Aynur Gül Karahan

Analysis of dissolved microcystins in surface water samples from Kovada Lake, Turkey

Dissolved (extracellular) microcystin (MC) concentrations were determined at 3 sampling stations on Lake Kovada, Turkey. The dominant species of cyanobacteria found in August and September of 2006 were Microcystis aeruginosa, Synechococcus sp., Phormidium limosum, Phormidium formosa and Planktothrix limnetica. MC concentrations in water were measured by ELISA and MC variants were examined by HPLC-PDA. Quantitative analysis by HPLC indicated that five MC variants (MC-LR, -RR, -LA, -LW, -LF) were identified in water samples from Kovada Lake. The maximum concentration of dissolved MC-LW was 98.9 microg l(-1) in October. MC-LR was only detected in May at a concentration of 0.5 microg l(-1). The cross reactivity of the antibody (MC10E7) to variants such as MC-LA MC-LW & MC-LF was low. Hence the results determined by ELISA were lower than those determined by HPLC in September and October samples due to differences in the specificity of the antibody to MC variants. Total extracellular MCs was quantified by ELISA and ranged from 0.73 to 48.5 microg MC-LR equivalents l(-1), which in some cases exceeded the WHO provisional Guideline Value for MC-LR in drinking water. This study confirms that the lakes of Turkey should be monitored for toxic cyanobacteria and for MCs to avoid or reduce the potential exposure of people to these health hazards.

Genotypic identification of some lactic acid bacteria by amplified fragment length polymorphism analysis and investigation of their potential usage as starter culture combinations in Beyaz cheese manufacture

In this study, 2 different starter culture combinations were prepared for cheesemaking. Starter culture combinations were formed from 8 strains of lactic acid bacteria. They were identified as Lactococcus lactis ssp. lactis (2 strains), Lactobacillus plantarum (5 strains), and Lactobacillus paraplantarum (1 strain) by amplified fragment length polymorphism analysis. The effects of these combinations on the physicochemical and microbiological properties of Beyaz cheeses were investigated. These cheeses were compared with Beyaz cheeses that were produced with a commercial starter culture containing Lc. lactis ssp. lactis and Lc. lactis ssp. cremoris as control. All cheeses were ripened in brine at 4 degrees C for 90 d. Dry matter, fat in dry matter, titratable acidity, pH, salt in dry matter, total N, water-soluble N, and ripening index were determined. Sodium dodecyl sulfate-PAGE patterns of cheeses showed that alpha(S)-casein and beta-casein degraded slightly during the ripening period. Lactic acid bacteria, total mesophilic aerobic bacteria, yeast, molds, and coliforms were also counted. All analyses were repeated twice during d 7, 30, 60, and 90. The starter culture combinations were found to be significantly different from the control group in pH, salt content, and lactobacilli, lactococci, and total mesophilic aerobic bacteria counts, whereas the cheeses were similar in fat, dry matter content, and coliform, yeast, and mold counts. The sensory analysis of cheeses indicated that textural properties of control cheeses presented somewhat lower scores than those of the test groups. The panelists preferred the tastes of treatment cheeses, whereas cheeses with starter culture combinations and control cheeses had similar scores for appearance and flavor. These results indicated that both starter culture combinations are suitable for Beyaz cheese production.

Identification of Lactic Acid Bacteria Isolated from the Fecal Samples of Healthy Humans and Patients with Dyspepsia, and Determination of Their pH, Bile, and Antibiotic Tolerance Properties

The research of novel probiotic strains is important in order to satisfy the increasing request of the market and to obtain functional products in which the probiotic cultures are more active and have better probiotic characteristics than those already on the market. In this study, the probiotic potential of Lactobacillus and Enterococcus strains isolated from human feces was investigated. One hundred seven strains of lactic acid bacteria were isolated from the fecal samples of 19 adult volunteers with stomach problems and the fecal samples of 12 healthy adult volunteers. The strains were identified by 16S rRNA analysis and examined for resistance to gastric acidity (pH 3.5) and bile salts (0.3% bile salt). The antibiotic susceptibility of the strains was also determined. The counts of lactic acid bacteria in the fecal samples ranged from 1.7 × 107 to 3.1 × 1010 CFU/g. The species present in those samples were found to be Lactobacillusplantarum, L. fermentum, Enterococcus faecium and E. durans. Results indicated that L. plantarum (AA1–2, AA17–73, AC18–88, AK4–11, and AK7–28), L. fermentum (AB5–18, BB16–75, and AK4–180), E. faecium (AB20–98 and BK11–50) and E. durans (AK4–14 and BK9–40) showed good pH and bile tolerance. These strains are potentially good candidates for use as health-promoting bacteria.

Effect of Transglutaminase on Physicochemical Properties of Set-style Yogurt

In this study, the effect of some ingredients such as skimmed milk powder, whey, sodium caseinate, calcium caseinate, whey protein concentrate (35, 60 kg/100 kg dry solids), whole milk powder, condensed milk and transglutaminase (TGase) on the properties of set-style yogurt was investigated. These protein and dry matter sources (2%) and TGase (1 U/g milk protein) were added into pasteurized milk and incubated prior to fermentation for 2 h at 40°C. After fermentation, enzyme action was stopped by heating for 1 min at 80°C. The control groups were conducted with addition of these materials into milk without TGase. All of the milk samples were inoculated with yogurt cultures at 45°C, until the pH was dropped to 4.4. Syneresis, gel-strength, acetaldehyde amounts, and the degree of TGase reaction were determined. As a result, yogurt products made from enzyme-treated milk showed increased gel strength and less syneresis. SDS-PAGE results showed that the enzyme TGase produced crosslink formation between different protein fractions of milk. In addition, it was also determined that TGase application caused a decrease in acetaldehyde amounts.

