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Abstract
Egg is an important part of human diet. It is one of the most nutritious foods we consume, and it can be prepared in many different ways by itself or as a food ingredient.
All of the amino acids which are essential for humans are found in eggs in such ideal proportions that egg protein is used as the standard against which all other protein foods are rated.
The Eggs become infected through a process of either transovarian transmission or with moist feces contaminated with Salmonella.
Following traversing of the egg shell and associated membrane by Salmonella, the egg is permanently contaminated.
The present study was conducted to evaluate microbiologically and chemically of three types (Balady, White and Brown eggs) commercially sold in certain supermarkets at Great Cairo.
The proximate chemical compositions of the three types of eggs under investigation were determined.
It could be concluded that Balady eggs had higher contents of protein, lipid and ash of yolk in comparison with the other two types of studied eggs.
Eggs contained 17 amino acids in different concentrations.
Eight of these amino acids are considered essential amino acids from the view point of nutrition. The results indicated that the total essential amino acids of egg yolk were: Balady (283.2)> Brown (268)> White eggs (247 mg/g sample).
The results of the microbial quality of the three types of investigated eggs indicated that Balady eggs were highly contaminated by different microorganism.
Moreover, 60.0% of the tested Balady eggs were found to contain Salmonella spp.
Therefore, this type of commercially sold eggs was selected for irradiation in order to control various microorganisms contaminating it and make it bacteriologically safe.
In this experiment, fresh shell Balady egg samples were exposed to 0, 2, 3 and 4 kGy.
Irradiated and unirradiated (control) samples were stored at 4±1°C for 35 days.
Microbiological, chemical, physicochemical, and sensorial properties were evaluated immediately after irradiation and during subsequent storage to estimate their shelf-life and to ensure their safety. Salmonella was detected in the surface or inside the eggs.
Irradiation doses of 3.0 or 4.0 kGy was sufficient in completely elimination of Salmonella spp. from fresh shell egg.
The results showed that Salmonella was detected in unirradiated shell eggs at any time of refrigerated storage.
Meanwhile, shell eggs exposed to 3 or 4 kGy were free from Salmonella throughout their cold storage.
The pH value of liquid egg white of unirradiated shell eggs was 8.2. While, the liquid egg yolk were 6.7.
The irradiation of shell eggs caused an increase in the pH value of both egg white and yolk and the increase was proportional with irradiation dose. Total carotenoids as affected by irradiation doses and period of storage at 4±1°C were also followed. At zero time of storage the carotenoids content of unirradiated egg yolk was 4.2 mg/100g yolk. I
rradiation of shell eggs reduced total carotene content of egg yolk samples.
The cholesterol value of unirradiated (control) samples was 13.6 mg/g yolk.
Irradiation reduced total cholesterol of egg yolk s amples and the reduction was proportional with irradiation dose.
Irradiation of shell eggs at 2, 3 and 4 kGy decreased the amount of total unsaturated fatty acids by 2.8, 3.9 and 5.1%, respectively.
The viscosity of unirradiated (control)of egg yolk samples at 25 rpm was 380 cP. Whilst, the viscosity of irradiated samples with doses of 2, 3 and 4 kGy decreased to 292, 250 and 238 cP, respectively.