Egg quality of two layer strains as influenced by extended storage periods and storage temperatures

Julius Kofi Hagan¹ and Francisca O Eichie²

¹ Department of Animal Science, School of Agriculture, University of Cape Coast
jhagan1@ucc.edu.gh
² Nigerian Institute of Animal Science (NIAS)

Abstract

The layer industry in Ghana employs the use of different strains of layers for egg production with eggs produced being stored for some time under different temperatures before use. A study was therefore carried out to determine the effect of strain of layers, different storage periods and different storage temperatures on the internal and external qualities of chicken eggs. A total of four-hundred and fifty (450) eggs from 56-week old layer strains were analysed for egg quality in a 2 X 5 X 3 factorial experiment involving two layer strains ((Lohmann brown and white); five storage periods of 0, 5, 10, 15 and 20 days and stored under three storage temperatures (refrigeration at 5⁰C, room temperature at 21 ⁰C and open market temperature at 32⁰C). The eggs were labeled and weighed and thereafter, ninety (90) of them (45 from each strain) were randomly sampled and analysed for internal and external quality same day. The remaining eggs were then stored under refrigeration (5⁰C) and in chambers at 21⁰C and 32⁰C for 5, 10, 15 and 20 days. Data obtained were subjected to three-way analysis of variance with strain, storage period and storage temperature as fixed factors using the General Analysis of Variance procedure of GenStat, Discovery Edition. There were no differences between the two layer strains with regard to egg weight and shell thickness but eggs from the Lohmann brown strains, were superior in haugh unit, an important determinant of egg freshness. Major egg quality traits (egg weight, albumen weight and haugh unit) were affected negatively by increasing storage periods; thereby reducing the quality of the egg. Eggs stored under refrigeration (5⁰C) maintained their quality as compared to those stored at 21 and 32⁰C. In order not to compromise egg quality there is need to consider the strain of layer to use, and for how long and at what temperature the eggs should be stored before use.

Keywords: albumen height, egg weight, haugh unit, lohmann brown, lohmann white, strain

Introduction

The quality of the egg, which according to Š e v č í k o v á (2003), is measured by the morphological, chemical, physical, organoleptic (sensual) and microbiological characteristics of the egg, also influences its acceptability by consumers or for industrial use (Stadelman 1996). The quality can be measured by both the internal and external characteristics. External quality focuses on egg weight, shell cleanliness, soundness of shell, texture, color and shape. These features are important to the processor as eggs with superior external qualities arrive in a better condition for the consumer (Sabbir et al 2013). The internal quality, on the other hand, is determined by the quality of the egg white (albumen), relative viscosity of albumen, shape and firmness of yolk, strength of yolk, size of air cell and presence and absent of blood or meat spot.

Albumen and yolk quality are not only important indicators of egg freshness but contribute to the formation and stabilization of the aerated structure in confectioneries. The yolk and albumen are enclosed by the eggshell, with cuticles present, containing proteins, polysaccharides and lipids, which allow the exchange of carbon dioxide, oxygen and water through the pores. Environmental factors such as temperature, humidity, the presence of CO ₂ and storage time are also of prime importance in the maintenance of egg quality (Samli et al 2005). Storage time and temperature appear to be the most crucial factors affecting albumen quality or Haugh unit. According to Samli et al (2005), initial albumen quality rapidly decreases with advancing flock age.

In Ghana and most part of Africa, eggs from the farm are stored for some time under different temperature regimes before they get to their final destination or to the final consumer. At the farm, the eggs are usually stored under room temperature (19-22⁰C) before sold to consumers (who also either store these eggs under room temperature or under refrigeration at 5⁰C before use). When the eggs reach the retailers, they also normally sell them in the open market under temperatures ranging from 28-34⁰CC. Eggs meant for processing or for industrial use need to be fresh, hence the need to consider how long and the temperatures within which such eggs are going to be stored before being use. There have been reports of deterioration of egg quality as a result of long or extended storage period (Monira et al 2003; Tilki and Saatci, 2004; Lengkey et al 2012 and Hagan et al 2013). However, there is not enough work on the effects of different storage temperatures or in combination with extended storage period on the quality of eggs from different strains. The objective of this study was therefore to examine the quality of eggs from the two commonest layer strains in Ghana (Lohmann white and brown) as influenced by extended storage periods and different storage temperatures.

Materials and method

Location of the experiment

The experiment was carried out at the Teaching and Research Farm of the School of Agriculture, University of Cape Coast. The farm is located at the eastern part of the University with average temperature range of 19-34 ⁰CC and humidity of 60-80%. Eggs were collected from Lohmann brown (brown feathered and laid brown-shelled eggs) and Lohmann white (white feathered and laid white-shelled eggs) which were being kept for an egg production trial.

