Food Science and Applied Biotechnology, 2019, 2(1), 67-73 Food Science and Applied Biotechnology Journal home page: www.ijfsab.com https://doi.org/10.30721/fsab2019.v2.i1 Dimitrova et al., 2019 Investigation of the antimicrobial activity of polyphenol-enriched extracts... Page 67 Research Article Investigation of the antimicrobial activity of polyphenol-enriched extracts against probiotic lactic acid bacteria Milena Dimitrova 1✉ , Galin Ivanov 1 , Kiril Mihalev 2 , Aleksandar Slavchev 3 , Ivelina Ivanova 4 , Radka Vlaseva 1 1 Department of Milk and Dairy Products Technology, Technological Faculty, University of Food Technologies, Plovdiv, Bulgaria 2 Department of Food Preservation and Refrigeration Technology, Technological Faculty, University of Food Technologies, Plovdiv, Bulgaria 3 Department of Microbiology, Technological Faculty, University of Food Technologies, Plovdiv, Bulgaria 4 Department of Analytical Chemistry and Physical Chemistry, Technological Faculty, University of Food Technologies, Plovdiv, Bulgaria Abstract The antimicrobial activity of polyphenol-enriched extracts from industrial plant by-products (strawberry and bilberry press residues and distilled rose petals) against probiotic lactic acid bacteria (Lactobacillus delbrueckii subsp. bulgaricus S10 and S19; Lactobacillus rhamnosus YW and S25; Lactobacillus gasseri S20; Streptococcus thermophilus S13 and S32) was investigated. The minimum inhibitory concentration (MIC) in most strains tested was found to be relatively high (from 6.25 mg.mL -1 to 12.50 mg.mL -1 ). The maximum concentration of polyphenols without any inhibitory effect (MCWI) ranges from 0.390 mg.mL -1 to 0.781 mg.mL -1 . The results from the present study showed that among the tested lactic acid bacteria, Lactobacillus delbrueckii subsp. bulgaricus S19, Lactobacillus rhamnosus YW and Streptococcus thermophilus S13 had the best growth characteristics in a polyphenol-enriched culture medium. These strains had the highest MIC and MCWI values and could thus be used as starter cultures for polyphenol-fortified fermented milk. Practical applications: Polyphenol-enriched extracts from industrial plant by- products (waste) – distilled rose petals (by-products of rose oil production) and strawberry and bilberry press residues (by-products of fruit juice production) can help improve economic outcomes and solve environmental problems in the food industry. Consequently, the development of functional fermented milks with a combination of probiotic starter cultures and polyphenol extracts represents a positive research direction for the food industry. Keywords: antimicrobial activity, polyphenol-enriched extracts, probiotics Abbreviations: MIC - Minimum inhibitory concentration MCWI - Maximum concentration of polyphenols without inhibitory effect ✉ Corresponding author: Milena Dimitrova, PhD student; Department of Milk and Dairy Products Technology, Technological Faculty, University of Food Technologies, 26 Maritza blvd. BG-4002 Plovdiv, Bulgaria, tel.: ++359 878 888 087; E-mail: milena_dimitrova17@abv.bg Article history: Received 5 June 2018 Reviewed 23 July 2018 Accepted 8 September 2018 Available on-line 19 March 2019 https://doi.org/10.30721/fsab2019.v2.i1.57 © 2019 The Authors. UFT Academic publishing house, Plovdiv