Importance of harmonised sample preparation for moisture and protein content determinations in official food control laboratories: A poultry meat case study.

Commission Regulation (EC) 543/2008 limits moisture and protein contents in poultry meat. However, this regulation leaves room for interpretation regarding sample homogenisation, potentially affecting comparability of laboratory results. Therefore, a proficiency test and sample homogenisation study were organised amongst 19 European National Reference Laboratories (NRL). In the proficiency test, three different pre-homogenised chicken samples (fillets, drumsticks and carcasses) were analysed. Only one NRL produced unsatisfactory results. In the homogenisation study, NRLs were supplied with uniform fillet, drumstick and carcass materials. Homogenisation was performed according to the NRLs in-house methods. Five NRLs did not return satisfactory results. As these NRLs produced satisfactory results in the proficiency test, their increase in z-scores was related to their homogenisation practices. Overall, scattering of individual results was higher for drumsticks compared to fillets and carcasses. Homogenisation practices for poultry meat introduced significant differences in moisture and protein results and standardisation is therefore advisable.

Proteins and peptides in parotid saliva of irradiated patients compared to that of healthy controls using SELDI-TOF-MS.

BACKGROUND: Radiotherapy to the head and neck area damages the salivary glands. As a consequence hyposalivation may occur, but also the protein composition of saliva may be affected possibly compromising oral health. The aim of our study was to compare the relative abundance of proteins and peptides in parotid saliva of irradiated patients to that of healthy controls. METHODS: Using Lashley cups and citric acid, saliva from the parotid glands was collected from nine irradiated patients and ten healthy controls. The samples were analyzed with SELDI-TOF-MS using a NP20 and IMAC-30 chip in the molecular weight range of 1-30 kDa. RESULTS: On the NP20 chip 61 (out of 217) and on the IMAC-30 chip 32 (out of 218) peaks differed significantly in intensity between the saliva of the irradiated patients and healthy controls. 55 % of the significant peaks showed higher intensity and 45 % showed lower intensity in the saliva of irradiated patients. The peaks may represent, amongst others, the salivary proteins lysozyme, histatins, cystatin, protein S100 and PRP's. CONCLUSIONS: Large differences were found in the relative abundance of a wide range of proteins and peptides in the parotid saliva of irradiated patients compared to healthy controls.

Identification of salivary proteins at oil-water interfaces stabilized by lysozyme and beta-lactoglobulin.

In this research, we investigated the interaction occurring between oil-in-water emulsion droplets, stabilized by different emulsifiers, i.e. lysozyme and beta-lactoglobulin (beta-lg), and salivary proteins (SPs) with a molecular mass (M(r)) above about 10kDa. Different techniques, i.e. infrared spectroscopy, Western blotting, PAS staining and SDS-PAGE coupled to MS, were employed for this purpose. This study demonstrated the interaction between several salivary proteins and the emulsifiers at the oil-water interfaces. In particular, results show that the high M(r) mucin MUC5B was strongly bound to lysozyme stabilized emulsions, whereas beta-lg stabilized emulsions associated with MUC7 and, moderately, with MUC5B. Furthermore, we observed that salivary proteins in the range M(r) 10-100kDa associated differently with emulsion droplets. A large majority of SPs was found to interact with lysozyme stabilized emulsion droplets whilst in case of beta-lg stabilized emulsions, the SPs distribute more evenly between the fraction associated and non-associated with the droplets. A clear example is alpha-amylase (M(r) approximately 55kDa) which predominantly associates with lysozyme stabilized emulsion droplets, but not with beta-lg emulsion droplets. To conclude, our findings indicate that adsorption/association of salivary protein components onto the emulsion droplets is related to the type of emulsifying proteins at the oil-water interfaces and it is probably driven by the overall net charge at the droplet's oil-water interfaces, i.e. positive for lysozyme stabilized emulsions and negative for beta-lactoglobulin stabilized emulsion at neutral pH.

Saliva as research material: biochemical, physicochemical and practical aspects.

Whole saliva is a complex mixture of proteins and other molecules which originate from several sources. The biochemical and physicochemical properties of saliva contribute to the numerous functions of saliva in, e.g., speech, maintaining oral and general health, and food processing. Interest in saliva has increased in the last few years for its potential to diagnose viral, bacterial and systemic diseases. The use of saliva as research material may pose particular problems due to its inherent variability and instability. This review describes practical aspects of salivary as research material with emphasis on protein biochemistry and physical chemistry.

Complex formation in mixtures of lysozyme-stabilized emulsions and human saliva.

In this paper, we studied the interaction between human unstimulated saliva and lysozyme-stabilized oil-in-water emulsions (10 wt/wt% oil phase, 10 mM NaCl, pH 6.7), to reveal the driving force for flocculation of these emulsions. Confocal scanning laser microscopy (CSLM) showed formation of complexes between salivary proteins and lysozyme adsorbed at the oil-water interface and lysozyme in solution as well. To assess the electrostatic nature of the interaction in emulsion/saliva mixtures, laser-diffraction and rheological measurements were conducted in function of the ionic strength by adding NaCl to the mixture in the range between 0 and 168 mM. Increasing the ionic strength reduced the ability of saliva to induce emulsion flocculation as shown by the decreased floc size and the effect on the viscosity. Turbidity experiments with varying pH (3-7) and ionic strength also showed decreased complex formation in mixtures between saliva and lysozyme in solution upon NaCl addition up to 200 mM. Decreasing the pH increased the turbidity, in line with the increase of the positive net charge on the lysozyme molecule. We conclude that electrostatic attraction is the main driving force for complex formation between saliva components and lysozyme adsorbed at the oil droplets and in solution.