Acids in fruit juices

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. 

JP Chaytor. The analysis of amino acids in fruit juices by high-performance liquid chromatography. J Sci Food Agric 37 1019-1026, 1986. 

A validated method (No. 63) for the analysis of benzoic acid, sorbic and para-hydroxybenzoic acids in fruit juices has been published in the IFU handbook (Anon, 1995e). In this method the resolution takes place on a C8 reverse-phase column. With this solvent system (methanolic/ammonium acetate, pH 4.55) sorbic and benzoic acids elute quite quickly and the less polar para-hydroxybenzoate esters elute much later. The method does stipulate that caution has to be taken by orange juice due to possible interferences by natural materials in the juice that elute close to benzoic acid. As sorbic and benzoic acids elute quite early in the chromatogram using this method, it would... 

Determination of sugars and organic acids in fruit juices... 

A method of determining airborne iodine has also been reported.241 Here, iodine is absorbed into 5% aqueous KI and spectrophotometrically determined at 590 nm in the form of its complex with starch. This method is selective with respect to bromine and chlorine, and the sensitivity of this method is 0.25 mg of I2 per m3 of air. The concentration of the, 31I isotope in water can be determined by a method involving isotope exchange in the starch-iodine complex.242 Flow-injection determination of ascorbic acid (0.1-40 mg/mL) has been proposed.243 Iodine is generated in the flow system as I3- ions, which are in turn exposed to starch to produce a steady signal at 350 and 580 nm. Ascorbic acid provides inversed maxima which are measured. This method is recommended for analysis of ascorbic acid in fruit juice, jam, and vitamin-C preparations. Use of the blue complex has also been reported for determination of sodium dichloro-isocyanurate in air.244 Obviously the blue reaction is applicable in the determination of amylose, amylopectin, and starch,245-252 as well as modified starches.245,253-255... 

Amakura, Y. Okada, M. Tsuji, S. Tonogai, Y. 2000. Determination of phenolic acids in fruit juices by isocratic column liquid chromatography. J. Chromatogr. A. 891 183-188. 

Marsili, N.R., Sobrero, M.S., and Goicoechea, H.C. 2003. Spectrophotometric determination of sorbic and benzoic acids in fruit juices by a net analyte signal-based method with selection of the wavelength range to avoid non-modelled interferences. Analytical and Bioanalytical Chemistry 376 126-133. 

The presence of fumaric acid in fruit juices can be the result of added synthetic malic acid and it is then considered as an index of adulteration. This is confirmed by analysis of D-malic acid, which is not normally present in malic acid from natural sources. Guidelines of the Association of the Industry of Juices and Nectars from Fruits and Vegetables of the European Economic Community (AIJN) considers 5 mg/kg as the limiting concentration for fumaric acid content in apple juices (Trifiro, Saccani, and Gherardi, 1997). 

Khrolenko, M. V., Wieczorek, P. P. (2005). Determination of glyphosate and its metabohte aminomethylphosphonic acid in fruit juices using supported-liquid... 

In order to familiarise the reader with the type of sample preparation required and the type of information provided by high performance liquid chromatography, an example depicting the analysis of organic acids in fruit juices follows. 

The standard addition method can be efficiently implemented in a flow system with multi-site detection, as demonstrated by the amperometric determination of ascorbic acid in fruit juices [87], Only one sample aliquot was inserted, and the sample zone was monitored under two different conditions, before and after the standard addition by confluence. Measurements related to the first and second detection sites were normalised and the matrix effect was efficiently circumvented. About 55 samples were rim per hour, yielding precise results in agreement with a reference procedure. 

J. Jakmunee, L. Pathimapomlert, S.K. Hartwell, K. Grudpan, Novel approach for mono-segmented flow micro-titration with sequential injection using a lab-on-valve system a model study for the assay of acidity in fruit juices, Analyst 130 (2005) 299. 

Nafcillin should be given with water only, as acid in fruit juices or carbonated water may inactivate it. Furthermore, it should be given on an empty stomach because food decreases its absorption. Clinical signs of overdose include neuromuscular irritability or seizures (see Table 23). 

It is the acid content of fruit that most aids their preservation by heat. Generally speaking the greater the acid content the less the exposure to heat required to sterilize. Biglow and Dunbar designate the kind of acid in fruit juices as follows ... 

