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Emulsifying Properties of Salted Yolk After Pasteurization and Storage1
Emulsifying Properties of Salted Yolk After Pasteurization and Storage1 O. J. COTTERILL, J. GLAUERT AND H . J. BASSETT Department of Food Science and Nutrition, University of Missouri-Columbia, 65201
Columbia,
Missouri
(Received for publication May 13, 1975)
POULTRY SCIENCE 55: 544-548, 1976
INTRODUCTION HIGH temperature—short time pasteurization condition of 67-69° C. for 3.75 min. has been recommended for egg products containing 10% salt (Cotterill and Glauert, 1967, 1969). Also, a low temperature—long time "hot-pack" process (52° C. for 2-3 days) was developed by Cotterill et al. (1974). Both of these conditions deviate from existing pasteurization requirements of 63.3° C. for 3.5 min. or 62.2° C. for 6.2 min. for salted egg products (Fed. Reg., 1972). More information is needed on the effect of these processes on the functional properties of salted egg yolk.
A
Thermal processing is generally considered harmful to the functional properties of egg products. The foaming property of egg white is very heat sensitive. Foaming of whole egg is damaged to a lesser degree by heat. However, there is increasing evidence that the emulsifying properties of egg yolk are
1. Contribution from the Missouri Agricultural Experiment Station. Journal Series Number 7304.
not damaged by moderate heat treatments (Miller and Winter, 1951; Palmer et al., 1969; McCready et al., 1971; Varadarajulu and Cunningham, 1972; and Cotterill etal., 1974). The highest temperatures investigated by these workers were 63.3°, 64.5°, 64.0° and 65.0° C , respectively, for 3-4 min. The last reference dealt with the "hot-pack" process which involved heat treatments up to 9 days at 52° C. Good methodology has not been developed for evaluating the emulsifying properties of yolk products. Many techniques have been used. Baldwin (1973) and Gorman (1973) as well as above references observed the viscosity and stability of mayonnaise and salad dressing. Stability was often determined by noting the amount of oil separation after centrifugation. Egg yolk is an oil-in-water (o/w) emulsion Corran, 1946; and Becher, 1957). The more polar surfactants (lecithin, cephalin, and lipoproteins) favor an o / w emulsion. Cholesterol, a less polar compound, favors a waterin-oil (w/o) emulsion. The type and stability of emulsions depend on a number of variables, including the level of emulsifier usage, 544
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 16, 2015
ABSTRACT The emulsifying properties of egg yolk containing 10% sodium chloride pasteurized by two methods were determined: One, a high temperature—short time method involved the use of heat treatments for five min. at 62°, 67°, 73°, and 78° C. The other, a low temperature—long time method involved holding times of 2, 4, 6 and 8 days at 52° C. Samples were evaluated immediately after pasteurization, as well as after storage for one week at 10° and -20° C. Phase inversion titrations with oil and water were used to determine emulsifying capacity. Natural egg yolk contains strongly polar phospholipids and lipoproteins, as well as weakly polar-cholesterol. The former supports o/w emulsions and the latter w/o emulsions. Neither emulsifier system appeared very sensitive to heat damage. Hence, salted egg yolk can be pasteurized at higher temperatures than previously used or investigated without damaging its emulsifying properties. Storing the product after pasteurization tended to reduce the oil needed to invert the emulsion from an o/w to w / o type, which suggests that storage may be more important than pasteurization conditions.
