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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Dairy Products

Classification: Agricultural -> dairy -> products

Citations 10

"Flow Injection Analysis Of Kjeldahl Nitrogen In Milk And Dairy Products By Potentiometric Detection"
Anal. Chim. Acta 1999 Volume 385, Issue 1-3 Pages 437-441
José F. C. C. Lima, Cristina Delerue-Matos and M. Carmo Vaz

Abstract: A flow injection analysis (FIA) system with a potentiometric tubular detector and a gas diffusion unit was developed for the determination of Kjeldahl nitrogen in milk and dairy products. The samples were digested by the Kjeldahl method and afterwards injected into the RA system without prior treatment. NaOH solution was introduced into the system to promote the conversion of ammonium ions to ammonia gas. The gas produced diffused through a gas-permeable membrane towards an acceptor channel (Tris-HCl, pH=7.5). When in contact with this solution, ammonia gas was reconverted to ammonium cation and carried to a tubular electrode sensitive to this species. Therefore, a PVC tubular ammonium ion-selective electrode was prepared without inner reference solution and with the sensor system based on nonactine and monactine dissolved in Tris-(2-ethylhexyl) phosphate. The results obtained with the developed FIA system were in good agreement with those of the reference method the relative deviations being less than 4%. Reproducibility of the method was assessed by the relative standard deviation, which was always less than 0.5% for 12 consecutive injections of sample digests. A sampling rate of 100 samples h-1 was obtained.
Ammonia Potentiometry Electrode Gas diffusion Kjeldahl Volatile generation Method comparison

"Determination Of Free Fatty Acids In Dairy Products By Direct Coupling Of A Continuous Preconcentration Ion-exchange-derivatization Module To A Gas Chromatograph"
Anal. Chem. 1994 Volume 66, Issue 5 Pages 628-634
Evaristo Ballesteros, Soledad Cardenas, Mercedes Gallego, and Miguel Valcarcel

Abstract: A flow injection ion-exchange system coupled to a gas-liquid chromatograph was used for the determination of free fatty acids in dairy products. The pretreatment module permits isolation and pre-concentration of free fatty acids on Amberlite IRA-400 and derivatization of eluted acids with acetyl chloride in methanol. The methyl esters are continuously injected via the injection port to prevent losses of the more volatile esters; they are quantified at the milligram per liter level with a FID detector. The method thus developed was applied to the determination of free fatty acids in milk, cream, and butter samples; fatty acids were also added to some samples to induce rancidity in order to assess the method performance. Copyright 1994, American Chemical Society.
Fatty acids, free Ion exchange GC Preconcentration Amberlite

"Online Dialysis With High Performance Liquid Chromatography For The Automated Preparation And Analysis Of Sugars And Organic Acids In Foods And Beverages"
J. Chromatogr. A 1995 Volume 705, Issue 2 Pages 195-203
Eric Vérette*, François Qian and Fabrice Mangani

Abstract: A quick, simple and robust technique is described for on-line clean-up and analysis of raw liquid food samples containing complex matrices such as dairy products, soft drinks, and fermented beverages. A completely automated sample preparation system (ASTED XL) provides an efficient way of removing macromolecular and microparticulate interferents by high-performance dialysis, prior to HPLC analysis of the sugars, organic acids and related compounds. Processing samples on-line in the concurrent mode permitted both high reproducibility and optimal throughput.
Sugars Acids, organic HPLC Sample preparation Dialysis

"Amperometric Flow Injection Measurement Of Protein In Dairy Products Using Glutaraldehyde"
Agric. Biol. Chem. 1987 Volume 51, Issue 10 Pages 2835-2836
Hiroyuki UKEDA, Shoko TANAKA, Kiyoshi MATSUMOTO and Yutaka OSAJIMA

Abstract: Protein was determined in dairy produce in a PTFE flow system (illustrated), based on simultaneous injection of glutaraldehyde and sample and then confluence before reaching the Clark O electrode (potential -0.8 V). Reaction was optimum at a glutaraldehyde concentration. of 10% and a reaction temperature of 30°C. The flow rate affected the rectilinear range and the slope of the calibration graph. Response was rectilinear from 1.0 to 4.0% of protein at 0.95 mL min-1, when 12 samples could be analyzed in 1 h. The limit of detection was 2 mM for L-glycine and 0.3% for nutrose (a Na salt of casein).
Protein Amperometry Electrode Heated reaction Merging zones

"Determination Of Nitrites And Nitrates In Milk And Its Products Using Flow Injection Analysis"
Latte 1988 Volume 13, Issue 5 Pages 410-411
Munksgaard, L.L.;Thymark, L.

