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Storage Stability of Japanese Quail (Coturnix coturnix japonica) Eggs at Room Temperature
MARKETING AND PRODUCTS Storage Stability of Japanese Quail (Coturnix coturnix japonica) Eggs at Room Temperature C. IMAI, A. MOWLAH, and J. SAITO Technical Laboratory of Q.P. Corporation, Sengawa-Cho, Cbofu-Sbi, Tokyo 182, Japan (Received for publication December 10, 1984)
1986 Poultry Science 65:474-480 INTRODUCTION
In Japan, about 20 million quail are reared each year by 300 farms (Sakurai, 1984) and their eggs are a popular item in the Japanese diet. The quail eggs are sometimes served without heating, though most of them are used after boiling. The storage stability of quail eggs has not been well studied, whereas there is a considerable literature dealing with the quality of stored hen eggs. The effect of storage on weight loss and on interior quality of quail eggs, such as albumen height, albumen index, yolk height, yolk index, and air cell size has been investigated by few researchers. Tanabe et al. (1972) reported that a good quality of oil-coated quail egg could be maintained for 120 days in a refrigerator and for 60 days in an unairconditioned room (22 to 31 C, RH 54 to 84%) and that uncoated eggs stored in the unconditioned room did not keep well. Tanabe et al. (1970) stated that the storage stability of quail eggs was superior to that of hen eggs because of their thicker shell membranes. Tanabe and Ogawa (1975) reported that albumen height and yolk height of the quail eggs purchased in summer were low, and a high incidence of
rotten eggs occurred. Pandey et al. (1982) reported that storage under refrigeration for 60 days did not produce a significant change in yolk and albumen index of quail eggs, but there was an increase in weight loss and air cell diameter. Because few investigations have been made of storage stability of unrefrigerated quail eggs, the present study was undertaken to investigate the microbiological storage stability of Japanese quail eggs to determine their shelf life in summer. The interior quality of the eggs was also investigated. MATERIALS AND METHODS
Quail Eggs. Unwashed quail (Coturnix coturnix japonica) eggs were packed in quail egg cases at a quail farm near Tokyo and delivered to the laboratory within 18 hr after lay. The eggs were stored at room temperature (23 to 33 C, RH 67 to 90%) in July for 28 days and periodically examined for bacterial counts, weight loss, and interior quality. Bacterial Counts on Shell Surface. The surface of each egg was wiped with a sterilized cotton piece using 10 ml of sterile water. The
474
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ABSTRACT Fresh quail eggs were stored at room temperature in July and periodically examined to evaluate microbiological quality, weight loss, and interior quality. Egg contents showed no marked change after storage for 14 days, but heavy contamination with gram negative bacteria or moulds was detected after storage for 21 and 28 days. The degree of contamination of the eggs after washing was heavier than that of unwashed eggs. An average of 4.0 X 10 s bacteria/egg were found on the shell surface of the fresh eggs. Gram positive bacteria predominated and their numbers decreased with storage. Salmonella and Staphylococcus aureus viae. found on the eggs, 6% and 1% respectively, but these pathogens were not detected after 14 days storage. The weight loss in the eggs was 2.99% after 14 days and 5.90% after 28 days. The yolk index decreased rapidly in comparison with hen eggs. Haugh unit values did not correlate well with storage time, whereas both the interior quality unit and albumen height seemed to be suitable for expressing interior quality. The yolks of eggs stored 21 days could not be readily separated from the albumen, either because of collapse of the yolk membrane or because of adhesion of the yolk to shell membranes. It was concluded from this study that shelf life of unrefrigerated quail eggs would not be greater than 14 days in summer and that washing of the eggs at farms should be avoided. (Key words: quail egg, Salmonella, Staphylococcus aureus, interior quality unit, yolk index)
475
STORAGE STABILITY OF QUAIL EGGS
ing mannit salt agar, and for Salmonella detection, 90 ml of lactose broth were added to the rest of the homogenate. The detection of Staphylococcus aureus and Salmonella was carried out following the method referred to above. Effect of Washing on Bacterial Count of Egg Contents. Fresh eggs were washed with a sterile brush in water at 45 C, sprayed with 200 ppm sodium hypochlorite, dried by warm air, packed in a clean quail egg case, and stored at room temperature for 21 days. The bacterial counts of egg contents were measured and compared with those of unwashed eggs stored for the same period. Weight Loss and Interior Quality. The weight loss, albumen height, Haugh unit and yolk index were periodically measured. The interior quality unit (1QU) was calculated following the equation 100 log (H + 4.18 - . 8 9 8 9 W 6 6 7 4 ) according to Kondaiah et al. (1983) using a computer, where H is albumen height in millimeters and w is egg weight in grams. Because the air cell height of intact eggs could not be measured because of the dark color of the shells, it was measured after boiling and peeling. For determining the ratio of shell: egg yolk:albumen, each egg was weighed and then broken into an egg-separator sieve. The egg yolk was rolled on a soft paper to remove adhered albumen and then weighed. The shell was weighed after removal of adhering albumen with soft paper. The albumen was calculated from total weight, shell weight, and egg yolk weight. The egg yolk and albumen were separately homogenized and analyzed for moisture, fat, protein, free glucose and pH by the methods of either Institute of American Poul-
TABLE 1. Bacterial survey of the surface of quail eggs Days of storage Measurement
0 Days
7 Days
14 Days
21 Days
28 Days
Bacterial count/egg Coliform count/egg Salmonella Staphylococcus aureus
4.0X 1 0 s ' 1.5 X 1 0 2 ' 6/100 2 1/1002
6.7X10" 9 X 10 2/100 0/100
2.4 X 10" <10 0/100 0/100
8.0 X 103 <10 0/100 0/100
4.8 X 10 3 <10 0/100 0/100
1 2
Logarithmic mean of 100 samples.
