Asparaginase – an enzyme for acrylamide reduction in food products - Enzymes in Food Technology - page 61

that is low water content and high temperature favour formation and low pH reduces forma-
tion. 15 Several alternative formation pathways have been identified but the general agreement
is that these are of far lesser quantitative importance. 15, 17, 19, 20 An overview of studies of
acrylamide formation and the major contributing factors has been given by Zhang and
Zhang. 21
As removal of acrylamide from prepared food products is impractical, reduction strategies
have focused on limiting the formation of acrylamide. Due to the high number of affected
product categories, the differences in acrylamide levels in these products and the broad
variety of parameters influencing formation, a range of methods and strategies have been
developed. 4, 6, 22
For cereal food products, moisture content and thermal input (time/temperature) play
a key role in acrylamide formation. The CIAA toolbox 2007 22 suggests the possibility of
lowering acrylamide levels by baking products to achieve less colour development but the
same final moisture content as is found in traditional products by utilizing lower baking
temperatures for longer times. Konings et al . 23 and Ahrne et al . 24 found 75% reduction of
acrylamide in crisp bread when baking temperature and oven speed were reduced. Other
technologies for reduction of acrylamide include adding amino acids, which compete with
asparagine in Maillard reactions, adding Ca ++ , lowering pH, optimizing ingredients and
carefully selecting raw materials to favour those low in acrylamide precursors. 22 By lowering
pH, the rate of formation of key Maillard reaction intermediates is decreased. However, even
though significant acrylamide reduction has been reported in literature, addition of acids
is probably of limited utility due to the development of acidic off-flavours, and potentially
insufficient browning and leavening of biscuits. 23, 25, 26 An example of ingredient optimization
is the replacement of ammonium bicarbonate by other suitable leavening agents, such as
sodium bicarbonate. Ammonium bicarbonate enhances acrylamide formation by indirectly
catalyzing the formation of sugar fragments, hereby generating more reactive carbonyls that
can take part in the Maillard reactions. 4, 27, 28 Amrein et al . 25 reported that the combined
use of sodium bicarbonate and sodium acid pyrophosphate (SAPP) in hazelnut biscuits led
to a 50% reduction in acrylamide compared to the use of ammonium bicarbonate. Raw
material control mainly focuses on low asparagine content, since this is the limiting factor
for acrylamide formation in cereal products. 29 Asparagine content in wheat flour differs
widely between varieties and harvests and with whole wheat and fibre content. Studies have
shown that more asparagine is found in high fibre flours (i.e. flours with higher ash content), 30
resulting in increased acrylamide levels in final products. 31, 32
For potato-based products, several studies have shown that the sugar content of the tuber
correlates directly with the acrylamide concentration in the final products. 27,28-36 Controlling
sugar levels is therefore currently the primary measure employed by the industry to reduce
acrylamide levels in chips and French fries. This is done by selecting potato cultivars with
low reducing sugar content and by controlling storage conditions from farm to factory.
Optimal storage temperature is between 8 ◦ C and 10 ◦ C, while storage at lower temperatures
leads to significantly increased levels of reducing sugars. Future concepts include breeding
new potato varieties with low reducing sugar and asparagine content. An enzymatic solution
focusing on removal of the reducing sugars has been suggested but is complicated by the fact
that so many different sugars can participate in the reaction. Reported product recipe changes
for potato products comprise adding competing amino acids, lowering pH and dipping in
Ca ++ -solutions. 4,37-40 Relevant process changes include decreasing cooking temperatures
or cooking duration, where especially vacuum frying has proven very efficient for reducing