YOLK EMULSIFYING PROPERTIES
METHODS AND MATERIALS Product Preparation. Liquid egg yolk (including adhering albumen) prepared from fresh eggs was blended in a Waring Blendor and filtered through cheese cloth. Salt (10%) was thoroughly mixed with the yolk by stirring at moderate speed with a "Mix-Mor" stirrer equipped with a 50 mm. propeller blade. This salted egg yolk (SEY) was divided into five aliquots. One aliquot was an unheated control. The other aliquots were individually heated in a hot water bath to 62°, 67°, 73° and 78° C. and held at the respective temperature for five minutes. Initially the water bath was ca. 10° C. higher than the specified temperature but equilibrated during the come-up period. The SEY was stirred constantly to assure uniform heating of the product in a stainless steel beaker. The product was cooled by placing the beaker in an ice water bath, after which it was transferred to plastic containers. One third of the samples were held at 10° C. for one week, another third were held at -20° C. for eight days and the remaining were tested immediately for possible change in emulsifying properties due to heating. Simultaneously SEY was pasteurized by the "hot-pack" method described by Cotterill et al. (1974) at 52° C. for 2, 4, 6 and 8 days.
These samples were divided and stored as was the SEY. Emulsifying Ability. The phase inversion point (InP) for the egg yolk-oil-water mixtures is easily detected visually or by electrical resistance. A w / o emulsion is greasy, translucent and viscous. An o / w emulsion is creamy, light yellow, opaque, and has a thin water-like consistancy. Electrical resistance, observed with a Simpson 260 VOM meter was used to determine this point of change from one phase to another. One technique for measuring emulsifying ability was termed a monophasic titration, since only the w / o phase was titrated. A w / o emulsion was formed by stirring 10 g. of SEY and 81 g. (90 ml.) of Mazola corn oil, both at 26-28° C , with a rubber spatula in the metal bowl of a K4-B Kitchen-Aid mixer. The mixer, equipped with a wire whip, was operated at speed 6 for 30 s e c , stopped, sides scraped, then mixed for another 30 sec. This w / o type emulsion was back-titrated with water to the InP. The amount of water needed to break the w / o emulsion was recorded as the InP. A second technique was termed a bi-phasic titration, since both the o / w and w / o emulsions were titrated to the InP. In this case, two electrodes were placed at opposite sides of 150 ml. beaker containing 20 g. of SEY and the conductance between them was measured with the VOM meter. Oil and water were titrated drop-wise through a hole in the stopper and the contents were stirred constantly with a 40 x 15 mm. magnetic stirring bar at room temperature. After noting the amount of oil required to bring the o / w emulsion to the InP, an additional 10 ml. of oil was added and mixed, thus converting the emulsion to a w / o type. Then, this emulsion was back-titrated with water to bring it to the InP, and the amount of water recorded. With the more viscous SEY samples, a metal spatula was used to facilitate
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 16, 2015
ratio of oil-to-water, the increase in potential energy (work) necessary to form the emulsion, and the relative solubility of the emulsifier in the two phases. As a general rule, the phase in which the emulsifier is most soluble is the continuous phase. For example, lecithin is more soluble in water than in oil, hence it promotes an o / w type emulsion. The emulsifying abilities of the various surfactants themselves are of prime importance in emulsion technology. This study evaluated the performance of both of these emulsion systems in salted egg yolk after various pasteurization and storage treatments.
545
546
O . J . COTTERILL, J . GLAUERT AND H . J . BASSETT
TABLE 1.—Phase inversion point (mono-phasic titration) of 10% salted egg yolk after pasteurization and storage Phase inversion point Stored
Treatment
10° C.
-20° C.
Average
(ml.) 273.5' 278.0 287.0 271.0 270.0
(ml.) 281.0 277.0 275.5 268.0 261.5
(ml.) 281.0 276.5 277.0 270.0 267.5
(ml.) 278.5a 277.2a 279.8a 269.7b 266.3b
275.9a
272.6a
274.4a
mixing. When titrating with oil, the mixture was considered inverted when the resistance rapidly changed from zero to 5 x 106 ohms. The end point for the back titration with water was at zero ohms. At this InP, the mixture suddenly became less viscous due to the change from a w / o to an o / w emulsion. The amounts of oil, or water, required to titrate to the InP in each case, were expressed as ml. per g. of SEY. RESULTS The emulsifying ability of both unheated and pasteurized SEY as indicated by the mono-phasic titration technique is shown in Table 1. Pasteurization at 62° and 67° C. for five minutes made no significant change in TABLE 2.—Phase inversion point (mono-phasic titration) of 10% salted egg yolk after "hot-pack' pasteurization and storage Holding time at 52° C.
