. and at natural humidity.
1197
1198
S. BORNSTEIN, B. LIPSTEIN AND U. NAHARI
TABLE 1.—Effect of hot-water treatment on Haugh unit values and weight loss after storage at 32°C. for 8 days Total No. of eggs
3 1 1 1 1 2 1 2 2 1 2 4 4 1 2 2 1
40 10 10 10 10 20 20 30 20 10 20 50 50 20 30 30 10
Temp, of Length of Average f Average t water treatment Haugh weight (°C.) (min.) units loss (%)
— 50 50 55 55 55 58 58 58 60 60 60 60 62 62 65 65
40.9 35.1 41.4 39.5 42.4 47.3 51.9 52.0 52.1 48.6 41.6 53.2 57.3 41.2 47.6 51.2 58.4
10 20 8 10 15 8 10 12 3 5 8 10 3 5 3 5
3.4 4.7 4.9 6.0 6.4 4.6 5.2 4.5 5.7 5.2 5.2 5.0 4.5 ' 2.7 3.9 4.5 4.1
* Lots of 10 or 20 eggs were tested on different dates. t Weighted average.
purpose of the authors, pasteurization of spoilage bacteria rather than stabilization of albumen quality. Figure 1 combines some of the results of the above table together with those of 68
1
1 _ \51
*> 60 -
{
1
° Live embryo • Devitalized embryo 35-58 Haugh units
5.8
64 — -
1
—
41 o
49 0
-
\ * o \
-
53 •
57 •
\52
52
39
§: 55
0
5.2
-
42 ^ " " - - - - ^ . t f 0
-«__
-
-
52 ~ 48
1 5
35
41
0
o
1 10
1 15
1
20
Treatment minutes FIG. 1. Effect of thermostabilization on the blastoderm ai:d on albumen quality.
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 26, 2015
No. of tests*
Table 2 of the previous report (Bornstein and Lipstein, 1962b). There is a striking similarity in conditions causing both embryo inactivation and albumen stabilization due to hot water treatment: those treatments which devitalized embryos also preserved albumen quality at 47 to 58 Haugh unit values, while those which failed allowed the latter values to decline to 35 to 42. The one exception to this generalization is the result obtained from 3 minutes immersion at 60°C; this was based only on 10 eggs and probably represents chance variation. The close correlation of the two types of data seems to indicate that albumen stabilization, parallel to embryo devitalization, may be the result of direct heat effect on the albumen. Fig. 1 also demonstrates that albumen stabilization is improved either by prolonging the treatment or by raising its temperature.
1199
THERMOSTABILIZATION OF EGGS
TABLE 2.—Effect of thermostabilization on evaporation of water through egg shells (%) Storage of 16 days at 32°C. Date' 8/8/60 8/9 8/10 mearf 1 2 3
Control
10 m at 5 J£
3.76(5)2 3.56(5) 6.17(3) 5.78(3) 4.52(5) 5.08(5) 4.61(13)4.88(13)
Storage of 14 days at 32°C. W
^
a
t
Date
Control
8/22 8/23 8/24 mean*
4.06(7) 4.11(8) 4.55(7) 4.60(9) 4.76(8) 4.27(9) 4.47(22)4.34(26)
Date of placing eggs in incubator. In parentheses—number of eggs. Weighted average.
