- Email: [email protected]
Physical and Functional Properties of Gamma Irradiated Liquid Egg White
1481
AMINO ACIDS IN BLOOD MEAL
cally ascertaining all the amino acid deficiencies of a given protein source, it is easy to conclude that certain amino acids might not be readily available in that protein source. Certainly this might have been suggested for blood meal when isoleucine supplementation alone did not greatly improve its nutritive value. There was no suggestion from earlier studies that other amino acids such as arginine and methionine might be equally or more limiting than isoleucine.
Blood meal as the only protein source was fed to male, crossbred chicks at 11 and 13% of the diet. It was found that isoleucine, methionine, and arginine were limiting amino acids and that isoleucine alone did not materially improve nutritive quality. Tryptophan was not found to be limiting although calculations based on the amino acid composition of the blood meal suggested its presence in borderline quantity. ACKNOWLEDGMENT The blood meal was generously supplied
REFERENCES Becker, D. E., I. D. Smith, S. W. Terrill, A. H. Jensen and H. W. Norton, 1963. Isoleucine need of swine at two stages of development. J. An. Sci. 22 : 1093-1096. Block, R. J., and K. W. Weiss, 19S6. Amino Acid Handbook, p. 341, Charles C Thomas, Springfield, Illinois. Grau, C. R., and H. J. Almquist, 1944. Beef blood in chick diets. Poultry Sci. 23: 486-490. Harper, A. E., 1964. In Mammalian Protein Metabolism edited by H. N. Munro and J. B. Allison, volume II, chapter 13, p. 123, Academic Press, New York, N.Y. Moore, S., D. H. Spackman and W. H. Stein, 1958. Chromatography of amino acids of sulfonated polystyrene resins. Anal. Chem. 30: 1185-1190. Rasmussen, O. G., C. R. Myers, M. M. Darrow and O. H. M. Wilder, 1958. The use of blood meal in livestock feeds. American Meat Institute Foundation, Bulletin No. 39. Spackman, D. H., W. H. Stein and S. Moore, 1958. Automatic recording apparatus for use in the chromatography of amino acids. Anal. Chem. 30: 1190-1206.
Physical and Functional Properties of Gamma Irradiated Liquid Egg White H. R. BALL* AND F. A. GARDNER Poultry Science Department, Texas A&M University, College Station, Texas 77843 (Received for publication February 13, 1968)
INTRODUCTION OSSIBILITIES of preserving foods by applications of ionizing radiations have prompted numerous investigations during the past decade. Most of these studies have been primarily concerned with the micro-
P
* Present address: Department of Food Science and Nutrition, University of Missouri, Columbia, Missouri 65201.
biological and organoleptic properties of irradiated foods. The possibility of control and elimination of Salmonella in egg products has received considerable attention. Results obtained in these studies indicate that ionizing radiation as a means of pasteurizing egg products has excellent potential (Ketchum et al., 1965). The ability of radiation pasteurization
Downloaded from http://ps.oxfordjournals.org/ at University of New Orleans on May 27, 2015
SUMMARY
by the American Industrial Meal Company, Philadelphia, Pennsylvania.
1482
H. R. BALL AND F. A. GARDNER
EXPERIMENTAL METHODS
To study the effects of gamma radiation on egg white functional and physical characteristics, samples of egg white were irradiated and held in frozen storage for periods up to 18 days. Cakes were prepared from both the irradiated and the non-irradiated control egg white and physical characteristics, including viscosity, surface tension and solids content, of both systems were determined. This experiment was divided into three treatment replications. Each replication included samples of all five radiation levels. Upon completion of sample radiation, the egg white from each treatment was divided into three sub-groups and then frozen and held at — 20°C. until evaluated. One subgroup of each radiation level was evaluated on each of three testing days. It was subsequently found that the replications functioned as an additional unplanned experimental treatment caused entirely by differences in post-radiation frozen storage. During this experiment, samples were kept in post-radiation frozen storage for periods of two to eighteen days. Sample preparations. A homogenous egg white system was prepared from day old, infertile eggs produced at the Texas A&M University Poultry Center. All egg white included in this experiment was initially blended to a constant flow time from a Zahn # 3 viscosimeter cup. The blended egg white was pooled in a large glass container and continuously stirred until transferred to half gallon plastic freezer containers. The egg white was then frozen and held at — 20°C. until thawed for radiation treatment. Control egg white samples were also prepared from the pooled egg white. These control samples were subjected to all environmental conditions to which the irradiated samples were subjected, but were not exposed to radiation. Prior to radiation, treatment samples
Downloaded from http://ps.oxfordjournals.org/ at University of New Orleans on May 27, 2015
to control Salmonella in egg products has been amply demonstrated. Comer et al. (1963) reported that 0.54 Mrad. of gamma radiation would be sufficient to destroy or control eighteen species of Salmonella in frozen whole egg. Other workers using different egg products, other sources of ionizing radiation, and various species of Salmonella have reported similar results (Proctor et al., 1953; Nickerson et al., 1957; Brooks et al, 1959; and Mossel, 1960). The results published by these workers are the primary sources of information concerning the physical and functional properties of irradiated egg products. Generally, slight reductions in functional efficiency and changes in some of the physical properties have been reported after irradiating egg white and whole egg with dosages sufficient to cause substantial decreases in bacterial numbers. Nickerson et al. (1957) noted a slight reduction in the volume of angel cakes made from irradiated fresh and frozen egg white. The foam generated from these egg white systems was less stable than foam generated from untreated egg white. A radiation odor was also noted. Impaired functional performance, a decrease in viscosity, and color changes have been attributed to the irradiation of frozen whole egg by Brooks et al. (1959). McArdle et al. (1954) had previously noted a reduction in albumen height of irradiated shell eggs as compared to the non-irradiated eggs. The functional performance of the treated eggs was reported as being similar to that of storage eggs. Only limited information is available concerning the effects of ionizing radiation on some of the more important functional and physical properties of egg products. This paper presents the results of a study of the effects of gamma radiation on selected physical and functional properties of liquid egg white.
