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Original article Effects of mineral oil coating on internal quality of chicken eggs under refrigerated storage Wannita Jirangrat,1Damir Dennis Torrico,1June No,1Hong Kyoon No2 Accepted in revised 27 November 2009 SummaryThe selected internal qualities weight loss, Haugh unit, yolk index, and albumen pH of noncoated and mineral oil-coated chicken eggs during 15 weeks of storage at 4 C and⁄or during 5 weeks of storage at 25 C were uated. Results indicated that, without refrigeration, the noncoated and mineral oil-coated eggs rapidly changed from AA to C and B grades as measured by Haugh unit, respectively, after 5 weeks of storage. However, the AA quality of the noncoated eggs could be maintained under refrigerated storage 4 C for at least 5 weeks. The mineral oil coating and refrigerated storage 4 C synergistically minimised weight loss and preserved the albumen and yolk qualities of chicken eggs during a long-term storage. At 4 C, the mineral oil-coated eggs preserved the initial AA grade for at least 15 weeks with l.19 weight loss. KeywordsEgg, Haugh unit, mineral oil coating, refrigerated storage, shelf life, yolk index. Introduction Eggs provide a unique, well-balanced source of nutri- ents, including essential unsaturated fatty acids linoleic 182n6, oleic acid, iron, phosphorus, trace minerals, and vitamins A, D, E, K and B, for people of all ages Watkins, 1995. However, eggs are highly perishable and their internal quality starts to deteriorate immedi- ately after they have been laid due to loss of moisture and carbon dioxide through the 7000–17 000 pores on the shell surface Caner Kim et al., 2009. Therefore, a protective barrier against transfer of moisture and carbon dioxide is needed to preserve the egg quality. Many coating materials have been applied on the surface of egg shells to preserve the internal quality of eggs, such as chitosan No et al., 2005; Kim et al., 2006, 2009; Caner Rhim et al., 2004; Biladeau Obanu Biladeau Kamel et al., 1980 revealed that eggs coated with mineral oil had signifi cantly better quality than non- coated eggs. Quality changes of eggs during storage are aff ected by various factors and one of them could be storage temperature. To date, there is little ination avail- able on the eff ect of refrigerated temperature on the internal quality of eggs coated with mineral oil during a long-term storage, except for Biladeau nevertheless, only minute quantity 0.1 of these eggs is exported Biladeau e-mail wprinyalsu.edu International Journal of Food Science and Technology 2010, 45, 490–495490 doi10.1111/j.1365-2621.2009.02150.x 2010 The Authors. Journal compilation 2010 Institute of Food Science and Technology long-term refrigerated storage on the internal quality of mineral oil-coated eggs will certainly provide valuable ination to egg industry as well as consumers. The objective of the present research was to uate the eff ect of refrigerated temperature 4 C on the selected quality weight loss, Haugh unit, yolk index, and albumen pH of mineral oil-coated eggs during 15 weeksofstorage.Inourpreviouswork Waimaleongora-Ek et al., 2009, eggs coated with mineral oil 26 mPa s viscosity maintained the internal quality up to 5 weeks of storage at 25 C. Therefore, quality of mineral oil-coated eggs stored at 4 C was also compared with that at 25 C after 5 weeks of storage. Materials and s Materials Mineral oil viscosity of 26 mPa s used as a coating material was obtained from PenrecoKarns City, PA., USA. The mineral oil was transparent, odourless and food grade. Unwashed, faeces-free, white-shell eggs from 58-weeks old, Hyline W-36 hens; a weight range of 50–70 g were obtained from Cal-Maine Foods Jackson, MS, USA. Immediately after collected from the farm and screened for defects and desirable weight range, eggs were stored in the cold room approximately 7 C before the next day coating. Before coating, eggs were kept at room temperature approximately 25 C for a couple of hours to avoid water condensation on the egg surface that could interfere with coating. Coating treatment and storage of eggs Eggs were weighed individually, coated with mineral oil using a sponge brush, wiped to remove excess oil, and allowed to dry overnight at room temperature. The noncoated eggs served as the control group. All eggs were placed in a small-end down position Kim et al., 2009 in cardboard egg racks, and stored in a refriger- ator at 4 C for 15 weeks or at room temperature 25 2 C for 5 weeks. Ten eggs per each treatment were taken at 5-week intervals for determination of weight loss, Haugh unit, yolk index, and albumen pH. Determination of weight loss Weight loss of the coated whole egg during storage was calculated as {[initial whole egg weight g after coating at day 0 – whole egg weight g after stor- age]⁄initial whole egg weight g after coating at day 0} 