Smoking 233pyrocatechol, phenol, and their various alkyl
derivatives. The highest yield of phenols,
especially of guaiacol and syringol and their
derivatives, compounds that are essential for
the sensory and preservative action of
smoking, is at 400 – 600 ° C.
Aldehydes and ketones of smoke form a
group of about 110 compounds, which
includes also a number of aldehydealcohols,
ketoalcohols, and ketoaldehydes. In the
smoke from alder and fi r wood, 28 and 34
carbonyl compounds, respectively, were
identifi ed (Borys 1978 ). Aliphatic and cyclic
carbonyl compounds, as well as furan deriva-
tives, are the products of pyrolytic degrada-
tion of cellulose and hemicelluloses, while
aromatic carbonyls are formed from lignin.
The total content of carbonyl compounds
ranges from about 25 to 110 mg/m^3 ; thus it is
similar to that of phenols. The carbonyls
present in the highest concentrations are acet-
aldehyde, formaldehyde, and acetone; also,
several O - heterocyclic carbonyls have been
identifi ed in wood smoke (e.g., furfuralde-
hyde and 5 - hydroxymethyl - 2 - furaldehyde).
Wood smoke contains several aliphatic
and aromatic alcohols, including methanol,
ethanol, allylalcohol, n - amylalcohol, benzyl
alcohol, and phenylethylalcohol. Methanol
may be the substrate for the generation of
formaldehyde and formic acid.
The group of carboxylic acids in wood
smoke consists of about 30 various com-
pounds. In the aliphatic fraction, the follow-
ing acids were identifi ed: acetic, propionic,
isobutyric, butyric, crotonic, isocrotonic,
valeric, isovaleric, heptanoic, caprylic, and
nonanoic (K ł ossowska 1979 ). Among the
dicarboxylic acids are oxalic, malonic,
fumaric, maleic, and succinic acids. Wood
smoke also contains several ketocarboxylic
acids. In the esters group, the methyl esters
of formic, acetic, butyric, and acrylic acids
were identifi ed, as well as the benzoic acid
ethyl ester.
One of the important groups of smoke
constituents contains aliphatic and aromaticvapor in the smoke is related to the humidity
of the wood and air. The relative humidity of
the smoke varies within a broad range and
can be controlled by the operator. Although
numerous investigations have been carried
out on the effect of the parameters of genera-
tion on the composition of the curing smoke,
it is still not possible to predict precisely the
contents of various compounds in the smoke.
However, it is known which factors affect the
generation of phenols, aldehydes, ketones,
alcohols, acids, esters, and hydrocarbons.
The concentrations of these fractions in the
curing smoke, in mg/m^3 of the aerosol or in
mg/100 g of wood, differ considerably as
reported by different investigators, since the
conditions of smoke production in various
experiments were different. The yield and
gross chemical composition of smoke
depends more on the temperature and oxygen
access than on the humidity and kind of
wood.
The Main Groups of Compounds
The phenolic fraction of wood smoke con-
sists of about 250 components, with 85 of
them identifi ed. Phenols are formed primar-
ily due to pyrolysis and oxidation of lignin,
at comparatively low temperature (200 –
400 ° C), and cellulose at 700 ° C. The total
contents of phenols depend on the kind of
wood, temperature, and the density of the
analyzed smoke. According to different data,
it may be from 10 to 200 mg/m^3 ; the yield of
phenols from 100 g of wood ranges from 50
to 5000 mg. This fraction includes com-
pounds containing one, two, or three hydroxyl
groups bound to the benzene ring, besides
alkyl or ether derivatives, as well as those
containing additional alcohol, aldehyde, acid,
and ester groups. Therefore, they differ in
water solubility, boiling point, sensitivity to
oxidation, chemical reactivity, sensory prop-
erties, and antibacterial activity. Among the
identifi ed phenols, those present in the
highest concentrations are syringol, guaiacol,