Possible Influence of Surfactants and Proteins on the Efficiency of Contact Agar Microbiological Surface Sampling

Agar contact microbiological sampling techniques, based on a transfer of the microorganisms present on a surface to a culture medium, are widely used to assess and control surface cleanliness and to evaluate microbial contamination levels. The effectiveness of these techniques depends on many environmental parameters that influence the strength of attachment of the bacteria to the surface. In the present study, stainless steel and high density polyethylene surfaces were inoculated with known concentrations of Staphylococcus epidermidis. Following an experimental design, the surfaces were sampled with different types of replicate organism direct agar contact plates and Petrifilm; results indicated that recovery rates were influenced by the presence of egg white albumin or Tween 80 in the inoculum solutions or by the introduction of surfactants into the contact agar of the microbiological sampling techniques. The techniques yielded significantly different results, depending on sampling conditions, underlining the need for a standardization of laboratory experiments to allow relevant comparisons of such techniques

Thermodynamic View of Primary Gushing

A spontaneous, wild, and uncontrolled liquid expulsion immediately upon opening non-shaken bottles of carbonated beverages defines primary gushing. The liquid volume resulting from primary gushing differs greatly even in the same laboratory. A thermodynamic investigation of the process can determine parameters responsible for this phenomenon. Although the required energy to provoke gushing is believed to be obtained mostly by the expansion of the nanobubbles, there are many other sources that might be significantly involved in this case. Providing the required energy via the explosion of the nanobombs breaks the weak hydrogen bond between CO 2 and water molecules and results in the release of the CO 2 . In this study, the authors claim that primary gushing is mainly linked to the CO 2 properties and consequently related to the liquid temperature at bottle opening (K), the pressure (bar), the CO 2 concentration (g/L), and the energy (N.m). © 2013 American Society of Brewing Chemists, Inc.status: publishe

Combined Modeling and Biophysical Characterisation of CO2 Interaction with Class II Hydrophobins: New Insight into the Mechanism Underpinning Primary Gushing

Although there is a common agreement that hydrophobins and CO2 are responsible for primary gushing of carbonated beverages, the bio-molecular mechanism of this phenomenon is not well understood. Here, hydrophobin HFBII has been produced, extracted, and purified. A gushing test and DLS analysis was performed and allowed the authors to design an MD simulation setup to investigate the interaction of CO2 molecules with HFBII in time. The results indicate that CO2 molecules tend to aggregate at the hydrophobic patch of HFBII twice as much as to the rest of the protein. A model is proposed that elucidates the "nanobomb" formation depicting a definite chemical and biophysical description of the primary gushing mechanism. © 2012 American Society of Brewing Chemists, Inc.status: publishe