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    Effect of oleaster (Elaeagnus angustifolia L.) flour addition combined with high-pressure homogenization on the acidification kinetics, physicochemical, functional, and rheological properties of kefir
    (Wiley, 2023) Gul, Latife Betul; Bekbay, Saya; Akgun, Abdullah; Gul, Osman
    In this study, the effects of peeled oleaster flour (OF) addition (0.5% and 1%) with high-pressure homogenization (HPH) at 100 MPa on acidification kinetics, physicochemical, functional, and rheological properties of kefir made from bovine whole milk were investigated. The fermentation kinetic parameters such as Vmax and T-f decreased by 23.63% and 20%, respectively, with 1% OF and application of HPH. The combined use of two treatments had a positive effect on Lactobacillus and Lactococcus counts, reaching a maximum of 9.63 and 9.31 log cfu/mL, respectively. Also, total phenolic contents and antioxidant activity reached maximum values of 85.31 mg GAE/g and 17.22%, respectively. The ?E value was more limited with HPH. The maximum firmness and water-holding capacity values were determined in the sample produced with 1% OF and application of HPH. Rheological analysis revealed that all kefirs exhibited shear thinning behavior, and the Ostwald-de-Waele (R-2 > .99) model was suitable to describe the rheological behavior of all kefir samples. The highest viscosity (0.049 Pa.s, at 50/s shear rate) and consistency index (1.115 Pa.s(n)) were observed in kefir with 1% OF and application of HPH. Kefir samples were characterized as weak gel behavior because storage modulus (G') was much greater than loss modulus (G) and the power-law model was used to characterize the viscoelasticity. The overall quality assessment indicated that the improvement of the fermentation process and the enhancement of textural and functional properties of kefir samples could be achieved with the addition of 1% OF and application of HPH.
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    Process optimization of a cereal-based fermented beverage (Boza) powder and investigating upscaling conditions
    (Wiley, 2023) Gul, Osman; Atalar, Ilyas; Tornuk, Fatih; Akgun, Abdullah
    Boza is a traditional fermented cereal-based beverage, which should be consumed within 3-5days after production due to its short shelf-life. Spray drying process is an excellent option to overcome this problem to make the product least perishable. The optimal spray drying conditions for boza powder production in a laboratory-scale spray dryer were investigated using, Response Surface Methodology. Air inlet temperature and feed flow rate were the main parameters that affected the responses such as powder yield, moisture content, cell viability, particle size, and solubility. The optimum spray drying conditions were 148 degrees C air inlet temperature, 9 degrees C feed temperature, and 10 ml/min feed flow rate. At these optimum conditions, deviations between predictive and experimental values were found very low. A 1.5 log cfu/g reduction in lactic acid bacteria (LAB) viability was achieved, however instant properties of boza powder should be improved by agglomeration processes. Laboratory and pilot scales were also compared at the determined optimum drying conditions. Approximately 0.4 log cfu/g difference in LAB viability was observed between the two scales. Practical ApplicationsBoza is one of the most valuable fermented cereal products due to its high nutritional value. The short shelf life of Boza limits its consumption and makes it a seasonal product. Spray drying technology could provide overcome these challenges and improve the usability and durability of boza beverages. However, the quality of a spray-dried product highly depends on process conditions. Therefore the effects of the spray drying process conditions on the physicochemical properties of boza powder and the scale-up conditions were investigated for the first time in this study.