10° C.
-20° C.
(days) 0 2 4 6 8
(ml.) 282.01 276.5 272.0 287.0 260.5
(ml.) 279.5 271.5 271.6 278.0 261.0
Average
275.6a
272.3a
Phase inversion point Stored
'Average of two replications.
Average (ml.) 280.8a 274.0b 271.8b 282.5a 260.7c
the amount of water required to reach the InP. Heating at 73° and 78° C. decreased the amount of water emulsified at the InP. When the InP for all treatments were averaged, the stored samples were not significantly different from the fresh samples. However, it appears that storing the unheated control increased the water emulsified at the InP, while storage decreased the InP for samples heated at 73° and 78° C. Table 2 shows the emulsifying ability of SEY pasteurized by the "hot-pack" process as determined by the mono-phasic method. A fresh sample was not analyzed. However, the stored samples (zero holding time) emulsified more water than the fresh untreated control in the previous experiment. While the two and four day treatments significantly decreased the InP, they were still equal to the fresh untreated control. After six days the InP increased to a level equal to the initial product. The product held for eight days had a significantly lower InP than the other holding times. Differences due to storage temperature were not significant. The above technique involved only a mono-phasic back-titration from a w / o emulsion formed by adding excess oil to SEY followed by the addition of just sufficient water to back-titrate to the InP. However, most products (salad dressing, mayonnaise, etc.) using egg yolk as an emulsifier are o / w
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 16, 2015
Unhealed control Pasteurized2—62° C. Pasteurized—67° C. Pasteurized—73° C. Pasteurized—78° C. Average 'Average of two replications. 2 Holding time was five minutes.
Fresh
547
YOLK EMULSIFYING PROPERTIES
type emulsions. This mono-phasic titration may have evaluated only the emulsifier(s) which favor the dispersion of w / o . Therefore, the bi-phasic titration method was developed so that the amount of oil as well as water required to invert both types of emulsions could be determined. In the bi-phasic titration, oil was added
The effect of holding time for the "hotpack" pasteurization process on the InP is shown in Figure 2. There was a slight reduction in both the amount of oil and water needed to reach the InP with increased holding time. Values for samples stored at —20° C. were lower than for those stored at 10° C.
FIG. 1. Phase inversion point (bi-phasic titration) for 10% salted egg yolk after pasteurization for five minutes. OIL ADDED
STORED AT
_
ltrc.
:
FIG. 2. Phase inversion point (bi-phasic titration) for 10% salted egg yolk after "hot-pack" pasteurization.
DISCUSSION It is assumed that a decrease in the amount of oil or water needed to invert the emulsion is an indication of reduced functional performance. Some differences or trends due to pasteurization were observed which suggest damage may have occurred. However, in view of the excessive heat treatments used, it is doubtful that these differences are important. Hence, salted egg yolk can be pasteurized at 67° to 69° C. for 3.75 min. These conditions were suggested by Cotterill and Glauert (1967, 1969) to provide a good assurance of a salmonellae negative product. Storage seemed to cause more damage than high temperature pasteurization. At first, this was not apparent because only the monophasic or back-titration technique was used. No significant differences between fresh and
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 16, 2015
until the o / w emulsion broke, then an excess of oil was added and back-titrated to the InP with water. The experiments were repeated using the same heat treatments as above (see Figure 1). Storing the samples at 10° C. and at -20° C. before observing emulsifying properties decreased the amount of oil needed to reach the InP. Pasteurization at 62° C. increased this oil requirement for both the fresh and stored samples. Improvements due to heating have been reported previously (see McCready et al., 1971; Varadarajulu and Cunningham, 1972; and Cotterill era/., 1974). However, some reduction occurred after pasteurization at higher temperatures and storage at 10° C. The amount of water needed to back-titrate to the InP followed similar patterns.
