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Storage Stability of Liquid Egg Products Below 0 C
MARKETING AND PRODUCTS Storage Stability of Liquid Egg Products Below 0 C C. IMAI, J. SAITO, and M. ISHIKAWA Technical Laboratory of Q. P. Corporation, Sengawa-Cho, Chofu-Shi, Tokyo 182, Japan (Received for publication September 11, 1985)
INTRODUCTION
MATERIALS AND METHODS
It has been reported that the freezing point of egg yolk was —.55 to —.60 and that of egg white was —.42 to —.46 C (Romanoff and Romanoff, 1949; Cotterill, 1977). Commercial liquid egg products are usually stored and transported at 4 to 5 C to prevent freezing and their shelf life is short. Suzuki et al. (1979) reported that unpasteurized whole egg with a low initial bacterial count could be stored for 5 days at 10 C and for 8 days at 5 C without remarkable bacterial multiplication and deterioration of flavor, taste, and functional properties; York and Dawson (1973) stated that pasteurized liquid whole egg could be stored for 12 days at 2 C. Egg products are frozen if a long period of storage is required, but many users prefer the convenience of using liquid products. Recently, a new food storage method called partial freezing, light freezing, or super chilling has been studied for the purpose of preserving fresh fish, and the application of this method to other foods has been examined (Uchiyama, 1984). The storage stability of liquid egg products below 0 C, however, has not yet been reported. The purpose of the present study was to apply the partial freezing technique to liquid eggs such as whole egg, egg yolk, and egg white and to determine the effect of this treatment on shelf life. Unpasteurized and pasteurized liquid egg products stored at various temperatures were examined bacteriologically, and the functional properties of the stored products were investigated.
Liquid Egg Products. Commercially produced unpasteurized and pasteurized liquid whole egg, egg yolk, and egg white were obtained from an egg-processing plant close to the laboratory. Temperatures of pasteurization were 62 C for whole egg, 65 C for egg yolk, and 56 C for egg white, with a holding time of 3.5 min in each case, using plate type pasteurizers with holding tubes. Procedure. Ten 500-g samples were taken from each liquid product and stored for 50 days in sealed sterile polythene bags at —.5 and —3 C in Sanyo Low Temperature Incubators MIR 151 (Sanyo Electric Co., Ltd., Tokyo). For comparison, 10 additional bags of liquid egg products were stored at 5 C, which is the temperature commonly used for storing liquid egg products. Bacteriological Tests. Each 10-g sample from all the stored samples was taken in a sterile polythene bag after being mixed well and homogenized with 90 ml of sterile water using a Stomacher. From this dilution and further series decimal dilutions, depending on the anticipated bacterial population, bacterial counts and coliform counts were determined using the Institute of American Poultry Industries (IAPI) method (1956). After estimating the bacterial count, 3 to 100 colonies, depending on the size of the colony count, were picked from a plate representing each storage condition. The strains were identified by the methods of Vanderzant and Nickelson (1969) and Cowan and Steel (1974). Confirmatory tests of
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ABSTRACT Pasteurized and unpasteurized liquid whole egg, liquid yolk, and liquid white were stored at 5, - . 5 , and - 3 C to determine their shelf life. In the pasteurized products stored at - . 5 and - 3 C, the shelf life was considerably extended without adversely affecting functional properties. In the unpasteurized products stored at —3 C, there was a slow growth of bacteria after freezing occurred. Pasteurization eliminated gram negative psychrophilic bacteria, and thus the pasteurized products can be stored well at low temperatures, whereas, in the unpasteurized products, the presence of psychrophiles significantly reduced the shelf life. The palatability and functional properties of the pasteurized egg products stored at —.5 and —3 C for 50 days compared favorably with the same products before refrigerated storage. (Key words: liquid whole egg, liquid egg yolk, liquid egg white, partial freezing storage, psychrophilic bacteria) 1986 Poultry Science 65:1679-1686
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RESULTS AND DISCUSSION
Growth of Bacteria in Liquid Egg Products at Low Temperatures. Figure 1 shows the change of bacterial counts in unpasteurized and pasteurized liquid whole egg stored at low temperatures. Each bacterial count plotted is the logarithmic mean of 10 samples. Bacteria grew rapidly in the unpasteurized whole egg samples. Bacteria grew rapidly in the unpasteurized whole egg samples stored at 5 C but not so rapidly in samples stored at —.5 or at —3 C. In the pasteurized whole egg, which had lower initial bacterial counts than the unpasteurized whole egg, the growth of bacteria was comparatively slow, and in the samples at —.5 and —3 C, the growth of bacteria was not apparent after 50 days. Figure 2 shows the change of bacterial counts in unpasteurized and pasteurized liquid yolk stored at low temperatures. The pattern of the change of bacterial counts in egg yolk was very similar to that in liquid whole egg. Figure 3 shows the change of bacterial counts in unpasteurized and pasteurized egg white stored at various low temperatures. The growth of bacteria in the unpasteurized whites
stored at 5 and —.5 C was much slower than in the whole egg or yolk stored at the same temperatures. In the pasteurized egg white, bacterial growth was slow at 5 C, and there was no growth in the whites stored at —.5 and —3 C. It is probable that the slower bacterial growth in egg white was caused by its natural high pH value and the presence of antibacterial components such as lysozyme and ovotransferrin (Board, 1977). In the unpasteurized whole egg, egg yolk, and egg white stored at —3 C, freezing was observed after 2 to 3 days. The reason that the pasteurized products were not frozen at —3 C was not clear. According to the past preliminary tests, it was supposed that slight denaturation of egg protein by pasteurization decreased the freezing points of liquid eggs. Growth of Coliform Bacteria in Unpasteurized Liquid Egg Products. Figure 4 shows the change of coliform count of unpasteurized whole egg and yolk stored at low temperatures. Coliform bacteria were not detected in the pasteurized liquid egg products. The coliform counts in whole egg and egg yolk increased at 5 and —.5 C but not at —3 C. In the egg white, the coliform count did not increase at any temperature tested. Microbial Flora of Stored Liquid Egg Products. Table 1 shows the microbial flora of unpasteurized liquid whole egg before storage and after storage at 5 C for 15 days, at —.5 C for 25 days, and at —3 C for 50 days. Included in this table are the findings using pasteurized
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FIG. 1. Change of bacterial counts of unpasteurized (closed symbols) and pasteurized (open symbols) liquid whole egg stored at low temperatures.
