2009_Book_FoodChemistry

438 8 Food Additives
Table 8.5. Amino acid sequence of thaumatin I. (Disulfide bonds: 9–204, 55–66, 71–77, 121–193, 126–177, 134–
145, 149–158, 159–164; the sequence YFD shown in bold type, which is localized in a β-turn, is regarded as
a part of the structure responsible for the cross reaction of thaumatin with antibodies against monellin as well as
for making contact with the sweetness receptor (cf. Table 8.4 and Fig. 8.7 and 8.8)
5 10 15 20 25 30 35 40
ATF EI VNRCS Y T VWA AAS KG DAALD AGGRQ LN S GE SWT I N
41VEP GTNGGKI WART D CYFDD S GS GI CKTGD CG GLL RC KRF
81GRP P TTLAEF S L NQ Y GKDYI DI S NI KGF NV P MNF S PT T RG
121CRGVRCAADI V GQC P AKLKA P GGGC NDACT VF QTS EY CCT
161 T G K C G P T E Y S R F F K R L C P D A F S Y V L D K P T T V T C P G S S N Y R
201 V T F C P T A
8.8.6 Curculin and Miraculin
Curculin is a sweet protein ( f sac, g (6.8) =550)
of known sequence (Table 8.6). It occurs in the
fruit of Curculigo latifolia. The sweet taste induced
by this protein disappears after a few minutes,
only to reappear with the same intensity
on rinsing with water. It is assumed that Ca 2⊕
and/or Mg 2⊕ ions in the saliva suppress the sweet
taste. Rinsing with citric acid (0.02 mol/l) considerably
enhances the impression of sweetness
( f sac, g (12)=970). Thus, like miraculin, curculin
acts as a taste modifier.
Miraculin is a glycoprotein present in the fruit
of Synsepalum dulcificum (a tropical fruit known
as miracle berry). Although it is tasteless, it has
the property of giving sour solutions a sweet taste
and therefore it is called a taste modifier. Thus,
lemon juice seems sweet when the mouth is first
rinsed with a solution of miraculin. The molecular
weight of this taste modifier is 42–44 kdal.
ception of other taste qualities. The active substance
has not yet been identified.
8.8.8 Stevioside
Leaves of Stevia rebaudiana contain approx. 6%
stevioside ( f sac, g (4) ∼ 300). Its structure is shown
in Formula 8.7. This compound is of interest as
a sweetener, however its toxic properties are unclear.
8.8.7 Gymnema silvestre Extract
The extract from Gymnema silvestre is related to
the taste modifier miraculin. It has the property
of eliminating the ability to perceive sweetness
for a few hours, without interfering with the per-
(8.7)
Table 8.6. Amino acid sequence of curculin
5 10 15 20 25 30 35 40
D NVL LS GQTL HADHS LQAGA YT LTI QNNCN L VKYQ NGRQI
41WAS NTDRRGS GCRLT LLS DG NL VI Y DHNNN DVNGS ACCGD
81A GKYALVLQK DGRF V I YGP V L WS LG P NGCR RVNG