548
O. J. COTTERILL, J. GLAUERT AND H . J. BASSETT
stored samples were detected when all treatments were averaged. Although, storage increased the water required for back-titration of the unheated control, this result was not verified by later experiments. With the bi-phasic titration, the reduced amount of oil needed to cause an inversion suggests that storage damaged the components responsible for stability of the o / w emulsion (i.e., polar compounds) more than those which favor the w / o type.
Baldwin, R. E., 1973. Functional properties in foods. In: Egg Science and Technology. Ed. W. J. Stadelman and O. J. Cotterill. Avi Publishing Co., Inc., Westport, Conn. 06880. Becher, P., 1957. Emulsions Theory and Practice. Reinhold Publishing Corp., N.Y. Corran, J. W., 1946. Some observations on a typical food emulsion. In: Emulsion Technology. Chemical Rubber Co., Inc., Brooklyn, N.Y. Cotterill, O. J., and J. Glauert, 1967. Pasteurization requirements to destroy salmonellae in egg products containing sugar and salt. Poultry Sci. 46: 1248. Cotterill, O. J., and J. Glauert, 1969. Thermal resist-
NEWS AND NOTES (Continued from page 530) for publication only if they meet rigorous scientific standards." VIRGINIA NOTES Roger A. Teekell, Professor of Poultry Science at Louisiana State University, Baton Rouge, has been appointed Head of the Department of Poultry Science at Virginia Polytechnic Institute and State University, Blacksburg, effective March 1. James R. Nichols, Dean of the College of Agriculture and Life Sciences, stated that "the poultry industry is an important part of Virginia's industry of agriculture and the Virginia Tech department of poultry science has a long history of effective service to the Commonwealth, through its extension, research and instruction programs. Teekell's appointment should contribute to the further strengthening of these programs since he
comes to Virginia Tech with an excellent record as a productive research scientist." Teekell, 45, is a native of Elmer, Louisiana, holds a Ph.D. degree in biochemistry and nutrition from Louisiana State University, whose faculty he joined in 1963 as an Associate Professor of Poultry Science. While in the Center of Agricultural Sciences at L.S. U., his research centered on intermediary metabolism of fatty acids and amino acids. He was promoted to Professor in 1968. Prior to joining the L.S.U. faculty, he was a Senior Chemist for Dow Chemical Company's Bioproducts Division at Freeport, Texas, where he conducted research on pesticide residues and pesticide metabolism. From 1958 to 1961, he served as Associate Scientist and Professor at the University of Tennessee, Knoxville, working with the Atomic Energy Commis-
(Continued on page 553)
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 16, 2015
REFERENCES
ance of salmonellae in egg products containing sugar and salt. Poultry Sci. 48: 1156-1166. Cotterill, O. J., J. Glauert, S. E. Steinhoff and R. E. Baldwin, 1974. Hot-pack pasteurization of salted egg products. Poultry Sci. 53: 636-645. Federal Register, 1972. Regulations governing the inspection of eggs and egg products. U.S. Department of Agriculture, Washington, D.C., July I. Gorman, J. M., 1973. Quality control and product specifications. In: Egg Science and Technology. Ed. W. J. Stadelman and O. J. Cotterill. Avi Publishing Co., Inc., Westport, Conn. 06880. McCready, S. T., M. E. Norris, O. J. Cotterill and R. Baldwin, 1971. Centrifuging liquid whole egg. 2. Effects of pasteurization on the composition and emulsifying properties of the precipitate fraction. Poultry Sci. 50: 1817-1823. Miller, C , and A. R. Winter, 1950. Pasteurized frozen whole egg and yolk for mayonnaise production. Food Res. 16: 44-49. Palmer, H. H., K. Ijichi, S. L. Cimino and H. Roff, 1969. Salted egg yolks. 1. Viscosity and performance of pasteurized and frozen samples. Food Technol. 23: 1480-1485. Varadarajulu, P., and F. E. Cunningham, 1972. A study of selected characteristics of hen's egg yolk. 2. Influence of processing procedures. Pasteurization and yolk fractionation. Poultry Sci. 51: 941945.