Numerator indicates the number of positive sair iples, and denominator indicates the number of tested samples.
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cotton and water were mixed together in a Stomacher. Total bacterial counts (plate count agar, 35 C for 48 hr) and coliform counts (desoxycholate agar, 35 C for 24 hr) of the wash water were measured periodically. Bacterial Counts of Egg Contents. Each egg was dipped in 200 ppm sodium hypochlorite solution at 50 C for 5 min, wiped with a cotton piece, washed with 95% ethanol, dried, and aseptically broken into a polyethylene bag. The egg contents were homogenized in a Stomacher, and the total bacterial count was measured using plate count agar. Microbial Flora on Shell and of Egg Contents. After counting the colonies on plate count agar, one to five strains representing different colony sizes and appearances were picked from each plate and were identified by the methods of Vanderzant and Nickelson (1969) and Cowan and Steel (1974). Salmonella and Staphylococcus Aureus on Shell Surfaces. For the detection of Salmonella, each intact egg was dipped into 50 ml of sterile lactose broth, gently shaken, and incubated at 35 C for 24 hr. Then the detection of Salmonella was carried out following the Association of Official Analycial Chemists (AOAC) method (1980). For the detection of S. aureus, .1 ml of sample water, which had been used for the total bacterial count of the shell surface, was placed on yolk-containing mannit salt agar, spread with an s bent glass rod, incubated at 35 C for 48 hr, and identified by the method of Suzuki (1973). Salmonella and Staphylococcus Aureus in Egg Contents. Each egg was aseptically broken into a polyethylene bag and homogenized in a Stomacher. For the detection of S. aureus, .1 ml of homogenate was spread on yolk-contain-
476
IMAI ET AL,
TABLE 2. Microbial flora of the shell surface of quail eggs
q a a a o a o
q q q
00 O r i m' ^
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Days of storage ODays
21 Days
(% identified strains)
3.8 1.9 6.2 .5 .5 1.4 2.9 100 210
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try Industry (IAPI, 1962) or the United States Department of Agriculture (USDA, 1961). Lysozyme activity of albumen was measured by the Japanese Pharmacopeia method (Shirota, 1982) using dried Micrococcus lysodeikticus and compared with that of hen egg albumen.
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RESULTS AND DISCUSSION
Bacterial Survey of Shell Surface of Quail Eggs. Table 1 shows the results of the bacterial survey on the shell surface of quail eggs. The average bacterial count on eggs before storage was 4.0 X 10 /egg, and the count gradually decreased during the storage period of 28 days. Considering the smaller surface area of quail eggs, it was thought that surface counts were similar to those found on unwashed hen eggs as reported by Board (1977) and Sashihara et al. (1979). The average coliform count before storage was 1.5 x 10 2 /egg and was less than 10/egg after 14 days. It has been reported that the number of bacteria on hen eggs decreases during storage, especially at high temperature (Genty and Quarks, 1972). The same tendency was observed in the case of quail eggs. Before storage, Salmonella was found on 6.0% of the eggs and S. aureus was detected on 1.0% of the eggs. Although a few Staphylococcus colonies were always found on yolkcontaining mannit salt agar, most of them were white in appearance and coagulase negative (not
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Gram positive Bacillus Coryneform Micrococcus Staphylococcus Streptococcus Gram negative Acinetobacter Aeromonas Alcaligenes Citrobacter Escherichia Pseudomonas Unidentified
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477
STORAGE STABILITY OF QUAIL EGGS
Microbial Counts of Egg Contents. Table 3 summarizes the microbial counts and presence of Salmonella and Staphylococcus aureus in the contents of quail eggs before and after storage. Before storage, bacteria were not detected in 97% of the eggs, and only very small counts of bacteria were detected in the remaining 3 eggs (3%). The number of contaminated eggs in-
creased with the storage period. After 14 days, there were 8 contaminated eggs (8%), and in these, bacterial counts were small (less than 1.0 X 10 4 /g). After 28 days, the number of contaminated eggs increased to 22 (22%), and the number of eggs contaning more than 1.1 x 10 microorganisms/g were 7 (7%). Comparing this result with the results of Imai and Saito (1983) using hen eggs which were washed and stored in August for a month, both the number of bacteria-contaminated eggs and the number of eggs contaminated with more than 1.1 x 10 4 bacteria/g were low in the case of quail eggs. Bacterial counts of washed eggs were measured after 21 days. The degree of contamination of washed eggs was much heavier than that of unwashed eggs and similar to that found in hen eggs washed and stored in August for a month (Imai and Saito, 1983). In Japan, quail eggs are distributed without washing and the value of this practice is confirmed by the above bacteriological findings. Salmonella and Staphylococcus aureus were not detected in the contents of quail eggs after any of the storage period investigated. Microbial Flora of Egg Contents. Table 4 shows the microbial flora of the contents of
