What is the use of eggshells, which our grandparents held in even greater esteem?

What is the eggshell made of?

The eggshell is mainly made up of mineral and, to a lesser extent, organic materials. Calcium carbonate (CaCO₃) makes up about 10% of the shell’s weight. 95-97%, mainly in the form of calcite crystals, is what gives the eggshell its hardness. The calcium carbonate found in the shell of a hen’s egg can be used in human nutrition, as it is a natural source of calcium with good biological utilization. After proper cleaning and fine grinding, it can be used as a raw material for nutritional supplements, contributing to the health of bones and teeth, as well as the prevention of osteoporosis. Its advantage is that it also contains trace elements (such as magnesium and phosphorus), which support the absorption of calcium. It is a sustainable solution, as it is made from a food industry by-product.

Eggshell contains traces of other mineral salts, including magnesium carbonate (MgCO₃), calcium phosphate (Ca₃(PO₄)₂), sodium, potassium and strontium ions in small amounts.

– It is little known that eggshell also contains several organic compounds that give the eggshell its elasticity. For example, proteins (e.g. ovocleidin, ovocalixin) that make up 1-3% and glycoproteins that regulate crystallization and shell structure. Due to its porous structure, the eggshell also contains an additional 1-2% water. The color of the eggshell is given by various pigments, so-called color clays, which can be the following: protoporphyrin IX in the case of brown-shelled eggs, and biliverdin, which results in a bluish-green hue – said Dr. Csaba Németh, food engineer, c. university professor, who mainly deals with the development of innovative egg-based foods.

What about the shell? A source of collagen and keratin?

Inside the eggshell are the so-called shell membranes (inner and outer membranes), which are layers rich in proteins, but are not part of the eggshell itself, but rather located underneath it. These contain additional usable compounds. The outer and inner shell membranes of the eggshell are biologically extremely valuable, predominantly organic layers, whose primary task is to protect the interior of the egg. Their composition consists mainly of proteins and bioactive molecules, which provide structural stability, elasticity and antimicrobial protection.

– One of the most important components of eggshell membranes is collagen, which forms a flexible yet high-tensile-strength framework. Due to this, eggshell membranes are an excellent raw material in joint and cartilage-protecting dietary supplements, skin care products, and are also used as biological carriers in tissue engineering. They can also be used as animal feed supplements to support joint health. They are also significant sources of keratin, a sulfur-rich, fibrous protein. This substance gives the membranes mechanical resistance and is therefore an important raw material in hair and nail care cosmetics. In addition, it can be used in the development of biodegradable polymer materials, as well as as a soil conditioner and a slow nitrogen source – said Dr. Csaba Németh.

The shells contain glucosamine, which is a basic building block of connective tissues. This compound plays a key role in maintaining cartilage health, which is why it is widely used in joint protection products and is also being studied for its anti-inflammatory effect. Its advantage is that it is an alternative to shellfish-derived glucosamine, so it may also be suitable for allergy sufferers.

They also contain chondroitin sulfate, which is responsible for the water-binding ability of cartilage. Thanks to this, it plays an important role in maintaining the load-bearing capacity of joints, and is often used in combination with glucosamine in cartilage protection products and in regenerative medicine.

A small amount of hyaluronic acid is also present in the shells. This polysaccharide has lubricating and shock-absorbing properties, which is why it is used in medical practice in joint injections, in the cosmetic industry as a moisturizing and wrinkle-filling agent, and in ophthalmology.