University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Website: @unf

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Classification: Food -> yogurt

Citations 8

"Sequential Determination Of Glucose And Fructose In Foods By Flow Injection Analysis With Immobilized Enzymes"
Anal. Chim. Acta 1987 Volume 202, Issue 1 Pages 199-205
P. Linares, M. D. Luque De Castro and M. Valcárcel

Abstract: Two enzymatic reactors, R1 containing immobilized hexokinase(I) and glucose-6-phosphate dehydrogenase(II) and R2 containing immobilized I, II and glucose-6-phosphate isomerase, were prepared by the method of Masoom and Townshend (cf. Ibid., 1986, 179, 399) and used in the determination of glucose(III) and the sum of III and fructose(IV) by flow injection analysis. Sample solution (100 µL) in 0.1 M phosphate buffer of pH 8.0 was injected into the carrier stream (1 mL min-1), viz, 0.1 M phosphate buffer (pH 8.0) containing Mg(II) (13.5 µg mL-1), ATP (1 µg mL-1) and NAD+ (1 µg mL-1), and passed sequentially through R1 (III only) and R2 (III plus IV) with use of valve-switching; fluorimetric detection was at 460 nm (excitation at 340 nm). Calibration graphs were rectilinear from 1 to 10 µM-III and -IV; coefficient of variation were generally 1.5%. For mixtures of III and (IV) in ratios of 1:6 to 6:1 the errors were +6.1 to -1.4% for III and +6.7 to -4.9% for IV. The method was successfully applied to fruit juices, yogurts, and dessert powders. The sampling rate was 30 h-1.
Glucose Fructose Fluorescence Immobilized enzyme Tecator

"Automatic Preparation Of Milk Dessert Slurries For The Determination Of Trace Amounts Of Aluminum By Electrothermal Atomic Absorption Spectrometry"
J. Anal. At. Spectrom. 1995 Volume 10, Issue 1 Pages 55-59
Marco A. Z. Arruda, Mercedes Gallego and Miguel Valcárcel

Abstract: Yogurt was manually homogenized and aspirated into a 200 µL sample loop of a flow injection system at 1.5 ml/min. The sample was injected into a carrier stream (0.7 ml/min) of 0.2% HNO3 which merged with a chemical modifier stream (0.3 ml/min) of 0.1 M magnesium nitrate/10 mM palladium nitrate. The solution passed through a mixing chamber and was loaded into a sample cup for 2 min (2 ml). The solution was analyzed for Al by ETAAS (furnace conditions tabulated). The calibration graph was linear for 40-400 µg/l of Al with a detection limit of 6 µg/l. The effects of foreign ions on the method are discussed.
Aluminum Spectrophotometry Automation Interface Interferences Slurry

"Chemiluminescent And Spectrophotometric Determination Of Peroxidase And Lactoperoxidase In Foods Using Flow Injection"
Analusis 1994 Volume 22, Issue 2 Pages 76-81

Abstract: Fresh or frozen vegetables were homogenized with 10 mM Tris hydrochloride buffer of pH 7 containing 1 M KCl. The mixture was centrifuged and the extract was purified on a Sep-Pak C18 cartridge. The resulting solution was injected into a carrier stream of 3 mM H2O2 (1 ml/min). The carrier and the reagent stream, 1.5 mM luminol in 0.1 M Na2CO3 buffer of pH 8.5 (1 ml/min) were mixed in a coil (30 cm x 0.5 mm i.d.) and the chemiluminescence was measured with a photomultiplier. The calibration graph was linear for 25-500 nM-peroxidase; RSD was 1.95% (n = 15) for 250 nM. Yogurt or curd was treated as above, but with a filtration step before the Sep-Pak cartridge. Milk was treated with rennet to precipitate the proteins, the mixture was filtered and passed through the Sep-Pak cartridge. The solution was injected into the carrier, 2 mM H2O2 (1.4 ml/min) and, after mixing, the carrier was merged with 5 mM guaiacol solution in 0.1 M phosphate buffer of pH 7 (1.4 ml/min) and mixed in a coil (80 cm x 0.5 mm i.d.) with detection at 436 nm. The calibration graph was linear from 25-300 nM-lactoperoxidase; RSD (n = 15) were 1.09 and 0.76%, for 20 and 200 nM, respectively.
Enzyme, peroxidase Enzyme, lactoperoxidase Chemiluminescence Spectrophotometry

"A Microdialysis Fibre Based Sampler For Flow Injection Analysis: Determination Of L-lactate In Biofluids By An Electrochemically-synthesized Bilayer Membrane-based Biosensor"
Biosens. Bioelectron. 1996 Volume 11, Issue 4 Pages 419-425
F. Palmisano, D. Centonze, M. Quinto and P. G. Zambonin*