TABLE 4. Microbial flora of the contents of quail eggs Days of storage 0 Days
7 Days
14 Days
21 Days
21 Days, washed
28 Days
• (% identified strains) • Gram positive Bacillus Coryneform Micrococcus Staphylococcus Streptococcus Gram negative Acinetobacter Aeromonas Alcaligenes Citrobacter Escherichia Flavobacterium Klebsiella Moraxella Pseudomonas Serratia Moulds Unidentified Number of tested strains
20.0 60.0
12.5
9.1
25.0 50.0
15.2 33.0
20.0
27.0 2.7 13.5 35.2
6.1 6.1
12.5
6.0 15.2 9.1
7.2
17.5
4.8 11.1 2.4
21.0 7.0
20.6 14.4 9.5 5.5 4.0 5.5 2.4
7.0 7.0 8.8 5.3
8.7 1.6
7.0 3.5 5.3
33
37
2.4 126
57
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aureus). Types of Salmonella found on quail eggs were S. typhimurium (80.0%) and S. thompson (20.0%), which were frequently detected from Japanese hen eggs. After 14 days, neither Salmonella nor Staphylococcus aureus were found on the eggs. Microbial Flora on the Shell Surface. Table 2 shows the microbial flora on the shell surface of quail eggs before storage and after storage for 21 days. Before storage, gram positive bacteria, especially Staphylococcus (not aureus) and Micrococcus were predominant, and the ratio of gram negative bacteria was small. After 21 days, the bacterial counts on the eggs decreased to 1/50 of the original count as shown in Table 1, and only the gram positive bacteria survived. It was stated by Board (1977) and Sashihara et al. (1979) that gram positive bacteria were also predominant on the surface of hen eggs.
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quail eggs before and after storage. In every storage period, gram positive bacteria were detected from several eggs. All the bacteria from the unwashed eggs, contaminated with bacteria more than 1.1 x 10 4 /g, were gram negative except three eggs contaminated with moulds in eggs stored 28 days. In washed eggs, gram negative bacteria were predominant (72.2%), but four eggs were heavily contaminated with Bacillus or Staphylococcus (not aureus). With the exception of these four eggs, the levels of gram positive bacteria were found to be less than 1.0 x 10 4 /g. This result agrees generally with the findings of Board (1977), Imai (1981), and Imai and Saito (1983) concerning hen eggs. Gram positive bacteria, however, seemed to occur more widely in quail eggs. Weight Loss and Interior Quality. Table 5 shows the weight loss and interior quality deterioration of quail eggs during storage. The weight loss and air cell height increased with time of storage. Comparison with hen eggs was difficult, because quail eggs are much smaller than hen eggs. The yolk index of quail eggs was almost the same as that of hen eggs before storage, and the decrease of the yolk index during storage was greater than that of hen eggs as reported by Imai (1983). The Haugh unit of fresh quail egg whites were almost the same as for hen eggs, but the decrease of Haugh units during storage was very small, although there was a large decrease in albumen height. There was, however, a considerable decrease in the interior quality unit during storage. Consequently, it would be better to use the yolk index, the interior quality unit, and albumen height for expressing the interior quality of quail eggs than to use the Haugh unit commonly used for hen eggs. Composition of Quail Eggs. Table 6 shows the composition of quail eggs during storage. After 21 and 28 days, it became difficult to separate the yolk from most of the eggs either because of weakened yolk membranes or because the yolk adhered to the shell membrane. With the increase of storage period, the percentage of egg yolk increased and the percentage of albumen decreased, but the shell percentage did not change. Comparing these percentages with those of quail eggs (shell 9.53%, egg yolk 32.06%, and albumen 58.45%) determined by Beev (1975), shell percent was slightly larger and yolk percent was slightly smaller. The percentages obtained in this
sto
478
STORAGE STABILITY OF QUAIL EGGS
479
TABLE 6. Effect of storage at room temperature on the composition of quail eggs Days of storage Composition, %
0 Days
7 Days
14 Days
21 Days
28 Days
Shell Egg yolk Albumen
10.51 + . 6 6 ' 3 1 . 1 4 + 1.30* 58.35 + 1.28*
10.55 ± .71 32.16 ± 1.70* 5 7 . 3 0 ± 1.87*
10.47 ± .73 33.22 ± 2 . 8 6 * 56.31 ± 2.39*
NT 2 NT NT
NT NT NT
'Mean ± standard deviation of 50 samples. 2
Not tested because of difficulty in separation of egg yolk from albumen.
