| Summary: | 碩士 === 國立屏東科技大學 === 食品科學國際碩士學位學程 === 105 === Nutrient sources consumed by humans and animals are mainly from agriculture, however agricultural productions are being reduced by diseases, insects, water pollution and climate change. For that reason, single cell protein (SCP) was found to be an excellent alternative. Among all the microbial sources of protein, yeast has attained the global acceptability and preferred for SCP. However, the cost to produce single cell protein is still high, consequently there is a need for cheaper alternative substrates to reduce production cost. In addition, light-emitting diode (LED) had been found as a potential factor which could affect cell growth. The present study was undertaken to optimize the biomass of S. cerevisiae P13, by using agricultural by-products (sugarcane molasses and cheese whey) as a cheap potential substrates, then testing the effect of LED on yeast growth.
Firstly, the effect of pretreatment sugarcane molasses and culture condition of the aeration and agitation in the flask fermentation was tested. The results show that pretreated sugarcane molasses does not significantly affect yeast growth. In order to reduce culture cost, sugarcane molasses without pretreatment was used for further processes. Using cotton cap significantly increased yeast biomass from 8.45±0.08 Log CFU/mL to 8.75±0.06 Log CFU/mL compared with using aluminum foil. However, agitation changing from 100~250 rpm did not influence cell mass. Therefore agitation was kept at 150 rpm as conventional use. The effect of nitrogen sources including yeast extract, peptone, NH4SO4 and NH4Cl were examined. Among them peptone was found as the most favorable for yeast growth and NH4Cl could be a potential economical inorganic nitrogen source. Hence peptone and NH4Cl were used for further optimization step. Moreover, the effect of sugarcane molasses concentration was investigated for proper range in further experiments which was screened out with a suitable range from 6~12%. The effect of medium components (sugarcane molasses, peptone, NH4Cl) were investigated by the central composite design (CCD) of response surface methodology (RSM) which predicted that medium content sugarcane molasses 10.78%, peptone 8.18 g/L, NH4Cl 1.41 g/L could enhance the production of yeast biomass to 8.81 Log CFU/mL compared with 8.37 Log CFU/mL culture in YM broth. Moreover, the optimized media allow a cost reduction of around 30% compared with YM broth. In addition, a scale up was done in a 10 L bioreactor content of 5 L optimum medium, with yeast biomass productivity reached 8.85±0.09 Log CFU/mL at 18 h cultivation time. On the other hand, the mixture culture mediums were tested in order to minimize culture cost. The mixture medium of sugarcane molasses/cheese whey demonstrated as an effective and inexpensive substrate for product development with 8.68±0.05 Log CFU/mL and cost reduction of approximately 70% in comparison with YM broth. However, the mixture mediums of sugarcane molasses/whey powder for both content 1% and 2% whey powder were not significantly different compared with control. Furthermore, the effect of LED on Saccharomyces growth was done in both shake flask and bioreactor using various LED and fluorescent light sources. Although, no remarkable difference was found in comparison with control which was cultured in the dark.
Overview, a suitable culture condition and optimum medium was found for high yeast biomass production. Mixture medium also demonstrated as an effective and inexpensive substrate for product development. LED light sources did not affect yeast growth in this study however there is need for further clarification.
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