weighted averages of both groups of eggs— irrespective of length of storage—are identical, namely 4.52%. These results clearly contradict the existence of a seal in thermostabilized eggs, which supposedly adheres to the inside of the shell membranes and constitutes a barrier for water vapor. Ionic Diffusion through Shells. While the purpose of the previous experiment had been to demonstrate the presence or absence of an internal shell-seal by means of water evaporation from the inside to the outside, the present experiment attempted to demonstrate this by means of diffusion from the outside to the inside of eggs. The results, presented in Table 3, do not show any slower diffusion through shells of heat-treated eggs than through shells of control eggs, but rather a non-significant trend towards the opposite direction. The latter may have been due to dissolution of the cuticle and part of the pore substance by the hot-water treatment. Again no trace was found of an effective barrier adhering to the inside of shells of heat-treated eggs. Storing Egg Contents in Plastic Bags. After the above experiments had failed to demonstrate the existence of an internal shell seal, it seemed appropriate to investigate the possibility of a direct heat effect, due to thermostabilization, on the liquid interior of eggs—in the absence of a surrounding shell. The replacement of natural egg shells by plastic bags was so successful
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Results of Table 1 indicate rather variable percent weight loss, which appears to be completely independent of the various treatments. With few exceptions weight loss ranged between 3.9 to 5.2 percent, regardless of thermostabilization. A large variability in weight loss from egg to egg in all lots was reported also by Scott and Vickery (1954). They, as well as Schmidt and Stadelman (1957), found little, or no, effect of thermostabilization on weight losses during storage. Goresline et al. (1950), on the other hand, reported marked moisture retention by stabilized eggs. In the latter case, however, eggs were immersed in hot oil, and oil alone, without heat-stabilization, could have reduced their weight loss. Thus only Bose and Stewart (1948) claimed a decrease in percentage weight loss during storage due to heat treatment. The absence of a clear-cut effect of thermostabilization on weight loss during storage raises doubts as to the existence of a thin film of coagulated albumen immediately beneath the shell membranes and to its sealing properties. Evaporation of Water through Egg Shells. Even if a decided moisture retention (or reduced weight loss) had been found in the above trials, this alone would not have sufficed to prove the existence of an internal seal of coagulated albumen. Reduced evaporation could have been the result of an increased viscosity of the albumen due to thermostabilization, as reported by several investigators, and reviewed by Funk (1955). In order to further clarify this point, the egg interior was replaced with water and the differential rate of weight loss was determined. The data obtained in this trial are presented in Table 2. There was no difference in the rate of evaporation through shells of eggs previously heat-treated as compared to shells of untreated controls. In fact, the
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S. BOENSTEIN, B . LlPSTEIN AND U . NAHARr
TABLE 3.—Effect of thermostabilization on ionic diffusion through egg shells
Trial no.*
Control
10 min. at 58°C.
No. of % NaCl eggs inside eggf
No. of % NaCl eggs inside egg
4 6 7 4 6 6
0.0087 0.0064 0.0071 0.0087 0.0100 0.0073
4 3 5 4 5 4
0.0095 0.0075 0.0099 0.0095 0.0090 0.0075
33
0.0078
25
0.0089
* Performed on different dates. t After immersion in a 1% solution of NaCl for 10 minutes. | Weighted average.
that in preliminary trials, and under standard conditions of incubation, we were able to obtain normal appearing embryos up to the 7th day of incubation. The death of embryos on the 7th day may have been due to improper gaseous exchange, to lack of calcium, or other disturbances. According to Table 4, there is no difference between thermostabilized and control eggs stored in the above fashion with regard to percent weight loss, to pH, and to yolk index. However, there is a significant difference in Haugh unit values. This difference is very similar to that obtained by Schmidt and Stadelman (1957) after storage for 5 weeks at 9.5°C. (Haugh unit TABLE 4.—Effect
of thermostabilization on the broken-out contents of eggs whtch had been transferred to plastic bags and stored for 8 days at 32''C* 10 minutes at 58°C.
Control Trial No.
Weight loss (%)
pH
Yolk index
Haugh units
Weight loss (%)
pH
Yolk index
Haugh units
1 2 3 4 5
7.7 8.2 4.8 3.9 5.6
9.6 9.6 9.6 9.6 9.5
0.20 0.21 0.24 0.21 0.23
42.3 43.3 44.4 38.8 42.3
7.5 8.1 5.0 4.6 5.3
9.6 9.6 9.6 9.5 9.5
0.23 0.22 0.26 0.24 0.23
73.4 67.3 73.8 69.0 54.2
Average!
5.9
9.6
0.22
42.1
5.8
9.6
0.24
67.9
* Every figure represents the mean of 4 to 6 eggs. f Weighted average of 5 lots totalling 26 eggs.