•Percentages differ significantly (P<.05) in each storage period.
of quail eggs before and after storage
Egg yolk Measurement Moisture, % Protein, % Fat, % Free glucose, % pH Relative activity of lysozyme, % 3
Albumen
ODays storage
7 Days storage
14 Days storage
0 Days storage
7 Days storage
14 Days storage
50.03 15.78 30.66 .23 6.35
51.18 15.31 29.91 .24 6.64
52.68 14.75 29.03 .26 6.98
88.04 10.98 Tr 2 .49 9.02 52.3
87.32 11.62 Tr .52 9.12
86.51 12.20 .12 .54 9.26
1
Mean of three determinations.
2
Trace.
'Lysozyme activity in hen egg albumen measured at the same time was calculated as 100%.
experiment were similar to those found in hen eggs by Powrie (1977). Analyses of Quail Eggs. Table 7 shows the results of analyses of quail eggs stored for 0, 7, and 14 days. With the increase of storage period, moisture contents increased in egg yolk and decreased in albumen. The results obtained from eggs before storage were comparable with the findings of Beev (1975) using quail eggs and with the findings of Cook and Briggs (1977) using hen eggs. The relatively low lysozyme activity of quail albumen, compared with hen albumen, would account for the finding of relatively more gram positive bacteria in quail eggs. From the results of this study, it seems that from the viewpoints of microbiology and interior quality, the shelf life of quail eggs should be a maximum of 14 days at room temperature in summer.
REFERENCES Association of Official Analytical Chemists, 1980. AOAC Methods. 13th ed. W. Horwitz, ed., Assoc. Offic. Anal. Chem., Washington, DC. Beev, K., 1975. Some morphological and chemical characteristics of Japanese quail eggs. Khranitelta Promishlenost 24(8/9): 31-32. Board, R. G., 1977. The microbiology of eggs. Pages 49—64 in Egg Science and Technology. 2nd ed. W. J. Stadelman and O. J. Cotterill, ed. Avi Publ. Co., Inc., Westport, CT. Cook, F., and G. M. Briggs, 1977. Nutritive value of eggs. Pages 92—108 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 of the Identification of Medical Bacteria. Univ. Press, Cambridge, UK. Gentry, R. F., and C. L. Quarles, 1972. The measurement of bacterial contamination on egg shells. Poultry Sci. 51:930-933. Imai, C , 1981. Effect of coating eggs on storage stability. Poultry Sci. 60:2053-2061. Imai, C , and J. Saito, 1983. Detection of spoiled eggs
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TABLE 7. Analyses'
480
IMAI ET AL. Shirota, K., 1982. Standards for Articles in Japanese Pharmacopeia. Yakugyo Jiho Co., Ltd., Tokyo,
Japan. Suzuki, A., 1973. Inspection Manual for Food Hygiene. Assoc. Food Hygiene Japan, Tokyo. Tanabe, Y., M. Kamiya, K. Nishikawa, T. Nakamura, and T. Takahashi, 1972. Methods for long term storage of poultry eggs. XI. Effect of paraffin oil coating on quail egg quality. Res. Bull. Fac. Agric. Gifu Univ. 33:315-322. Tanabe, Y., T. Nakamura, M. Inaba, and T. Takahashi, 1970. Methods for long term storage of poultry eggs. I. Effect of paraffin oil coating on chicken egg quality. Jpn. Poult. Sci. 7:186—194. Tanabe, H., and N. Ogawa, 1975. Methods for long term storage of poultry eggs. IX. Seasonal changes in internal quality of quail (Coturnix coturnix japonica) eggs from retail stores. Jpn. Poult. Sci. 12:282-285. United States Department of Agriculture, 1961. USDA Laboratory Methods for Egg Products. US Dept. Agric, Washington, DC. 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.
