Egg

Eggs are an excellent source of high quality protein, vitamins and minerals. The dietary protein is
utilized  to maintain and build muscles, nerves, blood and bones by the human body. Egg proteins are one of the best source of proteins that is utilized by human body for growth. The FAO, rated the whole
egg protein’s biological value at 93,7.

Egg is widely used in food formulation due to its many functional and technological properties such as emulsification, foaming, thickening and increasing nutritional value, as well as being consumed directly. The use of eggs in food formulations in shelled egg form causes food safety problems. For this reason, processed egg products such as pasteurized liquid egg, frozen liquid egg and egg powder are widely used in the industry. The short shelf life of pasteurized liquid egg (45-60 days) and the storage and transportation costs of frozen egg increase the importance of egg powder, which can be transported more easily, does not require special storage conditions, and has a longer shelf life (Koc et al. 2011).

Since whole eggs and egg yolks are heat sensitive, color loss or significant functional and technological properties changes during egg drying depending on drying temperature, time and final product moisture content. In egg white, on the other hand, there is a significant decrease in foaming ability due to the effect of heat treatment on proteins (Lechevalier et al., 2007). Anandharamakrishnan et al. (2007) reported that protein denaturation is directly related to drying conditions.

In a previous study, no significant sensorial differences were observed in different products (cakes, omelettes, donuts, macarons and mayonnaise) produced using spray-dried egg powder and fresh eggs (Chauhan and Sharma, 2003).

Refractance window dried egg yolk

In recent years, the demand for ready-to-eat foods has been increasing. These foods are generally marketed in powder form because they have a long shelf life, low storage and transportation costs, can be stored at room temperature and are hygienic. One of such products is powdered egg products. In egg powder production hot air drying, freeze drying and drum drying are used, while the most common technique is spray drying (Lechevalier et al. 2013).

In the spray drying method, the product to be dried is atomized and sprayed into the hot air, and drying takes place thanks to the evaporation of the water in the droplets. In order to prevent the damages caused by the high temperatures (>150 ℃) applied during spray drying, the powders should be cooled to 30ºC, which is below the glass transition temperature, quickly after drying (Lechevalier et al. 2013).

The biggest problem encountered in food powder production by spray drying technique is the sctickiness problem that occurs on the drying surfaces. As a result, product yield decreases significantly (20-50%). As a matter of fact, as the sugar content of the product increases, there is a great decrease in yield. This decrease in yield, which occurs during drying, increases the cost of the final product, but also reduces its quality. For this reason, there is a need for rapid, effective and industrial scale drying systems with higher efficiencies.

In a review published by Nindo and Tang (2007), it was reported for the first time that refractance window drying could be used for egg drying.

Therefore, our team was conducted a project, nationally funded by TUBITAK (The Scientific and Technological Research Council of Turkey), to determine the optimum conditions of egg powder production by refractance window drying. In this project liguid egg white, egg yolk and whole egg separately dried in natural and foamed form at 6 different temperatures (50-100ºC). According to the results, especially in terms of color and solubility properties drying in foamed form provided superior properties, while drying in natural form was better in flow properties and hygroscopicity. The increase in drying temperature caused a shorter drying time, but a greater change in color. No oxidation marker formation and microbial growth were observed during the drying of the products. The optimum drying conditions were determined as 80ºC in foamed form for egg white, 90ºC in foamed form for whole egg and 80ºC in foamed form for egg yolk.

In another study, Preethi et al (2020) dried egg powder using refractance window drying at 40-50ºC and compared the product with spray dried and freeze dried counterparts. According to the results of the study, refractance window dried egg white powder had superior flow characteristics and solubility. Additionally, refractance window drying provided better gel formation, color value, the hardness of gel, and emulsion properties. Moreover, better foaming properties were obtained by refractance window drying and freeze drying compared to spray drying. Due to shorter drying time and simplicity of dryer design, authors suggested to use of refractance window drying for egg white powder production.

Refractance window dried whole egg and egg white

Refractance window drying has some advantages over other drying techniques as stated above. Some of these advantages.

In addition of the advantages of refractance window drying of egg, InfraRWD offered some developments and new advantages.