Chemistry Reference
In-Depth Information
The use of an 'R-enzyme' has been reported by Antrim and Taylor
87
in the production
process of shredded wheat. The R-enzyme, also known as starch debranching enzyme or
pullulanase, will accelerate starch retrogradation and allow for a shortening of the holding
step.
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7.9
MISCELLANEOUS
7.9.1 Asparaginase to reduce acrylamide content in
wheat-based baked products
Acrylamide is known to be neurotoxic and has been classified as a probable carcinogenic com-
pound for humans, group 2A, by the International Agency for Research on Cancer (IARC) in
1994.
89
For this reason, the finding of high levels of acrylamide in carbohydrate-rich foods
processed at high temperatures as reported by the Swedish National Food Administration
in 2002
90
was taken as a serious concern worldwide. It became clear that a wide range of
cooked foods - prepared industrially, in catering, or at home - contain acrylamide at levels
in between a few parts per billion (ppb or µg/kg) and in excess of 3000 ppb. This includes
staple foods like bread, fried potatoes and coffee as well as specialty products like potato
crisps, biscuits, cookies, crisp bread and a range of other heat-processed products.
91
The
main formation mechanism of acrylamide in foods is the reaction of reducing sugars with
free asparagine in the context of the Maillard reaction. In many cooking processes, the Mail-
lard cascade is the predominant chemical process determining colour, flavour and texture
of cooked food. This reaction is based on highly complex reactions between amino acids
and sugars, that is common nutrients present in all relevant foods. The cooking process per
se - baking, frying, microwaving - seems to be of limited influence. It is the thermal input
that is crucial: that is the temperature and heating time to which the product is subjected.
Acrylamide is formed at temperatures above 120
◦
C.
Consequently, any intervention to reduce acrylamide formation has to take into account
that it is very difficult to decouple acrylamide formation from the main Maillard reaction pro-
cesses. In baked products, the formation of acrylamide is closely related to the combination of
moisture content and baking temperature/time. If baking temperatures could be kept low and
moisture content high, less acrylamide would be formed during baking even though longer
baking times would be required. However, many products baked according to this procedure
suffer significant changes to overall product quality (colour, flavour, texture, etc.).
92, 93
Reduction of pH in semi-sweet biscuits by addition of citric acid has shown to result
into 20-30% reduction of acrylamide
94
but addition of acidifiers in most cases will have
an impact on the organoleptic properties of the final product.
95
Model experiments have
also shown that in certain bakery products lower pH in combination with fermentation can
lead to an increase of another undesired process chemical, that is 3-monochloropropanediol
(3-MCPD).
96
In a number of baked products ammonium bicarbonate is used as a baking salt. However,
ammonium bicarbonate (and other ammonium salts) has shown to be strongly supportive to
acrylamide formation. Replacement by sodium bicarbonate results in lowering the acrylamide
content; however, product quality changes dramatically in most cases.
97, 98
In 2004, it was shown that the enzyme asparaginase is performing very well in reducing
the acrylamide content without any change in product quality.
99, 100
Up to 95% reduction
could be obtained in certain types of baked products without any change in the production
process. Asparaginase catalyzes the conversion of asparagine into aspartic acid; aspartic acid
