Fruit juices ascorbic acid

Ascorbic acid, dehydroascorbic acid, dlketogluconic acid, and glucose have been determined down to nanogram levels by h.p.l.c. on a hydrophilic, polyvinylalcohol gel, post-column derivatization with benzamldine, and fluorlmetric detection. The method was applied to ascorbic acid in fruit Juice.Ascorbic acid, its 2-sulphate, 2-phosphate, 2-0-methyl, and 6-bromo-6-deoxy derivatives, and a related non-enzymic browning product, 5-methyl-3,4-dihydroxy-... 

In pharmaceutical preparations and fruit juices, ascorbic acid is readily separated from other compounds by TLC on silica gel and quantified directly by absorption at 254 nm. Serum and plasma may be deproteinized with twice its volume of methanol or ethanol. Various ascorbic acid compounds in plant extracts and foods have been separated on cellulose layers and detected by spraying with 2,S dichlorophenol indophenol (36). Heulandite, a natural zeolite (particle size 45 p) has successfully been employed as an adsorbent and ascorbic acid and other hydrophilic vitamins have separated within 5 cm by ascending chromatography in dimethylformamide (37). HPTLC and OPLC methods have been developed to improve the separation of ascorbic acid from other water soluble vitamins, with mixed success (11). 

The important commercial feature of these juices, especially significant with blackcurrant and tomato juices, is their ascorbic acid (or vitamin C) content, of which loss by oxidation is known to be accelerated both by heat and by metal (particularly copper) contamination. The effect of copper has been carefully investigated for pure ascorbic acid", and more recently ascorbic acid in blackcurrant juice and model systems. There are, however, oxidation inhibitors of different kinds (which may themselves be heat-sensitive) present in various fruits, which give differing results. The presence of metals will also affect flavours", may cause discoloration, and may give rise to clouding effects, as in apple juice. ... 

The juice of many fruits and particularly those of the citrus family contain appreciable quantities of ascorbic acid (vitamin C). It is not possible to examine... 

Golden delicious apples Malus domestica) and tomatoes Solarium lycopersicum) were purchased at the local market. Fruits were peeled and sliced before treatment (4 h at 45 °C) with 0.1 % Pectinex Ultra Sp-L (Novo Ferment) in presence of 9 mM ascorbic acid. The insoluble material was then eliminated by centrifugation and the obtained juices dialysed against distilled water. 

Miller NJ and Rice-Evans CA. 1997. The relative contributions of ascorbic acid and phenolic antioxidants to tiie total antioxidant activity of orange and apple fruit juices and blackcurrant drinks. Food Chem... 

Ascorbic acid is probably the most labile bioactive compound in fruit juices and fruit and vegetable pieces, as we described in the first part of this chapter. Retention of this phytochemical after the nonthermal treatments ranged from 47% to 100%, depending on the intensity of the applied treatment and the product. For example, the greatest losses of vitamin C were found in fresh-cut red lettuce and melon treated with IR and HHP (Fan and others 2008 Wolbang and others 2008), respectively. However, the use of gamma radiation in various vegetables retained 100% of their total ascorbic acid content (Fan and others 2008). 

It may be concluded that PEF, HHP, and IR are adequate techniques for the retention of bioactive compounds in fruit and vegetable products and may even enhance bioactivity of juices, purees, and fresh-cut produce. A greater degradation of ascorbic acid in comparison with phenolics and carotenoids is usually observed. 

There is increasing interest in the use of specific sensor or biosensor detection systems with the FIA technique (Galensa, 1998). Tsafack et al. (2000) described an electrochemiluminescence-based fibre optic biosensor for choline with flow-injection analysis and Su et al. (1998) reported a flow-injection determination of sulphite in wines and fruit juices using a bulk acoustic wave impedance sensor coupled to a membrane separation technique. Prodromidis et al. (1997) also coupled a biosensor with an FIA system for analysis of citric acid in juices, fruits and sports beverages and Okawa et al. (1998) reported a procedure for the simultaneous determination of ascorbic acid and glucose in soft drinks with an electrochemical filter/biosensor FIA system. 

