Various chemical surfactants could affect permeability of yeast cells. In this study, effects of the surfactant addition upon yeast cells permeability and citric acid (CA) production by Yarrowia lipolytica strains DSM 3286 and M7 were investigated. The addition of Triton X-100 increased 1.4-1.8-fold of the maximum CA quantity achieved for both strains, with final CA concentrations ranging between 75-85 g/l that correspond to CA conversion yields per unit of glucose consumed of ~0.80-0.84 g/g. Scanning electron micrographs of yeast cells showed that the cells treated with Triton X-100 had altered cell structure and were smaller and narrower compared with the non-treated ones. The results showed that Triton X-100 could be used in order to increase the efficiency of CA production by Y. lipolytica strains.
Production of nanostructured materials, similar to the complex structure of nanocalcite of hard tissues, egg shell, teeth and bone, are an attractive field of research. Calcium phosphates with clinical applications, such as hydroxyapatite (HA) (Ca 10 (PO4) 6 (OH) 2 ) have been widely used in regeneration of bone and fabrication of medical implants, mainly due to the chemical composition and structure similarity between HA and the mineral part of bones and teeth, and also as gene and drug delivery is used. High surface area of HA make it useful for drug release. Moreover, it has antibacterial property and potential applications in rapid microbial detection, treatment of heavy metals from aqueous solutions. Biological synthesis has been attracted more attention for compatibility to human safety.
The neutraceutical and pharmaceutical application of essential fatty acids is much cleared. Alpha-linolenic acid (ALA) is omega-3 fatty acid and generally known to have beneficial effects in CVS, CNS and other diseases. The purpose of the present investigation is to produce essential fatty acid, especially ALA by Mucor circinelloides from oil wastes. Five oil wastes collected from food industries were used as carbon sources, and the contents of total lipids, biomass and fatty acids were examined during 168 h. The ability of oil waste degradation was determined by measuring of biochemical oxygen demand (BOD) and chemical oxygen demand (COD). Interestingly, 76 % reduction in BOD and 68 % reduction in COD by this strain were achieved, and M. circinelloides could be a good candidate for oil waste treatment. In order to enhance ALA production, fermentation variables were chosen in accordance with the fractional design and further optimized by the response surface method. The statistical model was constructed via central composite design. Following the optimization step, ALA production increased by approximately 44.3 %, when compared to the screening step. The results indicate that carrying out the fermentation under the conditions of oil waste 4.37 %, yeast extract at 0.65 g/l, (NH 4 ) 2 SO 4 at 0.38 g/l, an agitation rate of 180 rpm and fermentation time of 3 days will increase the ALA production up to 108.57 mg/l. In this study, a new renewable source of ALA was employed and optimized successfully for the production of valuable fatty acids.
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