GAMMA RADIATION OF EGG WHITE
determined by using Ostwald-Fenske type viscosimeters in a 20°C. bath. The viscosimeters were pre-rinsed with the egg white system to be measured and flow times were determined on 10 ml. portions. Flow time was converted to centipoises by obtaining the flow time of solutions of known viscosity and using methods presented by Daniels and Alberty (1955). Surface tension was determined using a Fischer Surface Tensiometer, Model 20. Solids were determined by drying the egg white to a constant weight at 105-107°C. in a forced draft, electric oven. Electrophoretic patterns were obtained using a Spinco Model R Paper electrophoresis system following the general procedure of Evans and Bandemer (1956). Relative protein concentrations were determined by using the Beckman Model RB Analytrol. Statistical determinations. Statistical analysis of the data was performed with analysis of variance and multiple regression analysis programs by the Data Processing Center, Texas A&M University. RESULTS AND DISCUSSION
Differences in the appearance and odor of irradiated egg white compared to control egg white were noted immediately post-radiation. The irradiated egg white had a transparent, dull greenish yellow color. The radiation odor was similar to a mixed sulfurous-ammonium odor. The odor and color persisted through freezing and thawing procedures prior to functional evaluation. A separation resulting in two layers occurred during thawing of the irradiated samples. The bottom layer was thicker and made up about two-thirds of the volume. No visible re-separation occurred after blending the two layers together. Statistical analysis of the physical data are presented in Table 1. The data collected from all samples was analyzed by
Downloaded from http://ps.oxfordjournals.org/ at University of New Orleans on May 27, 2015
were thawed for twelve hours in a constant temperature bath at 1S°C. All samples were held under similar temperature conditions during the period of radiation and during a short post-radiation storage period. In addition, radiation treatment methods were designed to permit a constant holding period between thawing prior to radiation and re-freezing for post-radiation frozen storage. After irradiation, the samples were stirred, pH measured, and then divided into three equal sub-samples which were then frozen and held at — 20°C. until thawed prior to evaluation. The freezing and thawing procedures used were found to exert no significant effects on physical and functional characteristics of the system. One sub-sample from each treatment in a replicate was used for each evaluation period. Sub-samples were thawed for five hours in a 1S°C. bath. After thawing, the sub-samples were reblended and aliquots were taken for physical and functional testing. The aliquots were held at 5°C. until used. Irradiation. The egg white was irradiated in half-gallon plastic freezer containers. Radiation treatments were 0.000, 0.432, 0.576, 0.720, and 0.864 Mrad. of gamma radiation. The radiation source was a 1.5 kilocurie, Co60 source located at the Nuclear Science Center, Texas A&M University. A constant dose rate of 600 rad per minute at 20°C. was used. Functional determinations. The methods of Gardner (1960) were used to prepare angel cakes and determine foam drainage. Because of limited sample size imposed by the radiation facility, the method of preparing the cakes was modified by reducing the ingredients by one-third, by using 60 g. of batter, and by using the bottom half of one-pound coffee cans as cake pans. The cakes were baked at 200°C. for 17 minutes. Physical determinations. Viscosity was
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separations obtained from the irradiated and control egg white systems, as illustrated in Figure 1, indicate changes occurring in Treatment Means 1 those portions of the strip where the immoGamma Radiation Viscosity (Mrad.) Solids Surface Tension bile (ovomucin), conalbumin, and the glo(dynes/cm.) Ccentipoises) (%) bulins (G2 and G3) normally appear. 11.45" 55. l a 5.26 ab 0.000 3.03 0.432 11.42 b 55.3b Data presented in Table 2 indicates that 11.39" 55.4b 2.91° 0.576 11.39° 2.84 d 0.720 55.8° there were significant changes in the rela0.864 2.81e 11.40 b o 55.4b Total tive concentrations of five of the proteins Observations 135 270 270 Regression Coefficients On due to radiation treatment. A significant inRadiation Treatment -2.92** (Change/Mrad.) -0.07** 0.62 n.s. crease in the relative concentration of lyPost-Rad. Storage (Change/day) -0.02" 0.10" —0.01 n.s. sozyme during post-radiation frozen stor1 age was noted. The possible significance of Means with different superscripts differ at the 0.05 level of probability. this observation will be discussed later. ** Significant at the 0.01 leveljof probability, n.s. Not Significant. The mechanisms by which the proteins were altered is not known. However, analysis of variance methods. When applimarked reductions of viscosity and changes cable, treatment means were separated by of electrophoretic patterns would indicate Duncan's multiple range test. The data was molecular degradation. Radiation-induced then subjected to multiple regression analymain chain scissions and disruption of mosis to isolate the effects of both radiation lecular structure have been reported (Bacq level and days in post-radiation frozen and Alexander, 1961). These changes can storage. Severe molecular damage of the be caused by direct absorption of the ionizegg white proteins was indicated. Viscosity ing energy by the protein or by reactions of the egg white system was reduced with of the protein with the highly reactive radieach increased level of radiation and deolysis products of water described by Allen clined to about 50% of its original value when exposed to 0.864 Mrad. Multiple (1961). regression analysis indicates no significant post-radiation storage effect on the viscosity of the test systems. A small but significant decrease in the concentration of egg white solids was affected by both radiation treatment and post-radiation frozen storage. It is difficult to suggest a causative mechanism which might be involved in this effect. Comparison of the pooled radiation data versus the •s control data indicates that the solids content of the irradiated groups was consistently lower than that of the controls throughout the storage period. Analysis of the surface tension of the test systems indicates a significant and positive regression 3 1 1 2 5 of surface tension associated with post-ra- ' - g o o diation frozen storage and not with the ra- FIG. 1. Typical electrophoretic patterns of gamma diation treatment used. Electrophoretic irradiated egg white. TABLE 1.—Averages and statistical analysis of solids, surface tension, and viscosity of gamma irradiated egg white
0.43B MRAD.
