Published in Scientific Bulletin. Series F. Biotechnologies, Vol. XXII
Written by Arzu KART, Hüseyin ÖZTÜRK

Killer activity is one of the mechanisms of antagonism among yeasts during fermentations. A variety of yeast species secrete a compound which is protein produced outside the cell and is called the killer toxin. Killer toxins are protein in nature and active at low pH. These toxins have a lethal effect against yeasts, bacteria and the moulds, except for their own species. Killer yeasts can be used to prevent the contamination of many spoilage yeasts which are sensitive to killer toxins in food processing via this mechanism during the food fermentations. In this way, it is possible to control of the food spoilage microorganisms and prolongation of the spoilage processes in foods by using of killer yeasts or direct using of killer toxins. The shelf life of foods can be extended by using killer features of yeast, so food resources can be better assessed and economic losses can be prevented. Therefore, it is important to determine the killer yeasts which are effective against spoilage food yeast. For these reasons, it is aimed to determine the effective killer yeast strains against spoiling food yeasts in this study. In the study, yeast isolation was performed to obtain spoilage yeasts from various spoiled fermented foods. At the same time, in this study, the yeasts, which were isolated from different products and obtained from Süleyman Demirel University Food Engineering Department laboratory, were evaluated to determine the killer activities against these spoilage yeasts isolated from various spoilage fermented products. It has been determined that those yeasts, which are effective against sensitive spoilage food yeasts, were investigated by using the agar diffusion method in the solid medium and have a low, medium and high spectrum activities as a result of quantitative experiments. The study was carried out under the 30°C incubation temperature and pH 4 acidic conditions to the determine the killer activity. The results that were obtained in the study were calculated and evaluated over the zone radius. It was determined that the yeasts obtained from laboratory, showed 50% killer activity against spoilage yeasts as a results of quantitative analyses in solid medium. These yeast isolates were classified according to their effect degrees. It was determined that the yeasts obtained from Süleyman Demirel University Department of Food Engineering, showed killer activity against spoilage yeasts isolated from spoilaged food products as a results of in vitro experiments.

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