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  • Author or Editor: A. Demirci x
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Phytase is an important feed and food additive, which is used in diets to increase the absorption of divalent ions, amino acids, and proteins in the bodies and to decrease the excessive phosphorus release in the manure to prevent negative effects on the environment. To date, phytase has been mostly produced in solid state fermentations with insignificant production volumes. Thus, there is a need to produce phytase in submerged fermentations, which can be scaled-up for commercial productions. Additionally, optimization of fermentation medium has not been studied well in the literature. Therefore, this study has been undertaken to improve Aspergillus ficuum phytase production in submerged fermentations by optimizing important nutrients in the fermentation medium (glucose, Na-phytate, and CaSO4) using Box-Behnken design of Response Surface Methodology. Also, effects of pH and temperature on phytase activity were studied. Optimum glucose, Na-phytate, and CaSO4 concentrations were determined as 126, 14, and 1.1 g l–1, respectively. Additionally, pH 5.5 and 55 ºC were determined as optimum for the produced A. ficuum phytase activity. Under these conditions, phytase activity was increased to 3.45 U ml–1, which is about 50% higher than the previous results. Furthermore, the lowest activity loss was observed under 4 ºC storage conditions during 1 week of storage.

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Menaquinone-7 (MK-7) is a type of vitamin K. MK-7 is produced via bacterial fermentation, and in order to reach the desired product purity, several downstream processing steps, including extraction, drying, ultrasonication, must be carried out. These processes, however, need to be carried out in such fashion to ensure the least amount of vitamin K lost and maximum recovery into the end-product. Therefore, in this study, drying, storage at 4 and −20 °C, and ultrasonication steps were evaluated under different conditions. Static liquid fermentations were conducted in McCartney bottles to explore the maximum MK-7 secretion potentials in different glycerol and glucose-based media compositions that were optimized in our previous studies. Maximum 32.5±0.4 mg l−1 and 14.6±0.4 mg l−1 concentrations were achieved in glycerol and glucose-based media, respectively. Concentrations of MK-7 produced under same fermentation conditions in 30 ml McCartney amber bottles with 3 ml of media in them and in 75 ml culture tubes with 20 ml media were compared. Also, ultrasonication, drying, and storage conditions were investigated to ensure the least amount of vitamin K is lost. Results showed that drying under forced air flow was the fastest, thus, demonstrated a better preservation of the vitamin, and should replace vacuum drying. Ultrasonication for 15 min seems to be safe and sufficient for phase transition for analysis. Also, storage at refrigerated temperatures seems to preserve MK-7 at least for one week. Furthermore, fermentations in McCartney bottles indicated how MK-7 concentrations are distributed in different zones of the static liquid broth. Culture tube results provided the conclusion as of how the metabolism of MK-7 changes in static fermentation when the scale-up process begins from McCartney bottle to culture tubes. Results in general showed a clearer road map to ensuring better quality and preservation of the valuable end-product, and illuminated more the path to further scaling up of the fermentation process for commercial production of MK-7.

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In the present study, the antioxidant and antimicrobial activities of three tea (Camellia sinensis) types (white tea — WT, green tea — GT, and black tea — BT) were compared and the relationships between total phenolic, tannin and flavonoid contents were determined. Regardless of the assays used, the highest total phenolic content (313.3±1.41 μg GAE/mg extract), total flavonoid (16.98±0.27 μg QE/mg extract) and total tannin content (266.79±2.59 μg TAE/mg extract) were determined in green tea extract, which also demonstrated the highest antioxidant capacity. Black tea extract showed the lowest phenolic content and antioxidant capacity. The EC50 value of DPPH scavenging activity was in the order of: ascorbic acid >GT>BHA>WT>BT>BHT. While the tea extracts exhibited antibacterial activity against Staphylococcus aureus, no inhibitory effects were observed against Escherichia coli and Salmonella enteritidis. All extracts exhibited antifungal activity against two afl atoxigenic moulds Aspergillus parasiticus NRRL 2999 and NRRL 465. The antibacterial activity of tea extracts decreased in the following order: GT>WT>BT DPPH scavenging activity strongly correlated with total phenolic content, reducing power, antimicrobial activity against S. aureus, A. parasiticus NRRL 2999, A. parasiticus NRRL 465 (P<0.05). These data suggest that green tea extract is more effective than white and black tea extracts as a potential source of natural antioxidants.

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Alpha keto acids are important food additives, which commonly produced by microbial deamination of amino acids. In this study, production of phenylpyruvic acid (PPA), which is the alpha keto acid of phenylalanine was enhanced in 2-l bench scale bioreactors by optimizing of fermentation medium composition using the Box-Behnken Response Surface Methodology (RSM). Optimum glucose, yeast extract, and phenylalanine concentrations were determined to be 119.4 g 1−1, 3.7 g 1−1, and 14.8 g 1−1, respectively, for PPA production, and 163.8 g 1−1, 10.8 g 1−1, and 9.8 g 1−1, respectively, for biomass production. Under these optimum conditions, PPA concentration was enhanced to 1349 mg 1−1, which was 28% and 276% higher than the unoptimized bioreactor and shake-flask fermentations, respectively. Moreover, P. vulgaris biomass concentration was optimized at 4.36 g 1−1, which was 34% higher than under the unoptimized bioreactor condition. Overall, this study demonstrated that optimization of the fermentation media improved PPA concentration and biomass production in bench scale bioreactors compared to previous studies in the literature and sets the stage for scale up to industrial production.

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