Flavanones naringin

Neohesperidin dihydrochalcone (NeoDHC) is a phenolic compound prepared from the bitter citrus flavanones naringin and neohesperidin (Horowitz Gentili, 1985). NeoDHC is a white solid with solubility in water of 0.5 g/1, which increases with temperature, but as use level is low, sufficient for most applications. 

When one examines the analytical methods which are presently available for these bitter compounds, it is clear why the study and control of bitterness in citrus has been so hampered and quality control virtually lacking. For the flavanone, naringin, only an approximate test is available (Davis Test) (see Chapter 5 for a discussion of this method) and for limonin there is no method available for monitoring in processing plants. 

The taste of fruits is influenced by phenolic compounds. The presence of tannins yields an astringent, harsh taste, similar to an unripe apple (or an apple variety suitable only for processing). Table quality apples are low in phenolic compounds. Flavanones (naringin, neohesperidin) are the bitter compounds of citrus fruits. 

Different extracts of Citrus were subjected to SPE on Cig cartridges to remove polar components. The retained flavonoids (mainly flavanones) were eluted with methanol-dimethyl sulfoxide, which enhanced solubility of hesperidin, diosmin, and diosmetin. Recoveries of eriocitrin, naringin, hesperidin, and tangeretin from spiked samples of mesocarp tissue exceeded 96%. Flavones were relatively abundant in the leaves. ... 

The flavanones have received less attention in comparison to flavonols and isoflavones, although their intake from the diet can be high and they exhibit promising biological activity. Little information is available about the absorption or the kinetic behavior of the flavanones naringenin, hesperetin and their glycosylated forms naringin, hesperidin, and narirutin. 

Dilute citrus juice (5 ml) with dimethylformamide (DMF, 10 ml) and 50 mM ammonium oxalate (10 ml), and then steam-bath for 10 min at 90°C. Cooling, adjust the volume to 50 ml with water, centrifuge (10 min at 2500 g), and then filter (Acrodisc, 5 and 0.45 /nm) the clarified juice. For standard preparation, prepare hesperidin (20 ppm) in DMF-water (2 1) solution and other flavanone glycosides (neohesperidin, eriocitrin, neoeriocitrin, naringin, and narirutin, 10 ppm) in the mobile phase. 

Another important interaction is that of limonin with the bitter flavanone glycoside naringin. Both of these bitter substances are present in grapefruit juice and Guadagni et al. (25) found that they interact at subthreshold levels in an additive way. Less than threshold amounts of limonin or naringin contribute to the bitterness of a mixture of the two compounds. The bitterness of the mixture can be predicted by adding the taste-unit contribution of each component (taste unit = concentration/ threshold). 

One of the earliest methods to measure the bitter naringin and other flavanones in grapefruit juice was developed by W. B. Davis in 1947 (12). This test is based on the reaction of dilute alkali with flavanones to form the corresponding yellow chalcones. The flavanone concentration is then determined by measuring the absorbance of the chalcones at 427 nm. Davis pointed out that the procedure was not specific for any flavanone but could be used to determine the principle flavanones in citrus juice, i.e., naringin in grapefruit juice and hesperidin in orange juice. 

He suggested that the method might also be suitable for the determination of flavones and flavonols. This method is still widely used to measure naringin in grapefruit juice albeit it is not specific for naringin, it is a simple, rapid and inexpensive method of analysis. However, since grapefruit contains both bitter and nonbitter flavanone glycosides, Davis values are only a crude approximation of bitterness. 

Hagen et a/L (42) determined the relative amounts of all the flavanone glycosides in Texas grapefruit. Their results are shown in Table III. Naringin is the dominant flavonoid in grapefruit and is primarily responsible for the immediate bitter taste in grapefruit. The equally bitter poncirin and the much less bitter neohesperidin are present in relatively small amounts and do not contribute significantly to overall bitterness. 

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 7. Maturity effects on naringin and other flavanone glycosides in juice sacs of Texas Ruby Red grapefruit (A) naringin by Davis value (B) total flavanone glycosides by TLC (C) naringin by TLC (25) and (D) naringin by...

Extraction and finisher pressures can greatly influence the flavonoid content of citrus juices. Generally, as the fruit is squeezed harder more juice is recovered. However, excessive extractor pressures produce juice of a lower quality (35). As shown in Figure 8, grapefruit flavanone glycoside concentrations increase with increasing extractor pressures. In the early portion of the season almost twice as much naringin was obtained under hard squeeze conditions than was obtained with the soft squeeze. The effect of finisher pressure is not as clear, and is dependent on the composition of the raw juice which, in turn, is dependent on the type of extractor used. 

Introduction. Naringin is a bitter flavanone glycoside found in grapefruit. It is not the only bitter compound in... 

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). 

Phenolics. The phenolics of citrus represent a varied and widely studied class of compounds. They range from the lipid-soluble methoxylated coumarins and psoralens to the water-soluble glycosides of the flavanones and flavones. They include the intensely bitter naringin and the highly insoluble hesperidin. Different classes within the group have characteristic UV spectra which have been used to detect adulterations in juices and oils. 

---