Columbia,
Missouri
(Received for publication May 13, 1975)
POULTRY SCIENCE 55: 544-548, 1976
INTRODUCTION HIGH temperature—short time pasteurization condition of 67-69° C. for 3.75 min. has been recommended for egg products containing 10% salt (Cotterill and Glauert, 1967, 1969). Also, a low temperature—long time "hot-pack" process (52° C. for 2-3 days) was developed by Cotterill et al. (1974). Both of these conditions deviate from existing pasteurization requirements of 63.3° C. for 3.5 min. or 62.2° C. for 6.2 min. for salted egg products (Fed. Reg., 1972). More information is needed on the effect of these processes on the functional properties of salted egg yolk.
A
Thermal processing is generally considered harmful to the functional properties of egg products. The foaming property of egg white is very heat sensitive. Foaming of whole egg is damaged to a lesser degree by heat. However, there is increasing evidence that the emulsifying properties of egg yolk are
1. Contribution from the Missouri Agricultural Experiment Station. Journal Series Number 7304.
not damaged by moderate heat treatments (Miller and Winter, 1951; Palmer et al., 1969; McCready et al., 1971; Varadarajulu and Cunningham, 1972; and Cotterill etal., 1974). The highest temperatures investigated by these workers were 63.3°, 64.5°, 64.0° and 65.0° C , respectively, for 3-4 min. The last reference dealt with the "hot-pack" process which involved heat treatments up to 9 days at 52° C. Good methodology has not been developed for evaluating the emulsifying properties of yolk products. Many techniques have been used. Baldwin (1973) and Gorman (1973) as well as above references observed the viscosity and stability of mayonnaise and salad dressing. Stability was often determined by noting the amount of oil separation after centrifugation. Egg yolk is an oil-in-water (o/w) emulsion Corran, 1946; and Becher, 1957). The more polar surfactants (lecithin, cephalin, and lipoproteins) favor an o / w emulsion. Cholesterol, a less polar compound, favors a waterin-oil (w/o) emulsion. The type and stability of emulsions depend on a number of variables, including the level of emulsifier usage, 544
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 16, 2015
ABSTRACT The emulsifying properties of egg yolk containing 10% sodium chloride pasteurized by two methods were determined: One, a high temperature—short time method involved the use of heat treatments for five min. at 62°, 67°, 73°, and 78° C. The other, a low temperature—long time method involved holding times of 2, 4, 6 and 8 days at 52° C. Samples were evaluated immediately after pasteurization, as well as after storage for one week at 10° and -20° C. Phase inversion titrations with oil and water were used to determine emulsifying capacity. Natural egg yolk contains strongly polar phospholipids and lipoproteins, as well as weakly polar-cholesterol. The former supports o/w emulsions and the latter w/o emulsions. Neither emulsifier system appeared very sensitive to heat damage. Hence, salted egg yolk can be pasteurized at higher temperatures than previously used or investigated without damaging its emulsifying properties. Storing the product after pasteurization tended to reduce the oil needed to invert the emulsion from an o/w to w / o type, which suggests that storage may be more important than pasteurization conditions.
YOLK EMULSIFYING PROPERTIES
METHODS AND MATERIALS Product Preparation. Liquid egg yolk (including adhering albumen) prepared from fresh eggs was blended in a Waring Blendor and filtered through cheese cloth. Salt (10%) was thoroughly mixed with the yolk by stirring at moderate speed with a "Mix-Mor" stirrer equipped with a 50 mm. propeller blade. This salted egg yolk (SEY) was divided into five aliquots. One aliquot was an unheated control. The other aliquots were individually heated in a hot water bath to 62°, 67°, 73° and 78° C. and held at the respective temperature for five minutes. Initially the water bath was ca. 10° C. higher than the specified temperature but equilibrated during the come-up period. The SEY was stirred constantly to assure uniform heating of the product in a stainless steel beaker. The product was cooled by placing the beaker in an ice water bath, after which it was transferred to plastic containers. One third of the samples were held at 10° C. for one week, another third were held at -20° C. for eight days and the remaining were tested immediately for possible change in emulsifying properties due to heating. Simultaneously SEY was pasteurized by the "hot-pack" method described by Cotterill et al. (1974) at 52° C. for 2, 4, 6 and 8 days.
