Chemistry Reference
In-Depth Information
O
COOH
CNH
2
N
N
Nicotinic acid
Nicotinamide
Figure 13.4.
Structures of nicotinic acid and nicotinamide.
Nicotinamide
ADP
O
NH
2
C
NH
2
N
N
OO
N
N
CH
2
OPOPOCH
2
N
OH OH
O
-
O
O
O
O
Ribose
O
P
OH
HO
OH
Figure 13.5.
Structure of nicotinamide-adenine dinucleotide (NAD
+
) and nicotinamide-
adenine dinucleotide phosphate (NADP
+
).
niacytin, and thus having a bioavailability of only 30%. In milk, almost all
niacin is in the free form.
Niacin is stable to sunlight, various storage conditions and heat treat-
ments as used in dairy processing. Exposing liquid milk to gamma radiation
(10 Gy) leads to a loss of about 30%, while niacin in milk powder survives
higher doses of radiation. During cheese production, most niacin passes to
the whey which can be compensated partly by an increase of the niacin
content in the outer layers due to microbial action during maturation (
10-
to 25-fold).
13.4.1.
Function of Niacin
The most important functions of niacin are the roles of NAD and
NADP as co-enzymes of dehydrogenases (cf. Biesalski and Back, 2002c).
The C4 position on the pyridine ring of the nicotinamide part of the molecule
