Nutritional Characteristics of Potatoes - The Potato: Botany, Production and Uses - page 322

low-temperature sweetening of the tubers posi-
tively under long-term storage conditions.

interesting to follow this approach in the fu-
ture and see whether it will be used in potatoes.

Vitamin B 8 (biotin)

Vitamin B 9 (folate)

Biotin ( Fig. 18.3f) is only reluctantly con-
sidered to be a vitamin (Food and Nutrition
Board, 1998), and the nomenclature for this
compound is inconsistent as some sources
refer to it as B 7 , B 8 , or H (Roje, 2007; Bailey
et al ., 2010; Fitzpatrick et al ., 2012). It partici-
pates as a cofactor in carboxylation reactions
of some enzymes involved in carbohydrate and
fatty acid metabolism (Lin and Cronan, 2011)
and in cell signaling and biotinylation of his-
tones via biotinidase (Kobza et al ., 2005; Zempleni,
2005). Like pantothenate, vitamin B 8 defi-
ciency is relatively rare in humans, and occurs
mostly in individuals that carry genetic defects
in the biosynthetic pathway or biotin metabol-
ism, as well as sometimes in women during
pregnancy (Said, 2002, 2012). The recom-
mended AI value for adults over 18 years is
0.03 mg day - 1 , according to the National Insti-
tute of Health. Data about the extent of vari-
ation in potato germplasm are not available;
however, limited data from chips show they
contain high concentrations (167% of AI in
100 g; Table 18.2 ) (Staggs et al ., 2004), which
would indicate that potato is an excellent diet-
ary source. Interestingly, overexpression of
biotin-binding proteins is currently discussed
as a method to increase resistance against
potato tuber moth ( Phthorimaea operculella )
(Meiyalaghan et al ., 2005). In some areas, the
insect represents a severe pest that damages foli-
age and tubers in the field and in non-refrigerated
stores, and causes significant loss in yield
(Nault et al ., 2001; Basavaraju et al ., 2009).
Experiments in tobacco showed that overex-
pressed biotin-binding proteins in the vacuole
resulted in a 100% lethality of feeding larvae
(Murray et al ., 2010), likely by interfering with
the insect's metabolism on consuming high
amounts of these biotin-binding proteins.
Since the insect cannot synthesize biotin, biotin-
binding proteins will, over time, deplete biotin
availability, causing death of the larvae. The
plant is not affected, as both proteins are re-
tained in the vacuole, and thus do not interfere
with the plant's biotin metabolism. It will be

Folate is involved in DNA biosynthesis, the
methylation cycle (synthesis of methionine and
the universal methyl group donor, S -adenosyl-
methionine), and the metabolism of iron-sulfur
clusters (Cossins and Chen, 1997; Scott et al .,
2000; Waller et al ., 2010). Folate has a crucial role
in photorespiration, a process unique to plants
(Cossins and Chen, 1997; Scott et al ., 2000).
Because of their high consumption, pota-
toes are important sources of folate. Brussaard
et al . (1997) reported that potatoes were the
most important vegetable source of folate in the
diet, supplying 10% of the total folate intake in
the Netherlands (Brussaard et al ., 1997). An-
other study estimated that potatoes were the
third most important overall source of folate in
the Dutch diet, providing 7% of the total folate
intake (Konings et al ., 2001). In Norway, pota-
toes provided 9- 12% of the total folate intake
(Brevik et al ., 2005), while in Finland, potatoes
supplied ~10% of the total folate intake (Alfthan
et al ., 2003). Analysis of a Greek population
found increased consumption of potatoes was
associated with decreased risk of low serum fol-
ate (Hatzis et al ., 2006).
Folate screening found a range of 12-37 µg
100 g - 1 FW in cultivars (Holland et al ., 1996;
Vahteristo et al ., 1997). More recently, system-
atic screening of potato cultivars, advanced
breeding lines, and primitive and wild species ex-
tended the range of folate concentrations (Goyer
and Navarre, 2007; Goyer and Sweek, 2011).
Primitive cultivated species contained up to
41.6 µg 100 g - 1 FW of folate, and the wild species,
Solanum boliviense , contained 115 µg 100 g - 1
FW of folate, which was more than double the
amount found in any modern variety. Thus, this
may be useful material to integrate into potato
breeding programs.

Effect of tuber enlargement and maturity

Folate content was lower in small tubers harvested
early in the season compared to large tubers
harvested later in the season (Goyer and Navarre,
2009), with decreases as high as 3.4-fold.