0.676 MRAO.
0.720 MRAO.
0,064 MRAD.
i 1 i
J
1 I l
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•J.COO MRAD.
1485
GAMMA RADIATION OF EGG WHITE
TABLE 3.—Averages and statistical analysis of specific volume, beating time, and foam drainage of gamma irradiated egg white i S S , *&d) 0.000 0.432 0.576 0.720 0.864 Total Observations
Specific Volume (ml cake/g. batter) 5.76"1 5.73" 5.72"a 5.66b 5.51 135
Radiation Treatment (Changt /Mrad.) -- 0 . 2 4 " Post-Rad. Storage (Change/day) 0.03"
Beating Time (sec.)
Foam Drainage (ml.)
19.4? 50.4 bb 50.2 b 50.2 55.6"
14.1» 20.5 bb 21.2 b 21.0b 19.5
135 135 Regression Coefficients On 40.5"
7.1"
-0.5"
- 0 . 0 1 n.s.
1 Means with different superscripts differ at the 0.05 level of probability. " Significant at the 0.01 level of probability, n.s. Not significant.
than the change observed in the non-irradiated controls. The overall effect of postradiation frozen storage on cake specific volume is illustrated in Figure 2. Data from all radiation treatment levels were combined and the pooled results compared to the data obtained from the non-irradiated controls. Improvement in the functional efficiency of the irradiated samples is obvious. It was also found that radiation increased the beating time required to generate a suitable egg white foam. All radiation levels effected a Zyi fold increase in beating time compared to that of the non-irradiated controls. A small but significant decrease in beating time was noted as an effect of
TABLE 2.—Regression coefficients of relative protein concentrations of gamma irradiated egg white on radiation treatment and post-radiation storage Protein
Radiation Treatment 1
Post-Radiation Storage2
0.06 -2.20 -4.92 -7.27 7.53 6.60
0.14** 0.01 -0.01 -0.13 0.01 -0.01
• CONTROL
Lysozyme Immobile Conalbumin Ovalbumin Globulin, G2 Globulin, G3
** Significant at the 0.01 level of probability. 1 Change in relative concentration per Mrad. 2 Change in relative concentration per day of post-radiation storage.
O IRRADIATED
DAYS POST-RADIATION FROZEN STORASE
FIG. 2. Effect of post-radiation frozen storage on the functional performance of gamma irradiated egg white.
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The functional data summarized in Table 3 indicates that the radiation treatments caused an increase in beating time and a decrease in foam stability and the specific volume of cakes prepared from the test systems. Multiple regression analysis indicates that significant improvement in the functional efficiency of the irradiated systems occurred during post-radiation frozen storage. The beating time required to generate an acceptable foam decreased and the specific volume of cakes made from the irradiated systems increased as storage time increased. These changes, which occurred during frozen storage, suggest an alteration in the protein portion of the egg white system. Analysis of the cake specific volume of the irradiated systems through eighteen days post-radiation frozen storage, indicates that all radiation treatments exerted an initial adverse effect on cake volume. The severity of this effect increased with increasing levels of radiation. However, the functional efficiency of all irradiated systems as measured by cake specific volume, improved during the eighteen day post-radiation storage period. There were no significant differences in the rates of function improvement among the four radiation levels during the eighteen day frozen storage period. The rate of change in function of each radiation group was significantly different
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B —IRRADIATED
FIG. 3. Illustration of the texture of cakes made from gamma irradiated (.864 Mrad.) and nonirradiated egg white.
