Neohesperidosides, flavanone

Naringin (= 2,3-Dihydroapigenin 7-0-rhamnosyl-glucoside 2,3-Dihydro-5,7,4 -Trihydroxyflavone 7-0-neohesperidoside) (flavanone O-glycoside) Propyl gallate (phenolic) Quercetin (= 3,5,7,3, 4 -Pentahydroxyflavone) (flavonol)... 

Among aglycones, the best known are naringenin and hesperidin. Their glycosylated forms occur commonly as O- or C-glycosides, usually as rutinosides (6-O-a-L-rhamnosyl-D-glucosides) and neohesperidosides (2-O-a-L-rhamnosyl-D-glucosides) attached at position 7. Flavanones contribute to the flavour of citrus [19]. Table 12 reports the structures of some common flavanones. 

Figure 4. Minor structural changes to the aglycone portion of the molecule can destroy bitterness. Adding a single double bond between Carbons 2 and 3 will convert bitter flavanone neohesperidosides to tasteless flavone neohesperidosides.

Chalcones and Pihydrochalcones. Chalcones and dihydro-chalcones are Intensely sweet compounds (39) that are effective in raising the threshold at which the bitterness of naringin and limonin is perceived (46). As illustrated in Figure 5, chalcones are easily formed fromTlavanone glycosides by the addition of alkali and dihydrochalcones are formed from hydrogenated chalcones. Like the flavanone neohesperidosides, the chalcones and dihydrochalcones vary in the intensity of their taste response. 

Figure 5. Conversion of bitter flavanone neohesperidosides to the corresponding intensely sweet chalcones and dihydrochalcones...

Both directly and indirectly, flavonoid composition affects the quality of individual citrus cultivars and hybrids. Some cultivars, such as the sour orange, are directly affected by the presence of bitter neohesperidosides to the point they are unpalatable. The quality of other cultivars may be indirectly affected due to the presence of bitterness suppressing flavone neohesperidosides. Certain hybrids, such as the K early, also contain bitter flavanone glycosides at levels which reduce its acceptability. Therefore, the knowledge of the relative type and... 

As previously discussed by Maier and co-workers (Chapter 4), in Navel, Shamouti and certain other orange cultivars, the presence of limonin, a bitter triterpenoid, causes many economic and organoleptic problems and greatly affects the taste quality of processed fruit. Limonin is also prevalent in the grapefruit but the intrinsic quality of this fruit is further complicated by the presence of naringin, a bitter flavanone neohesperidoside (Chapter 5). 

Because the flavonoid glycosides are non-volatile, GC has not routinely been used for flavonoid analysis. However, Greaser et al. (1992) have developed a method to analyze the hydrolyzed flavanone content by GC-MS. The method involves solvent extraction of the tissues, hydroylsis of the flavonoids to their respective aglycones, trimethylsilation, and analysis by GC-MS. While the method will accurately identify and quantify the flavonoid aglycones present in the sample, it cannot determine the relative amounts of the neohesperidosides and rutinosides, and would therefore only be able to give an estimation of the amount of bitter flavonoids in a sample. 

Matsumoto R, Okudai N (1991a) Early evaluation of citrus bitter component, flavanone neohesperidosides by enzyme immunoassay using anti-naringin antibody. J Jpn Soc Hortic Sci 60 191-200... 

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