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coliform bacteria were based on the Japanese Standard Method (Suzuki, 1973). Salad Dressing Test. Salad dressing was prepared according to the method of Gorman (1977) using 4.6% of liquid egg yolk and 52.7% of water instead of the 2.3% of dried egg yolk and 55.0% of water shown in the method. The viscosity of the dressing immediately after preparation was measured with a Tokyo Keiki Viscometer Type BH (Tokyo Keiki Co., Ltd., Tokyo). The dressing was placed in 100-ml (id 38 mm) glass bottles with screw cap, stored in a —15 C refrigerator, and the time taken for first visable separation to occur was observed. Whipping Power Height. Whipping heights of whole egg and egg white were measured by the IAPI method (1956). Palatability Test. A 120-g sample of liquid egg product was placed in a 500-ml beaker, coagulated to scrambled-egg consistency in a boiling water bath with occasional stirring, and evaluated against the flavor and taste of scrambled fresh liquid product according to the standard scores of the IAPI (1956). In this test, a score of 8 indicates no detectable off-flavor or taste and a flavor and taste comparable to a high quality fresh egg. A score of 0 means a pronounced repulsive flavor.
STORAGE OF LIQUID EGGS
20 Days
30 of
10
50
s t o r a g e
FIG. 2. Change of bacterial counts of unpasteurized (closed symbols) and pasteurized (open symbols) liquid egg yolk stored at low temperatures.
whole egg after storage for 50 days at the same three temperatures. In the unpasteurized whole egg, gram negative bacteria such as Aeromonas, Enterobacteriaceae, Acinetobacter, and Pseudomonas were predominant before storage. After storage at low temperatures, these gram negative bacteria were still predominant, but there were few gram positive bacteria such as Micrococcus, Staphylococcus, and Streptococcus, In contrast- in the pasteurized whole egg before storage, gram positive bacteria such as coryneform, Micrococcus, and Streptococcus had survived. Table 2 shows the microbial flora of the unpasteurized liquid yolk before storage and after storage at 5 C for 15 days, at —.5 C for 25
FIG. 3. Change of bacterial counts of unpasteurized (closed symbols) and pasteurized (open symbols) liquid egg white stored at low temperatures.
days, and at —3 C for 50 days, and of the pasteurized liquid yolk before and after storage at these temperatures for 50 days. Gram negative bacteria were always predominant in the unpasteurized yolk, but only gram positive bacteria were found in the pasteurized yolk. Table 3 shows the microbial flora of the unpasteurized liquid egg white before and after storage at these temperatures for 50 days and the flora of the pasteurized white before and after storage at 5 C for 50 days. As with the liquid whole egg and the liquid yolk, gram positive bacteria were also predominant in the pasteurized whites. Gram negative bacteria were predominant in the unpasteurized whites. Seviour and Board (1972), Sashihara et al. (1979), and Suzuki et al. (1979) reported that Gram negative bacteria such as Aeromonas, Enterobacteriaceae, Flavobacterium, and Pseudomonas were predominant in unpasteurized liquid egg products and in spoiled shell eggs, and Shafi et al. (1970), Payne et al. (1979), and Payne and Gooch (1980) stated that gram positive bacteria such as Bacillus, coryneform, Micrococcus, and Staphylococcus were predominant in pasteurized liquid egg products. The microbiological findings obtained in this study agreed generally with the results obtained by these researchers. Suzuki et al. (1979) reported that psychrophilic bacteria such as Aeromonas, Flavobacterium, and Pseudomonas became predominant in unpasteurized whole eggs stored at 5 and 10 C. In this study, using lower storage temperatures, the same tendency was observed.
FIG. 4. Change of coliform counts of unpasteurized liquid whole egg (closed symbols) and egg yolk (open symbols) stored at low temperatures.
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10
1681
1
4
3
2
Stored for 50 days.
Stored for 25 days.
Stored for 15 days.
Percentage of identified bacteria strains.
