Lemon juice phenolics

In Fig. 6 a characteristic HPLC chromatogram of lemon juice phenolics is shown. The main phenolics in lemon juice are flavanones and C-glucosylflavones. The small peaks at the beginning of the chromatogram correspond to hydroxycinnamic acid derivatives, which are minor constituents in lemon juice. 

Fig. (6). HPLC chromatogram of lemon juice phenolics (1) eriocitrin, (2) diosmetin 6,8-di-C-glucoside, (3) hesperidin, and (4) diosmetin 6-C-glucoside. HPLC conditions RP C g column (12 X 0.4 cm particle size 5 (im). Mobile phase acidified water (5% formic acid) (A) and methanol (B). Gradient 0 min- 10% B, 30 min- 40% B, 40 min- 80% B. Flow rate 1 mL/min.

Paper chromatography was used to estimate individual phenolics in lemon juice by Vandercook and Stephenson (119). After enzymatic hydrolysis of the juice, they found for eriodictyol, hesperitin, quercetin, phloroglucinol and umbel iferone average values of 20, 1.4, 2.2, 2.0 and 0.2 mg aglycone/100 ml, respectively. 

Vandercook and Rolle (11) investigated the ultraviolet absorption characteristics of alcoholic solutions of California-Arizona lemon juice. They reported that the ratio of the absorbance of 273-277 nm to the absorbance of 326-332 nm was essentially constant. From analyses of the spectra obtained of other fruit juices, they indicated if one were added to lemon juice its presence could be detected by a displacement of this ratio. Vandercook et aK (12) observed a significant increase in total poly-phenolic absorbance at 330 nm, of lemon juice, with extraction pressure. However, there was no significant change in the A/B absorbance ratio (273/326). 

A general method for the evaluation of phenolic compounds in fermented beverages, fruit juices and plant extracts was developed using gradient HPLC and coulometric detection. In a 10 p,L injection it was possible to identify and determine 36 different flavonoids and simple and complex phenols, without sample extraction, purification or concentration, in several kinds of beers, red and white wines, lemon juice and soya, forsythia and tobacco extracts. This may also be useful for the characterization of beverages and extracts . 

Another way to protect ascorbic acid from oxidation consists of the chelating mechanism. As has been discussed above, flavonoids with ortho-phenol structure have the ability to chelate bivalent metals, which may undergo the oxidation of ascorbic acid, and this mechanism of protection for anthocyanins is being proposed by Sarma et al [167], These former reports might explain what was proposed by Rusznyak and Szent-Gyorgyi more than six decades ago when they observed that the administration of lemon juice decreased the fragility and permeability of the capillary wall, where ascorbic acid alone had no protective effect, and led them to propose flavonoids as vitamin P. 

The antioxidant activity of different food products has been linked to their preventive role in cardiovascular disease [68 86 98 99]. Many of them are fruit and vegetables, although cereals, herbs and spices also show important antioxidant activity. Processed fruit products also provide important antioxidant protection as has been described for orange and lemon juice, [100], grape juice [91], grape pomace [101] and red wines [102-107]. Very pronounced in vitro antioxidant activity has been demonstrated in tea [99 108] and olives [27]. Many herbs and spices containing antioxidant constituents can be useful to prevent rancidity of meat and fish products [109-112]. Fibre also has antioxidant activity, mainly due to the presence of phenolic metabolites linked to the polysaccharides [87]. Thus, the antioxidant activity of barley leaves [93], pineapple peel fibre [113] and rice-hull [114] have been described. 

Flavonoids and simple and complex phenols Beer, red and white wines, lemon juice, and soya, forsythia and tobacco extracts RP-HPLC Coulometric-array [120J... 

The other phenolic compounds (mg 100 ml ) with high maximum values in nonalcoholic beverages were phlorin (3.0-10.8) and bergapten (0-1.9) in grapefruit pure juice, phlorin (9.1) in pummelo pure juice, anethole (0-6.7) and p-anisaldehyde (0-1.5) in fermel tea, phlorin (4.3) in lemon pure juice, phlorin (1.1-3.7) in blond orange pure juice, and 02 mers (2.2) in chocolate milk beverage. 

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