Lactic acid, derivative detection

The fermentation-derived food-grade product is sold in 50, 80, and 88% concentrations the other grades are available in 50 and 88% concentrations. The food-grade product meets the Vood Chemicals Codex III and the pharmaceutical grade meets the FCC and the United States Pharmacopoeia XK specifications (7). Other lactic acid derivatives such as salts and esters are also available in weU-estabhshed product specifications. Standard analytical methods such as titration and Hquid chromatography can be used to determine lactic acid, and other gravimetric and specific tests are used to detect impurities for the product specifications. A standard titration method neutralizes the acid with sodium hydroxide and then back-titrates the acid. An older standard quantitative method for determination of lactic acid was based on oxidation by potassium permanganate to acetaldehyde, which is absorbed in sodium bisulfite and titrated iodometricaHy. 

Experiments with glyceraldehyde and dihydroxyacetone showed them to be fermentable, but results with methyl glyoxal were conflicting. With Lebedev juice no lactic acid was formed, but with top yeast Neuberg reported that lactic acid was detectable. In 1913 he and Kerb therefore proposed sugar was converted to methyl glyoxal from which pyruvic acid and ethanol were derived ... 

Reeder and Rieger6 used ESR spectra to identify complex ions and to estimate formation constants for aqueous oxovanadium(iv) complexes with lactic acid, thiolactic acid, glycolic acid, and thioglycolic acid. Through the use of second-harmonic detection, which produces second-derivative spectra, the resolution was good enough that several of the individual species could be separately... 

Gorton et al. reported carbon paste electrodes based on Toluidine Blue O (TBO)-methacrylate co-polymers or ethylenediamine polymer derivative and NAD" " with yeast alcohol dehydrogenase for the analysis of ethanol [152,153] and with D-lactate dehydrogenase for the analysis of D-lactic acid [154]. Use of electrodes prepared with dye-modified polymeric electron transfer systems and NAD+/NADH to detect vitamin K and pyruvic acid has also been reported by Okamoto et al. [153]. Although these sensors showed acceptable performances, insensitivity to ambient oxygen concentration, sensor stability and lifetime still need to be improved to obtain optimal dehydrogenase based enzyme biosensors. 

In a number of other studies, GC-MS of DMOX derivatives has been utilized to determine the CLA isomer distribution from a variety of sources. The structures of pure isomers of 9c,llt-18 2 and 10f,12c-18 2, isolated by crystallization of a CLA mixture prepared by alkali-isomerization of linoleate, were confirmed (67). The presence of 9c,llt-18 2 was established in chocolate (49). In conjunction with GC-FTIR, all possible geometrical isomers of 9,11-18 2 (c,i > t,t > c,c and t,c) were detected in human adipose tissue (10). In dehydrated castor oil, although the 9,11 isomers (c/i, c,c and t,t) appeared to be the most abundant, 7,9- and 8,10-18 2 (c/t and but not c,c) were also detected with the aid of SPA (46). The presence of It, 9c-18 2 (as well as lower levels of 7c,9c-, lt,9t- and possibly 7c,9f-18 2) was confirmed in cow s milk, cheese, beef, and human milk and adipose tissue (9). Together with silver-ion HPLC, the isomer distribution in different tissues of pigs fed commercial CLA was determined (2). The CLA content of lactic acid bacteria (44), and the nature of the CLA isomers formed as a result of add-catalyzed methylation of allylic hydroxy oleates (secondary hpid autoxidation products) (47) were also established. 

The simultaneous detection of benzoic, citric, and lactic acid in soft drinks (168), benzoic acid in textile fibers (169), in Chinese traditional medicine from Daemonorops draco (170), in foods (171-173), and by fluorimetric detection and quantification (173a) have been effected. Alkyl 4-hydroxybenzoates have been separated by circular HPTLC (174), on silufol (preferred visualization, iodine vapor) (175), by reflectance spectrophotometry at 272 nm on sil G HR UV plates (176), and by remission photometry (177). Hydroxybenzoic acids in grape leaves, berries, and wine have been separated on micropolyamide layers (178), and preservatives in wine (179) on polyamide layers containing a fluorescent pigment. Silanized silica gel H (F254) has been employed for the quantitative analysis of alkyl 4-hydroxybenzoates by off the plate differential spectrophotometry (180). Salicylic acid and its derivatives have been analyzed by a variety of TLC procedures (181-190), Sources of error have been discussed (191) and manipulative problems examined (192). 

The esters produced by these derivatizing reagents usually enable the sensitive determination of their parent acids in foods, with detection limits occasionally comparable to those provided by intrinsically more sensitive techniques, such as electrochemistry. The UV (254 nm) and electrochemical detection (1.1 V) limits of the p-nitrobenzyl derivatives of lactic, formic, and acetic acid are the same, and are equal to 1.8, 0.9, and 1.1 ng, respectively (45). 

This is soluble in water and can be isolated from the raw wool by aqueous extraction. It contains potassium salts of fatty acids, such as oleic and stearic acids, and potassium carbonate is also present. The simpler organic acids, such as acetic, lactic, butyric, valeric, and capronic acids, have also been found both in the free state and as their potassium salts. Amino acids such as leucine, glycine, and tyrosine have been detected. Suint, therefore, is a complex mixture this might be expected because it is derived from sweat, which is known to be one of the means by which an animal discards unwanted waste products of its metabolism. 

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