Flavonoid concentration, juice

An alternate view is that juice flavonoid concentration decreases continually during maturation. Lime et ak (55) using the Davis Test found flavonoid concentration Tn TexasTuby Red grapefruit to decrease continually during the growing season. 

Flavonoids are present in other beverages besides wine and tea. For example, pomegranate and cranberry juice contain high concentrations of polyphenols and a strong antioxidant activity against LDL oxidation. Their antioxidant capacity depends not only on the amount but also on the type of flavonoids present (Aviram and Fuhrman 2003). 

RP-HPLC has been employed for the determination of flavonoids and other phenolic compounds in cranberry juice. The neutral and acidic analytes were preconcentrated octadecyl silica SPE cartridges conditioned with distilled water (neutral analytes) or with 0.01 M HC1 (acidic compounds). Hydrolysis of samples was carried out in aqueous methanol solution acidified with 6 M HC1 at 35°C for 16h. Chromatographic separation was performed in an ODS column (150 X 4.6mm i.d. particle size 5/.an). Solvents A and B were water-acetic acid (97 3, v/v) and methanol, respectively. The gradient started with 0 per cent B (flow rate, 0.9 ml/min), reached 10 per cent B in lQmin (flowrate, 1.0 ml/min) and increased to 70 per cent B in 40min (flowrate, 1.0 ml/min). Analytes were detected at 280 and 360 nm. Some typical chromatograms are presented in Fig. 2.71. The concentrations of flavonoids and phenolic acids are compiled in Table 2.69. It was stated that the SPE-HPLC procedure makes possible the simultaneous determination of phenolic compounds and flavonoids, therefore, it can be employed for the measurement of these classes of analytes in other fruit juices [188],... 

CONCENTRATIONS OF FLAVONOIDS AND PHENOLIC ACIDS IN CRANBERRY JUICE SAMPLES... 

Bronner, W.E. and Beecher, G.R., Extraction and measurement of prominent flavonoids in orange and grapefruit juice concentrates, J. Chromatogr. A, 705, 247, 1995. 

For fruits and their products, HPLC techniques for phenolics have been used to study the effect of processing, concentration, and storage on the phenolic composition of juices as well as a potential precursor for an off-flavor compound in juices. Phenolic analysis has been further applied to the detection of economic adulteration and especially to verify the authenticity of fruit juices. This is especially important when cheaper fruits can be added to more expensive ones in a fraudulent manner. In most fruits, the nonanthocyanin flavonoids consist mainly of flavonols and flavanols, with trace amounts of flavones. Glycosides are the predominant forms present. These most often are separated by reversed-phase HPLC on Cl8 columns with gradients consisting of acidified H20 and ACN, MeOH, or EtOH. 

Fractionate phenolic acids and flavonoids using Sephadex LH-20 column. For phenolic acids and flavonol glycosides, filter the fruit juice through 0.45-/nm (type HA) filter. For procyanidins apply juice onto the Sephadex LH-20 column, wash with 20% MeOH (30 ml), then elute with MeOH (15 ml), concentrate to dryness, redissolve in 2 ml H20, and filter through 0.45-/nm (type HA) filter. 

It has been established that the above phenomenon is caused by the presence of certain flavonoid compounds in fruit juice that influence blood circulation, increasing the permeability and elasticity of capillaries. This action is known as vitamin P activity, but the flavonoids showing this property are not classified as vitamins, because there are several substances with this activity and no serious deficiency diseases occur if they are not consumed. There are indications that these flavonoids have a useful protective action, in particular against some respiratory diseases, but they are readily decomposed in the body and it is impossible to maintain an effective concentration in the blood. 

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. 

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. 

Composition. Scientific data concerning liquids washed with water from orange juice finisher pulp was first published by Olsen et al. (30). They studied Brix/acid ratios, sucrose, reducing sugars, pH, pectic constituents, turbidity, pulp content, ascorbic acid, viscosity, and flavonoid content of experimental and commercial samples. Characterization of pulp-wash continued with publication of quality data (31), examination of pectic substances (32), microbiology (33), and comparison of pulp-wash with orange concentrate (34). 

Another important field of application concerns food and beverages, especially wine, juices, and tea (A2, A11, A17, B4, K12, V7, Yl). The antioxidant components of food include vitamin E (a-tocopherol), vitamin A (retinoids), vitamin C (ascorbic acid), and also fi-carotene (provitamin A), other carotenoids (of which more than 600 compounds have been identified), flavonoids, simple phenols, and glucobrasicins (H3). Unfortunately, the TAC value of a food is not informative on the bioavailability of its antioxidants. It has been estimated that polyphenols are normally present in blood plasma at concentrations of 0.2-2 //M (PI). However, it has been demonstrated that feeding rats a quercetin-augmented diet can increase their plasma levels of quercetin and its metabolites up to 10-100 //M (M27), and transient increases in the concentration of plant-derived phenolic compounds can take place after ingestion of food and beverages, which may affect blood plasma TAC (see later). 

The estimation of flavonoids by measuring the UV absorbance is one of the most common and convenient methods. The spectra of a number of flavonoids was reported by Mabry et al. (1970). The availability and measuring capabilities of flavonoids UV spectra greatly facilitated their identification in complex mixtures. The spectrophotometric determination of flavonoids facilitated the quantitative and qualitative analysis of samples. In general, UV absorption can be used to determine the concentration of flavonoids in samples, e.g. citrus juices. 

Flavonoids represent one class of bioactive compounds that may have multiple beneficial effects on several chronic diseases [3-4]. Cocoa represents an example of a potentially rich dietary source of flavonoids. High concentrations of flavonoids are present in certain cocoas, predominately as the flavanol monomers (-)-epicatechin (epicatechin) and (+)-catechin (catechin), and as oligomers of these monomeric base units which are known as the procyanidins (Figure 1) [5]. Other potential rich dietary sources of flavonoids include tea, wine, grape juice, apples, onions and certain nuts. 

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