Polyphenols - Fruit Ripening: Physiology, Signalling and Genomics - page 163

hesperidin and narirutin and contain
polymethoxyfl avones (Gil-Izquierdo et al. ,
2001). Flavanone glycosides are present in
citrus juices in substantial amounts (up to
about 700-800 mg l -1 ) in hand-squeezed
juice (Gil-Izquierdo et al. , 2001).
Chalcones (Fig. 9.1g) are a specifi c
group of fl avonoids in which the C-ring is
open (hence the different C numbering).
Naringenin chalcone is an upstream inter-
mediate in the fl avonoid biosynthesis
pathway and does not usually accumulate
in plants but has been detected in tomato
fruit (Hunt and Baker, 1980). It is the major
fl avonoid in cherry tomato, ranging from 7
to 28 mg per 100 g FW (Slimestad and
Verheul, 2005). Dihydrochalcones (Fig.
9.1h) have been detected in tomato (namely
the 3 c ,5 c C-diglucosides of phloretin
(Slimestad et al. , 2008) and C-diglycosides
of phloridzin (phloretin 2 c - O -glucoside)
(Vallverdu-Queralt et al. , 2010)) but this
family is mostly represented in apples,
with phloridzin, phloretin-xyloglucoside
and 3-hydroxyphloridzin accounting to-
gether for 2-6% of the total phenolic
composition (Vrhovsek et al. , 2004).

and anthocyanin polymers, have also been
detected in fruits such as strawberry
(Andersen et al. , 2004; Fossen et al. , 2004),
blackcurrants (Lu et al. , 2000), grapes
(Vidal et al. , 2004a,b; Gonzalez-Paramas et
al. , 2006) and cranberries (Tarascou et al. ,
2011), suggesting that they can form in
planta . Condensation products of fl avan-3-
ols with acetaldehyde have been detected
in persimmon (Tanaka et al. , 1994). Similar
products in which fl avan-3-ols are linked
through methylmethine bridges, often
called 'ethyl bridges', to anthocyanins and
fl avonols have also been detected in
cranberry extracts (Tarascou et al. , 2011).

9.2.2 Hydrolysable tannins

Ellagitannins and gallotannins, that is,
multiple esters of hexahydroxydiphenic
acid group(s) or gallic acid groups,
respectively, with a polyol (usually
glucose), belong to the hydrolysable tannin
class. Hydrolysis of ellagitannins releases
hexahydroxydiphenic acid (Fig. 9.2a),
which spontaneously lactonizes to ellagic
acid (Fig. 9.2b), while hydrolysis of
gallotannins yields gallic acid (Fig. 9.2c).
These reactions are commonly used to
detect and quantify them. Their occurrence
in fruits is rather limited. Gallotannins
have been reported in mangoes and
pomegranate. Ellagic acid conjugates and
ellagitanins are found in strawberry, pome-
granates, Rubus species (e.g. raspberries,
blackberries and cloudberries), muscadine
grapes and in some nuts (e.g. hazelnuts,
walnuts and pecans) (Clifford and Scalbert,
2000; Törrönen, 2009). When screened
in 33 fruits consumed in Finland,
ellagitannins were detected only in fi ve
species of berries, with contents ranging
from 1 mg per 100 g FW (in sea buckthorn)
to 330 mg per 100 g FW (in cloudberry)
(Koponen et al. , 2007). Major ellagitannins
in Rubus species (Mullen et al. , 2003) and
in strawberry (Buendia et al. , 2010) are the
dimeric sanguiin H-6 (Fig. 9.2d) and the
trimeric lambertianin. Ellagitannins are
abundant (up to 1.9 g l -1 found in juice due

Flavonoid reaction products
All fl avonoids are highly reactive. Their
reactions are well documented in food
transformation processes, and there is
some evidence of their occurrence in vivo .
Some changes have been attributed to
oxidation, especially for PA in seeds
(Kennedy et al. , 2000), and to formation of
covalent linkages between PAs and plant
cell walls (Matthews et al. , 1997; Kennedy
et al. , 2001). The seeds of the transparent
testa Arabidopsis mutant, tt10 , missing a
laccase gene, contains much higher PA
levels and a higher ratio of fl avonol
monomers to fl avonol dimers than the
brown wild-type seeds, confi rming that
seed coat browning results from fl avonoid
oxidation (Pourcel et al. , 2005), as
postulated in grape seeds (Kennedy et al. ,
2000). Various types of anthocyanin-
derived pigments, including fl avanol-
anthocyanin adducts, pyranoanthocyanins