Isolation and characterization of biogenic calcium oxalate crystals from Amorphophallus paeoniifolius

Amorphophallus paeoniifolius known as elephant foot yam is an underutilized tuberous food crop grown primarily in Africa, South Asia, and tropical Pacific islands. Aim of the present work was to isolate, identify and study various physicochemical characteristics of calcium oxalate crystals present in elephant foot yam. The calcium oxalate crystals from elephant foot yam were isolated using freeze thawing followed by aqueous extraction method. The optimum isolation conditions for maximum calcium oxalate yield was found as grinding time of 12.5 min, solid to liquid ratio of 1:2, temperature of 50 °C, grinding speed of 2000 rpm and 3 extraction cycles. Morphological characteristics of isolated calcium oxide crystals were studied using Scanning Electron Microscope and the presence of calcium oxalate crystals in the form of whewellite was confirmed. The purity of isolated calcium oxalate crystals was confirmed using Energy Dispersive x-ray Spectroscopy. The spherical and oval shapes of calcium oxalate crystals were confirmed using Transmission Electron Microscope. X-Ray Diffraction analysis has confirmed the tetragonal phase structure of isolated calcium oxalate crystals with good crystal stability. Calcium oxalate crystals from elephant foot yam were found stable at 175 °C using Thermal Gravimetric and Differential Scanning Calorimetric analysis.