Egg By-Products: Composition, Bioactive Potential, and Utilization in the Circular Economy

Egg products are a convenient and safe form of eggs, possessing valuable nutritional and functional properties. The egg processing industry is responsible for the enormous amounts of biomass in the form of animal by-products (ABPs). According to EU legislation, the ABPs are under strict control from the formation to the disposal of biomass, as they carry a risk to the ecosystem and public health. For this reason, restrictions have been introduced on their use after disposal, ranging from bioactive applications in medical, cosmetic, and pharmaceutical products, as well as feed. The shells are subject to special conditions for processing and use. The by-products of egg breaking are divided into solid (eggshells and eggshell membranes) and liquid (technical albumen) by-products. The biological value is determined by the composition, which varies significantly across the by-products. In the context of the circular economy, all egg by-products contain valuable substances that can be used in food and non-food industries. First, eggshells are the leading by-product, composing 95% of the inorganic substance calcium carbonate, which, after processing, can be used in agriculture, food and feed industries, and medicine. Second, there is a liquid by-product containing proteins from the egg white and a small part of fats from the yolk. Literature data on this by-product are scarce, but there is information about its use as a feed additive, while the extracted and purified proteins can be useful in pharmacy. Egg membranes constitute only 1% of the egg mass, but humanity has long known about the benefits of collagen, keratin, and glycosaminoglycans, including hyaluronic acid, which compose this material. The processed membranes can be used as a food additive, in cosmetics, medicine, or pharmacy, just like other egg by-products mentioned above. This literature review focuses on the possible methods and techniques for processing by-products and their potential application. The literature sources in this review have been selected according to their scientific and practical applicability. The utilization of these by-products not only reduces the impact on the environment but also facilitates the creation of value-added materials.