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Studies on Thermostabilization of Shell Eggs
Studies on Thermostabilization of Shell Eggs 1. DEVITALIZING FERTILIZED EGGS* S. BORNSTEIN AND B . LlPSTEIN Poultry Division, National and University Institute of Agriculture, Rehovot, Israel (Received for publication December 11, 1961)
A
CCORDING to Orel (1959), Pur- kynje, in his Latin report in 1825 and Czech paper in 1855, was the first to recommended dipping eggs into hot water, in order to coagulate the egg white in a thin layer on the egg shell and thus prevent water evaporation. Funk in a series of papers (1943 a, b, c, 1950, 1955) described a process which he termed "thermostabilization," in which the quality of shell eggs was maintained by (1) destroying the blastoderm and thus permanently stopping embryonic development in fertilized eggs, so that subsequently they react as infertile eggs, (2) stabilizing the thick albumen and (3) destroying many of the spoilage causing bacteria, thus obtaining a pasteurizing effect. Table 1 summarizes the recommendations, of various investigators, on optimal combination of treatment duration and temperature of the immersion media (water or oil) used for thermostabilization. These two variables depend upon initial egg temperature and upon the main purpose of the treatment. Unpublished data of this laboratory (Lipstein, 1960) indicated that the rate of internal egg quality deterioration is not higher in fertilized eggs than in infertile eggs. Nevertheless, the devitalization of fertilized eggs may be of practical importance in some areas. This is especially true for countries where fresh hatching eggs may find their way into regular market* Publication of the National and UniversityInstitute of Agriculture, Rehovot, Israel. 1961 Series, No. 442-E.
ing channels (during periods of sudden slumps in demands for chicks), and be subjected to high summer temperatures, which may cause a visible enlargement of the blastoderm. Although Funk (1943) showed that future embryonic development could be prevented by thermostabilization, this line of thought was followed only by Barott and McNally (1943). The purposes of this study were to determine the optimal immersion time and temperature for the prevention of future embryonic development and to elucidate the mode by which the blastoderm is devitalized. MATERIALS AND METHODS
Thirty-one lots of 10 or 20 eggs each (a total of 390 eggs), obtained from a breeding flock of S.C. White Leghorn hens, in their first year of production, were collected during morning hours, held for 1 to 2 hours at room temperature (usually about 18°C), individually weighed to the nearest quarter of a gram, and then treated by immersion into hot water. The temperature of the water was kept uniform by light manual stirring, and was stabilized by constant control with a thermometer and the addition of small quantities of nearly boiling water, as required. After the heat treatment, a few eggs were broken open immediately in order to check on albumen coagulation, while the remainder were placed for 8 days in an incubator at 32°C, a temperature simulating natural conditions. These eggs were subsequently reweighed, opened and examined visually.
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1193
THERMOSTABILIZATION OF EGGS TABLE 1.—Recommended heat treatments for thermostabilization of shell eggs* Immersion medium
Immersion time (min.)
oil water water water water water water water oil water oil water water water water oil water oil water water oil
10 15 5 20,10 1/12 30 30 15 16 51,2 16 1/20 15,5,3 13J,2 2 2 3 3 5 1
Temperature
Author
rc.) 60 54.51 58 / 55,59 100 54 54.5 54.5 54.5-57.0 60,62.5 54.5 100 54.5,60,63 57.5.62.5 62 \ 66.5/ 63 1 65.5/ 60,63,65.5 60 71
Funk (1943a, c) Funk (1943b) Barrott and McNally (1943) Romanoff and Romanoff (1944) Murphy and Sutton (1947) Bose and Stewart (1948) Funk (1950) Goresline et al. (1950) Salton et al. (1951) Carlin and Foth (1952) Feeney et al. (1953) Funk et al. (1954) Scott and Vickery (1954) Winter et al. (1954) Funk and Forward (1955) Funk (1955) Schmidt and Stadelman (1957) Carlin et al. (1958)
* Some of the variations in this table are probably due to different initial temperatures of the eggs, and some may be due to differences in the primary purpose of the treatment.
