Z. Yesim Ozbas

Chemical composition, antibacterial and antifungal activity of the essential oil of Thymbra spicata L. from Turkey.

The composition of the essential oil from aerial parts of Thymbra spicata L. from Turkey was analysed by GC-MS and its in vitro antimicrobial activity was examined. GC-MS analysis of the essential oil resulted in the identification of twenty-three constituents, representing 97.04% of the oil. The major compounds detected in the essential oil were carvacrol (60.39%), γ-terpinene (12.95%), and p-cymene (9.61%). The in vitro efficacy of the essential oil against 21 bacteria and seven Candida species was examined using disc diffusion and minimum inhibitory concentration (MIC) methods. The essential oil demonstrated strong anti-microbial activity in a wide spectrum against most microorganisms, particularly the yeasts tested. This is the first report on the anticandidal properties of the essential oil of T. spicata. In conclusion, this study confirms that T. spicata essential oil could be considered as a natural antimicrobial source.

EFFECTS OF PH AND TEMPERATURE ON GROWTH AND GLYCEROL PRODUCTION KINETICS OF TWO INDIGENOUS WINE STRAINS OF SACCHAROMYCES CEREVISIAE FROM TURKEY

The study was performed in a batch system in order to determine the effects of pH and temperature on growth and glycerol production kinetics of two indigenous wine yeast strains Saccharomyces cerevisiae Kalecik 1 and Narince 3. The highest values of dry mass and specific growth rate were obtained at pH 4.00 for both of the strains. Maximum specific glycerol production rates were obtained at pH 5.92 and 6.27 for the strains Kalecik 1 and Narince 3, respectively. Kalecik 1 strain produced maximum 8.8 gL-1 of glycerol at pH 6.46. Maximum glycerol concentration obtained by the strain Narince 3 was 9.1 gL-1 at pH 6.48. Both yeasts reached maximum specific growth rate at 30oC. Optimum temperature range for glycerol production was determined as 25-30oC for the strain Kalecik 1. The strain Narince 3 reached maximum specific glycerol production rate at 30oC. Maximum glycerol concentrations at 30oC were obtained as 8.5 and 7.6 gL-1 for Kalecik 1 and Narince 3, respectively.

Utilization of Whey and Grape Must for Citric Acid Production by Two Yarrowia lipolytica Strains

In this study, utilization of whey and grape must were investigated for citric acid production using Yarrowia lipolytica NBRC 1658 and a domestic strain Y. lipolytica 57. In addition to its use as a sole nutrient source, whey was also fortified with glucose or fructose as well as other nutrients. The best results for citric acid production were obtained in the medium containing whey supplemented with fructose. Maximum citric acid concentrations in this medium were 49.23 and 32.65 g/L for the domestic and NBRC 1658 strains, respectively. In grape must, maximum citric acid concentrations obtained using domestic and NBRC 1658 strains were 32.09 and 10.39 g/L, respectively. Both of the natural nutrient sources were found to be promising for utilization in citric acid production process. A domestic Turkish yeast strain was confirmed to be superior for citric acid production for the first time. This can be targeted for enhancing citric acid production efficiencies from locally available substrates such as whey or grape must.

Behaviour ofYersinia enterocolitica andAeromonas hydrophila in skim milk during fermentation by various lactobacilli

In this study, behaviour ofYersinia enterocolitica andAeromonas hydrophila in skim milk during fermentation by variouslactobacillus sp. were determined. pH values of the skim milk samples were also examined during fermentation. The amount of produced lactic acid and diacetyl/acetoin productions of theLactobacillus sp. were estimated. Antimicrobial effects of the lactobacilli onY. enterocolitica andA. hydrophila were also determined by an agar diffusion method. WhileY. enterocolitica was not inhibited and grew during fermentation,A. hydrophila was inhibited, in part, and the growth was retarded. Results were supported by the agar diffusion method forY. enterocolitica, whereas inhibition activity was not found forA. hydrophila. The highest lactic acid productions were estimated inL. bulgaricus (7.50 mg/ml) andL. acidophilus (5.63 mg/ml) and four out of sixLactobacillus sp. were found to be diacetyl/acetoin producers.