Experimental design and materials used

A total of four-hundred and fifty (450) eggs from 56-week old layer strains were analysed for quality in a 2 X 5 X 3 factorial experiment involving two layer strains ((Lohmann brown and white); five storage periods of 0, 5, 10, 15 and 20 days and three storage temperatures of 5⁰C (refrigeration), 21⁰C (room temperature) and 32⁰C (open market temperature). All the eggs were labeled and weighed within two hours of being laid. Ninety (90) of the fresh eggs (45 from each strain) were analysed for internal and external quality. The remaining eggs were then stored under refrigeration (5⁰C) and in chambers at 21 ⁰C and 32⁰CC for 5, 10, 15 and 20 days.

Egg quality analysis

On each day of analysis, 90 eggs (45 from each strain and 15 from each of the three storage methods) were analyzed. Eggs were evaluated on individual basis for internal and external quality traits. The following constituted external egg characteristics: egg weight (g), shell weight (g) and thickness (mm). The determinants of internal egg quality traits were: albumen weight (g), albumen height (mm), yolk height (mm), albumen pH and haugh unit (%). Total egg weight, yolk and eggshell were determined using an electronic balance with 0.01g precision (Mettler P 1210). Egg shell thickness was measured using digital vernier calipers as explained by Al-shami et al (2011). The shell thickness was determined by first cleaning the shells with tissue paper and air-drying at room temperature for 24 hours. Then, three pieces of shell was taken from the narrow end (sharp region), the middle side (equatorial region) and the broad end (blunt region) of each egg. This was after the shell membranes had been removed and then the thickness measured by a digital caliper to the nearest of 0.05 mm. The shell thickness (mm) was then calculated as an average of the thicknesses of the three pieces (Ehtesham and Chowdhury, 2002). For the determination of the internal qualities, individual eggs were broken out and the albumen and yolk height measurements taken using a tripod micrometer screw gauge (Nonga et al 2010). Albumen was carefully separated from the yolk and eggshells before weighing. Albumen weight was retrieved by subtraction as prescribed by (Parmar et al 2006) as: albumen weight = total weight - yolk weight - eggshell weight. After the egg had been broken onto a flat plate to determine the internal egg characteristics, a Roche yolk colour fan with values ranging from 1-14 representing pale yellow to deep yellow was used to compare the colour of the yolk. The albumen pH was obtained using a pH meter (Hanna Inst., Woonsocker, RI 02895). Haugh unit was then calculated from the values obtained from albumen height and egg weight by employing the formula proposed by Haugh (1937):

Data obtained were subjected to three-way analysis of variance (ANOVA) with strain, storage period and storage temperature as fixed factors using the General Analysis of Variance procedure of GenStat, Discovery Edition (Lawes, 2004). Where differences in means existed, the means were separated using the least significant difference (lsd) test at 5% level of significance. The statistical model used was as follows:

Where:

Y_ijk = observation on the ith strain,jth storage period and kth storage method

µ = overall mean

S_i = effedt of ith strains

Pj = effedt of jth storage period

T_k = effect of kth storage temperature

(SXP)_ij = the interaction effects of the ith strain and jth storage period

(SXT)_ik = the interaction effects of the ith strain and kth storage temperature

(PXT)_jk = the interaction effects of the jth storage period and the kth storage temperature

(SXPXT)_ijk = the interaction effects of the ith strain and jth storage period and kth storage temperature

e_ijk = random error

Results and discussion

Effects of strain of layer on egg quality

Results on the external and internal egg characteristics of the two layer strains are shown in Table 1. Results obtained showed that the two strains produced eggs which were not different in their external characteristics. This disagrees with the findings of Hagan et al (2013), Hanusova et al (2015) and Khatun et al (2016) who found significant strain effects on egg weight and shell thickness. Singh et al (2009) also found the Lohmann brown layers to have heavier eggs than their white-feathered counterparts. The shell thicknesses of the two strains recorded in the present study produced eggs with were within acceptable shell thickness (0.35-0.36mm) ranges which made them acceptable for egg production. According to Hagan et al (2013) the insignificant difference in egg weight between the Lohmann white and brown strains could be as a result of close relationship between the two strains, that is, the two strains might have descended from close ancestry.