Haugh units were determined according to the methods described by Kilpatrick et al. (1958).f Measuring Temperature of Blastoderm. By placing eggs horizontally the blastoderm was allowed to orient to an upward position, and a small hole was drilled through the shell at its highest point of curvature. Thermocouples (35 S.W.G.) attached to a galvanometer were then inserted through this hole for a depth of 3-4 mm., until they encountered the resistance of the yolk's vitelline membrane. Keeping the egg in this position it was suspended by wires in a water bath to a depth at which all but its highest point (containing the hole) was immersed. Different eggs were immersed for periods of 5 to 30 minutes in water baths of 50°C, 55°C, 58°C, 60°C, 62°C. and 6S°C; 5 eggs were treated individually for each respective temperature. Readings of the galvat Results of these measurements are reported in the next paper of this series.
nometer were taken immediately before immersion in the water bath and subsequently every 2 to 3 minutes. RESULTS AND DISCUSSION
Optimal Conditions for Devitalizing Blastoderm. As Table 2 shows the most TABLE 2.—Results of immersing fertilized eggs into water of different temperatures for different lengths of time No. of 3 1 1 1 1 2 1 2 2 1 2 4 4 1 2 2 1
Total Temp. o f ^ ™ f * Appearno. of water „,„„ f " ance of albumen (°C.) (min.) 40 10 10 10 10 20 20 30 20 10 20 50
so 20 30 30 10
— 50
— 10
50 55 55 55 58 58 58 60 60 60 60 62 62 65 65
20 8 10 IS 8 10 12 3 5 8 10 3 5 3 5
clear clear clear clear clear clear clear clear clear clear clear clear* clearf clear clearf opaque opaque
Embryonic development blood ring blood ring blood ring blood ring blood ring none none none none blood ring blood ring nonej none blood ring none variable none
* A few exceptional eggs contained small pieces of coagulated albumen. t About half of the eggs contained small pieces of coagulated albumen. X A few exceptional eggs contained enlarged blastoderms.
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S. BORNSTEIN AND B . LlPSTEIN
effective treatment was obtained by im- upper limit to certain temperature-time mersing eggs into water of 55°C. for a combinations in thermostabilization. period of IS minutes or 58°C. for 8 to 12 Eleven lots of 10 fertilized eggs each minutes. A water treatment of 8 minutes at were exposed to hot air of 60° C. for 3 to 15 60°C. gave borderline results. minutes and of 80°C. for 3 to 12 minutes—• These data agree relatively well with without obtaining any thermostabilization. those of Funk (1943b), who recommended It seems that the lower thermoconductivity 5 minutes at S8°C. as treatment for the of air, as compared to water, requires a prevention of embryonic development. more prolonged time for warming objects Moreover, they are practically identical in touch with it. with the results of Barott and McNally Effect of Thermostabilization on Blasto(1943), reproduced as Figure 5 in the com- dermal Temperature. Figure 1 shows the pilation of Funk (1955). He found that effect of various immersion temperatures on all embryo development was checked by warming rate of the blastoderm (or its imimmersion at temperatures between 50°C. mediate surrounding). It is apparent that and 56°C. for periods of time too short to at all times there was a marked difference produce opacity in the egg white. At tem- between the temperature of the water bath peratures between 56°C. and 61°C, how- and that of the blastoderm: after 20 minever, the immersion time necessary for em- utes at 50°C. the latter reaches only bryonic destruction was slightly longer than 40.8°C, and even after 30 minutes at that which produced barely perceptible al- 60°C. it only went up to 52°C. (not shown bumen opacity. According to our data the in Fig. 1). Similar phenomena have been latter phenomenon is not apparent at a described by Funk (1943c), Goresline et al. temperature of 58°C. and starts only at (1950) and by Scott and Vickery (1954) 60°C. Thus, at temperatures up to 59°C, under different experimental conditions. it is possible to destroy the blastoderm A comparison between the data of Figwithout visibly affecting egg albumen. ure 1 and those of Table 2 demonstrates According to Barott and McNally that any combination of immersion period (1943), the duration of water immersion and temperature which will raise the temrequired for the appearance of perceptible perature of the blastoderm to 44°C, and opacity varied from 4 minutes at 62°C. to above, will cause its destruction; vice versa, 44 minutes at 51.5°C. Saltan et al. (1951) any combination which fails to reach this have cautioned that above 64° C. complete internal temperature is ineffective. There control of bacterial rotting cannot generally was one exception with eggs dipped for be achieved without some coagulation of 8 minutes in water at 58°C: according to the albumen. Carlin and Foth (1952) Table 2 this treatment prevented subsefound gelatinous masses and increased tur- quent embryonic development, while acbidity when treating eggs for 8 minutes in cording to Figure 1 the average blastoderoil at a temperature of 62 °C. Winter mal temperature obtained by this treatet al. (1954) reported some coagula- ment was only 43.1°C. (however, 2 out tion when eggs were water-treated for 2 of 5 eggs did reach an internal temperature minutes at 64.5°C, while after a 2-minute of 44°C). These data seem to indicate that treatment in oil some coagulation will ap- the effect of thermostabilization on the ferpear only at 69 °C. Hence it must not be tilized egg is the direct result of heat-death forgotten that albumen coagulation sets an of the blastoderm.