Downloaded from http://ps.oxfordjournals.org/ at University of Otago on September 11, 2014
using a new type of inspection apparatus. Poultry Sci. 62:331-337. Institute of American Poultry Industry, 1962. Chemical and Bacteriological Methods for the Examination of Eggs and Egg Products. Inst. Am. Poult. Ind., Chicago, IL. Kondaiah, N., B. Panda, and R. A. Singhal, 1983. Internal egg-quality measure for quail eggs. Indian J. of Anim. Sci. 53:1261-1264. Pandey, N. K., C. M. Mahapatra, and R. P. Singh, 1982. Change in quality and acceptability of refrigerated quail (Coturnix coturnix japonica) eggs stored at room temperature. J. Food Sci. Technol., India 19(5):215-218. Powrie, W. D., 1977. Chemistry of eggs and egg products. Pages 65—91 in Egg Science and Technology. 2nd ed. W. J. Stadelman and O. J. Cotterill, ed. Avi Publ. Co., Inc., Westport, CT. Sakurai, H., 1984. Breeding of Japanese quails and their circumstances (1). Animal Husbandry (Japan) 38:563-568. Sashihara, N., H. Mizutani, S. Takayama, H. Konuma, A. Suzuki, and C. Imai, 1979. Bacterial survey on raw materials of liquid (frozen) whole eggs, its products, and manufacturing processes. J. Food Hyg. Soc. Jpn. 20:127-136.
1986 Poultry Science 65:474-480 INTRODUCTION
In Japan, about 20 million quail are reared each year by 300 farms (Sakurai, 1984) and their eggs are a popular item in the Japanese diet. The quail eggs are sometimes served without heating, though most of them are used after boiling. The storage stability of quail eggs has not been well studied, whereas there is a considerable literature dealing with the quality of stored hen eggs. The effect of storage on weight loss and on interior quality of quail eggs, such as albumen height, albumen index, yolk height, yolk index, and air cell size has been investigated by few researchers. Tanabe et al. (1972) reported that a good quality of oil-coated quail egg could be maintained for 120 days in a refrigerator and for 60 days in an unairconditioned room (22 to 31 C, RH 54 to 84%) and that uncoated eggs stored in the unconditioned room did not keep well. Tanabe et al. (1970) stated that the storage stability of quail eggs was superior to that of hen eggs because of their thicker shell membranes. Tanabe and Ogawa (1975) reported that albumen height and yolk height of the quail eggs purchased in summer were low, and a high incidence of
rotten eggs occurred. Pandey et al. (1982) reported that storage under refrigeration for 60 days did not produce a significant change in yolk and albumen index of quail eggs, but there was an increase in weight loss and air cell diameter. Because few investigations have been made of storage stability of unrefrigerated quail eggs, the present study was undertaken to investigate the microbiological storage stability of Japanese quail eggs to determine their shelf life in summer. The interior quality of the eggs was also investigated. MATERIALS AND METHODS
Quail Eggs. Unwashed quail (Coturnix coturnix japonica) eggs were packed in quail egg cases at a quail farm near Tokyo and delivered to the laboratory within 18 hr after lay. The eggs were stored at room temperature (23 to 33 C, RH 67 to 90%) in July for 28 days and periodically examined for bacterial counts, weight loss, and interior quality. Bacterial Counts on Shell Surface. The surface of each egg was wiped with a sterilized cotton piece using 10 ml of sterile water. The
474
Downloaded from http://ps.oxfordjournals.org/ at University of Otago on September 11, 2014
ABSTRACT Fresh quail eggs were stored at room temperature in July and periodically examined to evaluate microbiological quality, weight loss, and interior quality. Egg contents showed no marked change after storage for 14 days, but heavy contamination with gram negative bacteria or moulds was detected after storage for 21 and 28 days. The degree of contamination of the eggs after washing was heavier than that of unwashed eggs. An average of 4.0 X 10 s bacteria/egg were found on the shell surface of the fresh eggs. Gram positive bacteria predominated and their numbers decreased with storage. Salmonella and Staphylococcus aureus viae. found on the eggs, 6% and 1% respectively, but these pathogens were not detected after 14 days storage. The weight loss in the eggs was 2.99% after 14 days and 5.90% after 28 days. The yolk index decreased rapidly in comparison with hen eggs. Haugh unit values did not correlate well with storage time, whereas both the interior quality unit and albumen height seemed to be suitable for expressing interior quality. The yolks of eggs stored 21 days could not be readily separated from the albumen, either because of collapse of the yolk membrane or because of adhesion of the yolk to shell membranes. It was concluded from this study that shelf life of unrefrigerated quail eggs would not be greater than 14 days in summer and that washing of the eggs at farms should be avoided. (Key words: quail egg, Salmonella, Staphylococcus aureus, interior quality unit, yolk index)
475
STORAGE STABILITY OF QUAIL EGGS
ing mannit salt agar, and for Salmonella detection, 90 ml of lactose broth were added to the rest of the homogenate. The detection of Staphylococcus aureus and Salmonella was carried out following the method referred to above. Effect of Washing on Bacterial Count of Egg Contents. Fresh eggs were washed with a sterile brush in water at 45 C, sprayed with 200 ppm sodium hypochlorite, dried by warm air, packed in a clean quail egg case, and stored at room temperature for 21 days. The bacterial counts of egg contents were measured and compared with those of unwashed eggs stored for the same period. Weight Loss and Interior Quality. The weight loss, albumen height, Haugh unit and yolk index were periodically measured. The interior quality unit (1QU) was calculated following the equation 100 log (H + 4.18 - . 8 9 8 9 W 6 6 7 4 ) according to Kondaiah et al. (1983) using a computer, where H is albumen height in millimeters and w is egg weight in grams. Because the air cell height of intact eggs could not be measured because of the dark color of the shells, it was measured after boiling and peeling. For determining the ratio of shell: egg yolk:albumen, each egg was weighed and then broken into an egg-separator sieve. The egg yolk was rolled on a soft paper to remove adhered albumen and then weighed. The shell was weighed after removal of adhering albumen with soft paper. The albumen was calculated from total weight, shell weight, and egg yolk weight. The egg yolk and albumen were separately homogenized and analyzed for moisture, fat, protein, free glucose and pH by the methods of either Institute of American Poul-
TABLE 1. Bacterial survey of the surface of quail eggs Days of storage Measurement
0 Days
7 Days
14 Days
21 Days
28 Days
Bacterial count/egg Coliform count/egg Salmonella Staphylococcus aureus
4.0X 1 0 s ' 1.5 X 1 0 2 ' 6/100 2 1/1002
6.7X10" 9 X 10 2/100 0/100
2.4 X 10" <10 0/100 0/100
8.0 X 103 <10 0/100 0/100
4.8 X 10 3 <10 0/100 0/100
1 2
Logarithmic mean of 100 samples.
