A method for encapsulating high concentrations of essential oils into bakers' yeast (Saccharomyces cerevisiae) is described. The process involves mixing an aqueous suspension of yeast and an essential oil, which allows the oil to pass freely through the cell wall and membrane and remain passively within the cell. Oil droplets sequestered within the cell were clearly visible using confocal microscopy. Transmission electron microscopy demonstrated that the cell wall and membrane remain intact during the process. Cells quickly lost viability during the process and it appeared unnecessary for the cells to be viable for the process to occur. Encapsulated oil was recovered from the cells using a water/ethanol extraction procedure and analysed by gas chromatography. No significant differences were noted between encapsulated and unencapsulated oil profiles. The rate of permeation of oil into the yeast cells was found to increase significantly at higher temperatures due to the phase transition of the lipid membrane. The rates at which different essential oils permeated the cell varied considerably due to variations in terpene chemistry. The encapsulation of straight chain hydrocarbons highlighted the effects of molecular size, shape and the presence of hydroxl groups on the process. The process occurs by passive diffusion as a result of hydrophobic flavour components partitioning into the cell membrane and intracellular lipid. This paper briefly reviews the patented literature and reports some of the initial observations of the transport mechanisms involved during the accumulation of essential oils by yeast cells.
Pseudomonas fluorescens, Yersinia enterocolitica, and Listeria monocytogenes were shown to readily attach to both rubber and Teflon® surfaces. Sanitizer efficacy testing done in the laboratory with nonadherent bacteria could lead to false assumptions as to the sanitizer's true effectiveness under processing conditions where cells may be attached. The objectives in this study were: (a) evaluate the efficacy of in-use concentrations of sanitizers on bacteria attached to gasket materials, (b) compare bacterial attachment to rubber and Teflon® gaskets, (c) examine different methods of enumeration, and (d) compare sanitizer efficacy on attached and suspended bacteria. The goal reduction for all of the sanitizers tested was ≥3 log cycles or 99.9%. Results indicated that iodophor, hypochlorite, acid anionic, peroxyacetic acid, fatty acid, and quaternary ammonium sanitizers failed to provide an adequate reduction in the numbers of attached bacteria at levels of 104 to 105/mm2 in most cases. The test organisms attached in slightly higher numbers to the rubber surface versus Teflon®. Plate counts, impedance microbiology, and the direct epifluorescent filter technique were tested as methods of enumeration. Impedance microbiology was the best method of enumeration, since it allowed the estimation of both reversibly and irreversibly attached bacteria. The efficacy of sanitizers versus a bacterial suspensions resulted in a ≥ 5 log-cycle reduction. The same concentrations were relatively ineffective against the attached bacteria. The goal reduction was reached on the Teflon® surface with the iodophor, hypochlorite, and fatty acid sanitizers with a log-cycle reduction in the number of Yersinia enterocolitica of 3.09, 3.19, and 3.31, respectively. Pseudomonas fluorescens was reduced by 3.16 on both the rubber and Teflon® surfaces when exposed to the hypochlorite sanitizer.
Over the years, many tests and assays have been developed to estimate the quality and potential shelf-life of dairy products. These have ranged from simple, standard bacterial enumerations to more complex metabolite detections. This paper is a review of the parameters that have been used to estimate, or indicate the inherent quality of dairy products.
Direct-set cottage cheese packaged in barrier containers was flushed with 100% CO, 75% CO,:25% N,, 100% N,, or air, and stored at 4°C for 28 days. Quality was assessed by sensory, microbiological, and chemical tests. No change was observed in headspace gas composition during storage. Psychrotrophic and lactic acid bacteria counts increased for airtreated samples, but counts for cottage cheese packaged under modified atmospheres remained unchanged. Product discoloration was not observed. Acidity increased over storage life, but lactic acid did not contribute towards increased acidity. Sensory characteristics of cottage cheese packaged under modified atmospheres remained satisfactory after 28 days, with 100% CO, best.
Log phase cells of Listeria monocytogenes Scott A were heat shocked in Trypticase Soy + 0.6% yeast extract (TSYE) broth at 48°C for 10 min, followed by heating at 55°C for up to 50 min. Heat resistance was determined using nonselective (TSYE) and selective (McBride Listeria) enumeration media which were incubated under aerobic and anaerobic environments. D55°C-values for heat shocked cells were 2.1-fold higher than nonheat shocked cells (18.7 min vs. 8.89 min) when cells were enumerated on TSYE agar aerobically and 2.2-fold higher (26.4 min vs. 12.0 min) for cells enumerated anaerobically on TSYE agar. When cells were enumerated aerobically on McBride Listeria (ML) agar, D55°C-values for heat shocked cells were 1.4-fold higher than nonheat shocked cells (9.55 min vs. 6.69 min). No growth was observed on ML agar anaerobically. The physiological condition of the microorganism, the enumeration medium, and the growth environment greatly affected the heat resistance of logphase cells of Listeria monocytogenes Scott A.
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