Transcript Brief Introduction to Citrus Limonoids

Brief Introduction to Citrus
Limonoids
Jiaxing Li
TAMU-College Station
TAMUK-Citrus Center
Bitterness problem in citrus industry
• Cause 1. The
flavonoids e.g.
naringin-- species
related to pumello
• Cause 2. The
limonoids e.g.
limonin
Biochemistry of Limonoids in
Citrus
• A group of highly oxygenated tetracyclic
triterpenoids -- Citrus & related genera
• Tow forms in citrus:
1. Limonoid aglycones (LA) -- >50 isolated
from the Rutaceae (36 from Citrus&related
genera)
2. Limonoid glucosides (LG) -- 17 isolated
Biochemistry Cont.
• Relation between LA and LG
1. LA: bitter, insoluble in water
2. LG: non-bitter, water-soluble
3. LA glucosidated to LG--fruit maturation
--- Natural Debittering process
--- Occurs only in fruit tissues and seeds
Delayed bitterness
• PH<6.5
• Limonoid D-ring
lactone hydrolase
• Closed D-ring is
the key structure
An example of natural debittering
and delayed bitterness
• Navel oranges and Valencia oranges in
California
• Early to mid-season Navel juice has delayed
bitterness, Valencia dose not
• Reason: Short maturation period of the
Navel (2 months); 6 months for the Valencia
allow:
LA
LG
Structures of some of the major Limonoids in citrus
Structures Cont.
Biosynthesis of Citrus Limonoids
• Four groups of LA
1. Limonin group
2. Calamin group
3. Ichangensin group
4. 7α-acetate limonoid
• Biosynthetic pathways of each group of
these limonoids have been elucidated
Example of Biosynthetic pathways: limonin group
Analytical Methods of Citrus
Limonoids
• Thin-layer chromatography (TLC)
-- for limonoid detection
• Nuclear Magnetic Resonance (NMR)
-- determination of limonoid structure
• HPLC -- detection & quantification
• Radioimmunoassay --detection&quantif.
• HPLC-MS -- detection& quantification
Distribution of limonin in Citrus fruit and
vegetative tissues -- by Radioimmunoassay
• Limonin levels in
fruit and vegetative
tissue (White Marsh)
High: Seeds
Pith
Lamella
Albedo
Flavedo
Low: Juice vesicles
Limonin distribution within grapefruit leaves
• More concentrated
in areas adjacent to
the conductive
tissues
• flushing leaves >
mature leaves
Biological activities of citrus
limonoids
• Inducers of GST, a detoxifying enzyme in
mice and rats:
-- to inhibit formation of chemicallyinduced neoplasia in forestomach, small
intestine, colon, lung, skin and oral of lab
animals;
-- to inhibit the proliferation of breast cancer
cells in culture
Biological activities contd.
•
•
•
•
Antifeedant activity
insect repellents
growth disrupters
reproduction inhibitors
Limonoids and the Taxonomic Studies
of Citrus
• Theoretical bases
1. Plants have incorporated many secondary
metabolites into specialized physiological
functions such as reproduction and
intracelluar signaling
2. secondary metabolites are often
functionally unique at the species level.
3. Different compounds are responsible for
identical functions in different species.
Different Limonoid groups and the
Chemotaxonomy of the true-citrus tree
species and hybrids
Future research
• Nutritional research: determination of the
roles phytochemicals play in the long term
health of humans.
-- Food additives for cancer prevention
The End
• Thank You
• References
Mark A. Berhow, Shin Hasegwa, and Gary
D. Manners.Citrus Limonoids -- Functional
Chemicals in Agriculture and Food/ 2000,
American Chemical Society.