The internal egg characteristics are the major determinants of its quality. The egg white (albumen) of Lohmann brown layers were found to be superior in terms of weight and height as compared to that of Lohmann white, resulting in a better haugh unit of about 74% as compared to 67.7% for the Lohmann white strains. The present result corroborates that of Rajkumar et al (2009) who also reported better haugh unit in eggs from brown layers. Even though yolk colour is affected mainly by diets, there was a difference (p<0.05) in yolk colour between the two strains. The yolk colour observed was generally far below the minimum value of 9.0 as accepted by the International Markets as stated by Jones et al (2002). There is therefore the need to add green vegetables in the diets of intensively kept layers in order to improve the colour of the yolk.

Effects of different storage periods on egg characteristics

Table 2 shows the effects of extended storage period on egg characteristics. Egg weight significantly reduced just after 5 days of storage and reduced further thereafter. This agrees with findings of (Khan et al 2013; Hagan et al 2013 and Gomez-de-Travecedo et al 2014). According to Jones et al. (2002), commercial eggs are graded based on weights such as: “AA” (for egg weight above 62g), “A” (58g-62g) and grade “B” (52g-57g) and with eggs weighing below 52g being commercially unacceptable. Five days of storage significantly reduced the weight resulting in the downgrading of the eggs from grade “A” eggs (59.1g) to grade “B” egg (54.3g). Eggs stored for 20 days (50.9g) however could be graded as commercially unacceptable. This implies that the value of eggs and for that matter the market price is would reduce as eggs are stored beyond five days. The reduction in weight with increasing storage period, according to Jones et al (2002), might be due to the rapid loss of moisture from the egg content to the surrounding atmosphere through the egg shell pores.

Extended storage period did not significantly alter the shell weight, an observation which agrees with that of Khatun et al (2016). However, the thickness of the shell decreased significantly after 15 days of storage. According to earlier reports by Scott and Silversides (2000) and Moula et al (2009) because the shell is in direct contact with the surrounding atmosphere, drying is considerably fast and the shell becomes drier as storage period length increases, thereby making the shell lighter with age. The decrease in egg shell thickness might also be linked to the shrinking of the inner egg membrane and/or cuticle with increase storage time. Moula et al (2009) obtained similar result from a study on eggs from the Lohmann brown strains.

Results from the present study also show that albumen weight, albumin height and haugh unit significantly decreased with increasing storage period. This finding agrees with observations by Samli et al (2005), Raji et al (2009) and Tabidi (2011)). The freshness of the egg is measured by its haugh unit which is the measure of albumen thickness upon breaking of the egg. According to Tebesi et al (2012), lower haugh unit reflects lesser freshness. The significant decrease in haugh unit from 74.4 to 67.8% might be due to the decrease in egg weight and albumen height (two important determinants for haugh unit) during storage (Samli et al 2005; Khan et al 2014 and Aguna and Narinc, 2016). The reduction in albumen height is due to the reduction in the content and nature of ovomucin (Silversides and Budgell, 2004). The decreased ovomucin is brought about by factors such as proteolysis, cleavage of disulfide bonds, interactions with lysozyme and changes in the interaction between α and β ovomucin.

Again, the decrease in albumen weight observed in this study with increasing storage period might be due to the CO₂ and moisture loss from the egg which often result in watery albumen and breaking of the vitalline membrane, thus leading to the absorption of the albumen content by the yolk and consequently an increase in yolk weight and a decrease in albumen weight (Jin et al 2011; Hagan et al 2013 and Khan et al 2014). Scott and Silversides (2000) observed that albumen height decreased with increased storage period due to the fact that moisture and CO₂ are lost from egg stored in an open environment and this causes the air cell within the egg to enlarge. Also, the loss in CO₂ raises the egg’s pH to become more basic, hence inducing structural changes in the albumen; that is thinning of the albumen which consequently result in a decline in albumen height. The egg white (albumen) significantly turned towards alkaline with increasing storage period. This agrees with the results by Akyurek and Okur (2009) and Lengkey et al (2012) who also observed significant increase in pH of the albumen and yolk with increasing storage period.

From the results obtained, it could be seen that albumen height of fresh eggs (6.3 mm) declined significantly to 3.9 mm when the eggs were stored for 20 days. This albumen height is far below the albumen height of value of 11.5mm for extremely good and fresh eggs as stated by Scott and Silversides (2000). These are the standards for eggs to be accepted for use in the confectionery industry where eggs are used for the in making of cakes, chocolates, candy among other products.

