Interstrains comparison of the antimicrobial effect and mode of action of a Vietnamese Cinnamomum cassia essential oil from leaves and its principal component against Listeria monocytogenes.

The antibacterial activity of a Cinnamomum cassia essential oil (EO) and of its main component trans-cinnamaldehyde (90% w/w) was examined against five Listeria monocytogenes strains. The minimal inhibitory concentrations (MICs) of C. cassia EO against the five L. monocytogenes strains were identical (250 µg ml-1 ), while the minimal bactericidal concentrations (MBCs) ranged between 800 and 1200 µg ml-1 . In order to study if this EO and trans-cinnamaldehyde altered the five strains at the membrane level, fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) was measured in presence of different concentrations (1/2MIC, MIC, 2MIC) of these antibacterial agents. A concentration-dependent increase of fluorescence anisotropy of DPH in their presence reflecting a rigidification of the membrane was observed for the five strains. This modification of the membrane fluidity was associated with a perturbation of the selective membrane permeability, as a perturbation of the gradient between intracellular and extracellular pH was also observed.

Acid-base balance in chicken embryos (Gallus domesticus) incubated under high CO2 concentrations during the first 10 days of incubation.

Recent studies show the importance of differential CO2 levels during the first half of incubation of chicken eggs on embryonic and postnatal growth. However, it is not known how external higher CO2 levels affect embryonic acid-base balance. In this study, the effect of an early rise in CO2, between 25th and 96th hour of incubation to 1.5% and maintained at that level until 240 h of incubation, was investigated on air cell gases, blood gas parameters from ED10 onwards and on embryonic growth and hatching parameters. Higher external CO2 concentrations resulted in a faster acidification of albumen resulting in a faster decrease of albumen pH with development, illustrating the capacity of albumen to cope with higher environmental CO2. Moreover, PCO2 in blood was higher in CO2 incubated embryos at embryonic day 10 and 11 but without a change in blood pH. The additional increase in plasma HCO3- concentration at day 10 and 11 was responsible for buffering the higher PCO2 in CO2 incubated embryos in order to stabilize pH. However, effects of hypercapnia on blood acid-base parameters extinguished 2 days after termination of high CO2 incubation. Embryonic growth was modestly accelerated which was reflected in higher embryonic weights at day 6 and 10 and a significant earlier hatching; hatchling weights were not different between treatment groups.

Pressure-induced inactivation of E. coli beta-galactosidase: influence of pH and temperature.

In order to assess the feasibility of a high-pressure immunodesorption process using a beta-galactosidase-anti-beta-galactosidase complex as a model, the influence of high hydrostatic pressure on the activation of E. coli beta-galactosidase has been investigated. The irreversible activity loss of beta-galactosidase was studied as a function of pH and temperature for pressures comprised between atmospheric pressure and 500 megapascal (MPa; 1 MPa = 10 bar). This enabled us to establish a practical pressure-temperature diagram of stability for this enzyme. The stability domains determined thus appeared to be strongly dependent on the pH under atmospheric pressure of phosphate buffer employed for pressurisation. Therefore, to interpret meaningfully this result, the influence of pressure on the pH-activity curve of beta-galactosidase was investigated by using a high-pressure stopped-flow device. It appeared that the pH-activity curve of this enzyme was also reversibly affected by pressures lower than 150 MPa. An interpretation of these results in relation to the high-pressure induced changes of ionisation constants is proposed. For our practical purpose, the implications for the elaboration of a high-pressure immunodesorption process using beta-galactosidase as a tag, are discussed.

Quantification of the heat exchange of chicken eggs.

In the incubation process of domestic avian eggs, the development of the embryo is mainly influenced by the physical microenvironment around the egg. Only small spatiotemporal deviations in the optimal incubator air temperature are allowed to optimize hatchability and hatchling quality. The temperature of the embryo depends on 3 factors: (1) the air temperature, (2) the exchange of heat between the egg and its microenvironment and (3) the time-variable heat production of the embryo. Theoretical estimates on the heat exchange between an egg and its physical microenvironment are approximated using equations that assume an approximate spherical shape for eggs. The objective of this research was to determine the heat transfer between the eggshell and its microenvironment and then compare this value to various theoretical estimates. By using experimental data, the overall and the convective heat transfer coefficients were determined as a function of heat production, air humidity, air speed, and air temperature. Heat transfer was not affected by air humidity but solely by air temperature, embryonic heat generation, and air speed and flow around eggs. Also, heat transfer in forced-air incubators occurs mainly by convective heat loss, which is dependent on the speed of airflow. A vertical airflow is more efficient than a horizontal airflow in transferring heat from the egg. We showed that describing an egg as a sphere underestimated convective heat transfer by 33% and was, therefore, too simplistic to accurately assess actual heat transfer from real eggs.

Quantification and control of the spatiotemporal gradients of air speed and air temperature in an incubator.

Around the optimal incubator air temperature only small spatiotemporal deviations are allowed. However, air speed and air temperature are not uniformly distributed in the total volume of the incubator due to obstruction of the eggs and egg trays. The objectives of this research were (1) to quantify the spatiotemporal gradients in temperature and velocity and (2) to develop and validate a control algorithm to increase the uniformity in temperature during the entire incubation process. To improve the uniformity of air temperature, the airflow pattern and the air quality need to be controlled more optimally. These data show that the air temperature between the eggs at a certain position in a large incubator is the result of (1) the mean air temperature of the incubator; (2) the exchange of heat between the egg and its micro-environment, which is affected by the air speed at that certain position; (3) the time-variable heat production of the embryo; and (4) the heat influx or efflux as a result from the movement of hot or cold air in the incubator toward that position, which is affected by the airflow pattern. This implies that the airflow pattern needs to be controlled in a more optimal way. To maximize the uniformity of air temperature, an active and adaptive control of the three-dimensional (3-D) airflow pattern has been developed and tested. It was found to improve the spatiotemporal temperature distribution. The chance of having a temperature reading in the interval from 37.5 to 38.1 degrees C increased by 3% compared to normal operating conditions.