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score of 64 in thermostabilized eggs as compared to 41 in untreated eggs). The results of Table 4 are not directly comparable with those of Table 1 because of a difference in the source of eggs used. The marked differences in percentage weight loss between the trials (but not between the two groups within one trial) may have resulted from changing conditions of natural relative humidity, or may be due to the experimental technique: in trials 1 and 2 the plastic wall over the "aircell" was punctured by 10 small holes per egg, while in trial 3 the number of holes per egg was 3, and 6 for the last two trials. According to Table 1 the typical weight loss of shell eggs during 8 days at 32°C. ranged from about 4.1% to 5.2%; hence the weight loss of the first two trials was exaggerated by the excessive number of holes in the plastic "shell." The lack of effect of thermostabilization on weight loss was dealt with in a previous paragraph. Table 4 shows that neither pH nor yolk index were affected by thermostabilization. The latter's ineffectiveness with regard to pH has been mentioned by Bose and Stewart (1948) and Goresline et al. (1950). Except for Bose and Stewart (1948), most investigations (Funk, 1950; Goresline et al., 1950; Carlin and Foth, 1952; and Scott and Vickery, 1954), including the
THEEMOSTABILIZATION OF EGGS
SUMMARY Stabilization of albumen quality is best accomplished by immersing eggs for IS minutes in water at 55°C. or for 8-10 minutes at S8°C. These optimal conditions coincide with those of our previous report for devitalizing the blastoderm of fertilized eggs. This thermostabilization has no effect on weight loss of eggs during storage. Experiments with blown-out eggs filled with water have demonstrated that thermostabilization of eggs had no effect on the rate of water evaporation or of diffusion of NaCl, thus raising doubts as to the creation of an internal shell seal by this heat treatment. By storing egg contents in plastic bags,
in the absence of their natural shells, it was shown that the effect of thermostabilization is a direct heat-effect on the albumen, with no apparent result on the yolk. REFERENCES Barott, H. G., and E. H. McNally, 1943. Heat treating shell eggs. U. S. Egg Poultry Mag. 49: 320-322. Bornstein, S., and B. Lipstein, 1962a. Some characteristics of measures employed for determining the interior quality of eggs. To be pubished. Bornstein, S., and B. Lipstein, 1962b. A study of thermostabilization of shell eggs. 1. Devitalizing fertilized eggs. Poultry Sci. 4 1 : 1192-1196. Bose, S., and G. F. Stewart, 1948. Comparative and complementary effects of heat treating and oiling shell eggs on their keeping quality. Poultry Sci. 27: 228-233. Carlin, A. F., and J. Foth, 1952. Interior quality and functional properties of oiled and thermostabilized shell eggs before and after commercial storage. Food Technol. 6: 443-450. Feeney, R. E., J. M. Weaver, J. R. Jones and M. B. Rhodes, 1956. Studies of the kinetics and mechanisms of yolk deterioration in shell eggs. Poultry Sci. 35: 1061-1066. Funk, E. M., 1948. The relation of the yolk index determined in natural position to the yolk index as determined after separating the yolk from the albumen. Poultry Sci. 27: 367. Funk, E. M., 1950. Maintenance of quality in shell eggs by thermostabilization. Missouri Agr. Exp. Sta. Res. Bull. 467. Funk, E. M., 1955. Treating shell eggs to maintain quality. Missouri Agr. Exp. Sta. Bull. 659. Goresline, H. E., R. E. Moser, Jr and K. M. Hayes, 1950. A pilot scale study of shell egg thermostabilization. Food Technol. 4 : 426-430. Kilpatrick, L., A. W. Brant and H. L. Shrader, 1958. Equipment and methods for measuring egg quality. U. S. Dep. Agric, A.M.S., No. 246. Kolthoff, I. M., and V. A. Stenger, 1947. Volumetric Analysis. Vol. II. Interscience Publishers, Inc., New York. Schmidt, F. J., and W. J. Stadelman, 1957. Effects of antibiotics and heat treatment of shell eggs on quality after storage. Poultry Sci. 36: 1023-1026. Scott, W. J., and J. R. Vickery, 1954. Studies in the preservation of shell eggs. VII. The effect of pasteurization on the maintenance of physical quality. Austral. J. Appl. Sci. 5: 89-102.
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present study, showed no beneficial effect of thermostabilization on maintaining yolk index during storage. On the other hand, it has been reported that the basic causes for the deteriorative mechanisms of yolk and thick egg white are very similar or identical (Feeney et al., 1956), and that the rate of deterioration of their respective quality is rather parallel for eggs held at 32 °C. (Bornstein and Lipstein, 1962a). These findings raise doubts as to the effectiveness of thermostabilization in causing an internal carbon dioxide barrier. The present experiments with water evaporation and ionic diffusion have proved the absence of such a barrier or seal, and the storage experiments in plastic bags have demonstrated that the stabilizing effect is present also in the absence of egg shells and their membranes, and is restricted to the albumen. The obvious conclusion apears to be, therefore, that thermostabilization is the result of a direct heat effect on the albumen, similar to the direct heat effect on the blastoderm of fertilized eggs (Bornstein and Lipstein, 1962b). The data of Figure 1 represent, therefore, an identical mode of action by heat-treatment.
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