ANSWER
Salted eggs, usually made from duck eggs are very well welcomed amongst Asian countries due to their unique flavor, deep taste and rich nutrient content. Duck egg yolk comprises of approximately 30 to 33% lipids – and the oxidation of lipid of salted egg yolk causes rancidity (Xu et al., 2017).
Lipid is one of the important structural and functional compositions for salted egg. Heating can increase the oil exudation and the hardiness of the yolk, decreasing the springiness and pH value of the egg yolk (Xu et al., 2017). The increase of pickling temperature would accelerate lipid oxidation (Long et al., 2015).
The oxidation of lipid in salted egg yolk can be monitored by TBARS (Thiobarbituric acid reactive substances) and CDA (Conjugated Dienoic Acid) value. TBARS value determines lipid oxidation products, including malonaldehyde, which may be formed from polyunsaturated fatty acids. CDA value has been used as an indicator for the formation of hydroperoxides from polyunsaturated fatty acids (PUFA) (Kaewmanee et al., 2009). Oil exudation of salted egg yolk will rise with increased salting time (Xu et al., 2017).
By increasing the concentration of salt in the solution, the TBARS value of yolk would increase along with accelerated lipid oxidation (Xu et al., 2017; Long et al., 2015). Exterior of the yolk would show a higher oil exudation than the interior. This gradual denaturation of yolk proteins affected by salt might result in a greater loss in their emulsifying properties upon salting. As a result, a higher amount of free fat are released (Long et al., 2015; Kaewmanee et al., 2009).
The formation of lipid oxidation that cause rancidity in salted egg yolk is dependent on the processing conditions including cooking, salting time, concentration of salt solution, exposure to heat and oxygen and storage period (Kaewmanee et al., 2009).
References
Xu, L., Zhao, Y., Xu, M., Yao, Y., Nie, X., Du, H., Tu, Y. (2017). Effects of salting treatment on the physicochemical properties, textural properties, and microstructures of duck eggs. PLoS ONE, 12(8): e0182912. https://doi.org/10.1371/journal.pone.0182912
Long, M., Song, Y., Du, Q., Zhou, D., Cai, H. & Zhan G. (2015). Effect of pickling temperature and concentration of salt solution on lipid of duck egg yolk. Transactions of the Chinese Society of Agricultural Engineering, 31(18), 281-288.
Kaewmanee, T., Benjakul,, S. and Visessanguan. (2009). Effects of salting treatment on the chemical composition, textural properties, and microstructure of duck eggs. Journal of the Science of Food and Agriculture, 89(4), 625-633. https://doi.org/10.1002/jsfa.3492