Numerator indicates the number of positive sair iples, and denominator indicates the number of tested samples.
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cotton and water were mixed together in a Stomacher. Total bacterial counts (plate count agar, 35 C for 48 hr) and coliform counts (desoxycholate agar, 35 C for 24 hr) of the wash water were measured periodically. Bacterial Counts of Egg Contents. Each egg was dipped in 200 ppm sodium hypochlorite solution at 50 C for 5 min, wiped with a cotton piece, washed with 95% ethanol, dried, and aseptically broken into a polyethylene bag. The egg contents were homogenized in a Stomacher, and the total bacterial count was measured using plate count agar. Microbial Flora on Shell and of Egg Contents. After counting the colonies on plate count agar, one to five strains representing different colony sizes and appearances were picked from each plate and were identified by the methods of Vanderzant and Nickelson (1969) and Cowan and Steel (1974). Salmonella and Staphylococcus Aureus on Shell Surfaces. For the detection of Salmonella, each intact egg was dipped into 50 ml of sterile lactose broth, gently shaken, and incubated at 35 C for 24 hr. Then the detection of Salmonella was carried out following the Association of Official Analycial Chemists (AOAC) method (1980). For the detection of S. aureus, .1 ml of sample water, which had been used for the total bacterial count of the shell surface, was placed on yolk-containing mannit salt agar, spread with an s bent glass rod, incubated at 35 C for 48 hr, and identified by the method of Suzuki (1973). Salmonella and Staphylococcus Aureus in Egg Contents. Each egg was aseptically broken into a polyethylene bag and homogenized in a Stomacher. For the detection of S. aureus, .1 ml of homogenate was spread on yolk-contain-
476
IMAI ET AL,
TABLE 2. Microbial flora of the shell surface of quail eggs
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RESULTS AND DISCUSSION
Bacterial Survey of Shell Surface of Quail Eggs. Table 1 shows the results of the bacterial survey on the shell surface of quail eggs. The average bacterial count on eggs before storage was 4.0 X 10 /egg, and the count gradually decreased during the storage period of 28 days. Considering the smaller surface area of quail eggs, it was thought that surface counts were similar to those found on unwashed hen eggs as reported by Board (1977) and Sashihara et al. (1979). The average coliform count before storage was 1.5 x 10 2 /egg and was less than 10/egg after 14 days. It has been reported that the number of bacteria on hen eggs decreases during storage, especially at high temperature (Genty and Quarks, 1972). The same tendency was observed in the case of quail eggs. Before storage, Salmonella was found on 6.0% of the eggs and S. aureus was detected on 1.0% of the eggs. Although a few Staphylococcus colonies were always found on yolkcontaining mannit salt agar, most of them were white in appearance and coagulase negative (not
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477
STORAGE STABILITY OF QUAIL EGGS
Microbial Counts of Egg Contents. Table 3 summarizes the microbial counts and presence of Salmonella and Staphylococcus aureus in the contents of quail eggs before and after storage. Before storage, bacteria were not detected in 97% of the eggs, and only very small counts of bacteria were detected in the remaining 3 eggs (3%). The number of contaminated eggs in-
creased with the storage period. After 14 days, there were 8 contaminated eggs (8%), and in these, bacterial counts were small (less than 1.0 X 10 4 /g). After 28 days, the number of contaminated eggs increased to 22 (22%), and the number of eggs contaning more than 1.1 x 10 microorganisms/g were 7 (7%). Comparing this result with the results of Imai and Saito (1983) using hen eggs which were washed and stored in August for a month, both the number of bacteria-contaminated eggs and the number of eggs contaminated with more than 1.1 x 10 4 bacteria/g were low in the case of quail eggs. Bacterial counts of washed eggs were measured after 21 days. The degree of contamination of washed eggs was much heavier than that of unwashed eggs and similar to that found in hen eggs washed and stored in August for a month (Imai and Saito, 1983). In Japan, quail eggs are distributed without washing and the value of this practice is confirmed by the above bacteriological findings. Salmonella and Staphylococcus aureus were not detected in the contents of quail eggs after any of the storage period investigated. Microbial Flora of Egg Contents. Table 4 shows the microbial flora of the contents of
