Albumin/yolk quality of brown shell eggs stored under different packing conditions

For human nutrition, eggs are an important source of proteins, since they are considered as rich in proteins, with a low fat content, in the lipid portion higher concentrations of non saturated fatty acids. When added to other food, they perform different functions which favor them, such as color, viscosity, emulsification, jellification and foaming (Sarcinelli et al., 2007).
Within this context, the main objective in producing eggs for human consumption is that of providing the consumer the original quality of the product. Such a quality is a set of inherent characteristics of the egg, which determine its degree of acceptance, including physical features, as well as taste and odor. When eggs are produced, a small amount is of a bad commercial quality, because fresh eggs, with rare exceptions are of an excellent quality. The main problem related to eggs quality is to keep them within marketing channels. Nevertheless, there are endless ways of maintaining quality, so that it may reach the end consumer. To supply the consumer with eggs of an excellent quality, does not only increase their demand, but it also helps the producer to obtain better sales and price index. Hence, the knowledge of processing, of production, of marketing, and of the measuring methods of the quality of eggs are extremely important for the consumer (Moreng & Avens, 1990).
Certain strategies should be applied in the layers sector, due to the absence of refrigeration of the eggs at the sales points. Amongst these, packing acquires great importance to the consumers, when selecting a product from the shelves of the supermarkets, as well as the maintenance of the quality of eggs.  Considering that egg is a natural product, with no differentiation between the diverse farms, packing plays a very important role in making a difference, conditioning the consumer to given brands. Several companies have invested in the modernization of their packing, making them more attractive and practical, keeping its fundamental role of conditioning and protecting the quality of eggs, as a means to awaken the interest of the  consumers (Antunes, 2001).
Because of the above mentioned, we set forth the objective of evaluating the physical features of brown shell eggs, sanitized or not, stored in different packing conditions at room temperature.

One thousand two hundred fresh eggs were stored. Three hundred eggs were used for the analysis of internal quality. Half of the eggs were collected before the sanitation performed at the farms and the other half after such a procedure. Regarding sanitation, eggs were mechanically rinsed in chlorinated water (50 ppm) at 35 - 40 °C (Brazil, 1990).

The distribution of the eggs into 24 treatments was done at the Laboratory of Technology of Products of Animal Origen of the FCAV in Jaboticabal - SP. We used two groups (sanitized and none sanitized), distributed in PET (ethylene polytereftalate) trays, of one dozen eggs each and were subjected to three packing conditions: PVC film (plastic film of vinyl polychloride), partial vacuum and partial vacuum with sequestrant (absorbing) sachets of oxygen gas. A totally randomized design was used, with a factorial scheme  3x2x4+1 (packing conditions, sanitized or not, and storage periods + control - fresh eggs), with 4 replications of 3 eggs each. In such a way, one third of the trays, one dozen eggs each, was packed with PVC film, and the other two thirds were covered with plastic bags Protervac^® (0.1 mm, <85 O₂ cc/m²/24 h at 23 °C) with the following dimensions: 20 cm. (width) x 51 cm. (long) x 180 μ (thickness). These last ones were vacuum packed in a Selovac^® 200 B. O₂  sequestrant sachets were used, the capacity of absorbing 50 cc of O₂ gas, elaborated with a chemical powder compound with an iron oxide and zeolite base. The amount of O₂ absorbing sachets inside the packing was estimated according to the weight loss of eggs (Scatolini-Silva et al., 2010), the dimensions of the packing and the absorption capacity (according to the specifications of the manufacturer).

Eggs were stored during four periods (7, 14, 21 and 28 days), at room temperature and the initial analysis of the sanitized fresh eggs (control) was done on the day the eggs were removed from the cooperative (day 0). During the other days, corresponding to the analysis, eggs were weighted individually and after being broken, the quality of the albumin and of the yolk was analyzed, using the Haugh unit (by the equation: HU=100log(H+7,57-1.7W^0,37) and yolk index (GI=yolk height/yolk width), respectively. The results were subjected to analysis of variance and means compared by Tukey test at 5% significance level (SAS, 1999).

Table 1, shows the results of the values obtained with the Haugh unit (HU), yolk index (IG) for stored brown shell eggs. Table 2, shows the unfolding of the interaction between the storage period and the packing for the Haugh unit and Table 3, shows  the unfolding of the interactions between the storage period and packing, between the storage period and packing and sanitation and between packing and sanitation for the yolk index.

Table 1. Means obtained for the Haugh unit (UH) and yolk index (IG) of brown shell eggs stored in different packings.

In the same column, means followed by equal letters do not differ between them by the Tukey test at (5%).  *(P<0,05); ** (P<0,01). CV= Coefficient of variation. NS = Not significant.

Based on the data of Table 1, we observe the superiority (P>0,05) of values when comparing fresh eggs (control) with those which received some type of treatment for the studied characteristics. We can see that sanitation worsened (P<0,05) the HU of eggs. This suggests that when eggs are rinsed, it is necessary to improve storage conditions. Likewise, we observed that brown shell eggs had an initial quality under what was expected for fresh eggs of the strain used, which corresponds to the eggs of layers at the end of their productive cycle.

Table 2. Unfolding of the interaction between the storage period and packings for the Haugh unit (UH) of brown shell eggs.

In the same column, means followed by equal capital letters, do not differ between them by Tukey test at (5%); in the same line, means followed by equal small letters do not differ between them by Tukey test at (5%).

Table 2, shows that eggs, vacuum packed, were the only ones to preserve HU (P>0.05) with an increase in storage days, this is to say, such packing showed a better HU than eggs at 14, 21 and 28 days. Nevertheless, according to USDA (2000), such HU values are framed according to the "B" classification, this is, lower quality (UH<60).

These results which prove the maintenance of HU, agree with those of Leonel et al. (2007). They also found superiority of the vacuum condition in the storage of eggs for this characteristic.

Table 3. Unfolding of the interactions between the storage period and packing, between storage and sanitation, and between packing and sanitation for the yolk index (IG) of brown shell eggs.

In the same column, means followed by equal capital letters, do not differ between them by Tukey test at (5%); in the same line, means followed by equal small letters do not differ between them by Tukey test at (5%).

In Table 3, we see that the YI of eggs partially vacuum packed, were better throughout storage and that when they were not sanitized they were superior to the other eggs. Regarding the storage period, sanitation altered YI until day  28.

This, once again proved that the loss of CO₂ through the shell of the egg, is one of the main causes for the decay of albumin, due to the fact that it provokes degradation of the proteins in thick albumin. Souza (1997), described that such process happens because the enzymes which act on such proteins, hydrolyze amino acid chains, releasing the water which is bound to the molecules of the proteins. Because of osmosis, the released water from the albumin crosses the viteline membrane and is retained by the yolk, which is much more concentrated. The accumulation of water in the yolk, provokes weakening of the viteline membrane, thus, it breaks, liquefying the yolk.

The internal quality of the egg diminishes according to the storage time, at room temperature, in a more stressed manner in eggs packed in a plastic film, due to the fact that the packing of eggs under vacuum conditions preserved the quality features studied in this work.  Due to the fact that there was a in the internal quality of brown shell eggs, we conclude that sanitation, in PVC film storage conditions should be improved.

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