100
17.0 36.0 30.0 5.0 1.0 10.0 1.0
Gram negative Acinetobacter Areomonas Enterobacteriaceae Flavobacterium Moraxella Pseudomonas Unidentified
Gram positive Bacillus Coryneform Micrococcus Stapbylo co ecus Streptococcus Unidentified Number of tested strain
Before storage
Genus
100
2.0 2.0 4.0
52.0 2.0
20.0 12.0 6.0
100
20.0
1.0
6.0 26.0 22.0 7.0 1.0 17.0
Temperature of storage (C)
Unpasteurized whole egg
100
11.0
18.0
17.0 35.0 13.0 6.0
100
4.0 42.0 14.0 21.0 15.0
1.0 1.0 2.0
Before storage
TABLE 1. Microbial flora of liquid whole egg before and after storage1
://ps.oxfordjournals.org/ at University of South Dakota and School of Medicine on April 11, 2015 100
8.0
68.0 24.0
54
13
53.8 30.8 15.4
Temperature of storage (C)
Pasteurized whole egg
75.0 25.0
-r
>
M H
>
00
100
12.0 27.0 2.0 31.0 11.0 1.0 16.0
Stored for 15 days.
Percentage of identified bacteria strains.
"Stored for 50 days.
'Stored for 25 days.
2
1
Gram negative Acinetobacter Aeromonas Alcaligenes Enterobacteriaceae Flavobacterium Moraxella Pseudomonas Gram positive Bacillus Coryneform Micrococcus Staphylococcus Streptococcus Unidentified Number of tested strains
Genus
Before storage
100
4.0
18.0
48.0 2.0 28.0
100
3.0
6.0
100
28.0
18.0 1.0
6.0 7.0 18.0
11.0 42.0
60.0
Temperature of storage (C)
Unpasteurized egg yolk
100
4.0 54.0 11.0 14.0 16.0 1.0
Before storage
TABLE 2. Microbial flora of egg yolks before and after storage1
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9.0 23.0 36.0 30.0 2.0
36
2.8 50.0 19.2 16.7 11.3
Temperature of storage (C)
Pasteurized egg yolk
66.7
33.3
-3"
oo
w o o
5
a
P
so > o w o
H O
(A
1
2
Stored for 50 days.
Percentage of identified bacteria strains.
100
1.0
2.0 1.0
8.0 21.0 6.0 19.0 12.0 3.0 23.0 4.0
Gram negative Acinetobacter Aerornonas Alcaligenes Enterobacteriaceae Flavobacerium Moraxella Pseudomonas Unidentified
Gram positive Coryneform Micrococcus Staphylococcus Streptococcus Unidentified Number of tested strain
Before storage
Genus
100
2.0
6.0 20.0 6.0 30.0 2.0 2.0 32.0
57
38.6 7.0
76.0 2.0
100
5.3 31.6 3.5 5.3 8.7
10.0 6.0 2.0 4.0
~2
Temperature of storage (C)
Unpasteurized egg white
100
46.0 21.0 13.0 15.0 3.0
2.0
Before storage
TABLE 3. Microbial flora of egg whites before and after storage
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4.0 21.3 17.3 21.3
8.0
17.3
10.7
Temperature of storage (C)
Pasteurized egg white -32
> r
rfl H
>
2
STORAGE OF LIQUID EGGS
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TABLE 4. Characteristics of salad dressings prepared with stored egg y oiks Sample of egg yolk '
1
Resistance to storage at — 15 C
112,000
± 14,600*
Not separated after 20 days
115,000
± 14,600*
Not separated after 20 days
85,000 ± 126,000
Not separated after 20 days
14,200
Not separated after 20 days
± 16,400*
Stored for 50 days except Control 1.
2
Mean + standard deviation of five determinations.
3
Two bottles were taken for each observation. 'Values differ significantly (P<.05) between Control 1 and the others.
Storage at —.5 and —3 C was more effective in extending the shelf life of pasteurized egg products. Storage of unpasteurized products at these temperatures produced only a negligible improvement in the shelf life but was slightly superior to storage at 5 C. Pasteurization not only reduced the initial bacterial count of liquid products but also killed most of the gram negative psychrophilic bacteria, and consequently, storage of the pasteurized
products at —.5 or —3 C was superior to that of the unpasteurized products. Functional Properties of Stored Liquid Egg Products. In the results of repeated palatability test for scrambled eggs by seven skilled technologists, no significant difference (P«.05) was obtained between products before and after storage. In this test, only the pasteurized products were examined. The average scores were 8.0 for whole egg, egg yolk, and egg white
TABLE 5. Whipping height of stored liquid whole egg and egg white
Sample 1
Pasteurization
Whole egg Whole egg Whole egg, control 1 Whole egg, control 2 Egg white Egg white Egg white Egg white, control 3 Egg white, control 4 Egg white Egg white Egg white, control 5 Egg white, control 6
+ + + + + + + + +
— -
1
Stored for 50 days except samples before storage.
2
Mean + standard deviation of three determinations.
Storage temperature
Whipping height 2
(C)
(mm)
-.5 -3 Not stored -20 5 -.5 -3 Not stored -20 -.5 -3 Not stored -20
81 82 80 64 98 100 97 100 92 125 120 126 120
± 2.2* + 3.7* ± 2.9* ± 2.9 ± 2.9* ± 2.9* ± 2.2* ± 3.3* ± 2.4 ± 2.8** + 2.2** ± 1.4** ± 2.2**
*In whole egg values differ significantly (P<.05) between Control 2 and the others, and in pasteurized egg whites, values differ significantly (P<.05) between Control 4 and the others. **Values differ significantly (P<.05) between unpasteurized products and pasteurized products of egg whites.
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Pasteurized, stored at — .5 C Pasteurized, stored at — 3 C Control 1, pasteurized, not stored Control 2, pasteurized, 10% salted, stored at --20 C
Viscosity (cp) 2
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IMAI ET AL.
