Chemistry Reference
In-Depth Information
Temperature in the
core: 100-105°C
Asparagine and sugars are
transported to the surface with the
evaporating water
Temperature in the
crust: >120°C
Acrylamide formation takes place in
the outer parts of the potato where
temperature >120°C and water
content is low.
150
◦
C. The surface layer is
estimated to be approx. 2 mm (drawing is consistent with results in Gokmen et al.
84
).
Fig. 4.8
Reactions in a potato strip during frying at oil temperatures
>
more acrylamide in the surface than in the core when frying at 190
◦
C. Based on this model,
depleting or reducing asparagine in the outer layer would be expected to hinder or at least
reduce acrylamide formation quite significantly. However, identifying the action radius of
an externally applied enzyme and comparing this to the acrylamide formation zone is not
simple and remains speculative. Also, since diffusion of asparagine is a dynamic process,
fresh asparagine is very likely transported from the core towards the surface along with
evaporating water evolved during drying and frying.
4.4.2.2
Industrial production of French fries
In addition to the theoretical considerations concerning enzyme-substrate interaction in the
treatment of an intact potato strip, practical considerations have to be made regarding the
production process. A typical industrial French fry process is illustrated in Fig. 4.9.
Potatoes are initially washed, sorted, steam peeled and cut. Following cutting, the potato
strips are blanched in 2-3 sequential steps typically at 65-85
◦
C for 10-30 min. Blanching is
done to inactivate the endogenous enzymes in the potato, to partially cook the potato and to
leach out reducing sugars in order to prevent excessive browning of the final product. After
blanching, the potato strips are quickly dipped in a warm phosphate salt solution (SAPP) to
prevent greying of the final product. The dip is optionally combined with a dip in glucose to
control the final colour. The potatoes are dried in a drier with hot circulating air at 75-95
◦
C
for 5-20 min giving a weight loss of 5-25%. Finally, the potato strips are par-fried before
being quick-frozen and packed. Final frying is done at the restaurant or by consumers.
4.4.2.3
Lab-scale testing of asparaginase in French fries
The most simple and direct application point for an enzyme in the French fry production
process would be during blanching, where the peeled, cut potato strips are held in hot water
for 10-30 min, giving an enzyme a sufficient span of time for action. Unfortunately, typical