Orange juice and the acids in fruit juices may decrease the effect of certain antibiotics such as penicillin and erythromycin. For this reason, pharmacists recommend drinking water instead. 

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-... 

Deacidification of drinks Chitosan salts that carry a strong positive charge have been shown to be effective as dehazing agents. They may be nsed to control acidity in fruit juices or coffee drinks. 

Sometimes the proposed method is an indirect procedure to monitor the excess of oxidant or the color change of an auxiliary reagent such as the method described for the assay of azathioprine, either in pure form or in pharmaceutical formulations the methods are based on the oxidation of the drug with excess N-bromosuccinimide or chloramine-T and determining the consumed reagent by the decrease in color intensity of celestine blue or gall-ocyanine, respectively. Another example is the determination of ascorbic acid in fruit juice and pharmaceuticals on the basis of its inhibition effect on the reaction between hydrochloric acid and bro-mate. The decolorization of methyl orange due to the reaction products was used to monitor the reaction at 510 nm. 

Ingram, M. 1947a. An electrometric indicator to replace starch in iodine titrations of sulphurous acid in fruit juices. J. Soc. Chem. Ind. 66, 50. 

In addition to anion-exchange and ion-exclusion chromatography, organic acids in fruit juices can also be separated by reversed-phase chromatography in the ion-suppression mode. A suitable stationary phase for this type of application is Acclaim OA, a polar-embedded stationary phase optimized for hydrophilic organic acid separations. This column is compatible with 100% aqueous mobile phases and has excellent hydrolytic stability at low pH values. Retention,... 

Otsuka et al. (1986) used TLC to isolate and partially characterize degradation products of 2,3-diketo-L-gulonic acid (intermediates in the biosynthesis of ascorbic acid) the products were characterized by different spectrometric methods. Mandrou et al. (1988) devised a TLC procedure to determine ascorbic and dehydroascorbic acids in fruit juices and wine the sample was reacted with 2,4-dinitrophenylhydrazine to form the osazones the osazones were spotted on the TLC plate and quantified by. in situ densitometry at 494 nm. 

Calibrations for degrees Brix and acidity in fruit juices have been performed utilizing transflectance and a 45°C liquid cell [9]. The calibration parameters are presented in Table 22.2 to Table 22.4 with the wavelengths utilized for each calibration. 

L-Malic and citric acids are the major organic acids of fruits (Table 18.13). Malic acid is predominant in pomme and stone fruits, while citric acid is most abundant in berries, citrus and tropical fruits. (2R 3R)-Tartaric acid occurs only in grapes. Many other acids, including the acids in the citric acid cycle, occur only in low amounts. Examples are cis-aconitic, succinic, pyruvic, citramalic, fumaric, glyceric, glycolic, glyoxylic, isocitric, lactic, oxalacetic, oxalic and 2-oxoglutaric acids. In fruit juices, the ratio of citric acid to isocitric acid (examples in Table 18.14) serves as an indicator of dilution with an aqueous solution of citric acid. 

An attractive appearing reversed-phase h.p.l.c. method, in which ionization of sugar acids is prevented by use of acidic eluant fe.a.. pH 2), has been used for analysis with fluorometric detection of estriol 3- and 16-glucuronides in urine of nonpregnant women after initial concentration onto graphitized carbon black cartridges," and of L-ascorbic acid in fruit juice. 

Herraiz T. Occurrence of l,2,3,4-tetrahydro-P-carboline-3-carboxylic acid and 1 -methyl-1,2,3,4-tetrahydro-P-carboline-3-carboxylic acid in fruit juices, purees, and jams. Journal of Agricultural and Food Chemistry, 46 3484-3490 (1998). 

A new concept for microtitration using a LOV system with sequential injection of monosegmented flow has been proposed (Jakmunee et al., 2005). The performance of the system was demonstrated by the assay of acidity in fruit juices based on acid-base neutralization. Standard/sample solutions containing citric acid, indicator, and sodium hydroxide were sandwiched between air segments and then aspirated upon flow reversal and removal of the air segments, the change in the absorbance of the indicator color was monitored. 

Jackmunee, J., T. Rujiralai, and K. Grudpan. 2006. Sequential injection titration with spec-trophotometric detection for the assay of acidity in fruit juices. Anal. Sci. 22 157-160. 

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