Separation and quantitation of milk whey proteins of close isoelectric points by on-line capillary isoelectric focusing—Electrospray ionization mass spectrometry in glycerol–water media

“…Most simply, the ampholyte concentration is decreased to 1% or less, and the m/z scan range is usually from 700–2000 to reduce the background produced by commercial ampholytes [16–21]. As an example, Kuroda et al [22] decreased the concentration of ampholytes to 1% to minimize the interference of the ampholytes for absolute quantification of standard peptides and proteins.…”

Section: Introductionmentioning

confidence: 99%

On-line amino acid-based capillary isoelectric focusing-ESI-MS/MS for protein digests analysis

Zhu

Sun

Yang

et al. 2012

Analytica Chimica Acta

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Six amino acids with pIs that ranged from 3.2 to 9.7 were used as ampholytes to establish a pH gradient in capillary isoelectric focusing. This amino acid-based capillary isoelectric focusing (cIEF) was coupled with ESI-MS/MS using an electrokinetically pumped sheath-flow interface for peptide analysis. Amino acid-based isoelectric focusing generates a two-order of magnitude lower background signal than commercial ampholytes in the important m/z range of 300–1800. Good focusing was achieved for insulin receptor, which produced ~10-s peak width. For 0.1 mg/mL bovine serum albumin (BSA) digests, 24 ± 1 peptides (sequence coverage 47 ± 4 %) were identified in triplicate analysis. As expected, the BSA peptides were separated according to their pI. The concentration detection limit for the BSA digests is 7 nM and the mass detection limit is 7 fmole. A solution of six bovine protein tryptic digests spanning 5 orders of magnitude in concentration was analyzed by amino acid based cIEF-ESI-MS/MS. Five proteins with a concentration range spanning 4 orders of magnitude were identified in triplicate runs. Using amino acid based cIEF-ESI-MS/MS, 112 protein groups and 303 unique peptides were identified in triplicate runs of a RAW 264.7 cell homogenate protein digest. In comparison with ampholyte based cIEF-ESI-MS/MS, amino acid based cIEF-ESI-MS/MS produces higher resolution of five acidic peptides, much cleaner mass spectra, and higher protein spectral counts.

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“…The pH of yoghurt was about 4.7 at the low concentration of GABA, whereas the pI of casein and whey was about 4.7 and 5.2, respectively (Lecoeur et al . ). Lots of casein would precipitate at low concentration of GABA in the yoghurt.…”

Section: Resultsmentioning

confidence: 97%

Effect of γ‐aminobutyric acid on the physicochemical, rheological and sensory properties of yoghurt

Liu

Wang

Jiang

et al. 2015

Int J of Dairy Tech

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This study aimed to investigate the impacts of dairy processing conditions on the γ‐aminobutyric acid (GABA) content and the effect of GABA on the quality of the resulting yoghurt. Serial concentrations of GABA (0.05–1.0%, w/w, milk basis) were designed during the preparation of yoghurt. Colour and physicochemical and rheological properties of yoghurt were also examined. The results indicated that the fermentation process had no significant influence on GABA content. The GABA level greatly improved the texture properties of the resulting product at a concentration of 0.5% (w/w), whereas higher GABA concentrations impaired the texture. The lightness (L) value of yoghurt also increased in line with the GABA concentration.

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Separation and quantitation of milk whey proteins of close isoelectric points by on-line capillary isoelectric focusing—Electrospray ionization mass spectrometry in glycerol–water media

Cited by 33 publications

References 52 publications

Application of electric fields to clean ultrafiltration membranes fouled with whey model solutions

Application of electric fields to clean ultrafiltration membranes fouled with whey model solutions

On-line amino acid-based capillary isoelectric focusing-ESI-MS/MS for protein digests analysis

Effect of γ‐aminobutyric acid on the physicochemical, rheological and sensory properties of yoghurt

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