- Email: [email protected]
The Relationship Between the Water Transfer and the pH of Egg Contents in Stored Eggs
T h e Relationship Between the Water Transfer and the pH of Egg Contents in Stored Eggs CHARLES A. DENTON AND HARRY W. TITUS 1
Bureau of Animal Industry, Agricultural Research Administration, U.S. Department of Agriculture, Beltsrille Research Center, Beltsville, Md.
yolk and white. As the carbon dioxide is lost from the egg and the p H increases, the white becomes more, fluid and loses water to the yolk, the yolk becomes less viscous, and the yolk membrane is weakened. The deterioration of the yolk is considered to be caused, in part, by the transfer of water to the yolk. Sharp and Stewart (1931) showed by means of yolk index measurements that there is a correlation between the pH of the white and
T T HAS been known for some time that -*• the pH of egg white is dependent on the state of the equilibrium of the bicarbonate buffer system (Healy and Peter, 1925). Romanoff and Romanoff (1930) found the buffer system to be reversible in its reaction and that the pH of the system could be changed by varying the quantity of carbon dioxide present. The mechanism of the reaction, according to McNally (1943) is as follows:
• NaHC0 8 +dissolved C02TJ ^C0 2 U+2NaHC0 3 <=* C 0 2 U + N a 2 C 0 3 + H 2 0 pH 8.35
pH less than 8.35 A loss in carbon dioxide with the accompanying rise in pH starts immediately, after the egg inlaid, and the rate of both is dependent on the age of the egg and the conditions of storage (Sharp and Powell, 1931). J t is "also well known that special treatments, such as coating the shells or storing the eggs in an atmosphere containing carbon dioxide will retard the loss of carbon dioxide from the egg white. Sharp (1929) and Moran (1937) studied the relationship between the pH of egg white and the physical properties of the 1
Resigned. Present address: Limestone Products Corporation of America, Newton, New Jersey.
pH more than 8.35
the condition of the yolk. The purpose of this paper is to present the results of a study of the relationship between the quantity of water gained by the yolk and the pH of egg contents in stored eggs. MATERIALS AND METHODS
Five different storage experiments, designed to influence the loss of carbon dioxide from stored eggs, were carried out in this study. Seventy-two eggs, divided into 3 equal lots, were used ii; each experiment. The eggs of one lot, the fresh egg controls, were analyzed for the total solid content of their whites and yolks on
135
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 21, 2015
(Received for publication, July ,11,1944)
136
CHARLES A. DENTON AND HARRY W. TITUS
the day they were laid. Measurements of the pH were made on the whites and yolks using an electronic pH meter with a glass electrode. The eggs of the second and third lots, the stored egg controls and the eggs that were treated or stored in a special way were held in a cold room at a temperature of 29-31°F. The different treatments were as follows : Experiment 1. The eggs were placed in
Experiment 5. The eggs were placed in an airtight container over a 10 percent solution of sodium hydroxide. After a storage period of 12 weeks the eggs were removed for analysis. Each of the eggs was weighed to determine its loss in weight during storage. Measurements were made of the pH of the whites and yolks. The total solids were determined by first partially drying the whites and yolks in an air oven at 65°C. and then
TABLE 1.—Summary of experimental results
None (fresh-egg controls) Stored 12 wks ; in 100 percent carbon dioxide Shells covered with methyl methacrylate and stored 12 wks. Shells covered with paraffin and stored 12 wks. Stored 12 wks in 100 percent nitrogen Stored 12 wks. (Stored egg controls) Stored 12 wks. over 10 percent sodium hydroxide
Average1 pH of the yolks
Average pH of the whites
6.02± .02*
7.60±.05*
Average gain Average1 total Average loss Average1 total Average1 loss in water by solids con- in water by solids conin weight of eggs the whites the yolks tent of the tent of the during during during yolks whites storage storage storage grams
percent 52.65±.07
grams
percent 11.36± .07
grams
0.88
U.69±.22
0.5S+..09
6.62±.29
*6.95±.29
0,24
51.95± .14
6.94± .08
7.86+ .03
0.43
51.37±.23
1.81
11.90+.. 16
1.15+ .08
7.10± .08
8.09±.OS
0.50
S1.22± .23
0.43
11.46±.15
0.05±.01
6.97+.10
8.14±.04
0.70
50.71±.22
1.16
11.45±.20
0.69±.O4
7.53±.26
8.61+ .22
0.87
50.21±.09
2.75
12.22+. .07
2.12±.06
7.54+.16
9.33±.02
1.25
49.45±.30
1.93
12.01±.18
0.64±.04
1 2
Average and standard error. pH measurements made within 1 hour after egg was laid. Measurement of pH made within 20 to 24 hours after the eggs were laid gave average values of 8.34± .06 for the whites and 6.01± .02 for the yolks.
