Use of the o-Phthalaldehyde and N-Acetyl-L-Cysteine the Evaluation of Milk Proteins

Medina-Hernández, M.J.; Domingo, E. Bonet; Camañas, R. M. Villanueva; Garcı́a-Alvarez-Coque, M.C.

doi:10.3168/jds.s0022-0302(91)78342-2

Cited by 12 publications

(3 citation statements)

References 6 publications

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“…Using chiral thiols for derivative formation, NAC has been shown to be suitable to separate the enantiomers of most amino acid by reversed-phase HPLC (Seiler, 1993). NAC is preferable to other thiols such as mercaptoethanol and 3-mercaptopropionic acid due to its greater stability (Medina Hernández et al, 1991). The use of two short narrow bore columns in series resulted in good peak resolution and a relatively short run time (Molnar-Perl and Vasanits, 1999).…”

Section: Discussionmentioning

confidence: 98%

An improved HPLC method for the investigation of L‐selenomethionine metabolism in rat gut contents

Krittaphol

McDowell

Thomson

et al. 2009

Biomedical Chromatography

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Selenomethionine (SeMet) is a widely used nutritional supplement that has potential benefit for people living in selenium-deficient areas. Previous research has shown that selenium administered as SeMet undergoes significant enterohepatic recycling which may involve the gut microflora. In order to investigate this we have developed a simple method for the quantitation of l-SeMet in rat gut content suspensions prepared from jejunum, ileum, caecum and colon. After incubation of l-SeMet with gut content suspensions, samples were deproteinized with sulfosalicylic acid and derivatized with o-phthaldialdehyde (OPA) and N-acetyl-l-cysteine (NAC). Mass spectrometry confirmed the formation of a 1:1:1 derivative of l-SeMet with OPA and NAC. Samples were analysed by reversed-phase high-performance liquid chromatography with fluorescence detection. The assay was linear in the concentration range 0.5-100 microg/mL (r(2) = 0.9992) with a limit of detection of 0.025 microg/mL (signal-to-noise ratio of 5). Intra-day and inter-day accuracies were 91.1-92.8 and 91.7-95.5%, respectively with corresponding precisions as relative standard deviation of <5%. Incubation of l-SeMet with gut content suspensions from different parts of the rat intestine showed that l-SeMet metabolism occurs mainly in the caecum.

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Section: Discussionmentioning

confidence: 98%

An improved HPLC method for the investigation of L‐selenomethionine metabolism in rat gut contents

Krittaphol

McDowell

Thomson

et al. 2009

Biomedical Chromatography

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“…A commonly used reagent for the determination of free α- and ε- amino groups is ortho -phthaldialdehyde (OPA), which reacts with primary amino groups in the presence of a thiol compound such as N -acetyl- l -cysteine (NAC) to form a 1-alkylthio-2-alkyl-substituted isoindole. The fluorescent isoindole can absorb light at a wavelength of 340 nm and has been quantified spectrophotometrically [ 1 , 138 , 139 , 140 , 141 , 142 , 143 ].…”

Section: Methodsmentioning

confidence: 99%

Characterization of Conjugates between α-Lactalbumin and Benzyl Isothiocyanate—Effects on Molecular Structure and Proteolytic Stability

2021

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In complex foods, bioactive secondary plant metabolites (SPM) can bind to food proteins. Especially when being covalently bound, such modifications can alter the structure and, thus, the functional and biological properties of the proteins. Additionally, the bioactivity of the SPM can be affected as well. Consequently, knowledge of the influence of chemical modifications on these properties is particularly important for food processing, food safety, and nutritional physiology. As a model, the molecular structure of conjugates between the bioactive metabolite benzyl isothiocyanate (BITC, a hydrolysis product of the glucosinolate glucotropaeolin) and the whey protein α-lactalbumin (α-LA) was investigated using circular dichroism spectroscopy, anilino-1-naphthalenesulfonic acid fluorescence, and dynamic light scattering. Free amino groups were determined before and after the BITC conjugation. Finally, mass spectrometric analysis of the BITC-α-LA protein hydrolysates was performed. As a result of the chemical modifications, a change in the secondary structure of α-LA and an increase in surface hydrophobicity and hydrodynamic radii were documented. BITC modification at the ε-amino group of certain lysine side chains inhibited tryptic hydrolysis. Furthermore, two BITC-modified amino acids were identified, located at two lysine side chains (K32 and K113) in the amino acid sequence of α-LA.

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“…Lactulosyl lysine formation is conveniently monitored by measuring furosine concentrations (Erbersdobler, 1987) and can be indirectly measured by monitoring the amount of available amine (Hernández et al, 1991). Lactulosyl lysine in WPCs can be measured directly by mass spectrometry where the addition of one lactose molecule increases the molecular weight of the protein by 324 Da.…”

Section: Measuring Lactulosyl Lysine Levelsmentioning

confidence: 99%

Changes in Milk Proteins during Storage of Dry Powders

Higgs

Boland

2014

Milk Proteins

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Use of the o-Phthalaldehyde and N-Acetyl-L-Cysteine the Evaluation of Milk Proteins

Cited by 12 publications

References 6 publications

An improved HPLC method for the investigation of L‐selenomethionine metabolism in rat gut contents

An improved HPLC method for the investigation of L‐selenomethionine metabolism in rat gut contents

Characterization of Conjugates between α-Lactalbumin and Benzyl Isothiocyanate—Effects on Molecular Structure and Proteolytic Stability

Changes in Milk Proteins during Storage of Dry Powders

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