Qualitative and quantitative analysis of proteins and peptides in milk products by capillary electrophoresis

Abstract

Milk protein is an important component of the human diet throughout much of the world. The ability to assess the relative composition and integrity of milk proteins or peptides in dairy foods or food ingredients is important because these molecules have a profound effect on product functionality and quality. This communication describes two capillary electrophoretic methods that are useful for the analysis of proteins and casein-derived peptides in cheese and milk products. One technique, which uses a buffer containing citrate/phosphate (pH 3.3), 4 M urea, and a polymeric additive in a coated capillary, is useful for qualitative and quantitative analysis of proteins and peptides in milk, cheese, and whey products. The second method employs a citrate/phosphate buffer (pH 2.8) and a bare silica capillary, and is well suited for the analysis of small, casein-derived peptides in aqueous cheese extracts.

Contribution of Lactococcus lactis Cell Envelope Proteinase Specificity to Peptide Accumulation and Bitterness in Reduced-Fat Cheddar Cheese

“…The filtrate was collected and stored at Ϫ20°C until needed. Standard solutions of purified synthetic peptides were prepared as described by Strickland et al (36), and then reverse-phase HPLC was performed as described previously (4) Assembly of trained bitter sensory panel. Approximately 100 potential panelists were screened for the ability to taste bitterness using aqueous quinine sulfate (QS) solutions with duotrio testing (1).…”

Estimation of variation in concentration, phosphorylation and genetic polymorphism of milk proteins using capillary zone electrophoresis

“…When we do not use a reducing agent during sample preparation, a part of the a S2 -CN will still be present as dimers. Dimers have a different migration time during CZE analysis than monomers (Strickland et al, 2001). Before we performed this experiment, we first determined whether the reducing conditions used during normal analyses (17 mM DTT) were sufficient to reduce all dimers of a S2 -CN to their monomer form.…”

“…However, the actual assignment of peaks as different phosphorylation states of a S2 -CN has not been performed yet. The CZE method has also been used for quantitative determination of some individual proteins (Gomez Ruiz, Miralles, Aguera, & Amigo, 2004;Otte et al, 1997;Strickland, Johnson, & Broadbent, 2001), but has not been applied to determine the variation in concentration of all separated proteins in a large number of samples. Therefore, to estimate variation in concentration, phosphorylation and genetic polymorphism of milk protein by applying CZE, two actions have to be undertaken: (1) The nature of some previously unidentified peaks, that might be genetic variants or proteins that represent different phosphorylation states from known proteins, has to be established; (2) the method of de Jong et al (1993) has to be tested for its reproducibility in quantifying all main milk proteins in a large number of samples.…”

Analysis of α-lactalbumin, β-lactoglobulin A and B in whey protein powder, colostrum, raw milk, and infant formula by CE and LC

“…15% of total protein) fractions. The whey proteins are mainly composed of α-lactalbumin (α-Lac) and β-lactoglobulin (β-Lg; Strickland et al 2001). β-Lg usually has two isoforms, namely, β-lactoglobulin A (β-Lg A) and β-lactoglobulin B (β-Lg B).…”