| heal.abstract |
Screening of various lactic cultures from ACA-DC culture collection , for their ability to produce antimicrobial compounds, resulted in two promising producer thermophilus strains with quite broad inhibitory spectrum, namely Streptococcus thermohilus ACA-DCs20 and Streptococcus thermophilus ACA-DC 111. Both the antimicrobial compounds were effective against some bacteria associated with food spoilage and food-related health hazards, such as Clostridium, Enterococcus and Lisleria. The BACs20 bacteriocin was sensitive to proteolytic enzymes (pronase, trypsin, a-chymotrypsin), resistant to exposure to pH (1-12) and retained the full activity after heating to 30 min at 100°C. The BAC111 was resistant to a-chymotrypsin, inactivated below pH 4 and above pH 10 and lost the whole activity after 10 min at 60 °C. Different purification protocols for each bacteriocin showed that the activity has a MW of 2.5 and 30 KDa for BACs20 and BACH 1 respectively. The production of both bacteriocins was maximized in an fermentor under aerobic conditions held at a constant pH of 6.2 , where for the BA Cs20 the level of activity remained stable over 2 hours and then dropped sharply, contrary to the bacteriocin BAClll where no decline to activity was observed over a 24-period of fermentation. Both bacteriocins showed marked bactericidal action against a sensitive lactic strain of Lactococcus cremoris. This effect was concentration dependent for both cases. For BACs20 a concentration of 32AU/ml was able to drop the cfu 4 lag without recovering, contrary to the BAC111, where aconcentration of 8 AU dropped the cfu 3 lag.Studies on inhibition of growth of Clostridium sporogenes and Enterococcus faecalis by the above bacteriocins showed bacteriostatic and bactericidal effect, dependent on the concentration as well. |
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