It appears from this study that the functional properties and palatability of liquid egg products are not adversely affected by storage at —.5 and —3 C for 50 days, although the whipping height of egg white was slightly decreased by pasteurization. It is concluded that the storage of pasteurized liquid egg products at —.5 and —3 C markedly improved their shelf life without seriously affecting their functional properties and palatability. Unpasteurized products froze when stored at —3 C; at —.5 C, there was only a slight improvement in shelf life compared with storage at 5 C. REFERENCES Baldwin, R. E., 1977. Functional properties in foods.
Page 246—277 in Egg Science and Technology. 2nd ed. W. J. Stadelman and O. J. Cotterill, ed. AVI Publ. Co., Inc., Westport, CT. Board, R. G., 1977. The microbiology of eggs. Page 4 9 - 6 4 in Egg Science and Technology. 2nd ed. W. J. Stadelman and O. J. Cotterill, ed. AVI Publ. Co., Inc., Westport, CT. Cotterill, O. J., 1977. Freezing egg products. Page 145—160 in Egg Science and Technology. 2nd ed. W. J. Stadelman and O. J. Cotterill, ed. AVI Publ. Co., Inc., Westport, CT. Cowan, S. T., and K. J. Steel, 1974. Manual for the Identification of Medical Bacteria. 2nd ed. Univ. Press, Cambridge, UK. Gorman, J. W., 1977. Quality control and product specifications. Page 230—245 in Egg Science and Technology. 2nd ed. W. J. Stadelman and O. J. Cotterill, ed. AVI Publ. Co., Inc., Westport, CT. IAPA, 1956. Chemical and Bacteriological Methods for the Examination of Eggs and Egg Products. Inst. Am. Poult. Industries, Chicago, IL. Mori, T., 1971. Studies on the freezing storage of hen's eggs. Part II. Relationship between storing or thawing condition and changes of viscosity or foaming property of whole liquid egg after thawing. Jpn. Food Sci. Technol. 18:135-141. Payne, J., and J.E.T. Gooch, 1980. Survival of faecal streptococci in raw and pasteurized egg products. Br. Poult. Sci. 21:61-70. Payne, J., J.E.T. Gooch, and E. M. Barnes, 1979. Heat resistant bacteria in pasteurized whole egg. J. Appl. Bacteriol. 46:601-613. Romanoff, A. L., and A. J. Romanoff, 1949. The Avian Egg. 2nd ed. John Wiley & Sons, New York, NY. Sashihara, N., H. Mizutani, S. Takayama, H. Konuma, A. Suzuki, and C. Imai, 1979. Bacteriological survey on raw materials of liquid (frozen) whole egg, its products and manufacturing processes. J. Food Hyg. Soc. Jpn. 20:127-136. Seviour, E. M., and R. C. Board, 1972. The behavior of mixed infection in the shell membranes of the hen's eggs. J. Food Hyg. 13:33-43. Shafi, R., O. J. Cotterill, and M. L. Nichols, 1970. Microbial flora of commercially pasteurized egg products. Poultry Sci. 49:578-585. Suzuki, A., 1973. Methods for inspection of coliforms. Page 107—119 in Manual of the Inspection for Food Hygiene. I. Kawashiro, ed. Jpn. Assoc Food Hygiene, Tokyo, Japan. Suzuki, A., H. Konuma, S. Takayama, C. Imai, and N. Sashihara, 1979. Preservability of unpasteurized liquid whole eggs by chilling. J. Food Hyg. Soc. Jpn. 20:442-449. Uchiyama, H., 1984. Partial freezing (—3°C). J. Jpn. Inst. Cold Chain 10:76-85. Vanderzant, C , and R. Nickelson, 1969. A microbiological examination of muscle tissue of beef, pork, and lamb carcasses. J. Milk Food Technol. 32:357-361. York, L. R., and L. E. Dawson, 1973. Shelf life of pasteurized liquid whole egg. Poultry Sci. 52: 1657-1658.
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before storage, and for egg whites stored at —.5 and at —3 C; 7.9 for egg yolk stored at —.5 C; and 7.7 for whole egg stored at —.5 and at —3 C. Table 4 shows the characteristics of salad dressings prepared with the egg yolks stored at —.5 and —3 C for 50 days. Controls 1 and 2 were used in this experiment, because these products are commonly used in the Japanese mayonnaise and dressing industry. The salad dressings prepared with the yolks stored at —.5 and —3 C had a slightly higher viscosity than Control 1 (pasteurized yolk before storage) and a slightly lower viscosity than Control 2 (10% salted yolk, stored at —20 C), and had the same cold resistance as these controls. Table 5 shows the whipping height of the liquid whole egg and liquid whites stored at low temperatures. Control samples were used in this experiment because these products are preferably used in Japanese bakeries and confectionaries. The whipping height of pasteurized whole egg stored at —.5 and —3 C was not less than Control 1 (pasteurized, before storage) and was more than Control 2 (pasteurized, stored at —20 C). In egg whites, the whipping height was decreased by pasteurization at 56 C for 3.5 min but was not affected by storage at —.5 or —3 C for 50 days. Mori (1971) stated that the whipping height of whole egg decreased on storage at —20 C but hardly decreased after storage at - 5 to - 8 C. Baldwin (1977) stated that pasteurization adversely affected the whipping characteristics of egg white; the same tendencies were seen in this study.
