Hen egg yolk in food industry - A review of emerging functional modifications and applications

Background: Hen egg yolk (EY) has a variety of techno-functionalities, including emulsifying, gelling, and film-forming properties. However, the application of native EY and its fractions is still limited due to the insufficient functionalities. Thus, various modification treatments have been used to improve the functionalities. In addition, there has been increasing research interest to explore the potential of modified EY and its fractions for applications in developing value-added food products. Scope and approach: This review provides a brief introduction of EY structures, fractions, and components and focuses on discussing a wide range of existing modification methods and the mechanism of each method to change the structure and improve the desirable functionality of EY and its fractions. Three emerging applications of EY in food formulation industry, i.e. nutrient encapsulation and delivery system, unmodified EY substitutes, and edible films, are finally highlighted. Key findings and conclusion: Recent studies have shown that pre-treatment of EY and its fractions are often needed using enzymatic hydrolysis, complexing with polysaccharides, or other chemical, physical, and fermentation methods. The purpose of the pre-treatment is to dissociate the aggregated EY protein state, modify solution characteristics (such as solubility, hydrophobicity, and surface charge), so that the functionality is greatly improved, leading to more stable emulsion systems or other novel EY-based food products. By reviewing the new modification technology and application trends of EY, this review provides expert opinions of future research directions for the development of value-added EY derived food products.