These samples were divided and stored as was the SEY. Emulsifying Ability. The phase inversion point (InP) for the egg yolk-oil-water mixtures is easily detected visually or by electrical resistance. A w / o emulsion is greasy, translucent and viscous. An o / w emulsion is creamy, light yellow, opaque, and has a thin water-like consistancy. Electrical resistance, observed with a Simpson 260 VOM meter was used to determine this point of change from one phase to another. One technique for measuring emulsifying ability was termed a monophasic titration, since only the w / o phase was titrated. A w / o emulsion was formed by stirring 10 g. of SEY and 81 g. (90 ml.) of Mazola corn oil, both at 26-28° C , with a rubber spatula in the metal bowl of a K4-B Kitchen-Aid mixer. The mixer, equipped with a wire whip, was operated at speed 6 for 30 s e c , stopped, sides scraped, then mixed for another 30 sec. This w / o type emulsion was back-titrated with water to the InP. The amount of water needed to break the w / o emulsion was recorded as the InP. A second technique was termed a bi-phasic titration, since both the o / w and w / o emulsions were titrated to the InP. In this case, two electrodes were placed at opposite sides of 150 ml. beaker containing 20 g. of SEY and the conductance between them was measured with the VOM meter. Oil and water were titrated drop-wise through a hole in the stopper and the contents were stirred constantly with a 40 x 15 mm. magnetic stirring bar at room temperature. After noting the amount of oil required to bring the o / w emulsion to the InP, an additional 10 ml. of oil was added and mixed, thus converting the emulsion to a w / o type. Then, this emulsion was back-titrated with water to bring it to the InP, and the amount of water recorded. With the more viscous SEY samples, a metal spatula was used to facilitate
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 16, 2015
ratio of oil-to-water, the increase in potential energy (work) necessary to form the emulsion, and the relative solubility of the emulsifier in the two phases. As a general rule, the phase in which the emulsifier is most soluble is the continuous phase. For example, lecithin is more soluble in water than in oil, hence it promotes an o / w type emulsion. The emulsifying abilities of the various surfactants themselves are of prime importance in emulsion technology. This study evaluated the performance of both of these emulsion systems in salted egg yolk after various pasteurization and storage treatments.
545
546
O . J . COTTERILL, J . GLAUERT AND H . J . BASSETT
TABLE 1.—Phase inversion point (mono-phasic titration) of 10% salted egg yolk after pasteurization and storage Phase inversion point Stored
Treatment
10° C.
-20° C.
Average
(ml.) 273.5' 278.0 287.0 271.0 270.0
(ml.) 281.0 277.0 275.5 268.0 261.5
(ml.) 281.0 276.5 277.0 270.0 267.5
(ml.) 278.5a 277.2a 279.8a 269.7b 266.3b
275.9a
272.6a
274.4a
mixing. When titrating with oil, the mixture was considered inverted when the resistance rapidly changed from zero to 5 x 106 ohms. The end point for the back titration with water was at zero ohms. At this InP, the mixture suddenly became less viscous due to the change from a w / o to an o / w emulsion. The amounts of oil, or water, required to titrate to the InP in each case, were expressed as ml. per g. of SEY. RESULTS The emulsifying ability of both unheated and pasteurized SEY as indicated by the mono-phasic titration technique is shown in Table 1. Pasteurization at 62° and 67° C. for five minutes made no significant change in TABLE 2.—Phase inversion point (mono-phasic titration) of 10% salted egg yolk after "hot-pack' pasteurization and storage Holding time at 52° C.
