Internal quality of vacuum-packaged white shell eggs stored at ambient temperature

Introduction

The egg is known as one of most complete foods, since it is a rich source of nutrients with an excellent fat, carbohydrate, mineral, vitamin and, mostly, protein balance. The egg is the second best protein source that exists for human nutrition, only after mother's milk. Nevertheless, the egg is an excellent culture medium for pathogenic organisms, and because of being an animal-origin product, together with meat and meat derivatives, the egg is highly perishable, so that it can lose its quality readily. (Theron et al., 2003).

The selection of criteria to identify changes in egg quality implies considering the needs of such criteria for egg producers, processors, and consumers. For producers, quality is related with egg weight and eggshell integrity (defects, dirt, cracks, blood spots). For the consumer, these attributes are related with egg shelf life, appearance (yolk color, shell color), and sensorial traits. For processors, the easiness to remove the eggshell, separation between yolk and whites, and functional characteristics in addition to egg yolk color, particularly for pasta manufacturers and bakeries (Rossi and Pompei, 1995).

The quality of the eggs reaching consumer''''s table depends mainly on egg storage conditions. Once laid, a series of unavoidable changes start to occur in the egg that reduce its quality and, in the long range, result in egg spoilage. It is possible to delay but not completely prevent these changes.

Egg quality is used to describe the differences related with genetics, nutrition, environment, etc., and to show the eventual egg deterioration in the face of storage conditions. The internal egg quality traits include measures of the yolk and the albumin, since the eggs with abundant thick albumin and a yolk located in the center are considered fresh, and cause a good impression to the consumer. The external attributes include eggshell shape, cleanliness, and integrity (Garner and Campos, 1981).

This way, using vacuum packaging with oxygen binders for eggs that are not going to be refrigerated during storage, is an efficacious method to preserve egg quality traits (Scatolini-Silva et al., 2010).

For the above-mentioned reasons, the purpose of this study was to evaluate the physical characteristics (albumin quality [Haugh units, HU] and egg yolk quality [yolk index and yolk color]) of white shell eggs stored in different packaging systems, at ambient temperature.

Materials and Methods

The study was undertaken using 1,224 freshly collected, commercial, white shell eggs, laid by layers of the same age, strain and farming system. Once collected, the eggs were immediately taken to the Animal-Origin Food Technology Laboratory, Department of Technology, FCAV, UNESP, Jaboticabal, Brazil.

The eggs were packaged using various systems/materials i.e., 1) case wrapped in a vacuum-sealed plastic bag; 2) case wrapped in a vacuum-sealed plastic bag with an oxygen binder; 3) case wrapped in a vacuum-sealed plastic bag with an oxygen binder and a carbon dioxide binder; 4) case wrapped in a vacuum-sealed plastic bag with an oxygen binder and a carbon dioxide generator. These packages were subjected to the following storage periods: 0, 7, 14, and 21 days, at ambient temperature (25 ± 2°C).

At the end of each storage period, the eggs were broken open on a glass table for the physical analysis. Albumin quality was evaluated by determining HU, as described by Card and Nesheim (1968). In other words, eggs were first weighed individually using a precision balance, then broken and emptied. Albumin height was determined using a special height-measuring device (Egg Quality Micrometer). With egg weight (g) and albumin height (mm) data, HU were calculated using the following equation: UH= 100 log (H + 7.57 - 1.7W^0,37), where: HU = Haugh Units; H = albumin height (in millimeters); W = egg weight (in grams). And egg yolk quality was evaluated using the yolk index, obtained by measuring yolk height using the above mentioned height-measuring device and the yolk diameter using a calibrator. The ratio between these two parameters results in the yolk index (Translators notice: in Portuguese índice gema [IG]): IG = AG/DG, where: AG = yolk height (in mm); DG = egg yolk diameter (in mm). Egg yolk color was also determined using a standard color fan.

A completely-at-random design was used with a 4 x 3 + 1 factorial arrangement (4 packaging types, 3 storage periods + 1 control - fresh eggs), with 3 repetitions of 4 eggs each. Results were subjected to analysis of variance with the SAS software (1999), and the differences among means were compared using Tukey''''s test at a 5% significance level.

Results and Discussion

HU, yolk index (IG) and yolk color as determined with the color fan results for the eggs stored in the various packaging systems are shown in Table 1, which also shows a period x packaging system interaction on HU and yolk color, which details are shown in Table 2.

