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  The use of productive microorganisms in the production of primary and secondary metabolites is part of the knowledge of microbial biotechnology, which is carried out with the aim of using huge cellular factories and considering their inherent and latent ability to produce products. Investigating and optimizing the factors affecting the synthesis of metabolites will increase the growth of the strain and the yield of the product. In this regard, in this research, by using the response surface method (RSM) and Box-Behnken design, the fermentation production of cephalosporin C by Acromonium chrysogenum PTCC 5271, and the effect of three factors on the fermentation process, including pH of Fermentation culture media, rice bran and magnetite iron oxide nanoparticles have been measured at three levels. The obtained results showed that changes in the concentration of magnetite iron oxide nanoparticles and rice bran in the fermentation media significantly affect the amount of antibiotics produced. The highest amount of Cephalosporin C produced (224 mg/l) was obtained in the culture containing 0.04 mg/l magnetite iron oxide nanoparticles, 2.5 g/l rice bran and pH of 6.5. The optimized values ​​for the factors were calculated as 0.0325 mg/l, 2.6162 g/l, and 6.4545 respectively by the Mini Tab program, and finally the mathematical model for the response variable was obtained. Based on the results of this research, magnetite iron oxide nanoparticles and rice bran are suitable substrates in fermentation culture media and biological processes.

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Spirulina platensis is biomass rich in protein, iron and amino acids, vitamins, unsaturated fatty acids, antioxidants, and minerals. The aim of producing dairy desserts with Spirulina platensis is to create varieties in consumer food products, develop dairy products, and create enjoyable foods with nutritional characteristics appropriate for various age groups, especially children. The effect of multiple levels of spirulina (1-3% by weight), stevioside sweetener (0.5-1.5% by weight), and corn starch (1-3% by weight) on the characteristics of a dairy dessert were examined. Moreover, formulation optimization with variables at different levels was determined by applying the response surface method (RSM). The results indicated that the most influential parameter in the color, protein, and iron of dessert samples was the amount of spirulina. The amount of corn starch significantly affected the dessert tissuechr('39')s springiness, gumminess, chewing ability, stiffness, and viscosity in all samples (p<0.05). According to the results, the optimal sample formulation was selected with stevia composition at 0.05%, Spirulina platensis at 3%, and corn starch at 1% with a utility coefficient of 0.96. The optimal sample in the production laboratory and chemical, rheological, and color parameters were also evaluated. The results showed that the difference between the samples produced based on the optimal formulation and the values predicted by the software was not significant, indicating the modelchr('39')s high efficiency in predicting the quality properties of the produced dessert.