Multi-analytical characterisation of wheat biominerals: impact of methods of extraction on the mineralogy and chemistry of phytoliths

Abstract

Phytoliths from two different wheat species, Triticum monococcum and Triticum durum, known for their long-lasting significance to humans, were studied by a multi-analytical approach. Characterisation of phytoliths assisted in understanding their microstructure and behaviour after extraction from plants by the dry ashing and the wet ashing methods. The phytoliths extracted from different parts of the plant, namely the inflorescence and the stem-leaves, were characterised by optical microscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, energy-dispersive X-ray fluorescence spectroscopy (ED-XRF), elemental CHNS analysis, thermogravimetric and differential thermogravimetric analysis (TGA-DTGA) and scanning electron microscopy coupled by energy-dispersive spectroscopy (SEM/EDS). The plants were cultivated at the same period and under the same climatic conditions in the Pella area, northern Greece. The mineralogical and chemical composition of the recovered phytoliths is controlled by the extraction method, strongly suggesting that comparison of phytoliths extracted from plants is meaningful only if the method of extraction remains the same. Physicochemical characteristics of fresh phytoliths extracted from plants provided useful information on the their preservation state after laboratory processing that may further contribute to the study of aged phytoliths in archaeological sites.