post-radiation frozen storage. A decrease in foam stability of the systems was effected by all radiation levels. No post-radiation storage effect was observed. In addition, cakes made from the irradiated egg white possessed a much coarser texture than cakes made from the non-irradiated controls (Figure 3). Cakes prepared from the irradiated systems had larger and fewer air cells with thicker cell wall structure. The finished cakes had no detectable off-odor even though the radiation odor was present in the batter. The results of the evaluated physical properties indicate that impaired functional performance was the result of radiation damage of egg white proteins. MacDonnell et al. (19SS), Nakamura and Sato (1964). and Nakamura (1963) credit conalbumin and the globulins (lysozyme, globulin G2 and globulin G3) with the production of egg white foams and maintenance of cake texture. MacDonnell et al. (1955) also reported that ovomucin, denatured during the generation of egg white foams, functions as a foam stabilizer. The electrophoretic patterns of the irradiated egg white systems indicate decreases in the relative concentration of proteins appearing in the conalbumin and ovomucin (immobile frac-
tion) portions of the strip. The increase in the staining material in the globulin region of the strips masks changes in these proteins, but damage to the globulin fractions is indicated by the poor texture of angle cakes made from irradiated egg white. The events leading to improved function during post-radiation storage are not clearly evident. There is some evidence that the improved function may be the result of minor but important chemical changes in the damaged proteins. Some of the improvement in functional performance of the irradiated systems associated with post-radiation frozen storage can possibly be attributed to the significant increase in the relative concentration of lysozyme with post-radiation storage time (Table 2). MacDonnell et al. (1955) demonstrated that addition of chicken egg white globulins to lysozyme-deficient duck egg white improved the functional performance of the latter. Degradation of protein complexes such as the ovomucin-lysozyme complex suggested by Hawthorne (1950) could serve as a source of additional functional lysozyme. The results of this study indicate the apparent dynamic nature of irradiated egg white based on the marked changes of functional performance and other physical properties during frozen aging of the irradiated egg white. It should be noted that the dose rate used in this study was relatively low (600 rad. per minute) compared to the higher dose rates of ionizing radiations used by other investigators. If higher dose rates are used, the time of radiation is shortened and chances of secondary indirect effects of ionizing radiations would be reduced. SUMMARY
Homogeneous, liquid egg white was treated with 0.000, 0.432, 0.576, 0.720, and 0.864 Mrad. of gamma radiation from a 1.5 kilocurie, Co60 source. The irradiated sys-
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A-CONTROL
H. R. BALL AND F. A. GARDNER
GAMMA RADIATION OF EGG WHITE
REFERENCES Allen, A. O., 1961. The Radiation Chemistry of Water and Aqueous Solutions, pp. 24-30, 142-184. D. Van Nostrand Company, Inc., N.Y. Bacq, A. M., and P. Alexander, 1961. Fundamentals of Radiobiology, 2nd ed.: pp. 157-216. The MacMillan Company, N.Y. Brooks, J., R. S. Hannan and B. C. Hobbs, 1959. Irradiation of eggs and egg products. Int. J. Appl. Rad. Isotopes, 6: 149-54. Comer, A. G., G. W. Anderson and E. H. Garrard, 1963. Gamma irradiation of Salmonella species in frozen whole egg. Canadian J. Microbiol. 9: 321-27. Daniels, F., and R. A. Alberty, 1955. Physical Chemistry, p. 176. John Wiley & Sons, Inc., N.Y. Evans, R. J., and S. L. Bandemer, 1956. Separa-
tion of egg white proteins by paper electrophoresis. J. Agr. Food Chem. 4 : 802-811. Gardner, F. A., 1960. Chemical modification of egg white function. Ph.D. dissertation, University of Missouri, Columbia, Missouri. Hawthorne, J. R., 1950. The action of egg white lysozyme on ovomucoid and ovomucin. Biochim. et Biophy. Acta, 6: 28-35. Ketcham, H. W., J. W. Osburn, Jr. and D. Deitch, 1965. Current status and commercial prospectus for radiation preservation of food. Division of Isotopes Development, U. S. Atomic Energy Commission, at (49-ll)-2S24; p. 53. U. S. Department of Commerce, Washington, D.C. MacDonnell, L. R., R. E. Feeney, H. L. Hanson, A. Campbell and T. R. Sugihara, 1955. The functional properties of the egg white proteins. Food Technol. 9:49-53. McArdle, F. J., W. Marion and N. W. Desrosier, 1954. Sterilization of shell eggs by ionization. Poultry Sci. 3 3 : 1070. Mossel, D. A. A., 1960. The destruction of Salmonella bacteria in refrigerated liquid whole egg with gamma radiation. Int. J. Appl. Rad. Isotopes, 9: 109-112. Nakamura, R., 1963. Studies on the foaming property of the chicken egg white. Part VI. Spread monolayer of the protein fraction of the chicken egg white. Agr. Biol. Chem. 27: 427-432. Nakamura, R., and Y. Sato, 1964. Studies on the foaming property of the chicken egg white. Part IX. On the coagulated proteins under various whipping conditions (The mechanism of foaminess (1)). Agr. Biol. Chem. 28: 524-29. Nickerson, J. T. R., S. E. Charm, R. C. Brogle, E. E. Lockhart, B. E. Proctor and H. Lineweaver, 1957. Use of high voltage cathode rays to destroy bacteria of the Salmonella group in liquid and frozen egg white and egg white solids. Food Technol. 11: 159-166. Proctor, B. E., R. F. Joslin, J. T. R. Nickerson and E. E. Lockhart, 1953. Elimination of Salmonella in whole egg powder by cathode ray irradiation of egg magna prior to drying. Food Technol. 7: 291-96.
NEWS AND NOTES (continued from page 1469) COLORADO NOTES Dr. Donald D. Johnson, Associate Dean of the College of Agriculture at Colorado State University, has been named Dean, effective July 1. He
has been administering the College of Agriculture since January 1, following the resignation of Dr. H. H. Stonaker, the former Dean. The Department of Poultry Science, Colorado
(continued on page 1402)
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tems were then frozen and held until used for measurements of physical and functional characteristics. Radiation treatment caused a reduction in viscosity, and a slight decrease in percent solids. Analysis of the electrophoretic patterns indicate a decrease in the relative concentration of proteins appearing in the ovomucin, conalbumin, and ovalbumin portions of the pattern and an increase in the relative concentration of proteins appearing in the globulin portions of the strip. Angel cakes made from the irradiated egg white required longer beating times in their preparation and had poorer texture and reduced volumes. Foams generated from irradiated egg white were less stable, as indicated by more extensive foam drainage. Functional performance as measured by beating time and cake volume improved during post-radiation frozen storage.