1195
THERMOSTABILIZATION OF EGGS "i—r
55 °C
SOK
o Measurements by means of thermocouples • No effect on embryo, according to Table 2 x Embryo devitalized, according to Table 2
6 8 10 Duration of immersion FIG.
12 (min)
U
76
18
20
1. Effect of water bath temperature and duration of immersion on the temperature of the blastoderm.
SUMMARY AND CONCLUSIONS
REFERENCES
Fertilized eggs were subjected to thermostabilization by hot-water immersion in order to devitalize their blastoderms. Thirty-one tests involving 390 hatching eggs indicated that the most desirable combinations of immersion period and temperature were 15 minutes at 55°C. or 8 to 12 minutes at 58°C. The temperature of 30 blastoderms was determined at different stages of such hotwater treatment. It was shown that the temperature of blastoderms lags markedly behind that of the water bath, even after 30 minutes of immersion. Any temperaturetime combination which is sufficient to raise the temperature of the blastoderm to 44°C, or more, will devitalize it and prevent subsequent embryonic development.
Barott, H. G., and E. H. McNally, 1943. Heat treating shell eggs. U. S. Egg Poultry Mag. 49: 320-322. 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: 443-4S0. Carlin, A. F., M. Marcy and P. A. Hartman, 19S8. Studies of thermostabilized eggs. Iowa Farm Sci. 13: 126. Feeney, R. E., L. R. MacDonnell and F. W. Lorenz, 1953. High temperature treatment of shell eggs. Poultry Sci. 32: 899. Funk, E. M., 1943a. Stabilizing quality in shell eggs. U. S. Egg Poultry Mag. 49: 112-144. Funk, E. M., 1943b. Stabilizing quality in shell eggs. Missouri Agr. Exp. Sta. Res. Bui. No. 362. Funk, E. M., 1943c. Pasteurization of shell eggs. Missouri Agr. Exp. Sta. Res. Bui. No. 364. Funk, E. M., 1950. Maintenance of quality in shell eggs by thermostabilization. Missouri Agr. Exp. Sta. Res. Bui. No. 467. Funk, E. M., 1955. Treating shell eggs to maintain
ACKNOWLEDGEMENTS
The authors are indebted to Dr. A. Berman for help with the temperature determinations of the blastoderms.
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S. BORNSTEIN AND B . LlPSTEIN
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:
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
A
CCORDING to Orel (1959), Pur- kynje, in his Latin report in 1825 and Czech paper in 1855, was the first to recommended dipping eggs into hot water, in order to coagulate the egg white in a thin layer on the egg shell and thus prevent water evaporation. Funk in a series of papers (1943 a, b, c, 1950, 1955) described a process which he termed "thermostabilization," in which the quality of shell eggs was maintained by (1) destroying the blastoderm and thus permanently stopping embryonic development in fertilized eggs, so that subsequently they react as infertile eggs, (2) stabilizing the thick albumen and (3) destroying many of the spoilage causing bacteria, thus obtaining a pasteurizing effect. Table 1 summarizes the recommendations, of various investigators, on optimal combination of treatment duration and temperature of the immersion media (water or oil) used for thermostabilization. These two variables depend upon initial egg temperature and upon the main purpose of the treatment. Unpublished data of this laboratory (Lipstein, 1960) indicated that the rate of internal egg quality deterioration is not higher in fertilized eggs than in infertile eggs. Nevertheless, the devitalization of fertilized eggs may be of practical importance in some areas. This is especially true for countries where fresh hatching eggs may find their way into regular market* Publication of the National and UniversityInstitute of Agriculture, Rehovot, Israel. 1961 Series, No. 442-E.
ing channels (during periods of sudden slumps in demands for chicks), and be subjected to high summer temperatures, which may cause a visible enlargement of the blastoderm. Although Funk (1943) showed that future embryonic development could be prevented by thermostabilization, this line of thought was followed only by Barott and McNally (1943). The purposes of this study were to determine the optimal immersion time and temperature for the prevention of future embryonic development and to elucidate the mode by which the blastoderm is devitalized. MATERIALS AND METHODS
Thirty-one lots of 10 or 20 eggs each (a total of 390 eggs), obtained from a breeding flock of S.C. White Leghorn hens, in their first year of production, were collected during morning hours, held for 1 to 2 hours at room temperature (usually about 18°C), individually weighed to the nearest quarter of a gram, and then treated by immersion into hot water. The temperature of the water was kept uniform by light manual stirring, and was stabilized by constant control with a thermometer and the addition of small quantities of nearly boiling water, as required. After the heat treatment, a few eggs were broken open immediately in order to check on albumen coagulation, while the remainder were placed for 8 days in an incubator at 32°C, a temperature simulating natural conditions. These eggs were subsequently reweighed, opened and examined visually.
