Kombucha was prepared in a tea broth (0.5% w/v) supplemented with sucrose (10% w/v) by using a commercially available starter culture. The pH decreased steadily from 5 to 2.5 during the fermentation while the weight of the "tea fungus" and the OD of the tea broth increased through 4 days of the fermentation and remained fairly constant thereafter. The counts of acetic acid-producing bacteria and yeasts in the broth increased up to 4 days of fermentation and decreased afterward. The antimicrobial activity of Kombucha was investigated against a number of pathogenic microorganisms. Staphylococcus aureus, Shigella sonnei, Escherichia coli, Aeromonas hydrophila, Yersinia enterolitica, Pseudomonas aeruginosa, Enterobacter cloacae, Staphylococcus epidermis, Campylobacter jejuni, Salmonella enteritidis, Salmonella typhimurium, Bacillus cereus, Helicobacterpylori, and Listeria monocytogenes were found to be sensitive to Kombucha. According to the literature on Kombucha, acetic acid is considered to be responsible for the inhibitory effect toward a number of microbes tested, and this is also valid in the present study. However, in this study, Kombucha proved to exert antimicrobial activities against E. coli, Sh. sonnei, Sal. typhimurium, Sal. enteritidis, and Cm. jejuni, even at neutral pH and after thermal denaturation. This finding suggests the presence of antimicrobial compounds other than acetic acid and large proteins in Kombucha.

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Fermented tea drink, Kombucha, can inhibit the growth of Shigella sonnei, Escherichia coli, Salmonella enteritidis and Salmonella typhimurium. Several metabolites were analyzed every two days during a 14-day Kombucha fermentation. Levels of acetic acid and gluconic acid were found to increase with fermentation time. No lactic acid or ethanol was detected. Systematic investigation of the antimicrobial activity in Kombucha revealed the presence of antimicrobial compounds other than organic acids or proteins (enzymes) produced during fermentation or the tannins originally present in the tea broth.

The theoretical mathematical models described in this paper are used to evaluate the effects of fungal biomass inactivation kinetics on a non-isothermal tray solid-state fermentation (SSF). The inactivation kinetics, derived from previously reported experiments done under isothermal conditions and using glucosamine content to represent the amount of biomass, are described in different ways leading to four models. The model predictions show only signi®cant effects of inactivation kinetics on temperature and biomass patterns in the tray SSF after long fermentation periods.The models in which inactivation is triggered by low speci®c growth rates can predict restricted biomass evolution in combination with a fast temperature increase followed by a slower temperature decrease. Such inactivation might occur when substrate is limiting or products are formed in toxic concentrations.Temperature is predicted to be the key parameter. Oxygen concentration is predicted to become limiting only at high heat conduction and low oxygen diffusion rates. Desiccation of the substrate is predicted not to occur. IntroductionSolid-state fermentations (SSF) are applied for the production of, for example, enzymes, biopesticides, food, feed and ®ne chemicals. In SSF, microorganisms grow on a moist solid substrate without free-¯owing water. The chemical reactions necessary for growth are exothermic and thus temperature control is necessary. It depends strongly on the type of fermenter system used (tray, packed bed, rotating drum) what the effect of heat production is on temperature in the fermenter bed and thus on the results of the fermentation. A typical temperature course during fermentation in a tray system shows a steep increase to 40±45 C after a short lag phase, followed by a decline at a rate of 0.1 [5]±0.5 C [6] per hour, depending on the microorganism and type and size of system used.Simulation models can provide insight into the complex interaction between microbial growth, oxygen consumption and concomitant heat production, and oxygen and heat transport. Ideally, these models should take into account the effects of growth, maintenance and decay on respiration activity, each as functions of, for instance, time, temperature, nutrient and water availability.Several examples of models for fungal SSF processes can be found in the literature, describing different fermentation systems [7±12]. These reports focus on the biomass production phase of the fermentation and do not properly consider the period after growth has virtually stopped. Especially for secondary metabolite production, the latter period may be very important. Besides, in most SSF systems fungal biomass is present growing at different rates, depending on combined effects of several parameters, such as temperature, water activity, and oxygen and carbon dioxide concentration. Thus, all biomass is not necessarily in the same growth phase. This emphasizes the need for considering description of the post-growth stage in modelling SSF.In our models we describe the respiration ...

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