Chemistry Reference
In-Depth Information
CH
2
OH
CHO
CH
2
NH
2
HO
CH
2
OH
HO
CH
2
OH
HO
CH
2
OH
H
3
C
H
3
C
H
3
C
N
N
N
Pyridoxine
Pyridoxal
Pyridoxamine
Figure 13.8
Structures of pyridoxine, pyridoxal and pyridoxamine.
CHO
O
CH
2
NH
2
O
OP O
-
O
-
HO
HO
CH
2
CH
2
O
P
O
-
O
-
H
3
C
H
3
C
N
N
PLP
PMP
Figure 13.9.
Structure of the co-enzymes pyridoxal-5
0
-phosphate (PLP) and pyridoxamine-5
0
-
phosphate (PMP).
PN and PM and their phosphorylated forms are the predominant forms
in plant-derived foods, while in animal-derived foods PL and PLP predomi-
nate (Bitsch, 1993). In cow's milk, 14% of vitamin B6 is in the bound form and
86% in the free form (Jensen, 1995). It is sensitive to light and heat, partly
depending on the pH of the medium. PM and PN are more stable than PL,
particularly to light. In neutral and alkaline solutions, B6 is destroyed by UV
light. PL, PM and PN are generally stable to heat in acidic surroundings but
heat sensitive in an alkaline medium. The amount of reported loss differs in
different studies, maybe due to different experimental procedures. However,
some approximations can be given (cf. Biesalski and Back, 2002e).
Heat treatment leads to a loss (in %):
Insignificant effects in dried milk products
Pasteurization: 0-8%
UHT milk:
<
10%
Boiling: 10%
Sterilization: 20-50%
Evaporated milk: 35-50%
UV light leads to a reduction of 10-45%, depending on the intensity and
duration of exposure; gamma radiation (10 Gy) causes a loss of
90%.
