Zübeyde Öner

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.

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.

Assimilation of cholesterol and probiotic characterisation of yeast strains isolated from raw milk and fermented foods

In this study, cholesterol assimilation ratios and some probiotic characteristics of yeasts were investigated. For this purpose, yeasts were isolated from milk and foods that were naturally fermented and not containing starter culture. In vitro cholesterol assimilation properties were determined in media. The Cholesterol assimilation by yeast strains ranged between 1.36 and 73.33%. Twenty-one yeast strains showing high assimilation percentage were selected, and their acid tolerance, bile tolerance, bile salt deconjugation activity and survival in simulated gastrointestinal conditions were investigated. Among the strains assessed, 12 of them showed probiotic characteristics.

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.