61C-26 |
Bioprotectant concentrations for control of contaminant bacteria in alcoholic fermentation of sugarcane juice |
M. A. FRANCHI, M. Cristianini, and G. E. Serra. Food Technology Dept., Faculty of Food Engineering, UNICAMP, Cidade Universitária Zefferino Vaz, s/n°, Campinas - SP, 13081-970, Brazil Microbial contaminants during alcohol fermentation has been controlled by antibiotic addition and by acidification of centrifuged yeast cell suspension. To avoid yeast resistance to antibiotics, ethanol producers are continuously testing novel antimicrobials. Bioprotection, defined as use of biological means and produsts for microbiological safety and process control, was envisaged as a solution for yeast flocculation in bacteria contaminated fermentations, with productivity and yield losses. The aim of this work was to evaluate the effect of bioprotectants and potentiators (EDTA and Tween 20), or combinations among them, on growth kinetics of sugar-and-alcohol industry contaminant bacteria. A complete factorial design (24) was used to study the effects of nisin (2 to 10 ppm), lysozyme (0 to 30 ppm), EDTA (0 to 0.22 %) and Tween (0 to 0.1%) concentrations on lag phase time (time necessary to increase 0.1 units of absorbance - 107 cfu) and growth rate (slope of log phase growth) of Lactobacillus plantarum and Lactobacillus fermentum. The microorganisms were inoculated on MRS broth containing bioprotectants and potentiators and incubated at 37°C. The increase of optic density (550 nm) was measured. Nisin was the most effective against both microorganisms. Its effect over Lactobacillus plantarum was ten-fold higher then lysozyme for lag phase delay. Interactions were not significant. For lag phase delay of Lactobacillus fermentum only nisin was effective and synergism was observed with Tween. Obtained mathematical models gave optimized combinations of 7.2 ppm of nisin to 0.1% of Tween to 30 ppm of lysozyme for L. plantarum and 8.6 ppm of nisin to 0.1% of Tween to L. fermentum. There was no positive effect on reducing growth rate of any microorganism. The results suggested that bioprotectant combinations can be effective on delaying bacterial growth, thus keeping the contamination at harmless levels during the fermentation process, therefore preventing floculation.
Session 61C, Food Microbiology: General I
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