Molecular identification of some yeast strains isolated from various sugary foods

In this study, 37 yeast strains belonging to 19 different species, which had been isolated from various Turkish sugary foods, were characterized by molecular methods. Identification of yeast isolates at the species level was performed with restriction fragment length polymorphism–polymerase chain reaction (RFLP-PCR) by using five different restriction enzymes (MspI, HaeIII, AluI, RsaI, and ScrFI). For each enzyme, different restriction patterns obtained for endogenic yeast strains were compared to those obtained for the control (type or reference) strains. The strains could be identified when their digestion profiles obtained by all of the enzymes matched those of the control strains. Among the yeast strains, 16 could be identified adequately by RFLP-PCR. Tested yeast species were determined as Candida colliculosa, Candida guilliermondii, Candida kefyr, Candida lambica, Candida parapsilosis, Candida pelliculosa, Candida pulcherrima, Pichia anomala, Saccharomyces cerevisiae, Torulaspora delbrueckii and Zygosaccharomyces rouxii. Strain variation was determined by randomly amplified polymorphic DNA (RAPD-PCR) analysis by using (GTG)3 and M13 primers. The discrimination among the strains were detected by cluster analysis. Generally, strains of the same species clustered together with a few exceptions. By this way, all the strains in the same species could be differentiated by using both the primers.

The effect of some environmental parameters on the growth of yeasts originating from sugar containing foods

In this study, 65 yeast strains originating from sugar containing foods were tested for growth under different environmental conditions. In the experiments performed with glucose and NaCl, inhibition effect was observed at reduced aw levels. Most of the strains were able to grow at both 4 and 37°C. Of the tested pH values, the most adverse effect on growth of the yeasts was observed at pH 2.5. All of the strains were able to grow at both 5 and 20% CO2 levels. Acetic and propionic acids were found to be the most effective preservatives for inhibition of the strains. All of the yeasts, except aCandida glucosophila strain, failed to grow in the presence of 0.05% (w/v) sodium benzoate.

Yeast Identification During Fermentation of Turkish Gemlik Olives: Yeasts from Turkish Gemlik olives…

Naturally fermented black table olives of the Gemlik variety are one of the most consumed fermented products in Turkey. The objective of this work was to identify yeast strains isolated during their natural fermentation by using Restriction Fragments Lengths Polymorphism-Polimerase Chain Reaction (RFLP-PCR) and DNA sequencing methods. The study also focused on determining the effect of regional differences on yeast microflora of naturally fermented Gemlik olives. A total of 47 yeast strains belonging to 12 different species which had been previously isolated from the natural brine of Akhisar and Iznik-Gemlik cv. olives were characterized by molecular methods. Forty-two of the tested strains could be identified by RFLP-PCR to species level. These yeast species were determined as Candida mycetangi, Candida hellenica, Candida membranaefaciens, Candida famata, Candida pelliculosa, Saccharomyces cerevisiae, and Zygosaccharomyces mrakii. Five strains were identified by DNA sequencing. These strains belonged to three different species: Aureobasidium pullulans, Kloeckera apiculate, and Cryptococcus saitoi. The most frequent species were C. famata and C. pelliculosa in both regions. PRACTICAL APPLICATION This work studies the yeasts from Turkish table olives which could prove to be of importance to the food industry in that area. On the other hand, it compares identification by molecular and classical biochemical methods and offers an idea about the differences between the ecosystems of Gemlik olives in the Akhisar (AO) and Iznik (IO) regions. The study could be useful in characterizing a very important product and, in this way, could help to promote its marketing.

Yeasts from Traditional Cheeses for Potential Applications

Yeasts are associated with the secondary flora of many cheese types. Some yeast species such as Debaryomyces hansenii, Yarrowia lipolytica, Geotrichum candidum, Kluyveromyces lactis, Kluyveromyces marxianus, Candida zeylanoides, Candida utilis, Candida kefyr, and Saccharomyces cerevisiae can be frequently isolated from different traditional cheeses. By their metabolic activities, they may either cause spoilage or contribute to the cheese ripening process by causing desirable biochemical changes. Yeasts may contribute to cheese ripening by the metabolism of lactic acid, which in turn increases the pH and favors bacterial growth, as well as by their proteolytic and lipolytic activities, and metabolism of lactose, glucose, galactose, and organic acids. There are also reports about the interaction of yeasts with other microorganisms during cheese ripening. Because of their positive attributes, the yeast strains isolated from different traditional cheeses are proposed to be used as adjunct starters in cheese production. Yeasts originated from traditional cheeses may also be used as starter culture candidates in the production of other foods or they may be evaluated in biotechnological processes based on their biochemical traits.