1192
1193
THERMOSTABILIZATION OF EGGS TABLE 1.—Recommended heat treatments for thermostabilization of shell eggs* Immersion medium
Immersion time (min.)
oil water water water water water water water oil water oil water water water water oil water oil water water oil
10 15 5 20,10 1/12 30 30 15 16 51,2 16 1/20 15,5,3 13J,2 2 2 3 3 5 1
Temperature
Author
rc.) 60 54.51 58 / 55,59 100 54 54.5 54.5 54.5-57.0 60,62.5 54.5 100 54.5,60,63 57.5.62.5 62 \ 66.5/ 63 1 65.5/ 60,63,65.5 60 71
Funk (1943a, c) Funk (1943b) Barrott and McNally (1943) Romanoff and Romanoff (1944) Murphy and Sutton (1947) Bose and Stewart (1948) Funk (1950) Goresline et al. (1950) Salton et al. (1951) Carlin and Foth (1952) Feeney et al. (1953) Funk et al. (1954) Scott and Vickery (1954) Winter et al. (1954) Funk and Forward (1955) Funk (1955) Schmidt and Stadelman (1957) Carlin et al. (1958)
* Some of the variations in this table are probably due to different initial temperatures of the eggs, and some may be due to differences in the primary purpose of the treatment.
Haugh units were determined according to the methods described by Kilpatrick et al. (1958).f Measuring Temperature of Blastoderm. By placing eggs horizontally the blastoderm was allowed to orient to an upward position, and a small hole was drilled through the shell at its highest point of curvature. Thermocouples (35 S.W.G.) attached to a galvanometer were then inserted through this hole for a depth of 3-4 mm., until they encountered the resistance of the yolk's vitelline membrane. Keeping the egg in this position it was suspended by wires in a water bath to a depth at which all but its highest point (containing the hole) was immersed. Different eggs were immersed for periods of 5 to 30 minutes in water baths of 50°C, 55°C, 58°C, 60°C, 62°C. and 6S°C; 5 eggs were treated individually for each respective temperature. Readings of the galvat Results of these measurements are reported in the next paper of this series.
nometer were taken immediately before immersion in the water bath and subsequently every 2 to 3 minutes. RESULTS AND DISCUSSION
Optimal Conditions for Devitalizing Blastoderm. As Table 2 shows the most TABLE 2.—Results of immersing fertilized eggs into water of different temperatures for different lengths of time No. of 3 1 1 1 1 2 1 2 2 1 2 4 4 1 2 2 1
Total Temp. o f ^ ™ f * Appearno. of water „,„„ f " ance of albumen (°C.) (min.) 40 10 10 10 10 20 20 30 20 10 20 50
so 20 30 30 10
— 50
— 10
50 55 55 55 58 58 58 60 60 60 60 62 62 65 65
20 8 10 IS 8 10 12 3 5 8 10 3 5 3 5
clear clear clear clear clear clear clear clear clear clear clear clear* clearf clear clearf opaque opaque
Embryonic development blood ring blood ring blood ring blood ring blood ring none none none none blood ring blood ring nonej none blood ring none variable none
* A few exceptional eggs contained small pieces of coagulated albumen. t About half of the eggs contained small pieces of coagulated albumen. X A few exceptional eggs contained enlarged blastoderms.
