A laboratory simulation of the carbonization of sunflower achenes and seeds

Abstract

The current project describes physical and chemical alterations that result from the thermal exposure of sunflower achenes and seeds. Specifically, achenes and seeds were heated at temperatures ranging from 130 to 600 8C under anoxic conditions for 60 min. Changes were measured in mass, relative percentages of C and N, internal and external morphology, molecular composition by direct temperature-resolved mass spectrometry (DTMS) under EI conditions, and the reflectance on polished specimens. The main constituents of sunflower seeds are lipids and protein, while the pericarps or hulls enclosing the seeds have a ligno-cellulosic structure. The morphology of achenes and seeds remains intact following exposure which makes the identification of the residues possible. The results of the sunflower experiments were compared to previous experiments conducted with peas and wheat grains. Up to approximately 340 8C, the molecular conversion of polysaccharide and protein rich peas and wheat grains follow similar pathways, while the lignin present in sunflower achenes follows its own unique pathway, resulting in a different molecular composition. At higher temperatures the molecular composition of the three propagules becomes identical. In addition the reflectance of the three propagules is identical confirming the similarity in molecular composition. Lipids show a different behaviour compared to the other three biopolymers; from 370 8C no oils are observed in the heated specimens and the DTMS-EI measurements show no lipid markers. Apart from evaporation of the triacylglycerides it is suggested that steroids have a high resistance against thermal degradation and are converted into aromatic moieties. #

Morphological, chemical and physical changes during charcoalification of wood and its relevance to archaeological contexts

“…Charcoal residue is therefore an important source of information in helping our understanding of human economic and cultural developments over time. Although charcoalified wood is often abundant in archaeological sites, little is known regarding the morphological, physical and chemical changes associated with the charcoalification process of wood itself, even though such changes associated with carbonized fruits and seeds have been studied in detail (Braadbaart, 2004;Braadbaart et al, 2007, Braadbaart, 2008. Therefore we have undertaken a series of experiments aimed at increasing our knowledge regarding the changes associated with heating both wood and charcoal as a fuel, and thus being able to define the term charcoal in the archaeological context.…”

“…The morphological, physical and chemical properties of charcoal can differ depending upon two main variables associated with the heating process (Braadbaart et al, 2007;Braadbaart, 2008): (1) heat source related variables, which include temperature, time of exposure and heating rate ( C/min); and (2) wood property variables, which include taxon, size, thermal conductivity and porositydvariables that can also change during the charcoalification process itself. With increasing temperature the initial changes to occur are: (1) morphologicaldthe darkening of the wood which ultimately becomes black; (2) physicaldconsiderable mass loss, shrinkage, and possible anatomical distortion, of the original material resulting from the formation and loss of many volatiles; and (3) chemicaldthe continuous and gradual conversion of the cellulose, hemicellulose and lignin to predominantly aromatic moieties, and thereby forming a new chemically-distinct, carbonenriched end product (Shafizadeh, 1982;Boon et al, 1994;Braadbaart, 2004;Braadbaart et al, 2007).…”

Charred olive stones: experimental and archaeological evidence for recognizing olive processing residues used as fuel

“…These temperatures were selected because at the lower temperature oil will still be present and at the higher temperature the oil will be evaporated (Braadbaart et al 2007). Charring was performed in the tube oven as described above.…”

“…The presence of oil is asserted by the mass loss of modern OPR at 450°C of 79.8 wt% compared to a mass loss of about 72 wt% for modern stones. This difference can be explained by the presence of oil in the residue as oil evaporates when the temperature is higher than 340°C (Braadbaart et al 2007). The characteristic compact fibre structure of OPR makes it an excellent fuel for preparing food as it burns with a slow, long-lasting flame.…”

“…Earlier studies have assessed the physical and chemical changes, as a result of heating, of the properties of fruits and seeds like wheat grains, pea seeds and sunflower achenes and seeds (Braadbaart 2004;Braadbaart et al 2007). The results show that the chemical changes, which are characterized by the conversion of the fuel's constituent biomolecules into a material consisting of aromatic compounds, are also valid for the material discussed in this paper.…”