an airtight container in an atmosphere of 100 percent carbon dioxide under a pressure of 4 mm. of mercury above atmospheric pressure. Experiment 2. The shells of the eggs were covered with partially polymerized methyl methacrylate and stored at atmospheric pressure in standard pasteboard egg cartons. Experiment 3. The shells of the eggs were covered with a low melting point paraffin and stored at atmospheric pressure in standard pasteboard egg cartons. Experiment 4. The eggs were placed in an airtight container in an atmosphere of 100 percent nitrogen, under a pressure of 4 mm. of mercury above atmospheric pressure.
drying them to a constant weight under vacuum at 100°C. EXPERIMENTAL RESULTS AND DISCUSSION
A summary of the experimental results is presented in Table 1. The measurements made on the 5 fresh egg control lots were in excellent agreement, as were also those made on the eggs of the 5 stored egg control lots. This made it possible to consider all the fresh egg controls as a single lot and all the stored egg controls as a single lot (Table 1); it also tended to make valid all comparisons among the specially treated and specially stored lots, even though all five experiments were not made simultaneously. The
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 21, 2015
Treatment given the egg
WATER TRANSFER AND THE P H OF CONTENTS IN STORED EGGS
Smith (1931) reported that the yolks of eggs stored in 100 percent carbon dioxide gained about 25 percent less water than did those eggs stored at the same temperature in air. The results obtained in this investigation indicate a much larger difference between the two treatments of stored eggs. The yolks of the stored egg controls gained on an average 0.87 gram of water, whereas those of the eggs stored in carbon dioxide gained only 0.24 gram. In the experiments in which the shells of the eggs were not covered there is a striking relationship between the gain in water by the yolks and the pH of the whites (Fig. 1). However, in the case of the two experiments in which the egg shells were covered the yolks gained less water than was indicated by the straight line relationship. Presumably interference with the normal passage of carbon dioxide and water through the shell has an effect on the relationship between the gain in
water by the yolk and the pH of the white. In this connection it is of interest to note the difference in the effect of the two covering agents, methyl methacrylate and paraffin, on the retention of water and carbon dioxide in the eggs. The methyl methacrylate permitted the loss of much more water than did the paraffin, but was *
YOLKS (GRAMS)
/ /
UI
•E 0.8
> CD UJ
2 0.6 z o
z
o
UJ
o
/ °
0.4
<*
cc UJ
> <
0.2
' 0 6
7
8
9
.
10
AVERAGE pH OF THE WHITES
FIG. 1. Relationship between the gain in water by the yolks and the pH of the whites in stored somewhat more efficient in retaining the carbon dioxide. All the treatments reduced the loss of water to a considerable extent. Coating the shells with paraffin proved to be the, most effective treatment, for in this case the water loss was reduced from 2.12 to 0.05 gram. ( The pH of the yolks of the treated eggs
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 21, 2015
percentages of total solids in the whites and yolks of the two kinds of control lots and in the whites and yolks of the specially treated lots were used to calculate the gain in water by the yolks and the loss in water by the whites in the stored eggs according to the procedure described by Denton and Titus (1943). Under the different conditions of storage the average pH values of the egg whites varied from 6.95 to 9.33. The estimated gain in water by the yolks varied from 0.24 to^ 1.25 grams. In the experiment in which the eggs were stored in carbon dioxide and the pH of the whites had an average of 6.95 only 0.24 gram of water on the average was gained in the yolks. In contrast, when the eggs were stored over 10 percent sodium hydroxide solution and the pH of the whites increased to an average value of 9.33 there was an average gain of L25 grams of water by the yolks.