1194
S. BORNSTEIN AND B . LlPSTEIN
effective treatment was obtained by im- upper limit to certain temperature-time mersing eggs into water of 55°C. for a combinations in thermostabilization. period of IS minutes or 58°C. for 8 to 12 Eleven lots of 10 fertilized eggs each minutes. A water treatment of 8 minutes at were exposed to hot air of 60° C. for 3 to 15 60°C. gave borderline results. minutes and of 80°C. for 3 to 12 minutes—• These data agree relatively well with without obtaining any thermostabilization. those of Funk (1943b), who recommended It seems that the lower thermoconductivity 5 minutes at S8°C. as treatment for the of air, as compared to water, requires a prevention of embryonic development. more prolonged time for warming objects Moreover, they are practically identical in touch with it. with the results of Barott and McNally Effect of Thermostabilization on Blasto(1943), reproduced as Figure 5 in the com- dermal Temperature. Figure 1 shows the pilation of Funk (1955). He found that effect of various immersion temperatures on all embryo development was checked by warming rate of the blastoderm (or its imimmersion at temperatures between 50°C. mediate surrounding). It is apparent that and 56°C. for periods of time too short to at all times there was a marked difference produce opacity in the egg white. At tem- between the temperature of the water bath peratures between 56°C. and 61°C, how- and that of the blastoderm: after 20 minever, the immersion time necessary for em- utes at 50°C. the latter reaches only bryonic destruction was slightly longer than 40.8°C, and even after 30 minutes at that which produced barely perceptible al- 60°C. it only went up to 52°C. (not shown bumen opacity. According to our data the in Fig. 1). Similar phenomena have been latter phenomenon is not apparent at a described by Funk (1943c), Goresline et al. temperature of 58°C. and starts only at (1950) and by Scott and Vickery (1954) 60°C. Thus, at temperatures up to 59°C, under different experimental conditions. it is possible to destroy the blastoderm A comparison between the data of Figwithout visibly affecting egg albumen. ure 1 and those of Table 2 demonstrates According to Barott and McNally that any combination of immersion period (1943), the duration of water immersion and temperature which will raise the temrequired for the appearance of perceptible perature of the blastoderm to 44°C, and opacity varied from 4 minutes at 62°C. to above, will cause its destruction; vice versa, 44 minutes at 51.5°C. Saltan et al. (1951) any combination which fails to reach this have cautioned that above 64° C. complete internal temperature is ineffective. There control of bacterial rotting cannot generally was one exception with eggs dipped for be achieved without some coagulation of 8 minutes in water at 58°C: according to the albumen. Carlin and Foth (1952) Table 2 this treatment prevented subsefound gelatinous masses and increased tur- quent embryonic development, while acbidity when treating eggs for 8 minutes in cording to Figure 1 the average blastoderoil at a temperature of 62 °C. Winter mal temperature obtained by this treatet al. (1954) reported some coagula- ment was only 43.1°C. (however, 2 out tion when eggs were water-treated for 2 of 5 eggs did reach an internal temperature minutes at 64.5°C, while after a 2-minute of 44°C). These data seem to indicate that treatment in oil some coagulation will ap- the effect of thermostabilization on the ferpear only at 69 °C. Hence it must not be tilized egg is the direct result of heat-death forgotten that albumen coagulation sets an of the blastoderm.
1195
THERMOSTABILIZATION OF EGGS "i—r
55 °C
SOK
o Measurements by means of thermocouples • No effect on embryo, according to Table 2 x Embryo devitalized, according to Table 2
6 8 10 Duration of immersion FIG.
12 (min)
U
76
18
20
1. Effect of water bath temperature and duration of immersion on the temperature of the blastoderm.
SUMMARY AND CONCLUSIONS
REFERENCES
Fertilized eggs were subjected to thermostabilization by hot-water immersion in order to devitalize their blastoderms. Thirty-one tests involving 390 hatching eggs indicated that the most desirable combinations of immersion period and temperature were 15 minutes at 55°C. or 8 to 12 minutes at 58°C. The temperature of 30 blastoderms was determined at different stages of such hotwater treatment. It was shown that the temperature of blastoderms lags markedly behind that of the water bath, even after 30 minutes of immersion. Any temperaturetime combination which is sufficient to raise the temperature of the blastoderm to 44°C, or more, will devitalize it and prevent subsequent embryonic development.
Barott, H. G., and E. H. McNally, 1943. Heat treating shell eggs. U. S. Egg Poultry Mag. 49: 320-322. 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: 443-4S0. Carlin, A. F., M. Marcy and P. A. Hartman, 19S8. Studies of thermostabilized eggs. Iowa Farm Sci. 13: 126. Feeney, R. E., L. R. MacDonnell and F. W. Lorenz, 1953. High temperature treatment of shell eggs. Poultry Sci. 32: 899. Funk, E. M., 1943a. Stabilizing quality in shell eggs. U. S. Egg Poultry Mag. 49: 112-144. Funk, E. M., 1943b. Stabilizing quality in shell eggs. Missouri Agr. Exp. Sta. Res. Bui. No. 362. Funk, E. M., 1943c. Pasteurization of shell eggs. Missouri Agr. Exp. Sta. Res. Bui. No. 364. Funk, E. M., 1950. Maintenance of quality in shell eggs by thermostabilization. Missouri Agr. Exp. Sta. Res. Bui. No. 467. Funk, E. M., 1955. Treating shell eggs to maintain
ACKNOWLEDGEMENTS
The authors are indebted to Dr. A. Berman for help with the temperature determinations of the blastoderms.
1196
S. BORNSTEIN AND B . LlPSTEIN
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:
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