TABLE 4. Microbial flora of the contents of quail eggs Days of storage 0 Days
7 Days
14 Days
21 Days
21 Days, washed
28 Days
• (% identified strains) • Gram positive Bacillus Coryneform Micrococcus Staphylococcus Streptococcus Gram negative Acinetobacter Aeromonas Alcaligenes Citrobacter Escherichia Flavobacterium Klebsiella Moraxella Pseudomonas Serratia Moulds Unidentified Number of tested strains
20.0 60.0
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aureus). Types of Salmonella found on quail eggs were S. typhimurium (80.0%) and S. thompson (20.0%), which were frequently detected from Japanese hen eggs. After 14 days, neither Salmonella nor Staphylococcus aureus were found on the eggs. Microbial Flora on the Shell Surface. Table 2 shows the microbial flora on the shell surface of quail eggs before storage and after storage for 21 days. Before storage, gram positive bacteria, especially Staphylococcus (not aureus) and Micrococcus were predominant, and the ratio of gram negative bacteria was small. After 21 days, the bacterial counts on the eggs decreased to 1/50 of the original count as shown in Table 1, and only the gram positive bacteria survived. It was stated by Board (1977) and Sashihara et al. (1979) that gram positive bacteria were also predominant on the surface of hen eggs.
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quail eggs before and after storage. In every storage period, gram positive bacteria were detected from several eggs. All the bacteria from the unwashed eggs, contaminated with bacteria more than 1.1 x 10 4 /g, were gram negative except three eggs contaminated with moulds in eggs stored 28 days. In washed eggs, gram negative bacteria were predominant (72.2%), but four eggs were heavily contaminated with Bacillus or Staphylococcus (not aureus). With the exception of these four eggs, the levels of gram positive bacteria were found to be less than 1.0 x 10 4 /g. This result agrees generally with the findings of Board (1977), Imai (1981), and Imai and Saito (1983) concerning hen eggs. Gram positive bacteria, however, seemed to occur more widely in quail eggs. Weight Loss and Interior Quality. Table 5 shows the weight loss and interior quality deterioration of quail eggs during storage. The weight loss and air cell height increased with time of storage. Comparison with hen eggs was difficult, because quail eggs are much smaller than hen eggs. The yolk index of quail eggs was almost the same as that of hen eggs before storage, and the decrease of the yolk index during storage was greater than that of hen eggs as reported by Imai (1983). The Haugh unit of fresh quail egg whites were almost the same as for hen eggs, but the decrease of Haugh units during storage was very small, although there was a large decrease in albumen height. There was, however, a considerable decrease in the interior quality unit during storage. Consequently, it would be better to use the yolk index, the interior quality unit, and albumen height for expressing the interior quality of quail eggs than to use the Haugh unit commonly used for hen eggs. Composition of Quail Eggs. Table 6 shows the composition of quail eggs during storage. After 21 and 28 days, it became difficult to separate the yolk from most of the eggs either because of weakened yolk membranes or because the yolk adhered to the shell membrane. With the increase of storage period, the percentage of egg yolk increased and the percentage of albumen decreased, but the shell percentage did not change. Comparing these percentages with those of quail eggs (shell 9.53%, egg yolk 32.06%, and albumen 58.45%) determined by Beev (1975), shell percent was slightly larger and yolk percent was slightly smaller. The percentages obtained in this
sto
478
STORAGE STABILITY OF QUAIL EGGS
479
TABLE 6. Effect of storage at room temperature on the composition of quail eggs Days of storage Composition, %
0 Days
7 Days
14 Days
21 Days
28 Days
Shell Egg yolk Albumen
10.51 + . 6 6 ' 3 1 . 1 4 + 1.30* 58.35 + 1.28*
10.55 ± .71 32.16 ± 1.70* 5 7 . 3 0 ± 1.87*
10.47 ± .73 33.22 ± 2 . 8 6 * 56.31 ± 2.39*
NT 2 NT NT
NT NT NT
'Mean ± standard deviation of 50 samples. 2
Not tested because of difficulty in separation of egg yolk from albumen.