Evaluation of Enzyme-Linked Immunosorbent Assays (ELISAs) for the Determination of Microcystins in Cyanobacteria

Microcystin (MC) concentrations in cyanobacterial strains isolated from a freshwater lake and from Microcystis PCC 7806, were quantified by three different immunoassays. Polyclonal antibodies (PAbs) developed by linking the cyanobacterial hepatotoxin MC-LR, via 2-mercaptoethylamine to keyhole limpet hemocyanin and monoclonal antibodies (MAbs) against MC– Leucine/Arginine (LR) (MC10E7) were developed in-house as an ELISA kit, versus a commercial MC-LR enzyme-linked immunosorbent assay (ELISA). Depending on the MC variant used, the immunoassays showed different sensitivities to different variants. Statistical analyses were performed between immunoassays, the response of the ELISA, and MC concentrations in the samples. Overall good agreement was found among the ELISAs with no significant differences in the reaction of the antibodies (MAb, PAb) to the MCs (p >0.05). To a large degree, this finding was due to the cross-reactivity characteristics of the MAbs and PAbs used. High-performance liquid chromatography (HPLC) analysis was conducted to compare with the results obtained by ELISA and to determine the profile of MCs produced by the cyanobacteria.

Preventive Effect of Probiotics and α-Tocopherol on Ethanol-Induced Gastric Mucosal Injury in Rats

The protective effect of a probiotic mixture of 13 different bacteria and α-tocopherol on 98% ethanol-induced gastric mucosal injury was evaluated. Levels of gastric mucosal pro- and anti-inflammatory cytokines, malondialdehyde, and secretory immunglobulin A were measured. Rats were allocated into four groups: control, ethanol, probiotic, and α-tocopherol. The control and ethanol groups received skim milk for 14 days. Probiotic and α-tocopherol groups were administered probiotic mixture suspended in skim milk and 100 mg/kg α-tocopherol, respectively, by daily gavage for 14 days. On Day 15, gastric lesions were induced by administration of ethanol 98% (1 mL) to all rats except those in the control group. Probiotic, but not α-tocopherol, seemed to inhibit ethanol-induced gastric mucosal tumor necrosis factor-α, interferon-γ, and interleukin-2 production (P > .05). Ethanol caused the elevation of mucosal interleukin-4 level (compared to the control, P < .05). Probiotic pretreatment significantly suppressed the ethanol-induced increase of gastric mucosal interleukin-4 levels. Pretreatment with either probiotic or α-tocopherol inhibited the ethanol-induced increase of mucosal malondialdehyde concentration (P < .01 and P < .05, respectively). Probiotic pretreatment enhanced the gastric mucosal secretory immunoglobulin A concentration (P < .001). In conclusion, probiotic mixture and α-tocopherol reduced ethanol-induced gastric mucosal lipid peroxidation, suggesting that they may be beneficial for gastric lesions induced by lower ethanol concentration.

Determination of Transglutaminase Activity Using Fluorescence Spectrophotometer

An improved fluorometric assay for determining the activity of the microbial transglutaminase (TGase) in the culture medium samples has been developed. The assay procedure measures the fluorescence enhancement due to the incorporation of monodansyl cadaverine (Substrate A) into pentafluorophenylester of CBZ-Gln-Gly (Substrate Q) at λexc. 260 nm and λem 538 nm. The effect of the competitive inhibitors in the culture medium samples on TGase activity was determined. The assay was combined with HPLC method for determining enzyme activity as an international unit (IU). Enzymatic reaction was monitored by HPLC and the rate of product formation was measured via amine substrate consumption rate. A conversion factor was obtained using HPLC and fluorescence spectrophotometer data together. This was formulated for quantification of TGase activity as IU using fluorometric assay reported in this study. The detection limit of the assay was determined as 0.0014 IU (0.5 mg). TGase activity remained linear upto the enzyme concentraion of 20 mg. This technique dramatically decreases the incubation time of enzyme to a few minutes of activity measurement.

Nitric Oxide (NO) and Lactic Acid Bacteria-Contributions to Health, Food Quality, and Safety

In this article, the effects of nitric oxide (NO) and nitric oxide producer bacteria on food quality, safety, and human health care high lighted. NO, which was previously recognized as a toxic gas, has attracted attention in the last two decades due to its vital role in many physiological processes of animals and plants. Particularly, it is important to note from the point of view of food quality and safety that lactic acid bacteria, which are used as starter cultures in foods, also have the capability of producing NO. There have been several studies on the color development of meat products that originated from NO production of lactic acid bacteria. For this reason, it is also important to emphasize the different aspects of interactions between food and NO.

Contents Vol. 18, 2010

F. Barras, Marseille D.H. Bartlett, San Diego, Calif. P. Beguin, Paris I. Booth, Aberdeen L.J. Brady, Gainesville, Fla. Y.J. Chung, Jeonju P. Courvalin, Paris C.J. Dorman, Dublin J.S. Edwards, Albuquerque, N. Mex. M.Y. Galperin, Bethesda, Md. A. Goff eau, Louvain-la-Neuve C.F. Gonzalez, Gainesville, Fla. M. Gribskov, West Lafayette, Ind. G.F. Hatfull, Pittsburgh, Pa. P.J.F. Henderson, Leeds S. Horinouchi, Tokyo G. Klug, Giessen G.L. Lorca, Gainesville, Fla. J. Lutkenhaus, Kansas City, Kans. W. Qin, Th under Bay, Ont. M. Schaechter, San Diego, Calif. K.C. Schuster, Lenzing R. Skurray, Sydney F. Titgemeyer, Münster R. Vazquez-Duhalt, Cuernavaca H. Wolf-Watz, Umea X. Zhou, Pullman, Wash. Vol. 18, 2010