INTRODUCTION
MATERIALS AND METHODS
It has been reported that the freezing point of egg yolk was —.55 to —.60 and that of egg white was —.42 to —.46 C (Romanoff and Romanoff, 1949; Cotterill, 1977). Commercial liquid egg products are usually stored and transported at 4 to 5 C to prevent freezing and their shelf life is short. Suzuki et al. (1979) reported that unpasteurized whole egg with a low initial bacterial count could be stored for 5 days at 10 C and for 8 days at 5 C without remarkable bacterial multiplication and deterioration of flavor, taste, and functional properties; York and Dawson (1973) stated that pasteurized liquid whole egg could be stored for 12 days at 2 C. Egg products are frozen if a long period of storage is required, but many users prefer the convenience of using liquid products. Recently, a new food storage method called partial freezing, light freezing, or super chilling has been studied for the purpose of preserving fresh fish, and the application of this method to other foods has been examined (Uchiyama, 1984). The storage stability of liquid egg products below 0 C, however, has not yet been reported. The purpose of the present study was to apply the partial freezing technique to liquid eggs such as whole egg, egg yolk, and egg white and to determine the effect of this treatment on shelf life. Unpasteurized and pasteurized liquid egg products stored at various temperatures were examined bacteriologically, and the functional properties of the stored products were investigated.
Liquid Egg Products. Commercially produced unpasteurized and pasteurized liquid whole egg, egg yolk, and egg white were obtained from an egg-processing plant close to the laboratory. Temperatures of pasteurization were 62 C for whole egg, 65 C for egg yolk, and 56 C for egg white, with a holding time of 3.5 min in each case, using plate type pasteurizers with holding tubes. Procedure. Ten 500-g samples were taken from each liquid product and stored for 50 days in sealed sterile polythene bags at —.5 and —3 C in Sanyo Low Temperature Incubators MIR 151 (Sanyo Electric Co., Ltd., Tokyo). For comparison, 10 additional bags of liquid egg products were stored at 5 C, which is the temperature commonly used for storing liquid egg products. Bacteriological Tests. Each 10-g sample from all the stored samples was taken in a sterile polythene bag after being mixed well and homogenized with 90 ml of sterile water using a Stomacher. From this dilution and further series decimal dilutions, depending on the anticipated bacterial population, bacterial counts and coliform counts were determined using the Institute of American Poultry Industries (IAPI) method (1956). After estimating the bacterial count, 3 to 100 colonies, depending on the size of the colony count, were picked from a plate representing each storage condition. The strains were identified by the methods of Vanderzant and Nickelson (1969) and Cowan and Steel (1974). Confirmatory tests of
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ABSTRACT Pasteurized and unpasteurized liquid whole egg, liquid yolk, and liquid white were stored at 5, - . 5 , and - 3 C to determine their shelf life. In the pasteurized products stored at - . 5 and - 3 C, the shelf life was considerably extended without adversely affecting functional properties. In the unpasteurized products stored at —3 C, there was a slow growth of bacteria after freezing occurred. Pasteurization eliminated gram negative psychrophilic bacteria, and thus the pasteurized products can be stored well at low temperatures, whereas, in the unpasteurized products, the presence of psychrophiles significantly reduced the shelf life. The palatability and functional properties of the pasteurized egg products stored at —.5 and —3 C for 50 days compared favorably with the same products before refrigerated storage. (Key words: liquid whole egg, liquid egg yolk, liquid egg white, partial freezing storage, psychrophilic bacteria) 1986 Poultry Science 65:1679-1686
IMAI ET AL.
1680
RESULTS AND DISCUSSION
Growth of Bacteria in Liquid Egg Products at Low Temperatures. Figure 1 shows the change of bacterial counts in unpasteurized and pasteurized liquid whole egg stored at low temperatures. Each bacterial count plotted is the logarithmic mean of 10 samples. Bacteria grew rapidly in the unpasteurized whole egg samples. Bacteria grew rapidly in the unpasteurized whole egg samples stored at 5 C but not so rapidly in samples stored at —.5 or at —3 C. In the pasteurized whole egg, which had lower initial bacterial counts than the unpasteurized whole egg, the growth of bacteria was comparatively slow, and in the samples at —.5 and —3 C, the growth of bacteria was not apparent after 50 days. Figure 2 shows the change of bacterial counts in unpasteurized and pasteurized liquid yolk stored at low temperatures. The pattern of the change of bacterial counts in egg yolk was very similar to that in liquid whole egg. Figure 3 shows the change of bacterial counts in unpasteurized and pasteurized egg white stored at various low temperatures. The growth of bacteria in the unpasteurized whites
stored at 5 and —.5 C was much slower than in the whole egg or yolk stored at the same temperatures. In the pasteurized egg white, bacterial growth was slow at 5 C, and there was no growth in the whites stored at —.5 and —3 C. It is probable that the slower bacterial growth in egg white was caused by its natural high pH value and the presence of antibacterial components such as lysozyme and ovotransferrin (Board, 1977). In the unpasteurized whole egg, egg yolk, and egg white stored at —3 C, freezing was observed after 2 to 3 days. The reason that the pasteurized products were not frozen at —3 C was not clear. According to the past preliminary tests, it was supposed that slight denaturation of egg protein by pasteurization decreased the freezing points of liquid eggs. Growth of Coliform Bacteria in Unpasteurized Liquid Egg Products. Figure 4 shows the change of coliform count of unpasteurized whole egg and yolk stored at low temperatures. Coliform bacteria were not detected in the pasteurized liquid egg products. The coliform counts in whole egg and egg yolk increased at 5 and —.5 C but not at —3 C. In the egg white, the coliform count did not increase at any temperature tested. Microbial Flora of Stored Liquid Egg Products. Table 1 shows the microbial flora of unpasteurized liquid whole egg before storage and after storage at 5 C for 15 days, at —.5 C for 25 days, and at —3 C for 50 days. Included in this table are the findings using pasteurized
-a 10
D
20 Days
30 of
no
s t o r a g e
FIG. 1. Change of bacterial counts of unpasteurized (closed symbols) and pasteurized (open symbols) liquid whole egg stored at low temperatures.
