1,721,015 research outputs found
Determination of ascorbic acid in foodstuffs by microdialysis sampling and liquid chromatography with electrochemical detection
No full textA method for the determination of ascorbic acid in foodstuffs utilising microdialysis sampling coupled with LC with electrochemical detection is described. The application of the method to liquid food samples such as milk, yoghurt and fruit juices was evaluated. Compared with the classical method, the proposed procedure features straightforward sample preparation and improved sensitivity and selectivity. A sampling rate of 20 h-1 is possible, depending on the particular sample under study
Determination of benzoic and sorbic acids in food by microdialysis sampling coupled with HPLC and UV detection
No full textA sensitive, specific and rapid chromatographic procedure to determine benzoic and sorbic acids in different food products is described. The two antimicrobials were extracted from the food by using a microdialysis probe connected on-line to an HPLC column that allows separation of benzoic and sorbic acids revealed by a UV detector at 228 and 260 nm, respectively. The procedure was linear from 1 to 80 ppm, with a detection limit of 1 ppm for sorbic acid and 2 ppm for benzoic acid. The assay was successfully applied to non-alcoholic beverages and milk based products
Microdialysis sampling and high performance liquid chromatography with amperometric detection for sugar analysis in milk products
No full textA rapid and highly efficient method for the direct quantification of the major carbohydrates, glucose, fructose, sucrose and lactose in milk-based products is described. Rapid and selective monitoring of each sugar is accomplished by microdialysis sampling coupled with HPLC separation and amperometric detection with a chemically modified electrode. This new scheme offers simultaneous monitoring of sugars with little or no sample pretreatment. The results obtained from the application of the proposed procedure to milk and milk-based products are discussed
Determination of peroxide value in vegetable oils by an organic-phase enzyme electrode
No full textAn organic-phase biosensor is used for measuring the peroxide value in vegetable oils. Rapid flow injection monitoring of the peroxide value is accomplished by injecting the untreated oil sample directly into a chloroform carrier solution which transports it to the downstream horseradish-peroxidase (HRP) based flow detector. The Eastman AQ polymer is used for entrapping the HRP onto the detector surface. The new scheme offers convenient monitoring of low level peroxide values and high selectivity (accrued from the biospecificity of HRP towards peroxide species and from the low operating potential). The biosensor results are consistent with those obtained by the official iodometric method. Such development should facilitate quality control testing of oil products
High performance liquid chromatography of phenolic compounds in virgin olive oils using amperometric detection
No full textSimultaneous determination of glucose and galactose in dairy products by two parallel amperometric biosensors
No full textEvaluation by an electronic nose of olive oil oxidation during storage
No full textAn electronic nose based on an array of 12 Metal Oxide Semiconductor (MOS) sensors and 10 Metal Oxide Semiconductor Field–Effect Transistor (MOSFET) sensors was investigated to determine if it could be used to monitor olive oil oxidation during storage. Samples of extra virgin olive oil, olive oil and olive-pomace oil were stored at 40°C in the dark for 64 days. At established times, the three types of olive oil were evaluated for volatile compounds by the electronic nose and for peroxide value. The electronic nose data and the peroxide values were correlated and, on the basis of the correlation coefficients, a small number of sensors were selected. The responses of the selected sensors were analysed by Principal Component Analysis. The first principal component was able to discriminate olive oil samples on the basis of aging time. These results suggest that the electronic nose may be suitable for measuring changes in volatile compounds associated with olive oil oxidation during storage
Cobalt (II,III) oxide chemically modified electrode as amperometric detector in flow injection systems
No full textElectrochemical sensor detecting free sulphydryl groups: evaluation of milk heat treatment
No full textWe describe a new and rapid method for the evaluation of reactive sulfhydryl groups in whey proteins obtained after precipitation of casein by acetic acid at pH 4.6. The procedure is based on the use of a wire tungsten electrode operating at -0.2 V versus saturated calomel electrode in flow injection analysis. The method was applied to raw milks and to commercial pasteurized and UHT milks. Results showed that the tungsten electrode constituted a robust amperometric sensor that could be used to differentiate milks that underwent different heat treatments. The decrease of thiol content in the whey proteins from samples was in agreement with the whey protein content found by HPLC. The procedure is suitable for on-line quality control of heat-treated milks
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