Grapefruit flavanones

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. 

Lewinsohn E, Berman B, Mazur Y, Gressel J (1986) Glucosylation of exogenous flavanones by grapefruit Citrus paradisi) cell cultures. Phytochemistry 25 2531-2535... 

Tanner DC (2000) Structural elucidation of flavanone 7-O-glucosyltransferase in grapefruit (Citrusparadisi) seedlings. M.A. Thesis, East Tennessee State University... 

Erlund, L, Meririnne, E., Alfthan, G., and Aro, A., Plasma kinetics and urinary excretion of the flavanones naringenin and hesperetin in humans after ingestion of orange juice and grapefruit juice, J. Nutr., 131, 235, 2001. 

Fig. 12 HPLC separation of flavanone glycosides in grapefruit juice and orange juice.

A Ortuno, D Garcia-Puig, MD Fuster, ML Perez, F Sabater, I Porras, A Garcia-Lidon, JA Del Rio. Flavanone and nootkatone levels in different varieties of grapefruit and pummelo. J Agric Food Chem 43 1-5,1995. 

P Mouly, EM Gaydou, J Estienne. Column liquid chromatographic determination of flavanone glycosides in citrus. Application to grapefruit and sour orange juice adulterations. J Chromatog 634 129-134, 1993. 

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. 

Table III. Flavanone Glycosides in Texas Canned Grapefruit Juice...

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...

Figure 8. Effect of extractor pressure on total flavanone glycoside concentration for Florida grapefruit at different stages of maturity (35) ((9) hard squeeze (O)...

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). 

Flavanones are predominantly found in citrus fruits such as oranges, grapefruit, and lemons. They are usually present as mono- and diglycosides (Table 3.1). 

Flavanone glycosides hesperidin and naringin are responsible for the bitterness in oranges and grapefruit, respectively. 

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