1,721,034 research outputs found
Flow injection determination of choline in milk hydrolysates by an immobilized enzyme reactor coupled to a selective hydrogen peroxide amperometric sensor
No full textA choline oxidase (ChO) immobilized enzyme reactor (IMER) prepared by glutaraldehyde coupling of the enzyme on aminopropyl modified
controlled pore glass beads is described. The ChO–IMER was coupled, in a flow injection configuration system, to an interference free hydrogen
peroxide amperometric sensor based on a Pt surface modified by an overoxidized polypyrrole film. The resulting analytical device responds
selectively to choline and displays a sensitivity of 46.9±0.2CmM−1 and a limit of detection, calculated at a signal-to-noise ratio equal to 3, of
7M. Sensitivity remains constant for about 20 days and then starts to slowly deteriorate and after 2 months a 70% of the initial sensitivity was
still retained. The application to choline determination in milk hydrolysates is demonstrated. Short- and long-term drift observed in the analytical
response can be corrected by a bracketing technique
Rapid and automatable determination of ochratoxin A in wine based on microextraction by packed sorbent followed by HPLC-FLD
Full text linkThe development of miniaturized and automatized analytical methods for OTA determination, requiring a reduced use of solvents and a limited involvement of expert operators, is highly desirable. Therefore, a rapid and automatable method for the determination of OTA in wine using a microextraction by packed C18 sorbent followed by high performance liquid chromatography with fluorescence detection was developed and validated for a successful application in the context of wine production. Important experimental parameters, such as sample and eluent volumes, extraction mode, draw and dispense speeds, number of eluent passes up and down through the stationary phase, were optimized. The validation included the comparison of the sensitivities related to solvent-matched, matrix-matched and standard addition calibrations and the participation to a proficiency test in a inter-laboratory circuit. Matrix effects were also investigated. Accuracies relevant to real samples were estimated to range between 76 and 100%, at 0.2 μg/L, and between 84 and 108%, at 1.0 μg/L, in compliance with the EU Regulation 401/2006; the limits of detection and quantification were of 0.08 and 0.24 μg/L, respectively, i.e. much lower than the maximum level currently permitted for OTA in the European Union (2.0 μg/kg, corresponding to ca 2.0 μg/L). 60 different wines produced in the Foggia (Italy) area were analyzed for their OTA content using the developed method and none of them was found to overcome the maximum permitted limit
Identification of anthocyanins and anthocyanin-derived pigments in Primitivo red wine by HPLC-ESI-MS/MS
No full textCharacterization of caffeic acid enzymatic oxidation by-products by liquid chromatography coupled to electrospray ionization tandem mass spectrometry
No full text
Quantitation of Major Choline Fractions in Milk and Dietary Supplements using a Phospholipase-D Bioreactor Coupled to a Choline Amperometric Biosensor
No full textCurrent analytical methods lack the capacity of simultaneous determination of the content of free
choline and phosphatidyl-bound choline, mainly phosphatidyl choline, in raw milk. Quantitative
determination of total, free, and phosphatidyl-bound choline in milk and a dietary supplement is
described using a phospholipase D packed bioreactor coupled to a choline oxidase-based amperometric
biosensor. The response for choline and phosphatidyl choline was linear up to 0.5 mM and 1
mM, respectively, and the detection limits were 0.02 and 0.03 mM, respectively. The conversion
efficiency of phosphatidyl choline to choline was 50% at 0.2 mL min-1. The within days coefficient of
variation for choline and phosphatidyl choline determination in milk samples was 2.8% and 3.2%,
respectively. With the addition of an acid hydrolysis step, the method can quantify the concentrations
of total, free, phosphatidyl-bound, and non-phosphatidyl-bound choline esters, thus permitting
determination of major choline fractions in a complex matrix
Influence on ageing on lees on polysapolysaccharide glycosyl-residue composition of Chardonnay wine.
No full textDetermination of Choline in Milk, Milk Powder, and Soy Lecithin Hydrolysates by Flow Injection Analysis and Amperometric Detection with a Choline Oxidase Based Biosensor
No full textA fast-response and interference-free amperometric biosensor based on choline oxidase immobilized
onto an electropolymerized polypyrrole film for flow injection determination of choline in milk, milk
powder, and soy lecithin hydrolysates is described. The sensor displayed an Imax value of 1.9 ( 0.2
íA and an apparent Michaelis - Menten constant, k¢M, equal to 1.75 ( 0.07 mM. Detection limits of
0.12 íM could be obtained. Because even a slight deterioration of the anti-interference membrane
can adversely affect measurement accuracy, a real time monitoring of the biosensor selectivity has
been achieved by a dual Pt electrode flow-through cell where the enzyme modified electrode is coupled
to an enzyme-free electrode in a parallel configuration. Finally, bracketing technique (alternate
injections of sample and standards) allows a two-point calibration to be performed in real-time,
correcting for any drift in sensor response
Effect of harvest time on table grape quality during on-vine storage
No full textPostponing the harvest of grapes is a common practice in southern Italy, in order to delay harvest up to Christmas and make higher income from their sale. The aim of this work was to evaluate the effect of harvest time (over almost 3 months) on the quality of table grapes (cv. Italia). The experiment was repeated for two years (2010 and 2011). In 2010, grapes were harvested starting from 8 October and after 11, 27 and 48 days. In 2011, five harvest times were compared over a period of 56 days. Respiration rate, firmness, colour, sensory attributes, total soluble solids (TSS), pH, titratable acidity (TA), phenols and antioxidant activity were measured. In addition, in the second year, volatile compounds were evaluated
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