Downloaded from http://ps.oxfordjournals.org/ at University of South Dakota and School of Medicine on April 11, 2015
coliform bacteria were based on the Japanese Standard Method (Suzuki, 1973). Salad Dressing Test. Salad dressing was prepared according to the method of Gorman (1977) using 4.6% of liquid egg yolk and 52.7% of water instead of the 2.3% of dried egg yolk and 55.0% of water shown in the method. The viscosity of the dressing immediately after preparation was measured with a Tokyo Keiki Viscometer Type BH (Tokyo Keiki Co., Ltd., Tokyo). The dressing was placed in 100-ml (id 38 mm) glass bottles with screw cap, stored in a —15 C refrigerator, and the time taken for first visable separation to occur was observed. Whipping Power Height. Whipping heights of whole egg and egg white were measured by the IAPI method (1956). Palatability Test. A 120-g sample of liquid egg product was placed in a 500-ml beaker, coagulated to scrambled-egg consistency in a boiling water bath with occasional stirring, and evaluated against the flavor and taste of scrambled fresh liquid product according to the standard scores of the IAPI (1956). In this test, a score of 8 indicates no detectable off-flavor or taste and a flavor and taste comparable to a high quality fresh egg. A score of 0 means a pronounced repulsive flavor.
STORAGE OF LIQUID EGGS
20 Days
30 of
10
50
s t o r a g e
FIG. 2. Change of bacterial counts of unpasteurized (closed symbols) and pasteurized (open symbols) liquid egg yolk stored at low temperatures.
whole egg after storage for 50 days at the same three temperatures. In the unpasteurized whole egg, gram negative bacteria such as Aeromonas, Enterobacteriaceae, Acinetobacter, and Pseudomonas were predominant before storage. After storage at low temperatures, these gram negative bacteria were still predominant, but there were few gram positive bacteria such as Micrococcus, Staphylococcus, and Streptococcus, In contrast- in the pasteurized whole egg before storage, gram positive bacteria such as coryneform, Micrococcus, and Streptococcus had survived. Table 2 shows the microbial flora of the unpasteurized liquid yolk before storage and after storage at 5 C for 15 days, at —.5 C for 25
FIG. 3. Change of bacterial counts of unpasteurized (closed symbols) and pasteurized (open symbols) liquid egg white stored at low temperatures.
days, and at —3 C for 50 days, and of the pasteurized liquid yolk before and after storage at these temperatures for 50 days. Gram negative bacteria were always predominant in the unpasteurized yolk, but only gram positive bacteria were found in the pasteurized yolk. Table 3 shows the microbial flora of the unpasteurized liquid egg white before and after storage at these temperatures for 50 days and the flora of the pasteurized white before and after storage at 5 C for 50 days. As with the liquid whole egg and the liquid yolk, gram positive bacteria were also predominant in the pasteurized whites. Gram negative bacteria were predominant in the unpasteurized whites. Seviour and Board (1972), Sashihara et al. (1979), and Suzuki et al. (1979) reported that Gram negative bacteria such as Aeromonas, Enterobacteriaceae, Flavobacterium, and Pseudomonas were predominant in unpasteurized liquid egg products and in spoiled shell eggs, and Shafi et al. (1970), Payne et al. (1979), and Payne and Gooch (1980) stated that gram positive bacteria such as Bacillus, coryneform, Micrococcus, and Staphylococcus were predominant in pasteurized liquid egg products. The microbiological findings obtained in this study agreed generally with the results obtained by these researchers. Suzuki et al. (1979) reported that psychrophilic bacteria such as Aeromonas, Flavobacterium, and Pseudomonas became predominant in unpasteurized whole eggs stored at 5 and 10 C. In this study, using lower storage temperatures, the same tendency was observed.
FIG. 4. Change of coliform counts of unpasteurized liquid whole egg (closed symbols) and egg yolk (open symbols) stored at low temperatures.
Downloaded from http://ps.oxfordjournals.org/ at University of South Dakota and School of Medicine on April 11, 2015
10
1681
1
4
3
2
Stored for 50 days.
Stored for 25 days.
Stored for 15 days.
Percentage of identified bacteria strains.
100
17.0 36.0 30.0 5.0 1.0 10.0 1.0
Gram negative Acinetobacter Areomonas Enterobacteriaceae Flavobacterium Moraxella Pseudomonas Unidentified
Gram positive Bacillus Coryneform Micrococcus Stapbylo co ecus Streptococcus Unidentified Number of tested strain
Before storage
Genus
100
2.0 2.0 4.0
52.0 2.0
20.0 12.0 6.0
100
20.0
1.0
6.0 26.0 22.0 7.0 1.0 17.0
Temperature of storage (C)
Unpasteurized whole egg
100
11.0
18.0
17.0 35.0 13.0 6.0
100
4.0 42.0 14.0 21.0 15.0
1.0 1.0 2.0
Before storage
TABLE 1. Microbial flora of liquid whole egg before and after storage1
://ps.oxfordjournals.org/ at University of South Dakota and School of Medicine on April 11, 2015 100
8.0
68.0 24.0
54
13
53.8 30.8 15.4
Temperature of storage (C)
Pasteurized whole egg
75.0 25.0
-r
>
M H
>
00
100
12.0 27.0 2.0 31.0 11.0 1.0 16.0
Stored for 15 days.
