Dynamical changes in hydration water accompanying lysozyme thermal denaturation

We study the dynanfics of the first hydration shell of lysozyme to determine the role of hydra- tion water that accompanies lysozyme thermal denaturation. We use nuclear magnetic resonance spectroscopy to investigate both the translational and rotational contributions. Data on proton self-diffusion and reorentational correlation time indicate that the kinetics of the lysozyme fold- ing/unfolding process is controlled by the dynamics of the water molecules in the first hydration shell. When the hydration water dynamics change, because of the weakening of the hydrogen bond network, the three-dimensional structure of the lysozyme is lost and denaturation is triggered. Our data indicates that at temperatures above approximately 315 K, water behaves as a simple liquid and is no longer a good solvent.

Water and lysozyme： Some results from the bending and stretching vibrational modes

The dynamic or glass transition in biomolecules is important to their functioning. Also essential is the transition between the protein native state and the unfolding process. To better understand these transitions, we use Fourier transform infrared spectroscopy to study the vibrational bending and stretching modes of hydrated lysozymes across a wide temperature range. We find that these transitions are triggered by the strong hydrogen bond coupling between the protein and hydration water. More precisely, we demonstrate that in both cases the water properties dominate the evolution of the system. We find that two characteristic temperatures are relevant： in the supercooled regime of confined water, the fragile-to-strong dynamic transition occurs at TL, and in the stable liquid phase, T＊ 315 ± 5 K characterizes the behavior of both isothermal compressibility KT（T, P） and the coefficient of thermal expansion ap（T, P）.

The cold chain and the COVID-19 pandemic:an unusual increase in histamine content in fish samples collected in Southern Italy during lockdown

Objectives:We analysed 900 samples of fresh(250)and processed(650)fish products collected in Sicily(Southern Italy)in 2020 during the severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)pandemic(hereafter:COVID-19).Materials and methods:The samples were divided temporally based on four phases relating to the various restrictions imposed by the Italian government in this period.The validated method of ultrahigh-performance liquid chromatography combined with a diode array detector was then employed for the analysis.Results:The samples collected during the Phase I lockdown period and after it had ended(Phase II)revealed significant increases in the mean histamine levels:(41.89±87.58)mg/kg and(24.91±76.76)mg/kg,respectively.The 11(1.3%of the total)fresh fish samples that were identified as being non-compliant with Regulation(EC)No.2073/2005 were only found during these two periods.All the processed samples were always compliant.The histamine values decreased as the restrictions eased,achieving a mean value of(11.16±9.3)mg/kg(Phase III).Conclusions:There was an increase in the incidence offish samples that were non-compliant with Regulation(EC)No.2073/2005 compared to previous surveillance data.These results provide a first report on the effect of lockdown measures on food safety and the cold chain.Our findings must cause food safety operators to intensify their controls over fresh fish products in such periods to safeguard consumer health.Further studies are required to evaluate whether the same trend would be observed with other food contaminants.