Juice flavanone glycosides

Mouly, P.P. et ak, Differentiation of citrus juices by factorial discriminant analysis using liquid chromatography of flavanone glycosides, J. Agric. Food Chem., 42, 70, 1994. 

Marini, D. and Balestrieri, F., Multivariate analysis of flavanone glycosides in citrus juices, Ital. J. Food Sci., 1, 255, 1995. 

For the HPLC of flavanone glycosides in citrus, isocratic elution is often preferred because of the simplicity of the major flavanone glycosides occurring in citrus, and the flavanone glycosides are also present in citrus juice at fairly high levels. Furthermore, isocratic separations require no re-equilibration time between analyses and therefore are sometimes faster when only a few components are to be analyzed. 

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. 

The effective separation of all flavanone glycosides present from other components contained in citrus juice and fruit extracts within a reasonable period of time often requires gradient... 

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

Fig. 13 HPLC separation of flavanone glycosides and polymethoxylated flavones (PMFs) in orange juice spiked with didymin and PMFs.

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. 

AM Pupin, MJ Dennis, MCF Toledo. Flavanone glycoside in Brazilian orange juice. Food Chem 61 275-280, 1998. 

P Mouly, EM Gaydou, A Auffray. Simultaneous separation of flavanone glycosides and polymeth-oxylated flavones in citrus juices using liquid chromatography. J Chromatogr 800 171-179, 1998. 

PP Mouly, EM Gaydou, R Faure, JM Estienne. Blood orange juice authentication using cinnamic acid derivatives. Variety differentiations associated with flavanone glycoside content. J Agric Food... 

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). 

Hesperidin Solubility. Hesperidin, a tasteless flavanone glycoside, is the least soluble of all citrus flavonoids. It is found in practically every variety of citrus (5) and is the major flavonoid in sweet oranges and lemons. In fruit or leaves, hesperidin is found as a soluble complex which can be extracted with water or alcohol (5). During juice extraction, the complex is destroyed and hesperTdin slowly precipitates as fine, white, needle-shaped crystals. Once in the solid form, hesperidin can be redissolved in formamide, pyridine or in dilute alkali. 

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. 

Flavonoids have no odor or mouth feel and, in general, do not contribute significantly to the color of most citrus juices. Their primary effect on citrus quality is due to the bitter taste of certain flavanone glycosides. Thus, quantitative descriptions of desirable citrus qualities are usually based on the absence or maximum concentration limits for these compounds. 

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

Tatum et al. (29) used the presence of various methoxylated flavones from leaf extracts to distinguish between nucellar and zygotic seedlings. They also identified the predominant flavanone glycoside and three unidentified coumarins in their samples. Ting et al. (51) showed that there were quantitative as well as qualitative Hlfferences in the methoxylated flavone content from the juices of different citrus varieties. They further showed that certain blends of juices could be distinguished based on the amounts of methoxylated flavones found. 

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. 

Thus, the type of extractor, extractor pressure, juice pulp contact time as well as ultimate juice pulp content will all alter the amount of flavanone glycosides found in the juice. 

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