Choux pastry made from fresh eggs: a comparative study between chicken and duck eggs

Chicken and duck eggs are the two most consumed types of poultry eggs. There are many egg products, one of which is choux pastry. Choux pastry is usually made from chicken eggs and is popular because of its tasty aroma and flavour. Duck eggs are used to replace chicken eggs in choux pastry dough. The protein and lipid content of duck eggs is 20% and 70% higher on average than chicken eggs, respectively. Also, the quality of duck eggs, which included the Haugh unit (HU) score, albumen index, and yolk index, was 11%, 25%, and 20% higher, on average, than chicken eggs. Organoleptic tests conducted on 600 people resulted in choux pastry made from duck eggs having better colour and texture, respectively, with the criteria for enough dark brown colour and a firm texture. However, duck eggs have a lower aroma and taste, respectively, with the attribute of less butter aroma and non - savoury taste. The preference test showed that choux pastry made from chicken eggs is better than choux pastry made from duck eggs.


Introduction
Eggs from poultry are a source of nutrients needed by humans (Harlina et al., 2018;Wang et al. 2020). Among several poultry eggs, chicken and duck eggs are the most consumed (Yu et al., 2020). Several studies have shown that the protein content of duck egg whites, lyophilized, was higher than chicken (Hu et al., 2016). Therefore, several aspects of salted eggs, such as taste, orange colour, gritty texture, and oil exudation of duck eggs, are closer to customer expectations than chicken eggs (Yuan et al., 2018;Sun et al., 2020). The quality of salted egg products decreases along with the lipid oxidation of yolk (Harlina et al., 2015). The addition of antioxidants is a solution to overcome this (Harlina et al., 2019).
The albumen quality decreases with the increasing shelf life of the eggs. This decrease is characterized by a foul odour and dilutes albumen. It is due to environmental conditions such as pH and temperature (Tang et al., 2020). The pH condition highly affects the protein composition of eggs, particularly during salting (Panpipat and Chaijan, 2020). The effect of temperature, especially in cooking eggs, can cause changes in the yolk fatty acid composition (Özcan et al., 2019). In addition, the fishy odour caused by eggs is due to increased levels of trimethylamine (TMA) content and can cause fish odour syndrome in humans (Li et al., 2019). In addition to that, the level of TMA content in duck eggs is higher than in chicken eggs (Li et al., 2017). It causes the consumption of duck eggs to be lower than chicken eggs, apart from the outbreak of Salmonella, that attacked duck eggs between 1974and 1976in Germany (Owen et al., 2016 Chicken eggs are usually used as an ingredient in choux pastry dough. The savoury taste and aroma, which is a combination of chicken eggs and salted butter, attract people to eat this dish. The key to this dough is in the yolk. Therefore, duck eggs that have a higher ratio of yolk to chicken eggs will be used. The egg yolk ratio itself is influenced by many factors, one of which is the age of the birds (Du et al., 2019). Some studies say that the higher the age of the birds, the higher the ratio of the egg yolk (Ipek and Sozcu, 2017;Zhu et al., 2019). Several studies have also attempted to prolong the laying period of ducks for this reason (Zhu et al., 2017;Feng et al., 2018). Diet is one way to improve the quality of egg yolk (Zhang, Wang, Huang et al., 2020;. In addition, the factors of avian genes are also determined (Langley et al., 2017).
This study compared choux pastries made from chicken eggs with those made from duck eggs. As previously explained, duck eggs have many advantages over chicken eggs. The nutritional content of raw duck eggs is the same as salted duck eggs (Guo et al., 2020). It has led to the nutritional content and organoleptic tests on choux pastry made from duck eggs. Tests on chicken egg-based choux pastry have been carried out before with the influence of egg freshness and age of the chicken. This time, choux pastry is only affected by the freshness of the eggs because all the choux dough had the same recipe. Duck breeders rarely raise them for up to two years and sell their ducks when they are over a year old to use their meat.

Preparation of eggs and dough
Duck and chicken eggs are obtained directly from breeders on the first day of hatching. The type of duck chosen is the type commonly kept by breeders, the domestic duck. The age of ducks at five months was chosen as the initial age of laying eggs, to be compared with chicken eggs from the initial period of laying eggs as well. The chicken chosen is the ISA brown layer hen. Both ducks and chickens have the same laying period ranging from 5 months to 2 years.
Every choux dough consists of 225 g of high protein flour, 23 g of sugar, 150 g of salted butter, 375 mL of milk, and six eggs. Before the eggs are mixed into the dough, they are measured for freshness first. Freshness measurements and dough making were carried out on the first to forty days, once every ten days, to determine the effect of egg quality on the choux pastry dough. The flowchart of the process of measuring egg freshness and making choux pastry dough is presented in Figure 1. After the baking process, each choux pastry weighs an average of 50 g.

