Quantification and Physics of Cold Plasma Treatment of Organic Liquid Surfaces

Plasma treatment increases the surface energy of condensed phases: solids and liquids. Two independent methods of the quantification of the influence imposed by a cold radiofrequency air plasma treatment on the surface properties of silicone oils (polydimethylsiloxane) of various molecular masses and castor oil are introduced. Under the first method the water droplet coated by oils was exposed to the cold air radiofrequency plasma, resulting in an increase of oil/air surface energy. An expression relating the oil/air surface energy to the apparent contact angle of the water droplet coated with oil was derived. The apparent contact angle was established experimentally. Calculation of the oil/air surface energy and spreading parameter was carried out for the various plasma-treated silicone and castor oils. The second method is based on the measurement of the electret response of the plasma-treated liquids.Comment: 15 pages, 6 figures, 3 table

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Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.Includes bibliographical references (p. 83-84).by Sofya Pogreb.M.Eng

Resuscitation of Pulsed Electric Field-Treated Staphylococcus aureus and Pseudomonas putida in a Rich Nutrient Medium

Pulsed electric fields (PEFs) technology was reported to be useful as a disinfection method in the liquid food industry. This technology may lead to membrane permeabilization and bacterial death. However, resuscitation of viable but non-culturable cells and sublethally injured microorganisms in food was reported to be associated with foodborne outbreaks. The main aim of this study was to investigate the possible recovery of injured PEF-treated bacteria. The PEF treatment of Staphylococcus aureus and Pseudomonas putida led to a reduction of 3.2 log10 and 4.8 log10, respectively. After 5 h, no colony forming units (CFUs) were observed when the bacteria were suspended in phosphate buffer saline (PBS); and for 24 h, no recovery was observed. The PEF-treated S. aureus in brain-heart infusion (BHI) medium were maintained at 1.84 × 104 CFU mL−1 for about 1.5 h. While P. putida decreased to zero CFU mL−1 by the 4th hour. However, after that, both bacteria recovered and began to multiply. Flow cytometry analysis showed that PEF treatment led to significant membrane permeabilization. Mass spectrometry analysis of PEF-treated P. putida which were suspended in BHI revealed over-expression of 22 proteins, where 55% were related to stress conditions. Understanding the recovery conditions of PEF-treated bacteria is particularly important in food industry pasteurization. To our knowledge, this is the first comprehensive study describing the recovery of injured PEF-treated S. aureus and P. putida bacteria