Fjölrit RALA - 22.03.1979, Side 75

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5 . Thiamine (Vitamin B^):
The only measurements on thiamine in potatoes which have
been carried out and published in Iceland are measurements done
by Tómasson 1939-40. Tómasson's results show about 100 i.e.
per 100 g (0.3 mg/100 g). It was not recorded which variety
he measured.
According to J. Augustin (1975), the thiamine content of
potatoes is usually from 0.034 to 0.146 mg/100 g. Affecting
the content are the variety in question, fertilization and
soil. Increasing use of nitrogen fertilizer increases the
thiamine content up to a certain point. Potatoes grown in
humus soil contain considerably more thiamine than those
grown in sandy soils (J. Augustin, 1975).
It is common practice abroad to peel raw potatoes and
sell them in this condition to cafeterias. After peeling,
the potatoes are immediately placed in a sulphite solution
and then dried. The sulphite breaks down the thiamine into
inactive thiazole and pyrimidine sulphonic acid (T.E. Ogun-
tona and A.E. Bender, 1976). On storage, therefore, much of
the thiamine is destroyed. After a week's storage, 25% has
been destroyed. Further destruction occurs during cooking.
Potatoes which have been stored for a week and then boiled
have thus lost 35-40% of their thiamine (C.W. Mapson and
H.G. Wagner, 1961).
6. Riboflavin (Vitamin B^):
No recorded measurements on the content of Icelandic
potatoes are known to exist.
According to J. Augustin (1975), the riboflavin content
is usually from 0.01 to 0.05 mg/100 g. J. Augustin (1975)
believes that fertilization and type of soil have no effects
on the amount of riboflavin the potatoes will contain.
7. Niacin:
No recorded results of niacin measurements done on pota-
toes in Iceland are known to exist. According to J. Augustin
(1975), the niacin content in potatoes is usually from 0.53
to 3.10 mg/100 g. Increasing the use of nitrogen fertilization
causes a rise in the niacin content of potatoes up to a certain