Table 3.

Methods of calcium extraction from eggshell and their formulations

Sources of eggshells	Procedure	Amount of calcium extracted	References
Fast food industries, poultry farm, houses, bakeries, and hotels	Cooking 12 eggshells in 6 cups of filtered water for 10 min. Then underwent a drying process to achieve a granular and further extracted with 4% (w/v) HCl for 3 h form	0.6 g	Gaonkar and Chakraborty 2016
Different breeds of chicken and other birds found in Bangladesh: Rhode Island red, white Leghorn, domestic duck, and domesticated fowl	A commercially available blending machine was used for processing, sieving, and drying. Then 0.5g of the samples were taken and digested with H2O2 and ultra-pure HNO3. The resulting products transferred for dilution with double distilled water	Overall calcium content found in the eggshells varied from 248 to 386 mg/g	(Islam et al. 2019)
Bakery and white chicken	Researchers analyzed two methods of obtaining a refined eggshell power: mechanical processing, the other using household items such as a rolling pin and sieve to crush and segregate minute particles. Dissolution of the above-obtained products also employed home available resources like vinegar, orange juice, or lemon juice, either of which can also be used.Evaluations were carried out to determine the mineral content of the eggshells. Atomic absorption spectroscopy was used to evaluate the percentage of calcium present	Chicken eggshell powder provided nearly the same results as that of the calcium supplement when calcium absorption was analyzed as a parameter (45.59% ± 14.43% for eggshells and 39.88% ± 16.07% for the supplement)	Brun et al. 2013
Local bakery	Eggshells were subjected to washing, drying, and fragmentation processes. HCl solutions were prepared, to which 100 kg of the processed eggshells was added and stirred. The mixture was subjected to centrifugation and drying; the resulting supernatant was heated, giving rise to CaCl2 crystals	These crystals were determined by X-ray diffraction to have the composition of CaCl2.2H2O; yielding 87.38% (w/w) of eggshell calcium chloride	Garnjanagoonchorn and Changpuak 2007
Egg supplier company Ovopol	For comparison in terms of calcium supplementation, one of the tablets was formulated using calcium citrate extracted from eggshells, and the other derived from synthetic calcium carbonate. This procedure involved roasting the eggshells (for 2 h at 120 °C) with citric acid, followed by tableting. The synthetic calcium carbonate tablet was prepared by forming a granulate followed by drying at 60 °C for 24 h	Calcium content from the calcium citrate extracted from eggshells was 100.0 ± 1.4 mg; and the amount found in the synthetic tablets 100.0 ± 2.7 mg	Barbara et al. 2016