Food analysis oxidation

The problems encountered are numerous. Tryptophan is highly prone to degradation in acid digestions. This is especially the case in food analysis, where samples often contain significant quantities of carbohydrates that greatly exacerbate tryptophan s degradative tendencies. Cyst(e)ine is partially oxidized during acid hydrolysis and will likely be found in several forms cystine, cysteine, cysteine sulfinic acid, and cysteic acid. Methionine can be partially lost in simi-... 

Incineration is the usual method in food analysis. Organic matter is decomposed in an electric furnace within a temperature range of 400-600 °C. It is rather a long procedure and the ash it yields, consisting mostly of carbonates and oxides, is dissolved in a suitable acid or mixture of acids [12-16]. 

Gas-selective electrodes are used to a hmited extent in food analysis although, in certain areas of food production their use is quite common. The oxygen-selective electrode is often used on the production hnes for fruit and vegetable juices, where a vacuum has been apphed to remove air before packaging, this in order to check the residual oxygen content. S02-selective electrodes are used to determine the SO2 content of wines and other S02-treated liquids either directly or after the acid conversion of a component such as NaHSOa to SO2. Other electrodes are available for similar measurements, such as nitrogen oxide (for nitrite contents) and carbon dioxide (for either CO2 directly or CO2 from acid-converted carbonate or bicarbonate salts). There are perhaps other more accurate ways of determining such analytes, but the gas-selective electrode is... 

A. Berna, Metal oxide sensors for electronic noses and their application to food analysis. Sensors 10, 3882-3910 (2010). doi 10.3390/sl00403882... 

One of the few reported uses of fiber-optic biosensors in food analysis in combination with flow injection analysis is the determination of L-glutamate in soups and sauces. This amino acid plays a central role in the oxidative determination of other amino acids and is capable of sensitizing gustatory nerves. Although glutamate occurs naturally in some foods, it is also used as a flavor enhancer. The biosensor was... 

Chronopotentiometric analytical methods have also found application in the field of food analysis. In this technique, the oxidation or reduction of species at a constant current is carried out, and the transition time is measured as the quantitative characteristic [29]. In this context, recent chronopotentiometric methods have been reported for histamine determination in foodstuffs. One of these methods was based on the oxidation of the amine at a planar gold disc electrode in the presence of electrogenerated chlorine which facilitates charge transfer between the analyte and the electrode surface. Well-defined signals were observed at +1.15 V in hydrochloric acid medium, giving rise to a linear calibration plot in the 2- 1(X) mg/1 concentration range with an LOD of 0.27 mg/1 histamine. The method was applied to the determination of histamine in fermented sausages [30]. The same authors used a mercury film electrode to develop a chronopotentiometric method for histamine in cheese [29]. 

ME using different CSPE-CNTs (SWCNTs and MWCNTs) to analyze a wide group of analytes of food significance, such as dietary antioxidants, water-soluble vitamins, vanilla flavors, and isofiavones involved in representative food samples, has been deeply studied [52]. Ultrafast separations at lowered oxidation potentials resulted in well defined and resolved peaks with enhanced voltammetric current when compared to those obtained from unmodified screen-printed electrodes thus making CNTs an ideal material for electrochemical sensing in food analysis. MWCNTs offered better performance as compared to SWCNTs. 

The oxidized and reduced forms of the pyridine cosubstrate are readily distinguished by absorbance readings at 340 nm (Fig. 2.5). Therefore, whenever possible, enzymatic reactions which are difficult to measure directly are coupled with an NAD(P)-dependent indicator reaction (cf. 2.6.1.1) for food analysis. 

L-ascorbic acid (AA) and L-dehydroascorbic acid (DHAA) are the two main C vitamers occurring in nature [1]. In food analysis, the valuation of the vitamin C total content should account for both forms, since DHAA is readily reduced to AA in the animal body. D-isoascorbic acid (D-IAA), also known as erythorbic acid or D-araboascorbic acid, has analogous reductive properties but only 5% of the antiscorbutic activity of L-AA this epimer is a by-product of vitamin C, and is approved within the European Community as an antioxidant additive [62]. The capability of LC to distinguish the two ascorbic acid isomers and their primary oxidation products is very useful for analyzing processed foods. Forms used for supplementation are AA, sodium-, calcium-, or potassium-L-ascorbate and L-ascorbyl 6-palmitate [4]. 

In food analysis, a method for determining vitamin C should ideally account for AA, its salts, and its reversible oxidation product, DHAA, to give a total value for vitamin C. In addition, the ability to distinguish AA from its epimer D-isoascorbic acid (erythorbic acid) is useful in the analysis of processed foods. 

Oxidation decreases the quality of foods by producing low-molecular-weight off-flavor compounds, as well as by destroying essential nutrients, and it produces toxic compounds and dimers or polymers of lipids and proteins, which in turn contribute to diseases and accelerate the aging process. Its measurement is a leading objective of food analysis. Evaluating lipid oxidation status is a challenging task due to a number of facts. 

Analytical Techniques. Sorbic acid and potassium sorbate are assayed titrimetricaHy (51). The quantitative analysis of sorbic acid in food or beverages, which may require solvent extraction or steam distillation (52,53), employs various techniques. The two classical methods are both spectrophotometric (54—56). In the ultraviolet method, the prepared sample is acidified and the sorbic acid is measured at 250 260 nm. In the colorimetric method, the sorbic acid in the prepared sample is oxidized and then reacts with thiobarbituric acid the complex is measured at - 530 nm. Chromatographic techniques are also used for the analysis of sorbic acid. High pressure Hquid chromatography with ultraviolet detection is used to separate and quantify sorbic acid from other ultraviolet-absorbing species (57—59). Sorbic acid in food extracts is deterrnined by gas chromatography with flame ionization detection (60—62). 

SCHWARZ K, BERTELSEN L H, NISSEN L R, GORDNER P T, HEINONEN M I, HOPIA A, HUYNH-BA T, LOMBELET p, MCPHAIL D, SKIBSTED L H and TIJBURG L (2001) Investigation of plant extracts for the protection of processed foods against lipid oxidation. Comparison of antioxidant assays based on radical scavenging, lipid oxidation and analysis of the principal antioxidant components, Eur Food Res Technol, 212, 319-28. 

Masuda, T. et ah. Chemical studies on antioxidant mechanism of curcumin analysis of oxidative coupling products from curcumine and linoleate, J. Agric. Food Chem., 49, 2539, 2001. 

Sometimes, in different systems, the oxygen presence is undesirable because of its reactivity and tendency to oxidize the contact materials that leads to corrosion of metallic materials or depreciation of food quality. Also oxygen could inhibit different chemical reactions or could interfere in different analysis (RES, polaroghaphy, etc.). 

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