Figure 3.31 Analytical isotachophoresis. Ascorbic acid (vitamin C) is naturally present in many foods and is often added to others. Occasionally the cheaper isomer, is oascorbic acid, which has no vitamin action, is used and is distinguishable from the natural isomer by many analytical methods, (a) shows the analysis of a sample of commercial fruit juice while (b) shows the same fruit juice to which a known amount (4 nmol) of isoascorbic acid has been added. (Reproduced by permission of LKB, Stockholm, Sweden.)...

Schmid et al. used the same principle to develop sensors to be incorporated into FI systems for the determination of ascorbic acid in fruit juices [38] and that of lactic acid in dairy products [39]. The membrane used in both applications consisted of decacyclene dissolved in silicone rubber that was treated similarly as the membrane in glucose sensors (Fig. 3.4.B). The oxygen optrode was coated with a sheet of carbon black as optical insulation in order to protect it from ambient light or intrinsic sample fluorescence. Ascorbic acid oxidase or lactic acid oxidase was immobilized by adsorbing it onto carbon black and cross-linking it with glutaraldehyde. The FI system automatically buffered and diluted the food samples, thereby protecting the biosensor from a low pH and interferents. 

Removal of trace levels of oxygen. Traces of oxygen in wines and fruit juices cause discolouration and/or oxidation of ascorbic acid. Chemical... 

Ascorbic acid level in grapes is relatively low compared with other fruits. Zubeckis (5) in Canada reported that ascorbic acid in fresh grapes varied from 1.1 to 11.7 mg/100 ml juice, except for the variety Veeport. This Canadian variety contained a high content of ascorbic acid (33.8 mg/100 ml juice). More recently, Oumac (188) determined the ascorbic acid content of seven grape juices and found a range from 2.0 to 6.0 mg/100 ml. 

BL Ling, WRG Baeyens, P Van Acker, C Dewaele. Determination of ascorbic acid and isoascorbic acid by capillary zone electrophoresis application to fruit juices and to a pharmaceutical formulation. J Pharm Biomed Anal 10 717-721, 1992. 

Nutrients frequently consumed in sub-optimal concentrations by humans are proteins, calcium, non, vitamin A, thiamin (vitamin Bl), riboflavin (vitamin B2) and ascorbic acid (vitamin C). Some of these nutrients occur in higher concentrations in fruit juices than hi other foods. There is experimental evidence that indicates that ascorbic acid of natural origin is apparently superior to that of synthetic origin. 

Several components with antioxidant activity are found in fruit juices. These include ascorbic acid, tocopherols (vitamin E), beta-carotene and flavonoids. Beta-carotene has antioxidant activity that can quench the singlet oxygen that can induce precancerous cellular changes. 

Ascorbic acid. Many juices contain ascorbic acid or vitamin C, which is quantitatively the most important vitamin in soft fruits, ranging from a negligible level in some whortleberries to around 200 mg/100 g in blackcurrants. Ascorbic acid performs a valuable function as an antioxidant in minimising degradation of certain flavour principles, and it is often important for it to be included in the processed juice or in a soft drink formulation. Levels in the range 200-400 mg/kg are typical. It should be noted that ascorbic acid can be added to natural strength juice only if it is... 

Ingredients Carbonated water. Concentrated fruit juices (pineapple, grapefruit) (5% when reconstituted). Citric acid. Acidity regulator (sodium citrate). Artificial sweeteners (aspartame, saccharin). Flavourings. Preservative (sodium benzoate). Antioxidants (ascorbic acid, ascorbyl palmitate). Colour (lutein)... 

As with all methods, this approach has some limitations it uses acetonitrile, which is toxic, and the separation of glucose from fructose can sometimes be problematic after extended use of the column. However, sample preparation is easy since it requires only dilution to the required level (often 1 10) and filtration prior to analysis to remove particulate materials, which protects and extends the useful life of the column. The degradation of the resolution between glucose and fructose is caused by the partial inactivation of the column by materials in the matrix, but this resolution can be recovered by reducing the acetonitrile concentration in the solvent. The same column can also be used to assay the level of ascorbic acid (vitamin C) in a soft drink or fruit juice, although different detection and solvent systems are used. 

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