Study On Technological Parameter And Mechanism Of Solid-state Fermentaton For Producing Single Cell Oil By Mortierella Isabellina

In this study, the conditions and mechanism of solid-state fermentation (SSF) on agricultural byproducts by Mortierella isabellina to produce single cell oil (SCO) were explored. Mortierella isabellina which was used to produce SCO (esp. polyunsaturated fatty acids) in deep-liquid fermentation was tried to produce SCO in solid-state fermentation on agricultural byproducts. On this basis, we screened the medium and optimized the fermentation conditons. Meanwhile, physical and chemical properties of the products were compared with the previous substrate.The study specifically includes the following three tests.Experiment 1 Mortierella isabellina in deep-liquid fermentation to the conversion of in solid-state fermentationFeasibility of solid-state fermentation (SSF) on agricultural byproducts by Mortierella isabellina was studyed. At first, the trial identified the basic character of the original strain for producing SCO. Meanwhile, Single-factor experimental design using deep-liquid fermentation selected suitable carbon and nitrogen sources to determine the solid-state fermentation nutrient medium for the carbon and nitrogen sources compositon. Taking mixture of corn starch and wheat bran at the proportion of 1:1 as fermentative substrate, Mortierella isabellina had been used to produce SCO for 9 days in solid-state fermentation. The samples which be collected on 5th d,7th d and 9th d, and the contents of the crude fat, total energy and reducing sugar was determined respectively. The results showed that:during deep-liquid fermentation, pH decreased slightly from 6.0 to 5.5; the maximum values of biomass and the yield of SCO appeared on 132th h and 152th h, which was 5.25 g/L and 3.02 g/L; the best carbon source and nitrogen source was glucose and yeast extract. During solid-state fermentation, the reducing sugar concentration of fermentative substrate increased at first and then decreased; the total energy improved 7.32%,8.28% and 7.76% on 5th d,7th d and 9th d, respectively; the yield of SCO had an significantly improvement compared with previous fermentation (P< 0.01), in particular, the yield of SCO could reach 7.25 g/100 g on 9th d.Experiment 2 Optimal using of Mortierella isabellina for the solid-state fermentation medium and fermentation conditionsThe study aimed to improve the yield of SCO.Factorial trial and orthogonal trial were conducted to optimize the formulation of byproducts for fermentation and fermentative parameters for yield of SCO. The results showed that the optimal formula of byproducts was mixture of corn starch and wheat bran at the proportion of 1:3. The optimal fermentative parameters were 30% inoculum of Mortierella isabellina, 60%initial moisture content,60 g fermentation substrate per 250 mL, among which the last two factors had an significantly effect on the yield of SCO (P< 0.01). The results of fermentation under the optimal condition indicated that the yield of SCO could reached 10.18 g/100 g. Contents of y-linolenic acid (GLA) and docosahexaenoic acid (DHA) in SCO were 4.03% and 1.70%, respectively. Meanwhile, the total energy concentration of fermentative substrate was improved from 3779.77 cal/g to 4885.39 cal/g.Experiment 3 Study on oil-producing mechanism by Mortierella isabellina.The methods of scanning electron microscope (SEM) and X-ray diffraction (XRD) were taken to detect physicochemical properties of substrate and products. The results showed that Contents of neutral detergent fiber (NDF), acid detergent ligin (ADL), total starch and amylose were increased. Contents of the reducing sugar and protein of substrate were reduced. The analysis of SEM showed that after fermentation, granule of corn starch was eroded, and proportion of small starch granule increased. The results of XRD showed that the crystal type of corn starch was disappeared after the fermentation.In conclusion, solid-state fermentation on mixture of corn starch and wheat bran by Mortierella isabellina could produce single cell oil that contained high level of unsaturated fatty acids. The probable oil-producing mechanism was that physical structure of substrate was altered, and its hydrolysates were used to mycelial growth and oil production.