## 3 Results and Discussion
### Characterization of Eggshell-Waste-Derived Calcium Acetate and Calcium Hydrogen Phosphate  
The transformation process of ESW using 10% (\(w/v\)) acetic and 15% (\(w/v\)) \(o\)-phosphoric acid (Figure 2) ended with the production of calcium acetate monohydrate and calcium hydrogen phosphate powders shown in Figure 6.  
Both obtained ESW-derived Ca-salts were quite white (Figure 6), indicating that produced salts might be of high purity. Therefore, food-grade additive criteria analysis of calcium acetate and calcium hydrogen phosphate prescribed by the FAO [50; 51] and EU [48; 49] were applied for the analysis of ESW-derived calcium acetate and calcium hydrogen phosphate. Physicochemical analysis of ESW-derived calcium acetate monohydrate in comparison with the demands for food-grade additive is shown in Table 3, and ESW-derived calcium hydrogen phosphate in Table 4. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** &
\begin{tabular}{c} **Food Additive** \\ **Criteria 1** \\ \end{tabular} \\ \hline Dry matter [\%] & 98.78 \(\pm\) 0.94 & n. c. 2 \\ Calcium [\%. d.w.b.] 3 & 22.46 \(\pm\) 0.43 & n. c. \\ pH of 10\% solution & 7.01 \(\pm\) 0.26 & 6–9 \\ Soluble proteins [g/100 g.d.w.b.] & 0.15 \(\pm\) 0.09 & n. c. \\ Loss on Drrying [\%] & 2.60 \(\pm\) 1.39 & \textless{}11 \\ Water insoluble [\%] & 0.6 \(\pm\) 0.08 & \textless{}0.3 \\ Formic acid and oxidizable impurities [mg/kg] & 4392.42 \(\pm\) 337.86 & \textless{}1000 \\ Fluoride [mg/kg] & \textless{}10 & n. c. \\ As [mg/kg] & \textless{}1 & \textless{}3 \\ Pb [mg/kg] & \textless{}1 & \textless{}2 \\ Hg [mg/kg] & \textless{}0.015 & \textless{}1 \\ \hline \hline \end{tabular}  
* Food Additive Criteria of FAO [50] and EU [49]. 2 n. c—not included in criteria for additive. 3 d.w.b.—dry weight basis.  
\end{table} 
Table 3: Physicochemical Analysis of Eggshell-Derived Calcium Acetate Monohydrate. Figure 6: Eggshell-Waste-Derived Calcium Acetate Monohydrate (**a**) and Calcium Hydrogen Phosphate (**b**). ESW-derived Calcium Acetate Monohydrate contained 22.46 \(\pm\) 0.43% of calcium per dry weight basis. This was quite close to the theoretical amount of calcium in Ca(CH\({}_{3}\)COO)\({}_{2}\times\) H\({}_{2}\)O of 22.75%. While loss on drying at 155 \({}^{\circ}\)C, pH of 10% solution and amount of As, Pb and Hg completely fulfilled the criteria prescribed by the FAO [50] and EU [49], the amount of water insoluble, as well as formic acid and oxidizable impurities content were out of the prescribed criteria, indicating that some additional purification steps are necessary to obtain calcium acetate of food-grade additive purity. In addition to the prescribed criteria for additive purity, the amount of soluble proteins present in the produced calcium acetate monohydrate was determined, and based on the obtained results (Table 3), it can be concluded that soluble proteins were present in the minor amount of 0.15 \(\pm\) 0.09 g per 100 g of Ca(CH\({}_{3}\)COO)\({}_{2}\times\) H\({}_{2}\)O.  
ESW-derived calcium hydrogen phosphate contained 25.64 \(\pm\) 0.68% of calcium determined via complexometric titration and 23.57 \(\pm\) 0.07% of Ca and 17.25 \(\pm\) 0.20% of phosphorus determined by X-ray analysis (Table 4), indicating that the obtained CaHPO\({}_{4}\) is probably present in anhydrous form. This was additionally proven by the loss on drying and loss on incineration (Table 4), where ESW-derived CaHPO\({}_{4}\) fulfilled the criteria for calcium hydrogen phosphate anhydrous prescribed by the FAO [51] and EU [49]. Moreover, based on the analysis of fluoride, As, Cd, Pb, Hg and Al content, the obtained ESW-derived CaHPO\({}_{4}\) meet all criteria to be used as a food-grade additive (Table 4).