Effects of different storage temperatures on egg quality

Table 3 shows the egg quality as influenced by different storage temperatures. Eggs stored under refrigeration were significantly heavier than those stored under room and open market temperatures. Most eggs sold on the open markets in Ghana are subjected to temperatures ranging from 19-34⁰C. The mechanism involved in the shrinking or reduction in size of eggs when subjected to different storage temperatures is the differences in the ability to breakdown of carbonic acid to CO₂ and the slow-down of CO₂ loss (Raji et al 2009). These losses are known to cause the albumen and yolk to lose mucin fibre, which is responsible for its gel-like structure leading to loss of quality. Again, eggs that are stored over a long period under room temperature or in the open market have reduced albumen height from 7.8 to 4.0 cm in this present study (Table 3). This agrees with work by Alade et al (2013), who reported decrease of in albumen height from 0.65 to 0.54 cm when eggs were stored for 12 days under room temperature. It is noted that when eggs are stored for long period, the ovomucin layer which is responsible for the firmness of thick albumen becomes weaker. The albumen, therefore, spreads over wide range of area in abnormal manner that causes the increase in albumen length and width and consequently decreased in albumen height (Jadhav and Siddiqui, 2007).

Higher haugh unit was recorded for eggs which were stored under refrigeration as compared to those stored under room temperature. During refrigeration, there is no or minimal loss of CO₂ from the egg. To reduce the loss in quality of eggs that are to be stored over time before use, in the absence of refrigeration, Copur et al (2008) recommends the coating of eggs with propolis extract to improve the internal egg quality. This, according to the authors, would reduce chemical degradation in the egg. Jacqueline et al (2011), in a study using gelatin and oil reported a decrease in weight loss during storage. Again, Raji et al (2009) reported higher haugh unit for refrigerated eggs compared to other storage temperatures. Samli et al (2005) demonstrated that coating of eggs with oil could result in decrease in albumen pH. The progressive weakening of the vitelline membranes and liquefaction of the yolk may also be reduced by oiling the egg shell to prevent diffusion of water from the yolk.

When the eggs are stored under room or outdoor temperatures, because they are exposed, CO₂ passes through the pores of the eggshell, the pH of the albumen increases, resulting in the deterioration of the complex forming capacity of ovomucine and lysozyme, and the decrease in the viscosity and haugh unit, thereby reduction in quality. According to Scott and Silversides (2000) haugh unit gives a better indication of egg quality as it combines egg weight and albumen thickness, thereby reflecting the presence and the quality of Ovalbumin, Ovotransferrin, Ovomucoid, Ovomucin, Lysozyme, G2 Globulin, G3 Globulin and Avidin which are all albumen proteins. Therefore any method that is likely to maintain the haugh unit thereby maintaining the quality of the egg is recommended.

This present study found some significant interaction effects among strain, storage period length and storage temperatures with respect to albumen weight, albumen height and haugh unit with fresh eggs from Lohmann brown and stored under refrigeration being the heaviest (Table 4). This agrees with similar results by Singh et al (2009), Hagan et al (2013) and Khatun et al (2016) that the strain of layers used, how long the eggs are stored and the temperature within which the eggs are stored could affect the weight of the egg. It can also be observed that there is an interaction effects as far as haugh unit is concerned. This shows that the strain of layers, the length of storage of eggs and the storage temperature are very crucial in maintaining the quality of the egg. The results from the present study give an indication of the relevance of the strain of layers used and length of storage of eggs as far as egg external and internal qualities are concerned. The significant interaction effect means irrespective of the strain from which the eggs are obtained, if the eggs are stored over a long period (beyond five days) and stored under room or warm temperatures, the value would be compromised.

Conclusion

The results of this study show that eggs from different strains can differ in quality thereby influencing the ultimate use of the eggs. Owing to the importance of yolk and albumen to the egg breaking industry, users of eggs would pay premium price for eggs from Lohmann brown strains because of their superior internal quality. However, if egg weight is desired, then any of the strains could be considered. It was also observed that the major egg quality parameters like egg weight, albumen weight and haugh unit decreased with increasing storage period, hence the need to ensure that eggs are properly preserved (refrigerated) if they are going to be stored for longer periods. Otherwise eggs should not be stored at room or open market temperatures for more than five days. Furthermore, the significant interaction effect observed in some of the egg quality indicators is an indication of the need to consider the strain of layer, how long the eggs can be stored and also the temperature within which the eggs are stored so as not to compromise the quality.

Acknowledgement

The authors would like to express their profound gratitude to the Department of Animal Science of the University of Cape Coast, Ghana, for the technical and financial support for the execution of this work.

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Received 8 July 2019; Accepted 7 August 2019; Published 1 September 2019

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