Separation Methods of the Eggshell Membranes from Eggshell ^†

As a result of the technological processes of the egg industry, there are tons of egg shells, which raise environmental problems and costs for their management. For a superior valorization to obtain active principles with high biological and economic value, it is necessary to separate eggshell membranes from eggshells. Therefore, eco-friendly and efficient processes have been developed. The complete separation of membranes and shells increases the value of the resulting products. Several methods are known for obtaining the shell membrane [1].

Manual detachment of membranes is the simplest procedure. The detached membranes dried in the oven at 30 °C for 30 min, then ground and kept in the freezer.

Separation with dilute acids (acetic acid, hydrochloric acid, EDTA, sulfuric acid) dissolves the calcium carbonate of the shell and the membranes are recovered, washed with deionized water to remove the remaining acids and dry at room temperature or in the oven. Separation using acids is an efficient technique, but FTIR analyzes revealed the modification of the absorption bands corresponding to the organic structure of the membranes in the presence of HCl and EDTA-Na2 solutions. The acetic acid solution does not alter the chemical composition of the organic structure of the membranes [2].

Separation by flotation with dissolved air is a recently developed method, which has a high efficiency rate. The pressurized water is saturated with dissolved air and is pumped into a flotation basin. The air bubbles formed are microscopic and have the role of dragging the suspended matter towards the floating surface. The process takes two hours and allows the recovery of 96% of the membranes and 99% of the calcium carbonate present [3].

Separation of the membranes from the eggshells by microwave treatment is based on the fact that the membranes have a higher water content than the shells and absorb more energy from the electromagnetic waves, which leads to a differentiated heating of the two components followed by the expansion of the membranes, weakening of physical connections between shells and membranes and separation [4].

Another technique of separation is the passage of fragments of eggshells through a series of drills in aqueous environment heated by steam, the separation taking place in a cyclone. This process is used commercially [5].