Browsing by Author "Con A.H."

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Optimization of cryoprotectant formulation to enhance the viability of Lactobacillus brevis ED25: Determination of storage stability and acidification kinetics in sourdough
(2020-04-01) Gul L.B.; Gul O.; Yilmaz M.T.; Dertli E.; Con A.H.
In this study, various kinds of cryoprotectant (skim milk, lactose, and sucrose) formulations were tested to enhance the survival of Lactobacillus brevis ED25 after freezing and freeze-drying. A Box–Behnken experimental design was used to optimize cryoprotective medium and the highest cell survival was observed with the 17.28% skim milk, 2.12% lactose, and 10% sucrose cryoprotectant as the optimum condition. The structural and physicochemical characteristics of freeze-dried powder were acceptable for application with regards to particle surface morphology, moisture and water activity (Aw), glass transition temperature (Tg), Fourier transform infrared spectra, X-ray structure, and also storage stability under the refrigeration and room temperature conditions. Accelerated storage test based on Arrhenius equation could be used to predict the freeze-dried bacterial shelf life but only with a certain degree of predictability for long-term storage. The acidification kinetics of fresh and stored culture in sourdough fermentation was also described on the basis of the Gompertz equation. Practical applications: Freezing and storage are crucial factors for the viability and acidification power of starter culture. Therefore, various types and concentrations of cryoprotectants have been used to preserve the microorganisms. L. brevis ED25 has been a good potential for the manufacture of industrial sourdoughs and this research has aimed to investigate long-term protective effects of optimum cryoprotectant formulations on the viability of bacteria and also determine the acidification power in sourdough. The results showed the potential value of freeze-dried L. brevis ED25 culture for commercialization.
Optimization of fermentation conditions for sourdough by three different lactic acid bacteria using response surface methodology
(2022-01-12) Gul L.B.; Gul O.; Con A.H.
This study aimed to investigate optimal fermentation conditions for sourdough by freeze-dried Lactobacillus curvatus N19, Weissella cibaria N9 and Lactobacillus brevis ED25 isolated from Turkish sourdough previously. The central composite rotational design was applied to the optimization of fermentation parameters (temperature and time). The fermentation was carried out under a simulated sourdough system and biomass concentration, total acidity, and lactic and acetic acid formation were chosen as response variables. Results showed that the models developed for all variables were significant (p < 0.05) and there was no lack of fit in any of quantifications (p > 0.05), indicating the suitability for representing the relationship between variables and factors. While both of the independent parameters were effect the response, fermentation time was the most significant factor influencing the response. The validation experiments using the optimized condition showed a good agreement between the experimental and predicted values except the lactic and acetic acid formation for W. cibaria N9. In conclusion, freeze-dried L. curvatus N19 can be used as a starter culture to sourdough fermentation for bread industry due to optimum fermentation conditions (29oC temperature and 23h time).
Storage stability and sourdough acidification kinetic of freeze-dried Lactobacillus curvatus N19 under optimized cryoprotectant formulation
(2020-10-01) Gul L.B.; Con A.H.; Gul O.
In this study, the response surface methodology was used to optimize the cryoprotective agent (skimmed milk powder, lactose and sucrose) formulation for enhancing the viability of Lactobacillus curvatus N19 during freeze-drying and storage stability of cells freeze-dried by using optimum formulation was evaluated. Our results showed that the most significant cryoprotective agent influencing the viability of L. curvatus N19 to freezing and freeze-drying was sucrose and skim milk, respectively. The optimal formulation of cryoprotective agents was 20 g/100 mL skim milk, 3.57 g/100 mL lactose and 10 g/100 mL sucrose. Using the optimum formulation during freeze-drying, the cell survival was found more than 98%. Under the optimal conditions, although only storage of the cells at 4 °C for 6 month retained the maximum stability (8.85 log cfu/g), the employed protectant matrix showed promising results at 25 °C (7.89 log cfu/g). The storage stability of cells under optimized conditions was predicted by accelerated storage test, which was demonstrated that the inactivation rate constant of the freeze-dried L. curvatus N19 powder was 9.74 × 10−6 1/d for 4 °C and 2.08 × 10−3 1/d for 25 °C. The loss of specific acidification activity after the storage at 4 and 25 °C was determined.