Review: applications of mass spectrometry techniques in the investigation of milk proteome

The introduction of "soft" desorption/ionization methods such as electrospray ionization and matrix-assisted laser desorption/ionization has determined a breakthrough in the application of mass spectrometry to the structural analysis of proteins. The contemporary advancement of bioinformatics, together with the possibility to combine these mass spectrometric methods with electrophoretic or chromatographic separation techniques has opened up the new field of proteome analysis and, more generally, has established these approaches as indispensable tools for protein and peptide analysis in complex mixtures, such as milk and milk- derived foods. Here, a necessarily not exhaustive series of current applications of mass spectrometry-based techniques for the characterization of milk proteins will be summarized. These include the characterization of milk protein polymorphism, determination of the structural modifications induced on milk proteins by industrial processes, investigation of milk adulterations and characterization of milk allergens.     

Reveal Salmonella enteritidis test for detection of Salmonella enteritidis in shell eggs and environmental samples

Reveal Salmonella Enteritidis (SE) is a lateral flow-based immunodiagnostic assay used for rapid detection of Salmonella enterica serovar Enteritidis from pooled shell eggs and environmental samples. This assay uses highly specific antibodies to accurately detect S. Enteritidis. Studies were conducted to compare the performance of this test against reference procedures for detection of S. Enteritidis from both pooled shell eggs and environmental samples. Pooled shell eggs were inoculated with low levels ofS. Enteritidis and were enriched according to the procedure prescribed by the U.S. Food and Drug Administration. Uninoculated samples were included in each trial. Reveal SE exhibited 100% sensitivity and 100% specificity in comparison to the reference method in all trials. An abbreviated 48 h/(no hold) enrichment procedure was also developed and validated for detection ofS. Enteritidis from pooled shell egg samples. This shortened enrichment procedure can be used in conjunction with the Reveal SE test and offers a significant enrichment time savings of 96 h. Chi-square analysis revealed that there was no significant difference between the abbreviated Reveal method and the reference procedure for detection ofS. Enteritidis from pooled shell egg samples. Out of 245 natural drag swabs screened internally, only three samples tested Reveal SE positive and were confirmed by the reference procedure, resulting in 100% sensitivity and 100% specificity. An external laboratory screened 147 poultry house environmental samples and obtained 35 Reveal SE confirmed positives for Reveal SE sensitivity of 100% and specificity of 90%. Inoculation trials with drag swabs resulted in 96% sensitivity and 100% specificity. Thus, these data demonstrate that Reveal SE is a highly sensitive and specific assay for the detection of S. Enteritidis from both pooled shell eggs and environmental samples.     

Protonation thermodynamics of 1,10-phenanthroline in aqueous solution. Salt effects and weak complex formation

The protonation of 1,10-phenanthroline has been studied potentiometrically in different aqueous salt media (LiCl, NaCl, KCl, Me₄NCl, Et₄NI, MgCl₂, CaCl₂, SrCl₂, and BaCl₂) in the ionic strength range 0≤1≤1 M. This ligand forms two protonated species, [H(phen)]⁺ and [H(phen)₂]⁺; the monoligand species shows protonation constants strongly dependent on the medium. Medium effects were explained by the formation of some weak species: [H(phen)Cl]⁰, [M(phen)]²⁺ (M=alkaline earth metal cations). Formation thermodynamic parameters are reported.     

A comparison of equations for fitting protonation constants of carboxylic acids in aqueous tetramethylammonium chloride at various ionic strengths

The protonation of acetic, malonic, succinic, citric, 1,2,3-propanetricarboxylic, 2-methyl-1,2,3-propanetricarboxylic, 1,2,3,4-butanetetracarboxylic, and benzenehexacarboxylic acids was studied potentiometrically, at 25°C and at various ionic strengths in aqueous tetramethylammonium chloride, in the range 0 ≤I _c ≤ 3 mol-dm^-3 (0≤I _m≤ 4.4 mol-kg^-1). Protonation constants were fitted by several equations (Debye-Hückel type, Pitzer and Bromley equations) for the dependence on ionic strength. General equations, containing some common parameters, independent of the acid considered, are reported.     

Solvent effects on the activation parameters of the reaction between an α‐tocopherol analogue and dpph•: The role of H‐bonded complexes

The analysis of the activation parameters for the formal H‐atom transfer reaction between 2,2,5,7,8‐pentamethyl‐6‐chromanol (ChrOH) and 2,2‐diphenyl‐1‐picrylhydrazyl (dpph^?) reveals that these parameters are effective probes of the actual reaction mechanism. Indeed, the A factors measured in various polar and apolar solvents are localized in three distinct domains according to whether the reaction occurs via outer‐sphere electron transfer (ET) from the anion ChrO^? or hydrogen atom transfer (HAT). For instance, A = 5.9 × 10⁵ M^?1 s^?1 and E_a = 2.5 kcal mol^?1 in cyclohexane where the reaction proceeds by HAT, whereas in methanol, ethanol, and their mixtures with water where there is a substantial ET contribution A > 10⁹ M^?1s^?1 and E_a > 7 kcal mol^?1. Interestingly, in nonhydroxylic polar solvents, A～ 10⁷ M^?1s^?1 and the E_a values reflect the H‐bond accepting ability of the solvent in agreement with the “standard” kinetic solvent effects on HAT reactions. Addition of small quantities of pyridine accelerates the reaction rates in these solvents. This suggests that the H‐bonded complex (ChrOH···Py) is able to react via intermolecular ET with dpph^?. It is known, in fact, that pyridine lowers the oxidation potential of phenols by ～0.5 V and the ΔG_ET of ChrOH + dpph^? consequently decreases by about 10 kcal mol^?1. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 524–531, 2012     

Reactions of 3‐substituted chromones with ortho‐phenylenediamine

Chromones 1 react with diamine 2 to give various products depending on the nature of the position 3 substituent in the heterocycle.     

3‐Phenyl‐4H‐furo­[3,2‐c]­chromen‐4‐one

The crystal structure of the title compound, C₁₇H₁₀O₃, is the first example of a furocoumarin containing three fused rings. The tricyclic furocoumarin fragment is perfectly planar. The phenyl substituent forms a dihedral angle of 39.52 (8)° with the plane of the tricyclic system. The crystal packing involves centrosymmetric dimers interconnected by strong π‐interactions between their furo­[3,2‐c]­coumarin fragments [at distances of 3.42 (4) Å].