László Friedrich

Effect of high pressure treatment on liquid whole egg

In our tests, we artificially infected liquid whole egg samples with Salmonella enteritidis, Listeria monocytogenes, and Staphylococcus aureus bacteria, and then treated the samples in “Food Lab900” high hydrostatic pressure (HHP) instrument for 3–17 min at 200–400 MPa. Subsequently, the change of the viable cell count of the specific bacteria has been tested. In addition to the samples infected with various bacteria, non-infected samples were also treated in each test and the change in viable cell count, colour and viscosity of the samples upon the effect of the treatment. In summary, it can be concluded that in each test of our investigations, the viable cell count of S. enteritidis critical for egg products is reduced significantly, while the reduction of the total viable cell count was around two magnitudes. Additionally, based on our results, microbial destruction, reduction of enthalpy (denaturation of egg white) caused by the treatment at HPP, and colour change are primarily affected by the pressure level, while the changes in rheological properties are also significantly affected by the duration of high pressure treatment (p<0.05).

Small angle neutron scattering study of nanostructural changes in microbial transglutaminase-treated low-fat yogurt during fermentation

Small angle neutron scattering (SANS) studies of fermentation of bovine milk with and without microbial transglutaminase (mTG) are described. Use of mTG increased the quality of low-fat yogurt via cross-linking of milk proteins. The SANS method was suitable for simultaneous characterization of the fermentation process and the effect of mTG. A decrease of whey protein release into the supernatant of centrifuged low-fat yogurt samples showed how mTG was capable to cross-link them already after 1 h of fermentation. The applied SANS method can be used to follow the sol-gel transformation of fermented dairy products in general. Moreover it can be a special tool for detecting the activity of mTG during fermentation of low-fat yogurts.

Study of Long Term Post-Treatment of Whole Egg Powder at 50-55°C

Study of Long Term Post-Treatment of Whole Egg Powder at 50-55°C In our experiment whole egg powder samples (infected with Salmonella Enteritidis for microbiological tests) were treated at 50.38-54.62°C for 6.41-24.09 h and tested for decrease in Salmonella count or changes in their solubility and colour. Central Composite Rotational Design (CCRD) was used in our tests. In all tests performed within the testing range we achieved a decrease in Salmonella count of at least 5 magnitudes and in cases when the samples were treated at min. 52.5°C for at least 9 h no viable Salmonella could be detected in the whole egg samples at the end of treatments. Our measurements have shown that deterioration of solubility and discolouration was significantly affected only by the temperature change (p<0.05).