Percentage of identified bacteria strains.
"Stored for 50 days.
'Stored for 25 days.
2
1
Gram negative Acinetobacter Aeromonas Alcaligenes Enterobacteriaceae Flavobacterium Moraxella Pseudomonas Gram positive Bacillus Coryneform Micrococcus Staphylococcus Streptococcus Unidentified Number of tested strains
Genus
Before storage
100
4.0
18.0
48.0 2.0 28.0
100
3.0
6.0
100
28.0
18.0 1.0
6.0 7.0 18.0
11.0 42.0
60.0
Temperature of storage (C)
Unpasteurized egg yolk
100
4.0 54.0 11.0 14.0 16.0 1.0
Before storage
TABLE 2. Microbial flora of egg yolks before and after storage1
://ps.oxfordjournals.org/ at University of South Dakota and School of Medicine on April 11, 2015 100
9.0 23.0 36.0 30.0 2.0
36
2.8 50.0 19.2 16.7 11.3
Temperature of storage (C)
Pasteurized egg yolk
66.7
33.3
-3"
oo
w o o
5
a
P
so > o w o
H O
(A
1
2
Stored for 50 days.
Percentage of identified bacteria strains.
100
1.0
2.0 1.0
8.0 21.0 6.0 19.0 12.0 3.0 23.0 4.0
Gram negative Acinetobacter Aerornonas Alcaligenes Enterobacteriaceae Flavobacerium Moraxella Pseudomonas Unidentified
Gram positive Coryneform Micrococcus Staphylococcus Streptococcus Unidentified Number of tested strain
Before storage
Genus
100
2.0
6.0 20.0 6.0 30.0 2.0 2.0 32.0
57
38.6 7.0
76.0 2.0
100
5.3 31.6 3.5 5.3 8.7
10.0 6.0 2.0 4.0
~2
Temperature of storage (C)
Unpasteurized egg white
100
46.0 21.0 13.0 15.0 3.0
2.0
Before storage
TABLE 3. Microbial flora of egg whites before and after storage
/ps.oxfordjournals.org/ at University of South Dakota and School of Medicine on April 11, 2015 75
4.0 21.3 17.3 21.3
8.0
17.3
10.7
Temperature of storage (C)
Pasteurized egg white -32
> r
rfl H
>
2
STORAGE OF LIQUID EGGS
1685
TABLE 4. Characteristics of salad dressings prepared with stored egg y oiks Sample of egg yolk '
1
Resistance to storage at — 15 C
112,000
± 14,600*
Not separated after 20 days
115,000
± 14,600*
Not separated after 20 days
85,000 ± 126,000
Not separated after 20 days
14,200
Not separated after 20 days
± 16,400*
Stored for 50 days except Control 1.
2
Mean + standard deviation of five determinations.
3
Two bottles were taken for each observation. 'Values differ significantly (P<.05) between Control 1 and the others.
Storage at —.5 and —3 C was more effective in extending the shelf life of pasteurized egg products. Storage of unpasteurized products at these temperatures produced only a negligible improvement in the shelf life but was slightly superior to storage at 5 C. Pasteurization not only reduced the initial bacterial count of liquid products but also killed most of the gram negative psychrophilic bacteria, and consequently, storage of the pasteurized
products at —.5 or —3 C was superior to that of the unpasteurized products. Functional Properties of Stored Liquid Egg Products. In the results of repeated palatability test for scrambled eggs by seven skilled technologists, no significant difference (P«.05) was obtained between products before and after storage. In this test, only the pasteurized products were examined. The average scores were 8.0 for whole egg, egg yolk, and egg white
TABLE 5. Whipping height of stored liquid whole egg and egg white
Sample 1
Pasteurization
Whole egg Whole egg Whole egg, control 1 Whole egg, control 2 Egg white Egg white Egg white Egg white, control 3 Egg white, control 4 Egg white Egg white Egg white, control 5 Egg white, control 6
+ + + + + + + + +
— -
1
Stored for 50 days except samples before storage.
2
Mean + standard deviation of three determinations.
Storage temperature
Whipping height 2
(C)
(mm)
-.5 -3 Not stored -20 5 -.5 -3 Not stored -20 -.5 -3 Not stored -20
81 82 80 64 98 100 97 100 92 125 120 126 120
± 2.2* + 3.7* ± 2.9* ± 2.9 ± 2.9* ± 2.9* ± 2.2* ± 3.3* ± 2.4 ± 2.8** + 2.2** ± 1.4** ± 2.2**
*In whole egg values differ significantly (P<.05) between Control 2 and the others, and in pasteurized egg whites, values differ significantly (P<.05) between Control 4 and the others. **Values differ significantly (P<.05) between unpasteurized products and pasteurized products of egg whites.
Downloaded from http://ps.oxfordjournals.org/ at University of South Dakota and School of Medicine on April 11, 2015
Pasteurized, stored at — .5 C Pasteurized, stored at — 3 C Control 1, pasteurized, not stored Control 2, pasteurized, 10% salted, stored at --20 C
Viscosity (cp) 2
1686
IMAI ET AL.
