Determination of Liquid Egg Quality and Effects of Heat Treatment on Egg Proteins
Uysal, Reyhan Selin
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Egg is one of the fundamental food that has been consumed by human beings for many years due to its high nutritional value. Besides high nutrient content, it contributes to textural and sensory properties of food thanks to its functional properties (foaming, emulsifying, and gelling). Determination of the egg quality is an important concern for food industry because of the valuable position of the liquid egg in food production. There are two major phenomena that determine the liquid egg quality: adulteration and being damaged of the functional properties of egg proteins by heat treatment. In this context, the first aim of this study is detection of liquid egg adulteration with water. The other aim is to monitor the effect of heat treatment on egg proteins, and to demonstrate the effect of liquid egg heat-treated at different parameters on the final product quality. As the first step of adulteration detection, yolk-white ratio of the liquid eggs was determined by SDS-PAGE technique. Depending on the yolk-white ratio, it has been revealed whether egg sample is adulterated or not. As the second step, compositional analysis of liquid egg was performed by ATR-FTIR spectroscopy. Protein, lipid, moisture, and total soluble solid contents of many egg samples were determined. The actual values of the components were detected by reference methods. Data analysis was performed via PLS. The actual values of the components were compared to predicted values by the models, and determination of coefficient values (R2) for protein, lipid, moisture, and total soluble solid were obtained as 0.95, 0.992, 0.994, and 0.972, respectively. At last, liquid egg adulteration with water was also analyzed by ATR-FTIR and NIR spectroscopies. The analysis was performed using both liquid and dry samples. Data analysis was performed via PCA. Adulterated dry samples were classified by ATR-FTIR while both liquid and dry samples were classified by NIR spectroscopy. The effect of heat treatment on egg proteins was monitored by capillary electrophoresis and UV-VIS spectroscopy. Electrophoresis data were analyzed by PCA. Untreated and heat-treated egg samples were separated successfully from each other. Then, heat-treated samples were classified according to their heat treatment parameters. As the last part, sponge cake, was selected as a final product, and was analyzed to demonstrate the effect of heat-treated liquid eggs on the final product quality. Rheological behavior of the cake batter prepared using heat-treated liquid egg was investigated. It was observed that cake batter exhibits a pseudo-plastic behavior. Rheological measurement values were fitted to a power-law model. An increase in consistency index (K) was observed as the extent of heat treatment was increased. Heat treatment has an effect on flow behavior index (n) whereas any effect depending heat treatment parameters was not observed. Fundamental cake quality analyses (moisture loss, color, porosity, texture analysis (hardness, cohesiveness, and gumminess), and specific volume) were performed. The baked cakes prepared with heat-treated liquid eggs were found to have less porous and lower specific volume than untreated cakes. Heat-treated liquid eggs resulted in the formation of harder, sticky, and gumminess cakes.