1487
AMINO ACIDS IN BLOOD MEAL
cally ascertaining all the amino acid deficiencies of a given protein source, it is easy to conclude that certain amino acids might not be readily available in that protein source. Certainly this might have been suggested for blood meal when isoleucine supplementation alone did not greatly improve its nutritive value. There was no suggestion from earlier studies that other amino acids such as arginine and methionine might be equally or more limiting than isoleucine.
Blood meal as the only protein source was fed to male, crossbred chicks at 11 and 13% of the diet. It was found that isoleucine, methionine, and arginine were limiting amino acids and that isoleucine alone did not materially improve nutritive quality. Tryptophan was not found to be limiting although calculations based on the amino acid composition of the blood meal suggested its presence in borderline quantity. ACKNOWLEDGMENT The blood meal was generously supplied
REFERENCES Becker, D. E., I. D. Smith, S. W. Terrill, A. H. Jensen and H. W. Norton, 1963. Isoleucine need of swine at two stages of development. J. An. Sci. 22 : 1093-1096. Block, R. J., and K. W. Weiss, 19S6. Amino Acid Handbook, p. 341, Charles C Thomas, Springfield, Illinois. Grau, C. R., and H. J. Almquist, 1944. Beef blood in chick diets. Poultry Sci. 23: 486-490. Harper, A. E., 1964. In Mammalian Protein Metabolism edited by H. N. Munro and J. B. Allison, volume II, chapter 13, p. 123, Academic Press, New York, N.Y. Moore, S., D. H. Spackman and W. H. Stein, 1958. Chromatography of amino acids of sulfonated polystyrene resins. Anal. Chem. 30: 1185-1190. Rasmussen, O. G., C. R. Myers, M. M. Darrow and O. H. M. Wilder, 1958. The use of blood meal in livestock feeds. American Meat Institute Foundation, Bulletin No. 39. Spackman, D. H., W. H. Stein and S. Moore, 1958. Automatic recording apparatus for use in the chromatography of amino acids. Anal. Chem. 30: 1190-1206.
Physical and Functional Properties of Gamma Irradiated Liquid Egg White H. R. BALL* AND F. A. GARDNER Poultry Science Department, Texas A&M University, College Station, Texas 77843 (Received for publication February 13, 1968)
INTRODUCTION OSSIBILITIES of preserving foods by applications of ionizing radiations have prompted numerous investigations during the past decade. Most of these studies have been primarily concerned with the micro-
P
* Present address: Department of Food Science and Nutrition, University of Missouri, Columbia, Missouri 65201.
biological and organoleptic properties of irradiated foods. The possibility of control and elimination of Salmonella in egg products has received considerable attention. Results obtained in these studies indicate that ionizing radiation as a means of pasteurizing egg products has excellent potential (Ketchum et al., 1965). The ability of radiation pasteurization
Downloaded from http://ps.oxfordjournals.org/ at University of New Orleans on May 27, 2015
SUMMARY
by the American Industrial Meal Company, Philadelphia, Pennsylvania.
1482
H. R. BALL AND F. A. GARDNER
EXPERIMENTAL METHODS
To study the effects of gamma radiation on egg white functional and physical characteristics, samples of egg white were irradiated and held in frozen storage for periods up to 18 days. Cakes were prepared from both the irradiated and the non-irradiated control egg white and physical characteristics, including viscosity, surface tension and solids content, of both systems were determined. This experiment was divided into three treatment replications. Each replication included samples of all five radiation levels. Upon completion of sample radiation, the egg white from each treatment was divided into three sub-groups and then frozen and held at — 20°C. until evaluated. One subgroup of each radiation level was evaluated on each of three testing days. It was subsequently found that the replications functioned as an additional unplanned experimental treatment caused entirely by differences in post-radiation frozen storage. During this experiment, samples were kept in post-radiation frozen storage for periods of two to eighteen days. Sample preparations. A homogenous egg white system was prepared from day old, infertile eggs produced at the Texas A&M University Poultry Center. All egg white included in this experiment was initially blended to a constant flow time from a Zahn # 3 viscosimeter cup. The blended egg white was pooled in a large glass container and continuously stirred until transferred to half gallon plastic freezer containers. The egg white was then frozen and held at — 20°C. until thawed for radiation treatment. Control egg white samples were also prepared from the pooled egg white. These control samples were subjected to all environmental conditions to which the irradiated samples were subjected, but were not exposed to radiation. Prior to radiation, treatment samples
Downloaded from http://ps.oxfordjournals.org/ at University of New Orleans on May 27, 2015
to control Salmonella in egg products has been amply demonstrated. Comer et al. (1963) reported that 0.54 Mrad. of gamma radiation would be sufficient to destroy or control eighteen species of Salmonella in frozen whole egg. Other workers using different egg products, other sources of ionizing radiation, and various species of Salmonella have reported similar results (Proctor et al., 1953; Nickerson et al., 1957; Brooks et al, 1959; and Mossel, 1960). The results published by these workers are the primary sources of information concerning the physical and functional properties of irradiated egg products. Generally, slight reductions in functional efficiency and changes in some of the physical properties have been reported after irradiating egg white and whole egg with dosages sufficient to cause substantial decreases in bacterial numbers. Nickerson et al. (1957) noted a slight reduction in the volume of angel cakes made from irradiated fresh and frozen egg white. The foam generated from these egg white systems was less stable than foam generated from untreated egg white. A radiation odor was also noted. Impaired functional performance, a decrease in viscosity, and color changes have been attributed to the irradiation of frozen whole egg by Brooks et al. (1959). McArdle et al. (1954) had previously noted a reduction in albumen height of irradiated shell eggs as compared to the non-irradiated eggs. The functional performance of the treated eggs was reported as being similar to that of storage eggs. Only limited information is available concerning the effects of ionizing radiation on some of the more important functional and physical properties of egg products. This paper presents the results of a study of the effects of gamma radiation on selected physical and functional properties of liquid egg white.