Egg quality measurement
Egg quality is determined by the Haugh unit (HU), as presented in Equation (1), also by albumen and yolk index. These indexes are the ratio between the height and the diameter, as shown in Equation (2) and Equation (3), respectively.
Where H and W are albumen height (mm) and egg weight (g), respectively. AI is albumen index (dimensionless), AH is albumen height (mm), AD is albumen diameter (mm), and the same goes for the yolk.

Nutritional test
Carbohydrates, proteins, and lipids were tested using the Luff Schoorl, Kjehdahl, and Soxhlet methods. These three nutrients indicate colour, aroma, and taste in organoleptic tests. Also, the water content affects the texture of the choux pastry. The energy test results are obtained from the calorimeter.

Organoleptic test
Organoleptic tests and nutritional content are carried out for each choux pastry with a value range of at least five and a maximum of one. The tests carried out include colour, aroma, texture, and taste. In addition, a preference test was also carried out. Six hundred people represented enough to get an accurate result. ANOVA is used to test the relationship between two variables. Each test was carried out until it obtained a significant difference (p ≤ 0.05).

Results and discussion
Figure 2, Figure 3, and Figure 4 show the results of measuring egg quality. From the results of these measurements, it was evident that duck eggs have HU values, albumen index, and yolk index above chicken eggs. Furthermore, because the eggs were purchased on the first day of hatching, they had a high level of freshness. It was proven from the HU value above 70 for all eggs.
The nutritional content test results for each choux pastry are shown in Table 1. Since choux dough was made with the same recipe and baking process, the differences in this test were dominated by the nutritional content of the eggs. Fresh eggs were expected to have high protein and fat but low water content. In Table 1, it can be seen that the dough made from the first day's eggs had a lower protein content than the tenth day's eggs. The fat content of the first day's choux is lower than the twentieth day.
The egg is an embryo that will develop into a bird (Zhu et al., 2019). This development was reflected in the results of the protein and lipid tests in Table 1. Protein, lipids, and water are the main ingredients for forming eggs. Because of this, they influence each other in the composition of the egg. Other food ingredients, such as wheat flour and salted butter, played a role in the derivative of glucose, which dominated the rise of energy. It can also be seen in Table 1 that choux pastry made from duck eggs has a higher protein and lipid content than choux pastry made from chicken eggs.
The organoleptic test results of choux pastry were shown in Table 2. Choux pastry made from duck eggs had better colour and texture than choux pastry made from chicken eggs. The beta carotene content of duck eggs is higher than chicken eggs (Du et al., 2019), so the resulting choux pastry was darker in colour. Also, the water content of duck eggs was lower than chicken eggs and made the choux pastry texture firmer.
A different thing was shown by the aroma and taste test results in Table 2. Choux pastry from duck eggs tended to have a lower aroma and taste than choux pastry from chicken eggs. The TMA content of duck eggs, which is higher than chicken eggs (Li et al., 2017), caused excessive fishy odour in the choux pastry. Some people do not like this, which reduced the aroma of the choux pastry made from duck eggs. Duck eggs also have a higher mineral content than chicken eggs (Tang et al., 2020). It causes the taste of duck eggs to be saltier than chicken eggs. As salted butter was one of the ingredients of the choux dough, the choux pastry from duck eggs tended to be more bitter than choux pastry from chicken eggs.
The results of the preference test in Table 2 showed that choux pastry made from chicken eggs was better than choux pastry made from duck eggs. It was common because people paid more attention to smell and taste than colour and texture to choose preferences. It can also be used as a guide for choux pastry producers to pay more attention to the level of a favourite than the nutritional content contained in choux pastry. Meanwhile, the nutrition test results can be used as a reference in regulating the shelf life of eggs purchased from stores.

Conclusion
Duck eggs had better quality than chicken eggs. It was proven by the value of HU, albumen index, and yolk   index of duck eggs above chicken eggs. The nutrition test for choux pastry also showed that duck eggs had higher protein and lipid content than chicken eggs. Organoleptic tests showed that choux pastry made from duck eggs was superior in colour and texture. Meanwhile, in terms of aroma and taste, choux pastry made from chicken eggs was eminent. The higher beta carotene content and lower water benefited the choux pastry from duck eggs in colour and texture. Meanwhile, the higher TMA and mineral content in duck eggs was detrimental because it caused a sharper fishy odour and a more bitter taste. The liking test showed choux pastry from chicken eggs was better. It was because people paid more attention to smell and taste than to colour and texture.

Conflict of interest
The authors declare no conflict of interest.