•Percentages differ significantly (P<.05) in each storage period.
of quail eggs before and after storage
Egg yolk Measurement Moisture, % Protein, % Fat, % Free glucose, % pH Relative activity of lysozyme, % 3
Albumen
ODays storage
7 Days storage
14 Days storage
0 Days storage
7 Days storage
14 Days storage
50.03 15.78 30.66 .23 6.35
51.18 15.31 29.91 .24 6.64
52.68 14.75 29.03 .26 6.98
88.04 10.98 Tr 2 .49 9.02 52.3
87.32 11.62 Tr .52 9.12
86.51 12.20 .12 .54 9.26
1
Mean of three determinations.
2
Trace.
'Lysozyme activity in hen egg albumen measured at the same time was calculated as 100%.
experiment were similar to those found in hen eggs by Powrie (1977). Analyses of Quail Eggs. Table 7 shows the results of analyses of quail eggs stored for 0, 7, and 14 days. With the increase of storage period, moisture contents increased in egg yolk and decreased in albumen. The results obtained from eggs before storage were comparable with the findings of Beev (1975) using quail eggs and with the findings of Cook and Briggs (1977) using hen eggs. The relatively low lysozyme activity of quail albumen, compared with hen albumen, would account for the finding of relatively more gram positive bacteria in quail eggs. From the results of this study, it seems that from the viewpoints of microbiology and interior quality, the shelf life of quail eggs should be a maximum of 14 days at room temperature in summer.
REFERENCES Association of Official Analytical Chemists, 1980. AOAC Methods. 13th ed. W. Horwitz, ed., Assoc. Offic. Anal. Chem., Washington, DC. Beev, K., 1975. Some morphological and chemical characteristics of Japanese quail eggs. Khranitelta Promishlenost 24(8/9): 31-32. Board, R. G., 1977. The microbiology of eggs. Pages 49—64 in Egg Science and Technology. 2nd ed. W. J. Stadelman and O. J. Cotterill, ed. Avi Publ. Co., Inc., Westport, CT. Cook, F., and G. M. Briggs, 1977. Nutritive value of eggs. Pages 92—108 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 of the Identification of Medical Bacteria. Univ. Press, Cambridge, UK. Gentry, R. F., and C. L. Quarles, 1972. The measurement of bacterial contamination on egg shells. Poultry Sci. 51:930-933. Imai, C , 1981. Effect of coating eggs on storage stability. Poultry Sci. 60:2053-2061. Imai, C , and J. Saito, 1983. Detection of spoiled eggs
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TABLE 7. Analyses'
480
IMAI ET AL. Shirota, K., 1982. Standards for Articles in Japanese Pharmacopeia. Yakugyo Jiho Co., Ltd., Tokyo,
Japan. Suzuki, A., 1973. Inspection Manual for Food Hygiene. Assoc. Food Hygiene Japan, Tokyo. Tanabe, Y., M. Kamiya, K. Nishikawa, T. Nakamura, and T. Takahashi, 1972. Methods for long term storage of poultry eggs. XI. Effect of paraffin oil coating on quail egg quality. Res. Bull. Fac. Agric. Gifu Univ. 33:315-322. Tanabe, Y., T. Nakamura, M. Inaba, and T. Takahashi, 1970. Methods for long term storage of poultry eggs. I. Effect of paraffin oil coating on chicken egg quality. Jpn. Poult. Sci. 7:186—194. Tanabe, H., and N. Ogawa, 1975. Methods for long term storage of poultry eggs. IX. Seasonal changes in internal quality of quail (Coturnix coturnix japonica) eggs from retail stores. Jpn. Poult. Sci. 12:282-285. United States Department of Agriculture, 1961. USDA Laboratory Methods for Egg Products. US Dept. Agric, Washington, DC. 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.
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using a new type of inspection apparatus. Poultry Sci. 62:331-337. Institute of American Poultry Industry, 1962. Chemical and Bacteriological Methods for the Examination of Eggs and Egg Products. Inst. Am. Poult. Ind., Chicago, IL. Kondaiah, N., B. Panda, and R. A. Singhal, 1983. Internal egg-quality measure for quail eggs. Indian J. of Anim. Sci. 53:1261-1264. Pandey, N. K., C. M. Mahapatra, and R. P. Singh, 1982. Change in quality and acceptability of refrigerated quail (Coturnix coturnix japonica) eggs stored at room temperature. J. Food Sci. Technol., India 19(5):215-218. Powrie, W. D., 1977. Chemistry of eggs and egg products. Pages 65—91 in Egg Science and Technology. 2nd ed. W. J. Stadelman and O. J. Cotterill, ed. Avi Publ. Co., Inc., Westport, CT. Sakurai, H., 1984. Breeding of Japanese quails and their circumstances (1). Animal Husbandry (Japan) 38:563-568. Sashihara, N., H. Mizutani, S. Takayama, H. Konuma, A. Suzuki, and C. Imai, 1979. Bacterial survey on raw materials of liquid (frozen) whole eggs, its products, and manufacturing processes. J. Food Hyg. Soc. Jpn. 20:127-136.