Egg yolk is composed of 70% lipids and 30% proteins. It contains carotenoids such as zeaxanthin and lutein, vitamins.
Egg yolk has a high content of cholesterol and saturated fatty acids, which can promote cardiovascular disease. One egg yolk contains between 200 mg and 300 mg of cholesterol/100 g (1).
Egg yolk can increase the risk of microbial contamination and reduce the shelf life of products (2) ; for this reason, there is more interest in introducing new emulsifiers as alternatives to egg yolk. Some suitable options are hydrocolloids and polysaccharides (3).
Hen egg yolk has been studied and the effects of its antibodies on the immune responses of the intestinal mucosa of laboratory animals with Salmonella typhimurium have been determined. The results suggest a positive immune response (4).
Oral administration of hen's egg yolk influenced behaviour and cognitive functions in young and aged rats. It primarily led to mitigating the behavioural symptoms of aging and supported cognitive and memory learning in rats of both age groups (5).
Egg yolk studies
References______________________________________________________________________
(1) Bautista Villarreal M, Gallardo Rivera CT, García Márquez E, Rodríguez Rodríguez J, Núñez González MA, Chávez Montes A, Báez González JG. Comparative Reduction of Egg Yolk Cholesterol Using Anionic Chelating Agents. Molecules. 2018 Dec 5;23(12). pii: E3204. doi: 10.3390/molecules23123204.
(2) Abedinzadeh S, Torbati M, Azadmard-Damirchi S. Some Qualitative and Rheological Properties of Virgin Olive Oil- Apple Vinegar Salad Dressing Stabilized With Xanthan Gum - Adv Pharm Bull. 2016 Dec;6(4):597-606. doi: 10.15171/apb.2016.074.
(3) Dickinson E. Hydrocolloids at interfaces and the influence on the properties of dispersed systems. Food Hydrocoll. 2003;17(1):25–39. doi: 10.1016/S0268-005X(01)00120-5
(4) Li X, Yao Y, Wang X, Zhen Y, Chicken egg yolk antibodies (IgY) modulate the intestinal mucosal immune response in a mouse model of Salmonella typhimurium infection. Thacker PA, Wang L, Shi M, Zhao J, Zong Y, Wang N, Xu Y. - Int Immunopharmacol. 2016 Jul
(5) Lemieszewska M, Jakubik-Witkowska M, Stańczykiewicz B, Zambrowicz A, Zabłocka A, Polanowski A, Trziszka T, Rymaszewska Pro-Cognitive Properties of the Immunomodulatory Polypeptide Complex, Yolkin, from Chicken Egg Yolk and Colostrum-Derived Substances: Analyses Based on Animal Model of Age-Related Cognitive Deficits. J. Arch Immunol Ther Exp (Warsz). 2016 Oct
Egg Yolk 
