Nutritional Characteristics of Potatoes - The Potato: Botany, Production and Uses - page 327

20

18

16

14

12

10

8

6

4

2

0

Fig. 18.4. Total phenolics in baby potatoes grown in Washington State, USA, in 2010-2011. Phenolics were
measured by the FC method using freeze-dried samples. Potatoes were harvested 60- 80 days after planting.

purple potato, Magic Molly, to 15 other vegetables
(Navarre et al ., 2011). Russet Burbank had an
ORAC value of ~ 5 µmol Trolox equivalents (TE) g - 1
FW, which was comparable or superior to 8 other
vegetables, whereas Norkotah (~ 9 µmol TE g - 1
FW) had comparable or greater amounts than 11
other vegetables, rivaled spinach, and was double
that of tomato. Magic Molly (~ 34 µmol TE g - 1 FW)
had the highest amounts of all the vegetables
measured, surpassing both broccoli and Brussels
sprouts. More recently, we have identified pota-
toes with even higher amounts of antioxidants
than Magic Molly (Navarre, data not shown).
These antioxidant values are not mentioned to
show that potatoes are superior to other veget-
ables, but rather to emphasize the fact that pota-
toes can hold their own with other vegetables,
and the perception by some that they are just
“empty calories” or “provide only starch” ignores
a lot of data that contradict such misperceptions.

The most abundant phenolics in tubers are hy-
droxycinnamic acids, and chlorogenic acid can
account for up to 90% of a tuber's total soluble
phenylpropanoids in white potatoes (Malm-
berg and Theander, 1985). Several pathways
exist for chlorogenic acid (CGA) biosynthesis,
but the major pathway in Solanaceae is via the
enzyme, hydroxycinnamoyl-CoA:quinate hy-
droxycinnamoyl transferase (HQT) (Niggeweg
et al ., 2004). Red and purple potatoes usually
have considerably greater amounts of CGA
than white potatoes, but because of the pres-
ence of anthocyanins, CGA accounts for a
smaller percentage of the total phenylpro-
panoid content than in white potatoes (Na-
varre et al ., 2011). The R2R3 transcription
factor, StAN1 , appears to mediate CGA expres-
sion, in addition to regulating anthocyanins
(Payyavula et al ., 2013).
CGA is highly bioavailable in humans
(Monteiro et al ., 2007; Farah et al ., 2008), can
protect animals against degenerative, age-related
diseases, has antiviral and bacterial properties,
and can reduce the risk of some cancers and
heart disease (Nogueira and do Lago, 2007).
CGA is also thought to be antihypertensive
(Yamaguchi et al ., 2007), but whether it is the
cause of the hypotensive effect in people eating
purple potatoes is unknown (Vinson et al ., 2012).

Chlorogenic acid

Typically, tuber skin has a greater concentration
of phenylpropanoids than the flesh, but because
the flesh comprises a much greater percentage
of tuber mass than the periderm, the flesh con-
tains a majority of soluble phenylpropanoids.