GAMMA RADIATION OF EGG WHITE
determined by using Ostwald-Fenske type viscosimeters in a 20°C. bath. The viscosimeters were pre-rinsed with the egg white system to be measured and flow times were determined on 10 ml. portions. Flow time was converted to centipoises by obtaining the flow time of solutions of known viscosity and using methods presented by Daniels and Alberty (1955). Surface tension was determined using a Fischer Surface Tensiometer, Model 20. Solids were determined by drying the egg white to a constant weight at 105-107°C. in a forced draft, electric oven. Electrophoretic patterns were obtained using a Spinco Model R Paper electrophoresis system following the general procedure of Evans and Bandemer (1956). Relative protein concentrations were determined by using the Beckman Model RB Analytrol. Statistical determinations. Statistical analysis of the data was performed with analysis of variance and multiple regression analysis programs by the Data Processing Center, Texas A&M University. RESULTS AND DISCUSSION
Differences in the appearance and odor of irradiated egg white compared to control egg white were noted immediately post-radiation. The irradiated egg white had a transparent, dull greenish yellow color. The radiation odor was similar to a mixed sulfurous-ammonium odor. The odor and color persisted through freezing and thawing procedures prior to functional evaluation. A separation resulting in two layers occurred during thawing of the irradiated samples. The bottom layer was thicker and made up about two-thirds of the volume. No visible re-separation occurred after blending the two layers together. Statistical analysis of the physical data are presented in Table 1. The data collected from all samples was analyzed by
Downloaded from http://ps.oxfordjournals.org/ at University of New Orleans on May 27, 2015
were thawed for twelve hours in a constant temperature bath at 1S°C. All samples were held under similar temperature conditions during the period of radiation and during a short post-radiation storage period. In addition, radiation treatment methods were designed to permit a constant holding period between thawing prior to radiation and re-freezing for post-radiation frozen storage. After irradiation, the samples were stirred, pH measured, and then divided into three equal sub-samples which were then frozen and held at — 20°C. until thawed prior to evaluation. The freezing and thawing procedures used were found to exert no significant effects on physical and functional characteristics of the system. One sub-sample from each treatment in a replicate was used for each evaluation period. Sub-samples were thawed for five hours in a 1S°C. bath. After thawing, the sub-samples were reblended and aliquots were taken for physical and functional testing. The aliquots were held at 5°C. until used. Irradiation. The egg white was irradiated in half-gallon plastic freezer containers. Radiation treatments were 0.000, 0.432, 0.576, 0.720, and 0.864 Mrad. of gamma radiation. The radiation source was a 1.5 kilocurie, Co60 source located at the Nuclear Science Center, Texas A&M University. A constant dose rate of 600 rad per minute at 20°C. was used. Functional determinations. The methods of Gardner (1960) were used to prepare angel cakes and determine foam drainage. Because of limited sample size imposed by the radiation facility, the method of preparing the cakes was modified by reducing the ingredients by one-third, by using 60 g. of batter, and by using the bottom half of one-pound coffee cans as cake pans. The cakes were baked at 200°C. for 17 minutes. Physical determinations. Viscosity was
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A.
GARDNER
separations obtained from the irradiated and control egg white systems, as illustrated in Figure 1, indicate changes occurring in Treatment Means 1 those portions of the strip where the immoGamma Radiation Viscosity (Mrad.) Solids Surface Tension bile (ovomucin), conalbumin, and the glo(dynes/cm.) Ccentipoises) (%) bulins (G2 and G3) normally appear. 11.45" 55. l a 5.26 ab 0.000 3.03 0.432 11.42 b 55.3b Data presented in Table 2 indicates that 11.39" 55.4b 2.91° 0.576 11.39° 2.84 d 0.720 55.8° there were significant changes in the rela0.864 2.81e 11.40 b o 55.4b Total tive concentrations of five of the proteins Observations 135 270 270 Regression Coefficients On due to radiation treatment. A significant inRadiation Treatment -2.92** (Change/Mrad.) -0.07** 0.62 n.s. crease in the relative concentration of lyPost-Rad. Storage (Change/day) -0.02" 0.10" —0.01 n.s. sozyme during post-radiation frozen stor1 age was noted. The possible significance of Means with different superscripts differ at the 0.05 level of probability. this observation will be discussed later. ** Significant at the 0.01 leveljof probability, n.s. Not Significant. The mechanisms by which the proteins were altered is not known. However, analysis of variance methods. When applimarked reductions of viscosity and changes cable, treatment means were separated by of electrophoretic patterns would indicate Duncan's multiple range test. The data was molecular degradation. Radiation-induced then subjected to multiple regression analymain chain scissions and disruption of mosis to isolate the effects of both radiation lecular structure have been reported (Bacq level and days in post-radiation frozen and Alexander, 1961). These changes can storage. Severe molecular damage of the be caused by direct absorption of the ionizegg white proteins was indicated. Viscosity ing energy by the protein or by reactions of the egg white system was reduced with of the protein with the highly reactive radieach increased level of radiation and deolysis products of water described by Allen clined to about 50% of its original value when exposed to 0.864 Mrad. Multiple (1961). regression analysis indicates no significant post-radiation storage effect on the viscosity of the test systems. A small but significant decrease in the concentration of egg white solids was affected by both radiation treatment and post-radiation frozen storage. It is difficult to suggest a causative mechanism which might be involved in this effect. Comparison of the pooled radiation data versus the •s control data indicates that the solids content of the irradiated groups was consistently lower than that of the controls throughout the storage period. Analysis of the surface tension of the test systems indicates a significant and positive regression 3 1 1 2 5 of surface tension associated with post-ra- ' - g o o diation frozen storage and not with the ra- FIG. 1. Typical electrophoretic patterns of gamma diation treatment used. Electrophoretic irradiated egg white. TABLE 1.—Averages and statistical analysis of solids, surface tension, and viscosity of gamma irradiated egg white
0.43B MRAD.
