Analyses of calcium compounds in cladodes, soluble dietary fiber (SDF), and insoluble dietary fiber (IDF) of Opuntia ficus indica are reported. The characterization of calcium compounds was performed by using Scanning Electron Microscopy, Energy Dispersive Spectrometry, X-ray diffraction, and infrared spectroscopy. Atomic Absorption Spectroscopy and titrimetric methods were used for quantification of total calcium and calcium compounds. Whewellite (CaC 2 O 4 ⋅H 2 O), weddellite (CaC 2 O 4 ⋅(H 2 O) 2.375 ), and calcite (CaCO 3 ) were identified in all samples. Significant differences (P ≤ 0.05) in the total calcium contents were detected between samples. CaC 2 O 4 ⋅H 2 O content in cladodes and IDF was significantly higher (P ≤ 0.05) in comparison to that observed in SDF, whereas minimum concentration of CaCO 3 was detected in IDF with regard to CaCO 3 contents observed in cladodes and SDF. Additionally, molar ratio oxalate : Ca 2+ in all samples changed in a range from 0.03 to 0.23. These results support that calcium bioavailability in O. ficus indica modifies according to calcium compounds distribution.
Calcium carbonates and calcium oxalates were detected in cladodes, IDF, and SDF of O. ficus indica. Nevertheless, significant differences in total calcium, calcium carbonate, calcium oxalate contents, and molar oxalate : Ca 2+ ratio were observed in all samples. This means that calcium bioavailability in O. ficus indica varies according to calcium compounds distribution.