Abstract: A microdialysis sampler consisting of Spectra/por hollow-fiber regenerated cellulose (150 µm i.d; 9000 da mol. wt. cut-off) was inserted for ~2 cm in tygon tubing (10 cm x 0.5 mm i.d.) and sealed in. This sampler was used online for FIA to dilute the sample and remove surface active agents. FIA was carried out using a Gilson minipuls 3 pump, a six-way low pressure injection valve, a wall-jet flow-through cell, a PAR 400 detector and a Y-t chart recorder (schematic given). The sampler was coupled with a Pt/overoxidized polypyrrole/lactata oxidase/poly-o-phenylenediamine biosensor; preparation described previously (Anal. Chem.), 1995, 67, 1005). The enzyme electrodes were fitted to the wall-jet flow-through cell and left overnight at ± 0.7 V in 0.1 M phosphate buffer of pH 7 to complete poly (pyrrole) overoxidation. Calibration graphs were linear up to 10 mM lactate for standard lactate solutions. The method was applied to the analysis of bovine foetal serum; RSD was 1%. This technique can be used to analyze complex matrices such as serum, milk and yogurt with no sample pretreatment. A microdialysis fiber based, low volume sampler is described which can be used in flow injection analysis (FIA) when an on-line dilution of the sample and/or removal of high molecular weight interferents is required. This device used in combination with a lactate amperometric biosensor based on lactate oxidase electrochemically immobilized in a bilayer membrane of poly(o-phenylendiamine) and overoxidized poly(pyrrole) permits the extension of the linear range of response up to 10 mM lactate. Combining microdialysis sampling with FIA and amperometric detection at an interference-free and fast-response biosensor, lactate determination in complex media such as serum, milk and yoghurt can be easily achieved with a high sample throughput and no sample pre-treatment.
l-Lactate Sensor Electrode Electrode Electrode Electrode Interferences Hollow fiber membrane Dialysis

"Estimation Of Soluble L-lactate In Dairy Products Using Screen-printed Sensors In A Flow Injection Analyzer"
Biosens. Bioelectron. 1998 Volume 13, Issue 2 Pages 219-225
W. A. Collier*, P. Lovejoy and A. L. Hart

Abstract: Screen-printed lactate sensors, with an outer membrane applied by an air-brush, were mounted in a flow injection analyzer. Dild. extracts of buttermilk and yoghurt were passed over the sensors. The lactate concentration. in the extracts was determined with a high degree of accuracy and precision (based on variation among sensors). Fresh sensors were used for each new buttermilk or yoghurt sample, but individual sensors were capable of giving repeatable results, with standard lactate solutions, over a large number of injections.
l-Lactate Electrode Electrode Apparatus Detector

"A Rapid Ion-pair HPLC Procedure For Determination Of Tyramine In Dairy Products"
J. Food Sci. 1986 Volume 51, Issue 1 Pages 84-86

Abstract: A 2-g sample (yogurt, cheese or infant formula) was homogenized with ~40 mL of methanol, the homogenate was heated at 60°C for 15 min and the cooled product was diluted to 50 mL with methanol. A 20 µL portion of the filtered solution was analyzed by HPLC on a radially compressed column of Nova-Pak C18 (5 µm) equipped with a guard column of µBondapak C18/Corasil (37 to 50 µm). The mobile phase (1.5 mL min-1) was methanol - 0.05 M Na2HPO4 (3:17) containing heptanesulfonic acid as counter-ion, adjusted to pH 3.0 with 6 M H3PO4. Post-column derivatization was effected with phthalaldehyde and the products were detected by fluorimetry at 425 nm (excitation at 338 nm). The calibration graph for 20 to 400 ng of tyramine was rectilinear. Average recoveries (and coefficient of variation) were 95.3% (9%) for infant formula, 102% (1.6%) for yogurt and 95.2% (8.4%) for cheese.
Tyramine HPLC Fluorescence Post-column derivatization

"Characterization And Food Application Of An Amperometric Needle-type L-lactate Sensor"
J. Food Sci. 1996 Volume 61, Issue 2 Pages 286-290
Kim N, Haginoya R, Karube I.

Abstract: There have been increasing needs for biosensing in the food industry because it is accurate, rapid and efficient. A needle-type L-lactate sensor with a three-layer membrane system which uses lactate oxidase as the biological component was prepared. The sensor had an optimum pH around 9-10 and an optimum temperature at 45°C. The current response was stable over 40 days and specifically responded to L-lactic acid. The sensor gave accurate L-lactate measurements in kimchi and yogurt of 187.4±4.1 and 734.1±34.5 mg/dL, similar to those of a spectrophotometric L-lactate kit.
l-Lactate Sensor Amperometry Method comparison Optimization

"D- And L-lactate Determination In Dairy Products: Presentation Of A Fast Automated Analysis System"
Z. Lebensm. Unters. Forsch. 1995 Volume 201, Issue 6 Pages 537-540
Thomas Becker, Hanns-Ludwig Schmidt and Erika Lechner

Abstract: A flow injection system is presented, which is versatile, automated and has an integrated enzyme system. Its efficiency at determining D- and L-lactate separately in dairy products is compared with the officially used reference method (DIN 10335). By means of a mathematical elimination of matrix effects, the pretreatment steps can be clearly reduced. As a result of the immobilization of the enzymes, an appropriate automation software and an adaptation of the system developed to the given medium, the analysis could be performed within 5 min and was distinctly cheaper than alternative methods. The values determined in 15 different dairy products deviated from those of the reference method by 3% at a maximum. (21 References)
d-Lactate l-Lactate Spectrophotometry Immobilized enzyme Standard method