2009_Book_FoodChemistry

832 18 Fruits and Fruit Products
is the bitter compound of bitter oranges (Citrus
auranticus). The nonbitter isomer, hesperitin-7-
rutinoside (hesperidin) occurs in oranges (Citrus
sinensis) (cf. Table 18.23).
Removal of the bitter taste of citrus juices
and citrus fruit pulps is possible by enzymatic
cleavage of the sugar moiety using a mixture
of α-rhamnosidase and β-glucosidase. These
enzymes are isolated from microorganisms such
as Phomopsis citri, Cochliobolus miyabeanus or
Rhizoctonia solanii:
Naringin → Naringenin + Rhamnose
+ Glucose
A number of neutral or bitter flavanone glycosides
can be converted through ring opening to
sweet chalcones (II) which, by additional hydrogenation,
can be stabilized as sweet dihydrochalcones
(III):
(18.27)
18.1.2.5.4 Flavanones
Flavanones (Formula 18.28: R 1 =H,R 2 =OCH 3 :
isosacuranetin; R 1 =H,R 2 = OH: naringenin; R 1
= OH, R 2 =OCH 3 : hesperitin; R 1 ,R 2 = OH: eriodictyol)
occur mostly as glycosides in citrus fruits
(Table 18.23):
(18.28)
Table 18.24 shows that flavanone-7-rutinosides
are usually nonbitter, whereas flavanone-7-
neohesperidosides are generally bitter. The
intensity of the bitter taste is influenced by the
substitution pattern. Compounds with R 1 =H,
R 2 = OH, OCH 3 (e. g., naringin, poncirin) are an
order of magnitude more bitter than those with
R 1 = OH, R 2 = OH, OCH 3 (e. g., neohesperidin,
neoeriocitrin). Naringenin-7-neohesperidoside
(naringin) is the bitter constituent of grapefruit.
Hesperetin-7-neohesperidoside (neohesperidin)
(18.29)
The presence of a free OH-group in position R 1
or R 2 is necessary for a sweet taste. Table 18.25
shows that the dihydrochalcone of naringin
corresponds to saccharin in sweetness intensity,
whereas the dihydrochalcone of neohesperidin is
sweeter than saccharin by a factor of 20.
Conversion of naringin to highly sweet neohesperidin
dihydrochalcone (VII) is possible by al-