137
138
C«lS£fes A.-"DE*rtON A»i> HAiifcY W.
varied on the average from 6162 to 7*54, the yolks of the eggs stored in carbon dioxide having the lowest value. As the yolks of the- fresh eggs had a p H of about 6.0, it is apparent thaT the retention of CO2 in the eggs did not prevent—but only retarded—-the increase in the pH of the yolks. There appears to be no consistent correlation between the pH of the yolks and the gain in weight of the yolks. SUMMARY
and the pH of the whites. In the experiments in which the shells of the eggs were Covered there was a deviation from the straight line relationship. There was no consistent correlation between the pH of the yolks and the gain in weight by the yolks. ACKNOWLEDGMENT
The authors wish to acknowledge the assistance given by Mr. W. L. Kellogg in doing the analytical work. REFERENCES
Dertton, C. A., and H. W. Titus, 1943. Water transfer in stored eggs; Effect of protein content of the diet of chickens and of length of the storage period. Poultry Sci. 22:451-456. Healy, D. J., and A. M. Peter, 1925. The hydrogenion concentration and basicity of egg yolk and egg. Amer. J. Physiol. 74:363-368. McNally, E. H., 1943. Some characteristics of the . ovomucin gel of egg white. Poultry Sci. 22:25-29. Moran, R., 1937. Gas storage of eggs. J. Soc. Chem. Ind.56:96-101 T. Romanoff, A. L., and A. J. Romanoff, 1930. Effect of carbon dioxide on the pH of albumen in the developing eggs. Exp. Zool. 56:451-457. Sharp, P. F., 1929. The pH of the white as an important factor influencing the keeping quality of heri eggs. Science (N. S.) 69:278-280. -^. arid G. F. Stewart, 1931. Carbon dioxide and the keeping quality of eggs. U. S. Egg and Poultry Mag., 37(6) :30-32, 63-68. and.G. K. Powell, 1931. Increase in the pH of the White and yolk of hen's eggs. Ind. and Eng. Chem:, 23:196-499. Smith, A. J. M., 1931. Ann. Rept. Food Invest. Board: pp. 161-163.
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 21, 2015
Five different storage experiments, designed to influence the loss of carbon dioxide from stored eggs were carried out in this study. The eggs were held in a cold room at a temperature of 29-31°F. for 12 weeks under the following conditions: (1) In 100 percent carbon dioxide under a pressure of 4 mm. of mercury above atmospheric pressure; (2) in 100 percent nitrogen under a pressure of 4 mm. of mercury above atmospheric pressure; (3) over a 10 percent solution of sodium hydroxide; (4) the shells were covered with partially polymerized methyl methacrylate; (5) the shells were covered with paraffin. The eggs stored under carbon dioxide had the lowest pH values for the whites and yolks, whereas those stored over sodium hydroxide had the highest values. In the experiments in which the shells of the eggs were not covered there was a linear relationship between the gain in water by the yolks
TITUS
Bureau of Animal Industry, Agricultural Research Administration, U.S. Department of Agriculture, Beltsrille Research Center, Beltsville, Md.
yolk and white. As the carbon dioxide is lost from the egg and the p H increases, the white becomes more, fluid and loses water to the yolk, the yolk becomes less viscous, and the yolk membrane is weakened. The deterioration of the yolk is considered to be caused, in part, by the transfer of water to the yolk. Sharp and Stewart (1931) showed by means of yolk index measurements that there is a correlation between the pH of the white and
T T HAS been known for some time that -*• the pH of egg white is dependent on the state of the equilibrium of the bicarbonate buffer system (Healy and Peter, 1925). Romanoff and Romanoff (1930) found the buffer system to be reversible in its reaction and that the pH of the system could be changed by varying the quantity of carbon dioxide present. The mechanism of the reaction, according to McNally (1943) is as follows:
• NaHC0 8 +dissolved C02TJ ^C0 2 U+2NaHC0 3 <=* C 0 2 U + N a 2 C 0 3 + H 2 0 pH 8.35
pH less than 8.35 A loss in carbon dioxide with the accompanying rise in pH starts immediately, after the egg inlaid, and the rate of both is dependent on the age of the egg and the conditions of storage (Sharp and Powell, 1931). J t is "also well known that special treatments, such as coating the shells or storing the eggs in an atmosphere containing carbon dioxide will retard the loss of carbon dioxide from the egg white. Sharp (1929) and Moran (1937) studied the relationship between the pH of egg white and the physical properties of the 1
Resigned. Present address: Limestone Products Corporation of America, Newton, New Jersey.