It appears from this study that the functional properties and palatability of liquid egg products are not adversely affected by storage at —.5 and —3 C for 50 days, although the whipping height of egg white was slightly decreased by pasteurization. It is concluded that the storage of pasteurized liquid egg products at —.5 and —3 C markedly improved their shelf life without seriously affecting their functional properties and palatability. Unpasteurized products froze when stored at —3 C; at —.5 C, there was only a slight improvement in shelf life compared with storage at 5 C. REFERENCES Baldwin, R. E., 1977. Functional properties in foods.
Page 246—277 in Egg Science and Technology. 2nd ed. W. J. Stadelman and O. J. Cotterill, ed. AVI Publ. Co., Inc., Westport, CT. Board, R. G., 1977. The microbiology of eggs. Page 4 9 - 6 4 in Egg Science and Technology. 2nd ed. W. J. Stadelman and O. J. Cotterill, ed. AVI Publ. Co., Inc., Westport, CT. Cotterill, O. J., 1977. Freezing egg products. Page 145—160 in Egg Science and Technology. 2nd ed. W. J. Stadelman and O. J. Cotterill, ed. AVI Publ. Co., Inc., Westport, CT. Cowan, S. T., and K. J. Steel, 1974. Manual for the Identification of Medical Bacteria. 2nd ed. Univ. Press, Cambridge, UK. Gorman, J. W., 1977. Quality control and product specifications. Page 230—245 in Egg Science and Technology. 2nd ed. W. J. Stadelman and O. J. Cotterill, ed. AVI Publ. Co., Inc., Westport, CT. IAPA, 1956. Chemical and Bacteriological Methods for the Examination of Eggs and Egg Products. Inst. Am. Poult. Industries, Chicago, IL. Mori, T., 1971. Studies on the freezing storage of hen's eggs. Part II. Relationship between storing or thawing condition and changes of viscosity or foaming property of whole liquid egg after thawing. Jpn. Food Sci. Technol. 18:135-141. Payne, J., and J.E.T. Gooch, 1980. Survival of faecal streptococci in raw and pasteurized egg products. Br. Poult. Sci. 21:61-70. Payne, J., J.E.T. Gooch, and E. M. Barnes, 1979. Heat resistant bacteria in pasteurized whole egg. J. Appl. Bacteriol. 46:601-613. Romanoff, A. L., and A. J. Romanoff, 1949. The Avian Egg. 2nd ed. John Wiley & Sons, New York, NY. Sashihara, N., H. Mizutani, S. Takayama, H. Konuma, A. Suzuki, and C. Imai, 1979. Bacteriological survey on raw materials of liquid (frozen) whole egg, its products and manufacturing processes. J. Food Hyg. Soc. Jpn. 20:127-136. Seviour, E. M., and R. C. Board, 1972. The behavior of mixed infection in the shell membranes of the hen's eggs. J. Food Hyg. 13:33-43. Shafi, R., O. J. Cotterill, and M. L. Nichols, 1970. Microbial flora of commercially pasteurized egg products. Poultry Sci. 49:578-585. Suzuki, A., 1973. Methods for inspection of coliforms. Page 107—119 in Manual of the Inspection for Food Hygiene. I. Kawashiro, ed. Jpn. Assoc Food Hygiene, Tokyo, Japan. Suzuki, A., H. Konuma, S. Takayama, C. Imai, and N. Sashihara, 1979. Preservability of unpasteurized liquid whole eggs by chilling. J. Food Hyg. Soc. Jpn. 20:442-449. Uchiyama, H., 1984. Partial freezing (—3°C). J. Jpn. Inst. Cold Chain 10:76-85. Vanderzant, C , and R. Nickelson, 1969. A microbiological examination of muscle tissue of beef, pork, and lamb carcasses. J. Milk Food Technol. 32:357-361. York, L. R., and L. E. Dawson, 1973. Shelf life of pasteurized liquid whole egg. Poultry Sci. 52: 1657-1658.
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before storage, and for egg whites stored at —.5 and at —3 C; 7.9 for egg yolk stored at —.5 C; and 7.7 for whole egg stored at —.5 and at —3 C. Table 4 shows the characteristics of salad dressings prepared with the egg yolks stored at —.5 and —3 C for 50 days. Controls 1 and 2 were used in this experiment, because these products are commonly used in the Japanese mayonnaise and dressing industry. The salad dressings prepared with the yolks stored at —.5 and —3 C had a slightly higher viscosity than Control 1 (pasteurized yolk before storage) and a slightly lower viscosity than Control 2 (10% salted yolk, stored at —20 C), and had the same cold resistance as these controls. Table 5 shows the whipping height of the liquid whole egg and liquid whites stored at low temperatures. Control samples were used in this experiment because these products are preferably used in Japanese bakeries and confectionaries. The whipping height of pasteurized whole egg stored at —.5 and —3 C was not less than Control 1 (pasteurized, before storage) and was more than Control 2 (pasteurized, stored at —20 C). In egg whites, the whipping height was decreased by pasteurization at 56 C for 3.5 min but was not affected by storage at —.5 or —3 C for 50 days. Mori (1971) stated that the whipping height of whole egg decreased on storage at —20 C but hardly decreased after storage at - 5 to - 8 C. Baldwin (1977) stated that pasteurization adversely affected the whipping characteristics of egg white; the same tendencies were seen in this study.