0.676 MRAO.
0.720 MRAO.
0,064 MRAD.
i 1 i
J
1 I l
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•J.COO MRAD.
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GAMMA RADIATION OF EGG WHITE
TABLE 3.—Averages and statistical analysis of specific volume, beating time, and foam drainage of gamma irradiated egg white i S S , *&d) 0.000 0.432 0.576 0.720 0.864 Total Observations
Specific Volume (ml cake/g. batter) 5.76"1 5.73" 5.72"a 5.66b 5.51 135
Radiation Treatment (Changt /Mrad.) -- 0 . 2 4 " Post-Rad. Storage (Change/day) 0.03"
Beating Time (sec.)
Foam Drainage (ml.)
19.4? 50.4 bb 50.2 b 50.2 55.6"
14.1» 20.5 bb 21.2 b 21.0b 19.5
135 135 Regression Coefficients On 40.5"
7.1"
-0.5"
- 0 . 0 1 n.s.
1 Means with different superscripts differ at the 0.05 level of probability. " Significant at the 0.01 level of probability, n.s. Not significant.
than the change observed in the non-irradiated controls. The overall effect of postradiation frozen storage on cake specific volume is illustrated in Figure 2. Data from all radiation treatment levels were combined and the pooled results compared to the data obtained from the non-irradiated controls. Improvement in the functional efficiency of the irradiated samples is obvious. It was also found that radiation increased the beating time required to generate a suitable egg white foam. All radiation levels effected a Zyi fold increase in beating time compared to that of the non-irradiated controls. A small but significant decrease in beating time was noted as an effect of
TABLE 2.—Regression coefficients of relative protein concentrations of gamma irradiated egg white on radiation treatment and post-radiation storage Protein
Radiation Treatment 1
Post-Radiation Storage2
0.06 -2.20 -4.92 -7.27 7.53 6.60
0.14** 0.01 -0.01 -0.13 0.01 -0.01
• CONTROL
Lysozyme Immobile Conalbumin Ovalbumin Globulin, G2 Globulin, G3
** Significant at the 0.01 level of probability. 1 Change in relative concentration per Mrad. 2 Change in relative concentration per day of post-radiation storage.
O IRRADIATED
DAYS POST-RADIATION FROZEN STORASE
FIG. 2. Effect of post-radiation frozen storage on the functional performance of gamma irradiated egg white.
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The functional data summarized in Table 3 indicates that the radiation treatments caused an increase in beating time and a decrease in foam stability and the specific volume of cakes prepared from the test systems. Multiple regression analysis indicates that significant improvement in the functional efficiency of the irradiated systems occurred during post-radiation frozen storage. The beating time required to generate an acceptable foam decreased and the specific volume of cakes made from the irradiated systems increased as storage time increased. These changes, which occurred during frozen storage, suggest an alteration in the protein portion of the egg white system. Analysis of the cake specific volume of the irradiated systems through eighteen days post-radiation frozen storage, indicates that all radiation treatments exerted an initial adverse effect on cake volume. The severity of this effect increased with increasing levels of radiation. However, the functional efficiency of all irradiated systems as measured by cake specific volume, improved during the eighteen day post-radiation storage period. There were no significant differences in the rates of function improvement among the four radiation levels during the eighteen day frozen storage period. The rate of change in function of each radiation group was significantly different
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B —IRRADIATED
FIG. 3. Illustration of the texture of cakes made from gamma irradiated (.864 Mrad.) and nonirradiated egg white.