100. Weight loss of the noncoated whole egg was calculated as {[initial whole egg weight g at day 0 – whole egg weight g after storage]⁄initial whole egg weight g at day 0} 100. The weight of whole eggs was measured with a balance TS400S, Ohaus Corp., Flor- ham Park, NJ, USA. Ten measurements per treatment were taken. At 4 C storage, the averaged increasing rate of weight loss was calculated as [total weight loss after 15 weeks storage⁄15 week]. Determination of Haugh unit and yolk index The height of albumen and yolk was measured with a tripod micrometer Model S-6428, B.C. Ames Inc., Melrose, MA, USA. The yolk width was measured with a digital caliper General Tools Lee et al., 1996. At 4 C storage, the averaged decreasing rate of Haugh unit was calculated as [Haugh unit at week 0 – Haugh unit at week 15⁄15 week]. Ten measurements per treatment were taken. Measurement of albumen pH After measurement of Haugh unit and yolk index, the albumen was separated from the yolk. The thin and thick albumen were mixed thoroughly prior to measur- ing pH with a pH meter IQ150, IQ Scientifi c Instru- ments, San Diego, CA, USA. Ten measurements per treatment were taken. Statistical analysis For internal quality weight loss, Haugh unit, yolk index, and albumen pH of eggs, experiments were carried out in ten replicates per each treatment, and mean SD values were reported. Data were analysed using Analysis of Variance, followed by the Tukey’s studentised range test a 0.05 using the statistical analysis software SAS, 2003. Relationships between weight loss and storage time and between Haugh unit and storage time were established by a linear regression model along with the R2value. Pearson correlation coeffi cients r among weight loss, Haugh unit, yolk index, and albumen pH were calculated. Results and discussion Effects of mineral oil coating and storage temperature on weight loss Changes in weight loss of the control noncoated and mineral oil-coated eggs during 15 weeks of storage at 4 C are presented in Table 1. Overall, the weight loss signifi cantly increased with increased storage periods; however, mineral oil coating markedly reduced the Quality of mineral oil-coated eggs W. Jirangrat et al.491 2010 The Authors. Journal compilation 2010 Institute of Food Science and TechnologyInternational Journal of Food Science and Technology 2010 weight loss of eggs compared with that of the noncoated eggs, as also observed by previous workers Kamel et al., 1980; Waimaleongora-Ek et al., 2009. After 15 weeks of storage, the weight loss of noncoated and mineral oil-coated eggs was 12.44 and 1.19, respec- tively. Since the weight loss of both noncoated and mineral oil-coated eggs linearly increased R2 0.9 with storage time at 4 C Fig. 1, the averaged increas- ing rate of weight loss was calculated to be 0.829 and 0.079 per week, respectively, for the noncoated and mineral oil-coated eggs. Refrigerated storage 4 C inserted a signifi cant eff ect in minimising the weight loss of eggs Table 1. For example, the weight loss 8.71 of noncoated eggs after 10 weeks of storage at 4 C was slightly lower not signifi cant than that 9.23 of noncoated eggs after 5 weeks of storage at 25 C. The synergistic eff ect of mineral oil coating and refrigerated storage was also observedTable 1.Forexample,theweightloss 0.54 of mineral oil-coated eggs even after 10 weeks of storage at 4 C was signifi cantly lower than that 0.85 of mineral oil-coated eggs after 5 weeks of storage at 25 C. Compared with the noncoated eggs, the mineral oil coating eff ectively reduced the weight loss of eggs by at least ten times after 15 weeks at 4 C 1.19 for coated and 12.44 for noncoated eggs or after 5 weeks at 25 C 0.85 for coated and 9.23 for noncoated eggs Table 1. The latter was also observed by Waimaleongora-Ek et al. 2009. Jones 60 A 72; 31 B 59 and C 30. Storage time week Weight loss 0 2 4 6 8 10 12 14 0246810121416 Figure 1Relationships between weight loss and storage time week of the control noncoated C and mineral oil-coated MO eggs during 15 weeks of storage at 4 C. Quality of mineral oil-coated eggs W. Jirangrat et al.492 International Journal of Food Science and Technology 2010, 2010 The Authors. Journal compilation 2010 Institute of Food Science and Technology grade, Haugh unit, yolk index, and egg size Mueller, 1958, 1959 as well as storage conditions. Based on the correlation matrix of four internal quality parameters weight loss, Haugh unit, yolk index and albumen pH in Table 2, the increasing weight loss of egg was negatively related with the decreasing Haugh unit, yolk index and albumen pH. Weight loss of eggs during storage is caused mainly by the evaporation of water and, to a lesser extent, by loss of carbon dioxide from the albumen through the shell Obanu Stadelman, 1995b. Loss of carbon dioxide, in turn, aff ects Haugh unit, yolk index and albumen pH. According to