Abstract: International Dairy Federation methods for the determination of nitrites and nitrates in dairy products were adapted to flow injection analysis (FIA). Samples were defatted and deproteinized, nitrates were reduced to nitrites, and the nitrites were reacted with sulfanilamide and N-naphthylethylenediamine to form a colored product absorbing at 538 nm. The limit of detection for both nitrites and nitrates was <1 mg/kg. At 10 mg/kg the recovery of nitrates was 90-102% and the relative standard deviation was 2-11%. FIA permitted anal. of ~80 samples per day. FIA was superior to manual anal. in terms of all measures of performance. (SFS)
Nitrate Nitrite Spectrophotometry Method comparison

"Automated Determination Of Nitrate And Nitrite In Milk And Dairy Products By Continuous-flow Analysis"
Milchwissenschaft 1979 Volume 34, Issue 7 Pages 414-416
Nijhuis, H.;Heeschen, W.;Bluethgen, A.

Abstract: Nitrate is reduced to nitrite by means of an organic hydrazine sulfate solution Nitrite reacts with sulfanilamide and N-(-1-naphthyl)ethylendiamine-2HCl in an azo reaction. The resulting color is measured at 520 nm. For the determination of nitrate and nitrite contents in 1 sample the anal. must be carried out twice: first without hydrazine solution for the determination of the total amt. of nitrate and nitrite. The nitrate content is calculated from the difference of both measurements. The relative standard deviation is 0.66%. The recovery is 100% for nitrite and 99.7% for nitrate. Preservation of milk samples is possible by cooling (up to 3 days at 5°C) or freezing (up to 14 days at -20°C. (SFS)
Nitrite Nitrate Spectrophotometry Speciation

"Potentiometric Determination Of Chloride Ion In Milk And Dairy Products By FIA Titration"
Quim. Anal. 1995 Volume 14, Issue 2 Pages 121-124
Alegret, S.;Alonso, J.;Bartroli, J.;Garcia Raurich, J.;Martinez Fabregas, E.;Sanchez Rodriguez, J.

Abstract: A 100 µL portion of milk was injected into a carrier stream (1 ml/min) of 0.1 M KNO3 and passed into a 0.55 mL variable-volume dilution chamber. The stream then passed through a ground electrode to a flow-through reference electrode as previously described (Alegret et al., Ibid. 1987, 6, 278) and a tabular flow-through Ag25 heterogeneous membrane all-solid-state electrode for the detection of the end point of the titration. The calibration graph was linear for 0.4-0.8 M chloride. Results are discussed.
Chloride Potentiometry Electrode Titrations

"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

"Optimization Of Selenium Determination In Vegetables, Fruits, And Dairy Products By Flow Injection Hydride Generation Atomic Absorption Spectrometry"
Chem. Pap. 2003 Volume 57, Issue 3 Pages 155-157
M. Kore&#328;ovsk&aacute;

Abstract: A flow injection hydride generation atomic absorption spectrometric (FI-HG-AAS) method was developed for determination of selenium in vegetables, fruits, and dairy products after microwave digestion of samples. The experimental conditions for FIAS 400 (concentration of reducing agent and carrier acid, time of reduction, flow rate of argon carrier gas) were optimized. The linearity range under optimized conditions was 0.20-25.0 ?g dm -3.The detection limit of the proposed method was 0.06 ?g kg -1 and limit of quantitation was 0.20 ?g kg-1. The procedure was validated by the method of standard additions (5.0 ?g dm -3 and 10.0 ?g L-1 in vegetables, fruits, and dairy products) and the recoveries were from 88% to 104%. The accuracy was evaluated using BCR 150 skin milk reference material (found: 0.128 mg kg-1, Sx = 0.004 mg kg-1, certified: 0.132 mg kg-1, Sx = 0.010 mg kg-1). The combined standard uncertainty of selenium was 8.4%. The method was developed and used for determination of selenium in vegetables, fruits, and dairy products consumed in Slovakia.