Effect of storage period and method on internal egg quality traits of the Nigerian native chicken

V U Oleforuh-Okoleh and J Eze

Department of Animal Science, Rivers State University of Science and Technology,
PMB 5080, Port Harcourt, Nigeria
vivoleh@gmail.com
Department of Animal Science, Ebonyi State University, Abakaliki, Nigeria

Abstract

This study aimed at evaluating the effect of storage period and method on some internal quality traits of Nigerian native chicken eggs. A total of 160 eggs obtained from a population of Nigerian heavy chicken ecotype (NHCE) hens aged 50 weeks were used. Sixteen eggs were randomly allotted to one control group (0day/fresh), three storage periods (7, 14 and 21 days) and three storage methods (untreated, oiled, and white polythene). The control group comprised of eggs sampled fresh on the day of collection. The traits evaluated were: egg weight, albumen and yolk weight, albumen and yolk height, albumen and yolk index, albumen and yolk pH and haugh unit. All data obtained were subjected to ANOVA using multivariate procedure of the General Linear Model.

As storage time increased, egg weight, albumen and yolk weight, albumen and yolk index and haugh unit significantly (p<0.01) decreased. Albumen and yolk pH were 0.44 to 0.80% and 0.83 to 1.64% higher in eggs stored for 7 and 21days respectively, than in fresh eggs. It was observed that eggs coated with vegetable oil possessed better egg quality (as indicated by the haugh unit, and the albumen and yolk pH) than those in the untreated and white polythene group (p<0.05). To maintain optimum internal egg quality when stored at room temperature it is recommended that eggs from the native chicken should not be stored for more than 14 days and preferably should be treated by oiling.

Keywords: albumen, haugh unit, yolk, storage method, storage time

Introduction

Poultry egg is one of the cheapest, most affordable and acceptable animal product. Eggs possess two characteristics that make them valuable as foodstuff, namely, they are highly nutritious; and serve important roles in many food products because of their functional properties (Silversides and Scott 2001). Thus, they are excellent means by which the animal protein of the populace can be met. Kul and Seker (2004) noted that the quality of an egg is determined by various standards that are imposed on the exterior (quality of the egg shell) and interior (quality of the albumen and yolk) components of the egg. Though eggs are known to possess excellent keeping quality, like all food, they have limited shelf life. Deterioration of eggs starts soon after lay. Thus, egg handling and storage practices have a significant impact on the quality of eggs reaching consumers. Albumen and yolk quality are not only important indicators of egg freshness but are also important for the egg breaking industry because albumen and yolk have different market values (Samli et al 2005). Kiosseoglou and Paraskevopoulou (2006) noted that both albumen and yolk proteins of whole egg contribute to the formation and stabilization of the aerated structure in bakery products.

In most part of Nigeria, eggs are usually stored at ambient temperature until they are sold or consumed. To maintain the consumers’ acceptability, it is critical that proper storage is done. Various factors such as egg storage period and conditions, strain and age of hens are the major important factors influencing egg quality. Several studies have been done on effect of storage period and/or methods on egg quality characteristics of different breeds/strains of poultry birds (Monira et al 2003; Lengkey et al 2012, Tilki and Saatci 2004). There is, however, dearth of information in respect to preservation/storage of eggs from the Nigerian native chicken. The objective of this study was, therefore, to investigate how different storage periods and methods influence the internal quality traits of the Nigerian native chicken eggs.

Materials and methods

This study was done in the Department of Animal Science, Faculty of Agriculture and Natural Resources, Ebonyi State University, Abakaliki. Abakaliki lies between latitude 06^o 4’N and longitude 08^o 65’E in the derived savanna ecological zone of Nigeria with a humid dry climate. The annual mean rainfall ranges between 1500-2250mm with daily temperature of 29-36^oC and relative humidity of 85% (Nwakpu 2005). This study was carried out during the wet season (in the month of June) with an ambient temperature of 32^oC.

A total of 160 eggs obtained from a population of Nigerian heavy chicken ecotype (NHCE) hens, aged 50 weeks old, established and maintained in the Department of Animal Science Farm, University of Nigeria, Nsukka, were used for this study. All eggs for the study were collected on the same day and carefully transported to the experimental site. Freshly laid eggs were weighed within 5hrs of collection. Sixteen eggs each were randomly allotted to one control group, three storage periods (7, 14 and 21 days) and three storage methods. The control group comprised of eggs sampled fresh on the day of collection. All the eggs were stored at room temperature (30.5^oC) in a well ventilated laboratory. The storage methods were as follows:

1. Untreated: fresh eggs were put in cardboard egg crates and kept on the laboratory table.

2. Oiled: eggs were treated individually by spraying vegetable oil (refined palm oil) lightly round the eggs. The eggs were allowed to dry at room temperature before they were put in cardboard egg crates and left on the laboratory table.

