Margherita Rossi

Thermal denaturation and aggregation of egg proteins

Abstract The thermal denaturation of egg white and egg yolk proteins has been investigated by means of differential scanning calorimetry in natural, spontaneously aged samples. pH and protein content change with ageing. The overall endothermic signal from fresh egg white has been deconvoluted into three main gaussian components relevant to the denaturation of conalbumin, Iysozyme and ovoalbumin. The main modifications of the denaturation signal in aged egg white are attributed to progressive conversion of ovoalbumin to intermediate and Sovoalbumin conformations denatured at slightly higher temperatures. Aggregation of denatured proteins gives an exothermic signal that partially overlaps the denaturation peak. This implies some uncertainty in evaluation of each thermal effect, especially for non-aged samples. Nonetheless, the results obtained are comparable with the latest literature data on aqueous solutions of individual proteins. No deconvolution has been attempted for the endothermic DSC signal from egg yolk samples in the absence of literature on the DSC investigation of individual yolk proteins.

Effects of housing system and age of laying hens on egg performance in fresh pasta production: pasta cooking behaviour

BACKGROUND Very few studies concern the effects of layer housing systems and age on egg technological properties. Thus the aim of this work was to study the influence of these two factors on egg performance in fresh pasta production, focusing on pasta cooking behaviour. Samples of pasta subjected to analysis were prepared with eggs laid by Hy-Line Brown hens (from 27 to 68 weeks old) housed in cage, barn and organic systems. RESULTS Higher average values of weight increase and matter loss during pasta cooking were observed for samples prepared with eggs laid by older hens. Such cooking behaviour indicated the development of a weaker pasta protein network, resulting from a decrease in the quantity of albumen protein and an increase in fat content, which is due to the reduction in albumen/yolk ratio during hen aging. The housing system had a significant effect only on matter loss in cooking water, but differences between samples were so small as to be unlikely perceived by consumers. CONCLUSION Both hen age and housing system significantly affected pasta cooking behaviour, but the greatest effect was exerted by the hen age.

Chemical markers for the evaluation of raw material hygienic quality in egg products.

The aim of this research was to study uracil and lactic and acetic acids as chemical markers for hygienic quality evaluation of raw material in liquid pasteurized egg products. Uracil, absent in sound whole eggs, was formed in raw and pasteurized egg products as a consequence of high microbial contamination (>10(6) cfu/g) after a sufficient lag time, remaining stable at 4 degrees C but disappearing after 7 days of storage at 25 degrees C. Both lactic and acetic acids, starting from initial values of 1-7 mg/kg dry matter, presented trends similar to that of uracil; however, acetic acid never decreased during the storage of raw egg products. With few exceptions, all three metabolites were produced by Enterobacter cloacae, Escherichia coli, Morganella morganii, Serratia liquefaciens, Aeromonas hydrophyla, Pseudomonas fluorescens, Enterococcus avium, and Enterococcus faecalis, separately inoculated in whole egg samples. Uracil seems to be the most sensible marker, with a suggested limit corresponding to the detectable level.