In this study, we investigated whether wild-thyme (Thymus serpyllum) hydrosol had a preserving effect against spoilage of freshwater fish. Sensorial characteristics, chemical freshness indicator contents, and microbial counts (total aerobes, psychrotrophics, Enterobacteriaceae, fecal coliform bacteria, Aeromonas spp., and Pseudomonas spp.) of whole ungutted and gutted Transcaucasian barb (Capoeta capoeta capoeta Guldenstaedt, 1772) stored on ice produced from wild-thyme hydrosol and tap water at 4 degrees C for 20 days were compared. The results did not reveal any significant (P > 0.05) differences in the microbial counts, sensorial characteristics, pH, and total volatile basic nitrogen values between gutted and ungutted groups. Sensory evaluation and microbiological and chemical analyses indicated that the storage of the fish on ice produced from wild-thyme hydrosol had a significant increase in shelf life by at least 15 to 20 days.

IntroductionAflatoxins are secondary metabolites produced by molds that have carcinogenic, mutagenic, and teratogenic effects on humans and animals (1-3). Among the aflatoxins, aflatoxin B 1 (AFB 1 ) is one of the strongest known hepatocarcinogens and is classified as a category 1A carcinogen by the International Agency for Research on Cancer (4). Due to their importance in showing these effects in the consumption of contaminated foods, there is a serious effort made by the food industry to make products safe. Moreover, considering the tendency of consumers to prefer natural products because of the worry about possibly hazardous food additives, both researchers and producers are taking responsibility to investigate new ways as an answer to the consumer expectations.Although the different methods used at present are to some extent successful, they have major disadvantages with limited efficacy, possible losses of important nutrients, and normally high costs. Many workers in the field are of the opinion that the best solution for decontamination should be detoxification by biodegradation, giving a possibility for removal of mycotoxins under mild conditions without using harmful chemicals and without significant losses in nutritive value and palatability of decontaminated food and feed (5). A number of studies have found that some microorganisms, especially lactic acid bacteria, break down or bind to aflatoxins. Researchers have obtained different results in these studies conducted to investigate the in vitro aflatoxin binding/degradation effect of lactic acid bacteria (6-9). Zinedine et al. (10) indicated that the toxin binding level changes in some environmental conditions having different pH and temperature. Supporting this finding, Haskard et al. ( 7) also found that environmental conditions, acid and heating applications, and the structure of the bacteria had an important effect on the stability of the toxin-bacteria complex. In another study, Kabak (11) showed that the aflatoxin B 1 binding capability of probiotic lactic acid bacteria varied in vitro, and in food had 32%-46.5% of the in vitro toxin binding rate. Fuchs et al. (12) found that the effectiveness of lactic acid bacteria in detoxifying ochratoxin and patulin was affected by toxin concentration, cell density, pH of the environment, and whether the cells were viable. Based on these and similar results, Hernandez-Mendoza et al. (13) suggested that lactic acid bacteria bound the toxins to different extents depending on the environment and the amount of bile salt present.Another challenge for researchers is achieving the same good results when lactic acid bacteria are applied to food. First of all, certain temperatures and pH levels must be provided; otherwise, the microorganisms would not show their effects. Probably, a higher number of bacteria would

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SummaryThe aim of this study was to isolate bacteriocin-producing lactic acid bacteria (LAB) from foods. A total of 12700 LAB were isolated from foods and screened for their bacteriocin production. Among them, 601 isolate showed a clear antimicrobial activity against indicator strains. After neutralization 35 of the cultures retained active. The antimicrobial activities of strains were lost after treatment with proteases. The antimicrobial metabolites were heat stable and were active pH range of 2-12. The bacteriocin which produced by Lactococcus lactis ssp. lactis isolated from kashar samples was partially purified by ammonium sulphate precipitation, dialysis, following ion-exchange chromatography. It was also found that this bacteriocin was cationic. The apparent molecular mass of partially purified bacteriocin, as indicated by activity detection after Tricine-SDS-PAGE, was 2.4 kDa, 4 kDa or 15 kDa. In this study antimicrobial substance of LAB from food showed strong antibacterial activity against Gram-negative and Gram-positive indicator microorganisms. Those were also found that these bacteriocins were stable at temperatures used in food manufacturing and storage. Bacteriosinogenic LAB or bacteriocins might be useful as a natural preservative for inhibiting food-borne pathogens in particular Listeria monocytogenes in foods.Keywords: Animals food, Lactic acid bacteria, Bacteriocin, Antimicrobial activity Gıdalardan İzole Edilen Laktik Asit Bakterilerinin Bakteriyosin Üretme Yeteneklerinin Araştırılması ÖzetBu çalýşmada, gýdalardan bakteriyosinojenik laktik asit bakterilerinin (LAB) izolasyonu amaçlanmýştýr. Gýdalardan izole edilen toplam 12700 LAB'nin antimikrobiyel etkisi test edilmiştir. Bu izolatlardan sadece 601 adedi çalýşmada kullanýlan indikatör suşlara karşý antimikrobiyel etki göstermiştir. LAB'nin ürettiği laktik asitin ve hidrojen peroksitin güçlü antimikrobiyel etkisi göz önüne alýndýğýnda bu etkinin ortadan kaldýrýlmasý için katalaz ilavesiyle birlikte ortam nötrlendiğinde antimikrobiyel etkisini sürdüren sadece 35 izolat olduğu belirlenmiştir. İzolatlarýn etkisi proteolitik enzimlerin varlýğýnda kaybolmuştur. Üretilen antimikrobiyel etkili metabolitlerin gýda üretim ve muhafaza sýcaklýklarýnda ve geniş pH (pH 2-12) aralýğýnda aktivitelerini sürdürdükleri gözlenmiştir. Kaşar peynirinden izole edilen Lactococcus lactis ssp. lactis suşunun ürettiği bakteriyosin kýsmi olarak saflaştýrýlarak tanýmlanmaya çalýşýlmýştýr. İzole edilen bakteriyosinojenik suşlarýn Gram-negatif ve Gram-pozitif indikator mikroorganizmalara karşý oldukça güçlü antimikrobiyel etkiye sahip olduğu belirlenmiştir. Bakteriyosinojenik LAB ve/veya onlarýn bakteriyosinleri gýda kaynaklý patojenlerden özellikle Listeria monocytogenes'in inhibisyonu için doğal bir katký maddesi olarak kullanýlabilir.