2009_Book_FoodChemistry

490 9 Food Contamination
(9.3)
As a result of their widespread use, the PCBs also
came into contact with food. Because of their persistence
and solubility in fat, they accumulated
like in the case of DDT (cf. 9.4.2.1). Therefore,
they have been increasingly identified in fatty
foods since their discovery. This and the fact that
PCBs can produce highly toxic dioxins (cf. 9.10)
in the combustion process led to the banning of
the production and application of PCBs in 1989.
In Germany, the contamination with PCB, e. g., in
milk fat (mg/kg) has subsequently fallen on average:
0.012 (1986), 0.007 (1992), 0.003 (2001).
9.7 Harmful Substances
from Thermal Processes
9.7.1 Polycyclic Aromatic Hydrocarbons
(PAHs)
Burning of organic materials, such as wood
(wood smoke and its semi-dry distillation product,
the wood smoke vapor phase), coal or fuel
oil, results in pyrolytic reactions which yield
a great number of polycyclic aromatic hydrocarbons
(abouot 250 have been identified) with more
than three linearly or angularly fused benzene
rings, that are carcinogenic to varying extents.
The quantity and diversity of compounds generated
is affected by the conditions of the burning
process. Benzo[a]pyrene (Bap) (Formula 9.4)
usually serves as an indicator compound.
(9.4)
Contamination of food with polycyclic compounds
can be caused by fall-out from the
atmosphere (as often occurs with fruit and leafy
vegetables in industrial districts), by direct drying
of cereals with combustion gases, by smoking or
roasting of food (barbecuing or charcoal broiling;
smoking of sausage, ham or fish; roasting of
coffee). PAHs accumulate in high-fat tissues.
The content in meat and processed meat products
should not exceed 1 µg/kg end-product measured
as Bap. A reduction of Bap contamination to
this limiting value has been achieved by the use
of modern smoking techniques. A maximum of
5µg/kg Bap is tolerated in smoked fish. Values
less than 1.6µg/kg were found in 95% of the
samples tested in food monitoring in 2005.
9.7.2 Furan
Furan is possibly a carcinogenic substance. It
occurs in heated food, especially in roasted coffee.
Isotopic dilution analyses with [ 2 H 4 ]-furan
as the internal standard yielded 2.5–4.3mg/kg
furan in differently produced coffee powders.
Baby food, e.g., carrot mash and potato/spinach
mash contained 74 and 75 µg/kg respectively.
Furan is formed from amino acids which yield
acetaldehyde and glycolaldehyde on thermal
degradation (Fig. 9.4). Aldol condensation,
cyclization and elimination of water are the
reaction steps. Other precursors of furan are
carbohydrates, polyunsaturated fatty acids and
carotinoids (Fig. 9.4). Furan can also be formed
from the thermolysis of ascorbic acid.
9.7.3 Acrylamide
Polyacrylamide, produced from monomeric
acrylamide (2-propenamide), has been used for
decades in various industrial processes, e. g.,
as a flocculant in the treatment of drinking
water. Especially for reasons of occupational
health and safety, numerous toxicological studies
on acrylamide have already been conducted.
These studies have shown above all that on high
exposure, acrylamide (i) binds to hemoglobin
in the blood, (ii) is metabolized to reactive
epoxide glycidamide and (iii) is carcinogenic
on chronic exposure in animal tests. For this
reason, acrylamide was put about 20 years ago