Table 1. Haugh Units (UH), yolk index (IG) and yolk color (color fan) for the eggs stored in the different packaging systems

	UH	IG	Color (fan)
*Control* vs. Factorial
Control	78.57	0.44	7.40
Factorial	55.46	0.35	7.60
F test	51.71**	83.90**	1.90 NS
*Storage time in days (P A)*
7	60.94	0.37	7.67
14	57.24	0.35	7.67
21	48.19	0.32	7.45
F test	18.13**	28.77**	3.29*
*Packaging (E)*
1 - Only vacuum	56.96	0.35	7.46
2 - O₂binder	49.58	0.32	7.43
3 - O₂ & CO₂ binders	42.79	0.31	7.66
4 - O₂ binders & CO₂ generators	72.51	0.43	7.83
F test	51.37**	102.01**	5.09*
F Int. P AxE	6.61**	1.96 NS	2.21*
CV (%)	17.03	8.14	5.97

^{In the same column, means followed by the same capital letters are not statistically different as per Tukey''''s test (5%). In the same line, means followed by the same small case letters are not statistically different as per Tukey''''s test (5%); *(P<0.05); ** (P<0.01); CV = Coefficient of variation; NS = Not significant. O2 - oxygen gas, and CO2 - carbon dioxide.}

Regarding yolk index, the controls were within the values compatible with fresh eggs, since in accordance with Card and Nesheim (1968) mean yolk index values of fresh eggs are around 0.42 and 0.40, and when this value reached 0.25 the yolk is so fragile that it is impossible to measure it without causing rupture. The maximum storage time of 21 days and all treatments yielded values exceeding this rupture level (0.25). Among the packaging systems, those with oxygen binders and carbon dioxide generators resulted in yolk index values within those expected for fresh eggs, meaning that their yolk quality was preserved.

Table 2. Results of the storage time x packaging system interaction on Haugh Units (HU) and yolk color (color fan)

Packaging	Storage Period - HU
7	14	21
1 - Only vacuum	55.88^Ba	61.43^ABa	53.57^Ba
2 - O₂ binders	56.21^Ba	51.53^Ba	40.99^Ba
3 - O₂ & CO₂ binders	55.28^Ba	48.59^Ba	24.48^Cb
4 - O₂ binders & CO₂ generators	76.39^Aa	67.42^Aa	73.71^Aa
Packaging	Storage Period - Color
7	14	21
1 - Only vacuum	7.40^Aa	7.70^ABa	7.30^Aa
2 - O₂ binders	7.50^Aa	7.30^Ba	7.50^Aa
3 - O₂ & CO₂ binders	8.00^Aa	7.70A^Bab	7.30^Ab
4 - O₂ binders & CO₂ generators	7.80^Aa	8.00^Aa	7.70^Aa

As shown in Table 2, HU showed reduced values, which was expected due to egg storage. At 21 days of storage, both packaging with only vacuum, and packaging No. 4 (oxygen binder/CO2 generator) had very similar values to those obtained with 7-day storage. Also, packaging No. 4 had the best HU values, differing from all others.
Regarding the color determined using the color fan, a higher variation was observed with increasing storage periods, with the lowest values at 21 days.

Conclusion

The use of oxygen binders and carbon dioxide generators in the vacuum-sealed egg packaging systems yielded the best values in terms of Haugh Units, egg yolk index, and egg yolk color, thus preserving the internal quality of the eggs stored at ambient temperature.

Bibliography

Card LE & Nesheim MC. 1968. Produción Avícola. Editorial Acribia- Zaragoza- Espanha.

Garner FA & Campos EJ. 1981. Shell egg quality in Brazilian retail market. Arquivo da Escola de Veterinária - UFMG 33(2):305-311.

Rossi M & Pompei C. 1995. Changes in some egg components and analytical values due to hen age. Poultry Science 74:152-160.

SAS Institute. 1999. SAS user''''s guide: statistics. Release 8.02. Cary.

Scatolini-Silva AM, Borba H, Giampietro A et al. 2010. Embalagem à vácuo como alternativa para manutenção da qualidade de ovos armazenados em condições de ambiente. In: VIII Congresso De Produção E Comercialização De Ovos, 2010, São Pedro, SP. Anais. APA. p. 273-275.

Theron H, Venter P, Lues JFR. 2003. Bacterial growth on chicken eggs in various storage environments. Food Research International 36:969-975.