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    Optimization of ultrasonic-assisted osmotic dehydration as a pretreatment for microwave drying of beetroot (Beta vulgaris)
    (Sage Publications Ltd, 2023) Memis, Habibe; Bekar, Fevzi; Guler, Cagri; Kamiloglu, Aybike; Kutlu, Naciye
    The aim of this study was to optimize drying conditions during ultrasonic-assisted osmotic dehydration and subsequent microwave drying of red beetroot using the Box-Behnken design. For this purpose, ultrasonic-assisted osmotic dehydration was performed at different ultrasonic powers (50, 75, and 100 W), sonication times (20, 40, and 60 min), and salt concentrations (0%, 15%, and 30%). The subsequent drying procedures were conducted with 231, 518, and 805 W microwave power. The best condition was selected as 5.15% salt concentration, 20 min sonication time, 50 W ultrasonic power, and 716.45 W microwave power. The responses obtained under optimum conditions were determined as 68.06%, 9.54 mg GAE/g dm, 28.23, 42.66, and 3.08 for DPPH center dot % inhibition, total phenolic content, L*, a*, and b* values, respectively. While favorable impacts on color were detected for the applied pretreatments, the DPPH center dot scavenging activities of the dried beetroot were determined to be more significant after ultrasonic-assisted osmotic dehydration. Furthermore, the drying kinetics of beetroot were evaluated according to the Midilli et al. model. When the fit to the model was investigated, it was compatible at R-2 > 0.90 level. As a result, the ultrasonic-assisted osmotic dehydration pretreatment performed before the microwave drying method preserved the quality characteristics of beetroot samples and was successfully applied.
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    Production of Gamma-Aminobutyric Acid by Levilactobacillus brevis AK19B: Strain Characterization and Process Optimization Using Box-Behnken Design
    (Springer, 2026) Memis, Habibe; Kamiloglu, Aybike
    Levilactobacillus brevis AK19B strain demonstrated promising probiotic potential as a hydrophilic lactic acid bacterium with valuable phytase activity. It also exhibited strong antioxidant properties and maintained viability in bile salt-rich environments, suggesting robustness in gastrointestinal conditions. To maximize gamma-aminobutyric acid (GABA) production, a Box-Behnken design was applied to assess the effects of monosodium glutamate (MSG) concentration, NaCl concentration, pH, and temperature. The results showed that these factors significantly influenced GABA synthesis, with their interactions well-modeled by a quadratic response surface. Optimal conditions were identified as pH 5.136, MSG concentration of 297 mM, temperature at 26 degrees C, and NaCl concentration of 2.82%, under which the predicted GABA production reached 43.85 mg/mL. These findings highlight AK19B as a promising candidate for functional food applications and industrial GABA biosynthesis.