3. White polythene: untreated eggs were put in cardboard egg crates and wrapped in white polythene bags of 0.2mm thickness and then left on the laboratory table.

On each sampling day, eggs were weighed and broken on a white tile with flat surface. The length, height and width of the albumen and yolk were measured using an electronic vernier caliper. The yolk was carefully separated from the albumen and both components weighed individually. All weights were obtained using a sensitive scale balance (Mettler P 1210). The albumen and yolk pH were obtained using a pH meter (Hanna Inst., Woonsocker, RI 02895).

The following variables were estimated from traits measured

• Haugh unit (HU) = 100 log (H - 1.7 W^0.37 + 7.57)

 Where, HU = Haugh unit, H = observed height of the albumen (mm) and W = weight of egg (g) (Haugh 1937).

All data were subjected to ANOVA using multivariate procedure of the General Linear Model (SPSS 2010) using storage time and storage method as the fixed factors. Post-Hoc multiple comparison for observed means were done using Bonferroni of the software.

Results and discussion

The internal egg quality traits are important properties for quality determination of table eggs. Result of the effect of storage period on the internal egg quality traits of the NHCE eggs as shown in Table 1 revealed that there was a negative (p<0.01) effect of storage period on all parameters studied. Mean egg weight loss significantly (p<0.01) increased from 1.91g at 7 day to 3.60g by 21day of storage. There have been reports on decreased egg weight as storage time increased (Walsh et al 1995; Demirel and Kırıkçı, 2009). Khan et al (2013) and Gomez-de-Travecedo et al (2014) noted, however, that the rate of loss tends to vary depending on the storage temperature.

Similarly, the albumen and yolk weight, albumen and yolk index and Haugh unit (HU) significantly (p<0.05) decreased with increased storage time. The present findings collaborates the reports of Tabidi (2011) and Raji et al (2009). The haugh unit is an important trait in egg grading and highly influenced by the albumen quality, particularly the albumen height. The content and nature of ovomucin appear to be primarily responsible for determining albumen height (Silversides and Budgell, 2004). Stevens (1996) attributed the reduction in albumen height to proteolysis of the ovomucin, cleavage of disulfide bonds, interactions with lysozyme, and changes in the interaction between α and β ovomucin. In the present study, using the USDA (1977) standards for egg quality cited in Aduku and Olukosi (2000), the egg quality of the NHCE was of AA quality between the 0 -7days of storage and B quality by the 21 days of storage.

The mean pH of the albumen of the NHCE (8.36) as obtained from the control group falls within the normal albumen pH of chicken eggs as reported by Waimaleongra-Ek et al (2009). The albumen and yolk pH increased significantly (p<0.01) with storage time. Lengkey et al (2012) obtained a similar result from a study carried out on duck eggs. Akyurek and Okur (2009) also observed significant increases in pH of albumen and yolk (from 7.945 - 9.217 and 6.052 - 6.198 respectively) with increased storage time. They noted that the vitelline membrane tend to deteriorate with storage time, thus allowing nutrients in the yolk to become available to any micro organism present in the albumen, thereby enhancing degradation process in the egg. Lapao et al (1999) reported that the rise in albumen pH with storage time is associated with a decrease in albumen height and viscosity. The present findings, generally, affirm the reports of Tilki and Inal (2004) and Singh et al (2011) that egg quality are at maximum when eggs are laid and their values decrease with increasing storage time.

There were variations (p<0.05) in all the internal egg quality traits evaluated with respect to storage method (Table 2). Fresh eggs, as expected, had better quality in terms of HU, albumen and yolk weight, index, and pH. The result indicates that egg weight loss was higher (p<0.01) in untreated eggs than in those treated with oil or those stored in white polythene bag.

Findings of Nadia et al (2012) showed that gelatin coating treatments for eggs can reduce the change in weight of the egg and the albumen, thereby ensuring the retention of the good quality traits of the egg. Results of the present study collaborates the report of Copur et al (2008) which demonstrated that coating of eggs with propolis extract improved interior egg quality during storage. Dudusola (2009) and Heath (1977) observed decreases in albumen pH in oiled eggs. Formm (1969) and Obanu and Mpieri (1984) indicated a progressive weakening of the vitelline membranes and liquefaction of the yolk caused mainly by diffusion of water from the yolk and noted that such chemical degradation in the egg can be inhibited by oiling the shell.

Conclusion

This study was undertaken with the aim of investigating the effect of different storage periods and methods on internal egg quality traits of Nigerian native chicken eggs. The findings reveal that there were observable trends that rapid deterioration of eggs occurred as storage time increased and that the quality was affected by the method of storage. It was observed that eggs from the Nigerian heavy ecotype chicken can be stored at room temperature for up to 14 days as A quality, however treating by oiling the shell would reduce evaporation of water and CO₂ from the pores thereby aid in maintaining the acid-base balance and retaining high quality.

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Received 15 April 2016; Accepted 19 April 2016; Published 2 June 2016

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