Juice acid determination

The content of ascorbic acid, in milligrams per 100 mL, in orange juice is determined by a redox titration using either 2,6-dichlorophenolindephenol or N-bromosuccinimide as the titrant. 

Bertotti, M. Vaz, J. M. Telles, R. Ascorbic Acid Determination in Natural Orange Juice, /. Chem. Educ. 1995, 72, 445M47. 

N Naulet, P Tesson, N Couler, GJ Martin. Optimization of analytical methods for origin assessment of orange juices. II. Determination of the amino acid composition. Analusis 25 42-47, 1997. 

Berry et al. (54) evaluated foam-mat dried instant orange juice and determined that its flavor was acceptable over 26 weeks when stored at 21.1°C. At 29.4°C flavor changes were observed after two to four weeks with samples in the pH range of 4 to 6. The flavor stability of the instant orange powder was directly related to pH when stored at 29.4°C. Stability was improved by using more acidic juices, addition of acid, or removal of sugar. 

The acid content in concentrated citrus juices is determined as the total titratable acid calculated as anhydrous citric... 

The United States Standards for citrus juices, except lemon or lime products, specify that the citric acid determination (factor for citric acid equals 0.06A) be calculated as grams per 100 grams juice, e.g. 

Figure 8.2 Pomegranate juice polyphenols and antioxidant potency in comparison to other fruit juices. Total polyphenol concentration in the different juices was determined using quercetin as a standard. LDL (100 pg of protein/milliliter) was preincubated with increasing volume concentration (0-25 pL) of the juices. Then, 5 pmol/L of CuS04 was added, and the LDL was further incubated for 2 hours at 37°C. The extent of LDL oxidation was measured by the thiobar-bituric acid reactive substance (TBAR) assay, and the ICh, values (the concentration needed to get 50% inhibition) are given. Results are given as mean S.D. of three different experiments.

Ascorbate electrodes for ascorbic acid determination in food (251), fruit juices (252) or pharmaceutical preparations (253) are based on the following reaction ... 

Ion-exclusion chromatography finds numerous applications for identification and determination of acidic species in complex matrix materials, such as dairy products, coffee, wine, beer, fruit juice, and other commercial products which can be quickly analyzed with minimal sample preparation before injection (usually only filtration, dilution, or centrifugation). Organic acid determination is also of great importance in biomedical research (e.g., physiological samples, in which most of the Krebs cycle acids (tricarboxylic acid cycle) are present). 

A gastric tube is inserted orally, or nasal intubation may be used if the patient has a hyperactive gag reflex. X-ray or fluoroscopic confirmation that the tip of the radio-opaque tube is in the lowest portion of the stomach is necessary. Ten or 15 minutes after the patient has become calm and adjusted to the presence of the tube, the patient is positioned with the trunlc upright and inclined sfightly to the left. Gastric juice is then aspirated and discarded. After checking that no further juice can be aspirated, note the time and collect and transfer to plastic bottles aU gastric juice that can be aspirated over the next 60 minutes. The patient must be asked to expectorate aH saliva during the collection period. The total volume of the collected juice is recorded and free acid determined by titration as described below. 

Quantitation of citric, malic, and tartaric acids that are typically present in fruit juices has been carried out routinely by liquid chromatography, by using either refractive index or low wavelength UV detection. However, HPLC methods are very sensitive to matrix interferences and may often exclude the reliable detection or accurate quantitation of acids at levels below 50 ppm. Although HPLC methodology is known for its shortcomings, GC determination of fruit juice acids has not been widely employed because of the difficulty in isolation and derivatization of the acids (Barden et al., 1997). 

