Amperometric flow‐injection determination of citric acid in food using free citrate lyase and co‐immobilized oxalacetate decarboxylase and pyruvate oxidase

Abstract

A flow-injection analytical system for the determination of citrate in food has been developed. Citrate lyase, oxalacetate decarboxylase, and pyruvate oxidase were used, and the latter two enzymes were co-immobilized. Hydrogen peroxide, which was produced by three enzyme reactions, was monitored amperometrically with a platinum electrode. The carrier solution used was 0.1 M phosphate buffer (pH 7.0) containing lOmM MgC12, 80pM thiamine pyrophosphate (TPP), and 10pM flavine adenine dinucleotide (FAD). The detection limit was 0.02mM, and the range of determination was 0.lLl.OmM. The relative standard deviation was 1.23% for 10 successive determinations at the 0.5 mM level. The determination frequency was about 15 tests per hour. The present system was applied to the determination of citrate in several fruits. The results showed good agreement with those obtained using a conventional method (F-kit method).

Sensor for Hydrogen Peroxide Based on Prussian Blue Modified Electrode: Improvement of the Operational Stability

“…10 Hydrogen peroxide is present in countless biological reactions as the main product of several oxidases, 11,12 and is an important parameter for the monitoring of these bio-processes. [11][12][13][14] Many analytical techniques are available to determine H2O2, including fluorometry, 15 chemiluminescence, 16 photometry 17 and voltammetry. 18 Among applications, the determination of hydrogen peroxide has been realized in matrices such as foods [19][20][21] and pharmaceutics [22][23][24] and in the environment.…”

“…[25][26][27] In recent years, one of the most widely used electroanalytical methods relies on the use of peroxidase. 12,14,28 A number of PBmodified electrodes and also electrodes modified with similar metal-ion cyanide complexes have been reported and proposed for highly selective monitoring of hydrogen peroxide. However, until now, these electrodes still face a number of drawbacks with regards to long-term stability and sensitivity to pH-changes.…”

Study of the Electrochemical Behavior of Disperse Blue 1‐Modified Graphite Electrodes. Application to the Flow Determination of NADH

“…Only ascorbic acid (6 mM) exhibits significant positive interference (190%). This problem is acute for the majority of CME×s and could be either minimized by suitable alkaline pretreatment of the samples or eliminated by using ascorbate oxidase [23].…”

Citrate selective electrodes for the flow injection analysis of soft drinks, beers and pharmaceutical products

“…By reaction with citrate (CIT) lyase and oxaloacetate decarboxy-lase, the analyte is converted into pyruvic acid, which is subsequently determined by differential pulse polarography [20]. Alternatively, pyruvic acid is made to react with pyruvate oxidase for a succeeding ampero-metric quantification [21][22][23]. Other similar methods resort to CIT lyase and malate/lactate dehydrogenase enzymes, and are connected to the UV-Vis quantifi-cation of nicotinamide adenine dinucleotide (NADH) [24,25].…”

“…Considering the high selectivity of enzymes towards a substrate, this strategy permits minimiza-tion of interferences. Furthermore, enzymes are im-mobilized in a reactor [22][23][24][25] or at the surface of an electrode [21] in order to prevent their high con-sumption. However, because enzymes are costly, react slowly, and require a frequent replacement, applica-tion of these methods turns out to be expensive and slow.…”