Chemistry Reference
In-Depth Information
Fig. 23.4
Routes for exploring
processes for the use of superheated
water in natural product extraction.
although higher temperatures resulted in degrada-
tion [24]. This opens up the possibility of extraction
of lipids from natural products, followed by separa-
tion of the fatty acids.
In an attempt to produce sugars directly from
barley seeds, these were extracted with superheated
water in our laboratory. Unfortunately, at the tem-
perature required for hydrolysis a dark-brown
extract was obtained that smelled of burning. At a
lower temperature, however, a pleasant cooking
aroma was obtained, due to the Mailliard reaction.
Similar results were obtained with other vegetable
materials and superheated water could be used to
manufacture food flavours.
The most interesting results were obtained with
green Java coffee beans. Extraction at around 200°C
produced a brown liquid that had the aroma of
coffee. The apparatus is shown in Fig. 23.6, with the
cell and preheating coil shown in the oven and the
'coffee' produced on the left side of the picture.
The stainless-steel vessel to the right-hand side of
the pump is used to pressurise water with oxygen in
some experiments. Extractions were carried out
using both deoxygenated water and water oxy-
genated by air at atmospheric pressure and by
oxygen at 5 bar, although the product was not much
affected by the presence of oxygen. Following
extraction, the cell contents were examined. After all
the experiments the beans were found to be whole.
Water appeared to have permeated throughout the
individual beans and all the beans were homoge-
neously dark brown. They had expanded to about
double their initial size and the strong smell from the
beans was bitter and burnt.
The extracts were analysed by head-space gas
chromatography coupled to mass spectrometry. In
Fig. 23.5
Superheated water extraction pilot plant.
the valuable chamomile oil is formed by oxidation
during its production.
Reactions in superheated water are well charac-
terised [22]. In relation to plant materials, the
hydrolysis of starch and cellulose to sugars has been
studied widely up to the present [23]. Superheated
water has been used as a solvent and reagent for the
hydrolysis of triglycerides, some containing unsatu-
rated acids, in the temperature range 260-280°C,