Phenolic and furfural compounds in apple juice were determined by HPLC using a combination of ELD and DA-UVD. LOD for ELD were 4 to 500 times greater than those for spectrophotometric detection. The content of phenolics varied from 30 to 115 mgL, including major phenolic components such as chlorogenic acid (95), p-coumaroylquinic acid (98) and phloridzin (96) and minor ones such as caffeic acid (25), p-coumaric acid (26), ferulic acid (69), gallic acid (8), protocatechuic acid (27) and catechin (3) . The same methods were also applied for the analysis of maple products. The phenolic content was dependent on the source of the product. Application of reverse osmosis to maple sap caused a relative decrease of aldehydes and alcohols and an increase of phenolic acids. 

A.P.S. Paim, B.F. Reis, An automatic spectrophotometric titration procedure for ascorbic acid determination in fruit juices and soft drinks based on volumetric fraction variation, Anal. Sci. 16 (2000) 487. 

Ascorbic acid was determined by titration with 2,6-dichloro-phenol-indophenol (18). The color of the juice was determined directly with a Gardner Tristimulus Colorimeter, model KL 10. The instrument was calibrated against a white plate, L=91.6, a=1.8, b=+l.8. 

A simple procedure for the rapid determination of the total acidity in wines and fruit juices was patented by Holzbach (1936). He prepared alkaline pieces of filter paper corresponding to 0.05% to 0.01 % acid, which he added to the solution. Bromocresol was used as an indicator, and from the number of pieces of alkaline paper added the acidity was calculated. A simple blue patented German indicator, useful for aU except the medium-to-dark red wines, was employed by Larsen (1961). Indicators, such as acridine and umbeUiferone, which are fluorescent in ultraviolet light for the end point in the acidity determination, were proposed by Volmar and davera (1931). One advantage of these was that they can be used in red wines. 

Figure 1-4. Electrometric titration of samples of gastric juice obtained from human subjects after stimulation of secretion by a histamine analog. Intersections of the curves with the dashed line on the left represent that would be obtained by titration to the Topfer indicator endpoint (pH 3.5), and the intersections with the dashed line on the right represent titratable acidity determined by titration to the phenol-phthalein endpoint (pH 9.4). (From Moore EW, Scarlata RW. The determination of gastric acidity by the glass electrode. Castroentero/ogy 49 178-188, 1965.)...

Ascorbic acid (vitamin C) appears naturally in most fresh fruits and fruit juices but is often added during the manufacture of juices or soft drinks as a preservative or antioxidant. A simple, fast, and direct SIA method for ascorbic acid determination in juices was... 

Schaffar, B. P. H., B. A. A. Dremel, and R. D. Schmid. 1989. Ascorbic acid determination in fruit juices based on a fiber optic ascorbic acid biosensor and flow injection analysis. In Biosensors Applications in Medicine, Environmental Protection and Process Control, eds. R. D. Schmid, and F. Scheller, pp. 229-232. New York VCH Publishers. 

Two techniques for sorption-spectroscopic determination of ascorbic acid have been proposed. The first one is the recovery by silica modified with tetradecyl ammonium nitrate of blue form of molibdophosphoric HPA in the presence of vitamin C. And the second one is the interaction between the ascorbic acid in solution and immobilized on silica ion associate of molibdophosphoric acid with lucigenine. The detection limits of vitamin C are 0.07 and 2.6 mg respectively. The techniques were successfully applied to the determination of ascorbic acid in fmit juices. 

The method described above is applicable to a wide range of samples for the determination of amino acids in different matrices. For example, the amino acid composition and distribution of single enantiomers has been determined in protein hydrolysates, orange juice (Fig. 7-11), yogurt and seawater [23]. 

Apples (Red Belle de Boskoop, Jonagold or Mutzu) were cut and milled (1.5 mm) and 5% (w/w) of a 2% ascorbic acid solution was added immediately. Enzyme preparations (25 mg enzyme protein / kg mash) were added and the mash was incubated for 2 hours at 20°C whereafter it was pressed. The resulting apple juice was pasteurised at 85°C to discontinue further enzyme degradation. The cloud was measured as turbidity in EF/F units [15]. The cloud stability was determined by a centrifugation test as the amount of turbidity remaining after centrifugation at 4,200 x g for 15 minutes [15]. 

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