10° C.
-20° C.
(days) 0 2 4 6 8
(ml.) 282.01 276.5 272.0 287.0 260.5
(ml.) 279.5 271.5 271.6 278.0 261.0
Average
275.6a
272.3a
Phase inversion point Stored
'Average of two replications.
Average (ml.) 280.8a 274.0b 271.8b 282.5a 260.7c
the amount of water required to reach the InP. Heating at 73° and 78° C. decreased the amount of water emulsified at the InP. When the InP for all treatments were averaged, the stored samples were not significantly different from the fresh samples. However, it appears that storing the unheated control increased the water emulsified at the InP, while storage decreased the InP for samples heated at 73° and 78° C. Table 2 shows the emulsifying ability of SEY pasteurized by the "hot-pack" process as determined by the mono-phasic method. A fresh sample was not analyzed. However, the stored samples (zero holding time) emulsified more water than the fresh untreated control in the previous experiment. While the two and four day treatments significantly decreased the InP, they were still equal to the fresh untreated control. After six days the InP increased to a level equal to the initial product. The product held for eight days had a significantly lower InP than the other holding times. Differences due to storage temperature were not significant. The above technique involved only a mono-phasic back-titration from a w / o emulsion formed by adding excess oil to SEY followed by the addition of just sufficient water to back-titrate to the InP. However, most products (salad dressing, mayonnaise, etc.) using egg yolk as an emulsifier are o / w
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 16, 2015
Unhealed control Pasteurized2—62° C. Pasteurized—67° C. Pasteurized—73° C. Pasteurized—78° C. Average 'Average of two replications. 2 Holding time was five minutes.
Fresh
547
YOLK EMULSIFYING PROPERTIES
type emulsions. This mono-phasic titration may have evaluated only the emulsifier(s) which favor the dispersion of w / o . Therefore, the bi-phasic titration method was developed so that the amount of oil as well as water required to invert both types of emulsions could be determined. In the bi-phasic titration, oil was added
The effect of holding time for the "hotpack" pasteurization process on the InP is shown in Figure 2. There was a slight reduction in both the amount of oil and water needed to reach the InP with increased holding time. Values for samples stored at —20° C. were lower than for those stored at 10° C.
FIG. 1. Phase inversion point (bi-phasic titration) for 10% salted egg yolk after pasteurization for five minutes. OIL ADDED
STORED AT
_
ltrc.
:
FIG. 2. Phase inversion point (bi-phasic titration) for 10% salted egg yolk after "hot-pack" pasteurization.
DISCUSSION It is assumed that a decrease in the amount of oil or water needed to invert the emulsion is an indication of reduced functional performance. Some differences or trends due to pasteurization were observed which suggest damage may have occurred. However, in view of the excessive heat treatments used, it is doubtful that these differences are important. Hence, salted egg yolk can be pasteurized at 67° to 69° C. for 3.75 min. These conditions were suggested by Cotterill and Glauert (1967, 1969) to provide a good assurance of a salmonellae negative product. Storage seemed to cause more damage than high temperature pasteurization. At first, this was not apparent because only the monophasic or back-titration technique was used. No significant differences between fresh and
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 16, 2015
until the o / w emulsion broke, then an excess of oil was added and back-titrated to the InP with water. The experiments were repeated using the same heat treatments as above (see Figure 1). Storing the samples at 10° C. and at -20° C. before observing emulsifying properties decreased the amount of oil needed to reach the InP. Pasteurization at 62° C. increased this oil requirement for both the fresh and stored samples. Improvements due to heating have been reported previously (see McCready et al., 1971; Varadarajulu and Cunningham, 1972; and Cotterill era/., 1974). However, some reduction occurred after pasteurization at higher temperatures and storage at 10° C. The amount of water needed to back-titrate to the InP followed similar patterns.