pH more than 8.35
the condition of the yolk. The purpose of this paper is to present the results of a study of the relationship between the quantity of water gained by the yolk and the pH of egg contents in stored eggs. MATERIALS AND METHODS
Five different storage experiments, designed to influence the loss of carbon dioxide from stored eggs, were carried out in this study. Seventy-two eggs, divided into 3 equal lots, were used ii; each experiment. The eggs of one lot, the fresh egg controls, were analyzed for the total solid content of their whites and yolks on
135
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 21, 2015
(Received for publication, July ,11,1944)
136
CHARLES A. DENTON AND HARRY W. TITUS
the day they were laid. Measurements of the pH were made on the whites and yolks using an electronic pH meter with a glass electrode. The eggs of the second and third lots, the stored egg controls and the eggs that were treated or stored in a special way were held in a cold room at a temperature of 29-31°F. The different treatments were as follows : Experiment 1. The eggs were placed in
Experiment 5. The eggs were placed in an airtight container over a 10 percent solution of sodium hydroxide. After a storage period of 12 weeks the eggs were removed for analysis. Each of the eggs was weighed to determine its loss in weight during storage. Measurements were made of the pH of the whites and yolks. The total solids were determined by first partially drying the whites and yolks in an air oven at 65°C. and then
TABLE 1.—Summary of experimental results
None (fresh-egg controls) Stored 12 wks ; in 100 percent carbon dioxide Shells covered with methyl methacrylate and stored 12 wks. Shells covered with paraffin and stored 12 wks. Stored 12 wks in 100 percent nitrogen Stored 12 wks. (Stored egg controls) Stored 12 wks. over 10 percent sodium hydroxide
Average1 pH of the yolks
Average pH of the whites
6.02± .02*
7.60±.05*
Average gain Average1 total Average loss Average1 total Average1 loss in water by solids con- in water by solids conin weight of eggs the whites the yolks tent of the tent of the during during during yolks whites storage storage storage grams
percent 52.65±.07
grams
percent 11.36± .07
grams
0.88
U.69±.22
0.5S+..09
6.62±.29
*6.95±.29
0,24
51.95± .14
6.94± .08
7.86+ .03
0.43
51.37±.23
1.81
11.90+.. 16
1.15+ .08
7.10± .08
8.09±.OS
0.50
S1.22± .23
0.43
11.46±.15
0.05±.01
6.97+.10
8.14±.04
0.70
50.71±.22
1.16
11.45±.20
0.69±.O4
7.53±.26
8.61+ .22
0.87
50.21±.09
2.75
12.22+. .07
2.12±.06
7.54+.16
9.33±.02
1.25
49.45±.30
1.93
12.01±.18
0.64±.04
1 2
Average and standard error. pH measurements made within 1 hour after egg was laid. Measurement of pH made within 20 to 24 hours after the eggs were laid gave average values of 8.34± .06 for the whites and 6.01± .02 for the yolks.
an airtight container in an atmosphere of 100 percent carbon dioxide under a pressure of 4 mm. of mercury above atmospheric pressure. Experiment 2. The shells of the eggs were covered with partially polymerized methyl methacrylate and stored at atmospheric pressure in standard pasteboard egg cartons. Experiment 3. The shells of the eggs were covered with a low melting point paraffin and stored at atmospheric pressure in standard pasteboard egg cartons. Experiment 4. The eggs were placed in an airtight container in an atmosphere of 100 percent nitrogen, under a pressure of 4 mm. of mercury above atmospheric pressure.
drying them to a constant weight under vacuum at 100°C. EXPERIMENTAL RESULTS AND DISCUSSION
A summary of the experimental results is presented in Table 1. The measurements made on the 5 fresh egg control lots were in excellent agreement, as were also those made on the eggs of the 5 stored egg control lots. This made it possible to consider all the fresh egg controls as a single lot and all the stored egg controls as a single lot (Table 1); it also tended to make valid all comparisons among the specially treated and specially stored lots, even though all five experiments were not made simultaneously. The
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 21, 2015
Treatment given the egg
WATER TRANSFER AND THE P H OF CONTENTS IN STORED EGGS
Smith (1931) reported that the yolks of eggs stored in 100 percent carbon dioxide gained about 25 percent less water than did those eggs stored at the same temperature in air. The results obtained in this investigation indicate a much larger difference between the two treatments of stored eggs. The yolks of the stored egg controls gained on an average 0.87 gram of water, whereas those of the eggs stored in carbon dioxide gained only 0.24 gram. In the experiments in which the shells of the eggs were not covered there is a striking relationship between the gain in water by the yolks and the pH of the whites (Fig. 1). However, in the case of the two experiments in which the egg shells were covered the yolks gained less water than was indicated by the straight line relationship. Presumably interference with the normal passage of carbon dioxide and water through the shell has an effect on the relationship between the gain in
water by the yolk and the pH of the white. In this connection it is of interest to note the difference in the effect of the two covering agents, methyl methacrylate and paraffin, on the retention of water and carbon dioxide in the eggs. The methyl methacrylate permitted the loss of much more water than did the paraffin, but was *
YOLKS (GRAMS)
/ /
UI
•E 0.8
> CD UJ
2 0.6 z o
z
o
UJ
o
/ °
0.4
<*
cc UJ
> <
0.2
' 0 6
7
8
9
.
