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    Control of Listeria monocytogenes contamination in fresh beef by using lactococcin BZ
    (Wiley, 2017) Yildirim, Zeliha; Yerlikaya, Sabire; Oncul, Nilgun
    The aim of this study was to investigate the inhibitory effect of lactococcin BZ produced by Lactococcus lactis spp. lactis BZ against Listeria monocytogenes in raw beef. Lactococcin BZ depending on concentration (400-3,200 AU/ml) reduced the counts of L. monocytogenes attached to meat surface (from 4.71 log CFU/g to undetectable level, and from 7.92 to 3.64 log CFU/g) in 5 min. When meat samples were simultaneously inoculated with lactococcin BZ and L. monocytogenes, lactococcin BZ reduced the count of non-attached Listeria cells in 5 min by 1.58-5.03 (undetectable level) log cycles in the low inoculum (5.03 log CFU/g) and 1.11-5.58 log cycles in the large inoculum (7.86 log CFU/g) compared to control samples. Also, lactococcin BZ at 400-3,200 AU/ml reduced the number of L. monocytogenes in meat samples inoculated at 2.45, 4.42, and 7.29 log CFU/g throughout 12 day storage at 4 degrees C and maintained its biological activity. In addition, lactococcin BZ adsorbed to meat surface and adsorption did not adversely affected antilisterial activity. Practical applicationsIn this study, we investigated the inhibitory effect of lactococcin BZ produced by Lactococcus lactis spp. lactis BZ against Listeria monocytogenes during, after or before attachment on raw beef. It was observed that lactococcin BZ depending on its concentration (400-3,200 AU/ml) and amount level of Listeria cells (4.71 or 7.92 log CFU/g) reduced the cell counts of L. monocytogenes in the meat samples very effectively. Lactococcin BZ at 1,600 and 3,200 AU/ml showed strong antilisterial activity toward L. monocytogenes before, during and after attachment to meat samples, but its antilisterial activity was higher before or during attachment than after attachment. Therefore, lactococcin BZ could be potential alternatives to chemical preservatives for meat industry.
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    Inhibitory effect of enterocin KP in combination with sublethal factors on Escherichia coli O157:H7 or Salmonella Typhimurium in BHI broth and UHT milk
    (TUBITAK SCIENTIFIC & TECHNICAL RESEARCH COUNCIL TURKEY, 2014) Yildirim, Zeliha; Ilk, Yaselin; Yildirim, Metin; Tokatli, Kader; Oncul, Nilgun
    The effects of physical and chemical sublethal treatments on the antibacterial activity of enterocin KP produced by Enterococcus faecalis KP against Escherichia coli O157:H7 and Salmonella Typhimurium were investigated. Enterocin KP was not active against intact cells of E. coli O157: H7 or S. Typhimurium. However, the use of enterocin KP together with ethylenediaminetetraacetic acid (50 mM), sodium tripolyphosphate (50 mM), sublethal heating (60 degrees C for 10 min), cold shock (-20 degrees C for 2 h), or acid stress (mixture of 40% lactic acid, 16% propionic acid, 16% acetic acid) in BHI medium decreased the cell number of E. coli O157: H7 by 7.27, 6.28, 3.39, 3.06, 4.20 log and S. Typhimurium by 7.21, 6.20, 3.64, 3.38, 3.98 log cfu/mL, respectively. The combination of enterocin KP with ethylenediaminetetraacetic acid decreased the cell number of E. coli O157: H7 in UHT milk to undetectable level, enterocin KP plus sodium tripolyphosphate or enterocin KP plus sublethal heating caused a reduction by 6.07 and 5.68 log cycles. The results of this study showed that enterocin KP could be applied as a biopreservative to inhibit E. coli O157: H7 and S. Typhimurium in combination with physical and food grade chemical hurdles.