FAO 2003, a weight loss of 2–3 is common in marketing eggs and is hardly noticeable to consumers. A weight loss of 1.19 Table 1 was observed with mineral oil-coated eggs after 15 weeks of storage at 4 C. This study, thus, demonstrated that both mineral oil coating and refrigerated storage at 4 C were synergistically eff ective in minimising weight loss of eggs during a long-term storage. Effects of mineral oil coating and storage temperature on Haugh unit Changes in the Haugh unit of the control noncoated and mineral oil-coated eggs during 15 weeks of storage at 4 C and during 5 weeks of storage at 25 C are shown inTable 1.Overall,theHaughunit signifi cantly decreased with increased storage periods; however, this decrease progressed at a much slower rate for mineral oil-coated eggs Fig. 2. After 15 weeks of storage at 4 C, the Haugh unit of noncoated and mineral oil- coated eggs decreased from the initial value of 84.12 to 62.90 and 74.44, respectively. Since the Haugh unit of both noncoated and mineral oil-coated eggs linearly decreased R2 0.9 with storage time at 4 C Fig. 2, the averaged decreasing rate of Haugh unit was calcu- lated to be 1.415 and 0.645 per week, respectively, for the noncoated and mineral oil-coated eggs. Mineral oil coating was eff ective in preserving the albumen quality of eggs at 25 C. The Haugh unit of noncoated and mineral oil-coated eggs dropped from the initial value of 84.12 to 20.13 and 55.80, respectively, after 5 weeks of storage at 25 C Table 1. As with the mineral oil coating, refrigerated storage 4 C also inserted a signifi cant eff ect in preserving the albumen quality. After 5 weeks of storage, the Haugh unit of the noncoated eggs was at least 3.5 times higher when stored at 4 C compared with that at 25 C. The synergistic eff ect of mineral oil coating and refrigerated storage 4 C in preserving the albumen quality was obvious after 15 weeks of storage. Eggs can be classifi ed into four grades based on the Haugh unit AA above 72, A 72–60, B 59–31, and C below 30 grades Lee et al., 1996. The higher the Haugh unit value, the better the albumen quality of eggs. Table 1 shows changes in classifi ed egg grade during 15 weeks of storage at 4 C and during 5 weeks of storage at 25 C. The grade generally decreased with increasing storage time; however, the pattern diff ered depending on the storage temperature. At 4 C, the noncoated eggs changed from the AA to A grade after 10 weeks; this A grade remained until the end of 15 weeks of storage Table 1. In contrast, the mineral oil-coated eggs preserved the initial AA grade for the entire 15 weeks of storage at 4 C. Biladeau Jones Biladeau Rhim et al., 2004. During storage, the loss of carbon dioxide from eggs through the eggshell pores results in an increase in albumen pH value to 9.6 Knight et al., 1972; Heath, 1977; Li-Chan et al., 1995; Kemps et al., 2007. In contrast, egg yolks have a pH range of 6.0–6.5 that was relatively constant during storage Caner, 2005. Changes in the albumen pH of noncoated and mineral oil-coated eggs during 15 weeks of storage at 4 C were dissimilar as shown in Table 1. The albumen pH of noncoated eggs increased from the initial value of 8.71 to 9.33 after 5 weeks and then continuously decreased to 8.53 after 15 weeks of storage. On the other hand, the albumen pH of mineral oil-coated eggs gradually decreased from 8.71 to 7.96 after 15 weeks of storage. Biladeau Obanu Biladeau Goodwin et al., 1962; Sabrani Scott Silversides Scott, 2001. Conclusions This study indicated that, without refrigeration, the noncoated and mineral oil-coated eggs rapidly changed from AA to C and B grades as measured by Haugh unit, respectively, after 5 weeks of storage. However, the AA quality of noncoated eggs can be maintained under refrigerated storage 4 C for at least 5 weeks. The mineral oil coating and refrigerated storage 4 C synergistically minimised weight loss and preserved the albumen and yolk quality of chicken eggs during a long- term storage. At 4 C, the mineral oil-coated eggs preserved the initial AA grade for at least 15 weeks Quality of mineral oil-coated eggs W. Jirangrat et al.494 International Journal of Food Science and Technology 2010, 2010 The Authors. Journal compilation 2010 Institute of Food Science and Technology with less than 2 weight loss. There were no observed black spots or moulds on the egg surface during the long-term storage. This ination will be valuable to egg industries for the purpose of egg sales export. Further long-term storage studies are needed with diff erent initial egg qualities and egg sizes since the quality and shelf life of eggs may vary depending on the initial egg qualities, particularly Haugh units, and egg size under refrigerated temperature. Further studies are also needed under realistic commercial scale conditions as conditions used in a large-scale commercial egg production w