10
AVERAGE pH OF THE WHITES
FIG. 1. Relationship between the gain in water by the yolks and the pH of the whites in stored somewhat more efficient in retaining the carbon dioxide. All the treatments reduced the loss of water to a considerable extent. Coating the shells with paraffin proved to be the, most effective treatment, for in this case the water loss was reduced from 2.12 to 0.05 gram. ( The pH of the yolks of the treated eggs
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 21, 2015
percentages of total solids in the whites and yolks of the two kinds of control lots and in the whites and yolks of the specially treated lots were used to calculate the gain in water by the yolks and the loss in water by the whites in the stored eggs according to the procedure described by Denton and Titus (1943). Under the different conditions of storage the average pH values of the egg whites varied from 6.95 to 9.33. The estimated gain in water by the yolks varied from 0.24 to^ 1.25 grams. In the experiment in which the eggs were stored in carbon dioxide and the pH of the whites had an average of 6.95 only 0.24 gram of water on the average was gained in the yolks. In contrast, when the eggs were stored over 10 percent sodium hydroxide solution and the pH of the whites increased to an average value of 9.33 there was an average gain of L25 grams of water by the yolks.
137
138
C«lS£fes A.-"DE*rtON A»i> HAiifcY W.
varied on the average from 6162 to 7*54, the yolks of the eggs stored in carbon dioxide having the lowest value. As the yolks of the- fresh eggs had a p H of about 6.0, it is apparent thaT the retention of CO2 in the eggs did not prevent—but only retarded—-the increase in the pH of the yolks. There appears to be no consistent correlation between the pH of the yolks and the gain in weight of the yolks. SUMMARY
and the pH of the whites. In the experiments in which the shells of the eggs were Covered there was a deviation from the straight line relationship. There was no consistent correlation between the pH of the yolks and the gain in weight by the yolks. ACKNOWLEDGMENT
The authors wish to acknowledge the assistance given by Mr. W. L. Kellogg in doing the analytical work. REFERENCES
Dertton, C. A., and H. W. Titus, 1943. Water transfer in stored eggs; Effect of protein content of the diet of chickens and of length of the storage period. Poultry Sci. 22:451-456. Healy, D. J., and A. M. Peter, 1925. The hydrogenion concentration and basicity of egg yolk and egg. Amer. J. Physiol. 74:363-368. McNally, E. H., 1943. Some characteristics of the . ovomucin gel of egg white. Poultry Sci. 22:25-29. Moran, R., 1937. Gas storage of eggs. J. Soc. Chem. Ind.56:96-101 T. Romanoff, A. L., and A. J. Romanoff, 1930. Effect of carbon dioxide on the pH of albumen in the developing eggs. Exp. Zool. 56:451-457. Sharp, P. F., 1929. The pH of the white as an important factor influencing the keeping quality of heri eggs. Science (N. S.) 69:278-280. -^. arid G. F. Stewart, 1931. Carbon dioxide and the keeping quality of eggs. U. S. Egg and Poultry Mag., 37(6) :30-32, 63-68. and.G. K. Powell, 1931. Increase in the pH of the White and yolk of hen's eggs. Ind. and Eng. Chem:, 23:196-499. Smith, A. J. M., 1931. Ann. Rept. Food Invest. Board: pp. 161-163.
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 21, 2015
Five different storage experiments, designed to influence the loss of carbon dioxide from stored eggs were carried out in this study. The eggs were held in a cold room at a temperature of 29-31°F. for 12 weeks under the following conditions: (1) In 100 percent carbon dioxide under a pressure of 4 mm. of mercury above atmospheric pressure; (2) in 100 percent nitrogen under a pressure of 4 mm. of mercury above atmospheric pressure; (3) over a 10 percent solution of sodium hydroxide; (4) the shells were covered with partially polymerized methyl methacrylate; (5) the shells were covered with paraffin. The eggs stored under carbon dioxide had the lowest pH values for the whites and yolks, whereas those stored over sodium hydroxide had the highest values. In the experiments in which the shells of the eggs were not covered there was a linear relationship between the gain in water by the yolks
TITUS