548
O. J. COTTERILL, J. GLAUERT AND H . J. BASSETT
stored samples were detected when all treatments were averaged. Although, storage increased the water required for back-titration of the unheated control, this result was not verified by later experiments. With the bi-phasic titration, the reduced amount of oil needed to cause an inversion suggests that storage damaged the components responsible for stability of the o / w emulsion (i.e., polar compounds) more than those which favor the w / o type.
Baldwin, R. E., 1973. Functional properties in foods. In: Egg Science and Technology. Ed. W. J. Stadelman and O. J. Cotterill. Avi Publishing Co., Inc., Westport, Conn. 06880. Becher, P., 1957. Emulsions Theory and Practice. Reinhold Publishing Corp., N.Y. Corran, J. W., 1946. Some observations on a typical food emulsion. In: Emulsion Technology. Chemical Rubber Co., Inc., Brooklyn, N.Y. Cotterill, O. J., and J. Glauert, 1967. Pasteurization requirements to destroy salmonellae in egg products containing sugar and salt. Poultry Sci. 46: 1248. Cotterill, O. J., and J. Glauert, 1969. Thermal resist-
NEWS AND NOTES (Continued from page 530) for publication only if they meet rigorous scientific standards." VIRGINIA NOTES Roger A. Teekell, Professor of Poultry Science at Louisiana State University, Baton Rouge, has been appointed Head of the Department of Poultry Science at Virginia Polytechnic Institute and State University, Blacksburg, effective March 1. James R. Nichols, Dean of the College of Agriculture and Life Sciences, stated that "the poultry industry is an important part of Virginia's industry of agriculture and the Virginia Tech department of poultry science has a long history of effective service to the Commonwealth, through its extension, research and instruction programs. Teekell's appointment should contribute to the further strengthening of these programs since he
comes to Virginia Tech with an excellent record as a productive research scientist." Teekell, 45, is a native of Elmer, Louisiana, holds a Ph.D. degree in biochemistry and nutrition from Louisiana State University, whose faculty he joined in 1963 as an Associate Professor of Poultry Science. While in the Center of Agricultural Sciences at L.S. U., his research centered on intermediary metabolism of fatty acids and amino acids. He was promoted to Professor in 1968. Prior to joining the L.S.U. faculty, he was a Senior Chemist for Dow Chemical Company's Bioproducts Division at Freeport, Texas, where he conducted research on pesticide residues and pesticide metabolism. From 1958 to 1961, he served as Associate Scientist and Professor at the University of Tennessee, Knoxville, working with the Atomic Energy Commis-
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REFERENCES
ance of salmonellae in egg products containing sugar and salt. Poultry Sci. 48: 1156-1166. Cotterill, O. J., J. Glauert, S. E. Steinhoff and R. E. Baldwin, 1974. Hot-pack pasteurization of salted egg products. Poultry Sci. 53: 636-645. Federal Register, 1972. Regulations governing the inspection of eggs and egg products. U.S. Department of Agriculture, Washington, D.C., July I. Gorman, J. M., 1973. Quality control and product specifications. In: Egg Science and Technology. Ed. W. J. Stadelman and O. J. Cotterill. Avi Publishing Co., Inc., Westport, Conn. 06880. McCready, S. T., M. E. Norris, O. J. Cotterill and R. Baldwin, 1971. Centrifuging liquid whole egg. 2. Effects of pasteurization on the composition and emulsifying properties of the precipitate fraction. Poultry Sci. 50: 1817-1823. Miller, C , and A. R. Winter, 1950. Pasteurized frozen whole egg and yolk for mayonnaise production. Food Res. 16: 44-49. Palmer, H. H., K. Ijichi, S. L. Cimino and H. Roff, 1969. Salted egg yolks. 1. Viscosity and performance of pasteurized and frozen samples. Food Technol. 23: 1480-1485. Varadarajulu, P., and F. E. Cunningham, 1972. A study of selected characteristics of hen's egg yolk. 2. Influence of processing procedures. Pasteurization and yolk fractionation. Poultry Sci. 51: 941945.