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    Inhibitory Effect of Lactococcin BZ Against Listeria innocua and Indigenous Microbiota of Fresh Beef
    (FACULTY FOOD TECHNOLOGY BIOTECHNOLOGY, 2016) Yildirim, Zeliha; Yerlikaya, Sabire; Oncul, Nilgun; Sakin, Tuba
    In this study, the effect of lactococcin BZ on microbiological quality of fresh beef is investigated. For this purpose, the meat samples were treated with various amounts of lactococcin BZ (200-2500 AU/mL), a bacteriocin produced by Lactococcus lactis spp. lactis BZ, and kept at 4-5 degrees C for 12 days. During storage, the microbiological properties of the meat samples with or without lactococcin BZ were determined. Inhibitory effect of lactococcin BZ depended on its amount. The higher the amount of lactococcin BZ, the higher the inhibitory activity. Treatment with lactococcin BZ at the level of 2500 AU/mL resulted in 4.87, 3.50 and 3.94 log cycle decrease in the counts of mesophilic, psychrotrophic and lactic acid bacteria, respectively, and 1.90.10(4) and 1.04.10(2) CFU/g reduction in conform and faecal conform bacteria, respectively, at the end of storage as compared to their initial numbers in the control sample. However, the counts of these bacteria in control samples increased during storage. Also, lactococcin BZ at 1600 AU/mL showed very strong antilisterial effect against Listeria innocua in fresh meat and reduced the cell numbers from 6.04 log CFU/g to undetectable level on the 6th day of storage. In conclusion, lactococcin BZ has a potential use as a biopreservation agent to improve safety and shelf life of raw beef.
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    Microbiological, antimicrobial and antioxidant characteristics of commercial Turkish kefirs
    (M H Schaper Gmbh Co Kg, 2021) Oncul, Nilgun; Ozbey, Ayse; Erinc, Hakan; Yildirim, Zeliha
    In this study, the microbiological properties, physicochemical characteristics, antimicrobial and antioxidant activities of Turkish commercial kefir products were investigated. The enumeration of Lactococci, aerobic lactobacilli, anaerobic lactobacilli, acetic acid bacteria (AAB) and yeast were performed by spread plate technique and counted as 7.35, 6.62, 6.85, 6.24 and 2.35 log CFU/g, respectively. Antimicrobial activity of kefir was evaluated using the disk diffusion method. Ten microorganisms, including seven Grampositive strains and three Gram-negative strains were tested. While Listeria monocytogenes, L. ivanovii and Escherichia coli were the sensitive bacteria for all kefir samples, L. plantarum, Staphylococcus aureus, Bacillus cereus and E. coli O157:H7 are the resistant bacteria. The means of pH, total phenolic content, Trolox Equivalent Antioxidant Capacity (TEAC) and lipid peroxidation were 4.03, 4.39 mg GAE/100mL, 0.15 mu mol Trolox/mL and 7.23%, respectively. From the beneficial health properties point of view, kefir appears to be a promising food.
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    The inhibitory effect of lactoccocin BZ against Escherichia coli on fresh beef
    (M H Schaper Gmbh Co Kg, 2024) Oncul, Nilgun; Tokatli, Kader; Yildirim, Zeliha
    During the processing of fresh meat, there is a risk of contamination with foodborne pathogenic E. coli. The use of bacteriocins is considered to ensure the safety of fresh meat. In this context, the impact of lactococcin BZ on the E. coli population in fresh beef has been investigated. The antibacterial activity of lactococcin BZ was observed in meat samples inoculated with E. coli both during and after attachment condition (10(3) and 10(6) CFU/mL), and over a 12 days storage period in refrigeration (4 degrees C). Different amounts of lactococcin BZ (ranging from 400 to 3200 AU/mL) were applied to fresh meat for varying treatment durations (0-30 minutes). Following the application of lactococcin BZ at levels of 800, 1600, and 3200 AU/mL during attachment, E. coli counts were immediately reduced by 3.62 log units. At high inoculum dose, lactococcin BZ (3200 AU/mL) decreased the pathogen by approximately 6 log units in 5 minutes during attachment. E. coli exhibited sensitivity to lactococcin BZ (400, 1600, and 3200 AU/mL) both in low and high inoculum doses after attachment to fresh beef. Furthermore, the inhibitory effect of lactococcin BZ increased with its concentration over the 12 days of refrigerated. In conclusion, lactococcin BZ demonstrated inhibitory effect against E. coli in fresh beef, suggesting its potential use as a biopreservative in the meat industry.