post-radiation frozen storage. A decrease in foam stability of the systems was effected by all radiation levels. No post-radiation storage effect was observed. In addition, cakes made from the irradiated egg white possessed a much coarser texture than cakes made from the non-irradiated controls (Figure 3). Cakes prepared from the irradiated systems had larger and fewer air cells with thicker cell wall structure. The finished cakes had no detectable off-odor even though the radiation odor was present in the batter. The results of the evaluated physical properties indicate that impaired functional performance was the result of radiation damage of egg white proteins. MacDonnell et al. (19SS), Nakamura and Sato (1964). and Nakamura (1963) credit conalbumin and the globulins (lysozyme, globulin G2 and globulin G3) with the production of egg white foams and maintenance of cake texture. MacDonnell et al. (1955) also reported that ovomucin, denatured during the generation of egg white foams, functions as a foam stabilizer. The electrophoretic patterns of the irradiated egg white systems indicate decreases in the relative concentration of proteins appearing in the conalbumin and ovomucin (immobile frac-
tion) portions of the strip. The increase in the staining material in the globulin region of the strips masks changes in these proteins, but damage to the globulin fractions is indicated by the poor texture of angle cakes made from irradiated egg white. The events leading to improved function during post-radiation storage are not clearly evident. There is some evidence that the improved function may be the result of minor but important chemical changes in the damaged proteins. Some of the improvement in functional performance of the irradiated systems associated with post-radiation frozen storage can possibly be attributed to the significant increase in the relative concentration of lysozyme with post-radiation storage time (Table 2). MacDonnell et al. (1955) demonstrated that addition of chicken egg white globulins to lysozyme-deficient duck egg white improved the functional performance of the latter. Degradation of protein complexes such as the ovomucin-lysozyme complex suggested by Hawthorne (1950) could serve as a source of additional functional lysozyme. The results of this study indicate the apparent dynamic nature of irradiated egg white based on the marked changes of functional performance and other physical properties during frozen aging of the irradiated egg white. It should be noted that the dose rate used in this study was relatively low (600 rad. per minute) compared to the higher dose rates of ionizing radiations used by other investigators. If higher dose rates are used, the time of radiation is shortened and chances of secondary indirect effects of ionizing radiations would be reduced. SUMMARY
Homogeneous, liquid egg white was treated with 0.000, 0.432, 0.576, 0.720, and 0.864 Mrad. of gamma radiation from a 1.5 kilocurie, Co60 source. The irradiated sys-
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A-CONTROL
H. R. BALL AND F. A. GARDNER
GAMMA RADIATION OF EGG WHITE
REFERENCES Allen, A. O., 1961. The Radiation Chemistry of Water and Aqueous Solutions, pp. 24-30, 142-184. D. Van Nostrand Company, Inc., N.Y. Bacq, A. M., and P. Alexander, 1961. Fundamentals of Radiobiology, 2nd ed.: pp. 157-216. The MacMillan Company, N.Y. Brooks, J., R. S. Hannan and B. C. Hobbs, 1959. Irradiation of eggs and egg products. Int. J. Appl. Rad. Isotopes, 6: 149-54. Comer, A. G., G. W. Anderson and E. H. Garrard, 1963. Gamma irradiation of Salmonella species in frozen whole egg. Canadian J. Microbiol. 9: 321-27. Daniels, F., and R. A. Alberty, 1955. Physical Chemistry, p. 176. John Wiley & Sons, Inc., N.Y. Evans, R. J., and S. L. Bandemer, 1956. Separa-
tion of egg white proteins by paper electrophoresis. J. Agr. Food Chem. 4 : 802-811. Gardner, F. A., 1960. Chemical modification of egg white function. Ph.D. dissertation, University of Missouri, Columbia, Missouri. Hawthorne, J. R., 1950. The action of egg white lysozyme on ovomucoid and ovomucin. Biochim. et Biophy. Acta, 6: 28-35. Ketcham, H. W., J. W. Osburn, Jr. and D. Deitch, 1965. Current status and commercial prospectus for radiation preservation of food. Division of Isotopes Development, U. S. Atomic Energy Commission, at (49-ll)-2S24; p. 53. U. S. Department of Commerce, Washington, D.C. MacDonnell, L. R., R. E. Feeney, H. L. Hanson, A. Campbell and T. R. Sugihara, 1955. The functional properties of the egg white proteins. Food Technol. 9:49-53. McArdle, F. J., W. Marion and N. W. Desrosier, 1954. Sterilization of shell eggs by ionization. Poultry Sci. 3 3 : 1070. Mossel, D. A. A., 1960. The destruction of Salmonella bacteria in refrigerated liquid whole egg with gamma radiation. Int. J. Appl. Rad. Isotopes, 9: 109-112. Nakamura, R., 1963. Studies on the foaming property of the chicken egg white. Part VI. Spread monolayer of the protein fraction of the chicken egg white. Agr. Biol. Chem. 27: 427-432. Nakamura, R., and Y. Sato, 1964. Studies on the foaming property of the chicken egg white. Part IX. On the coagulated proteins under various whipping conditions (The mechanism of foaminess (1)). Agr. Biol. Chem. 28: 524-29. Nickerson, J. T. R., S. E. Charm, R. C. Brogle, E. E. Lockhart, B. E. Proctor and H. Lineweaver, 1957. Use of high voltage cathode rays to destroy bacteria of the Salmonella group in liquid and frozen egg white and egg white solids. Food Technol. 11: 159-166. Proctor, B. E., R. F. Joslin, J. T. R. Nickerson and E. E. Lockhart, 1953. Elimination of Salmonella in whole egg powder by cathode ray irradiation of egg magna prior to drying. Food Technol. 7: 291-96.
NEWS AND NOTES (continued from page 1469) COLORADO NOTES Dr. Donald D. Johnson, Associate Dean of the College of Agriculture at Colorado State University, has been named Dean, effective July 1. He
has been administering the College of Agriculture since January 1, following the resignation of Dr. H. H. Stonaker, the former Dean. The Department of Poultry Science, Colorado
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tems were then frozen and held until used for measurements of physical and functional characteristics. Radiation treatment caused a reduction in viscosity, and a slight decrease in percent solids. Analysis of the electrophoretic patterns indicate a decrease in the relative concentration of proteins appearing in the ovomucin, conalbumin, and ovalbumin portions of the pattern and an increase in the relative concentration of proteins appearing in the globulin portions of the strip. Angel cakes made from the irradiated egg white required longer beating times in their preparation and had poorer texture and reduced volumes. Foams generated from irradiated egg white were less stable, as indicated by more extensive foam drainage. Functional performance as measured by beating time and cake volume improved during post-radiation frozen storage.
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