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Inulinase production by Rhodotorula glutinis was carried out in this study, using leek (Allium ampeloprasum var. porrum) as an alternative carbon source due to its high inulin content and easy availability. Taguchi orthogonal array (OA) design of experiment (DOE) was used to optimize fermentation conditions. For this purpose, five influential factors (leek concentration, pH, incubation temperature, agitation speed, and fermentation time) related to inulinase production were selected at four convenient levels. The results showed that maximum inulinase activity was obtained as 30.89 U/mL, which was close to the predicted result (30.24 U/mL). To validate the obtained results, analysis of variance (ANOVA) was employed. Consequently, leek has a great potential as an effective and economical carbon source for inulinase production, and the use of Taguchi DOE enhanced enzyme activity about 2.87-fold when compared with the unoptimized condition.

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Investigation various nitrogen sources effects on the production of invertase by Aspergillus niger was researched in this study. Invertase is a precious enzyme used in many industries like food, pharmacy, confectionery, invert syrup production. Taguchi design of experiment (DOE) was preferred to optimize the cultivation conditions. L16 (43) orthogonal array was selected in the current study including nitrogen source, initial pH of the medium and incubation time at four levels for statistical optimization. The data showed that optimized version of invertase production was achieved using proteose peptone, 5.5 initial pH and 3 days for incubation time. Bacto peptone had higher enzyme activity than casein and yeast extract. pH of the medium was found as the most efficient factor among nitrogen source and incubation time. Besides, percentage contribution of the nitrogen source and incubation time were indicated at similar rates (9 and 10%, respectively). The highest enzyme activity was defined as 45.87 U/ml, which was found to be closer to the predicted result (46.33 U/ml). As a conclusion, proteose peptone increased the invertase activity and use of Taguchi DOE supported quick and effective optimization.

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