Food Chemistry

832 18 Fruits and Fruit Products

(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: erio-
dictyol) 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)

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

asPhomopsis citri, Cochliobolus miyabeanusor

Rhizoctonia solanii:

Naringin→Naringenin+Rhamnose

+Glucose

A number of neutral or bitter flavanone glyco-

sides can be converted through ring opening to

sweet chalcones (II) which, by additional hydro-

genation, can be stabilized as sweet dihydrochal-

cones (III):

(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 neohes-

peridin dihydrochalcone (VII) is possible by al-