Studies On Control Of Total Amount Of Bacteria In Process For Producing Chlorella Pyrenoidosa Powder With A Novel Cultivation Mode Called "Sequential Heterotrophy-Dilution-Photoinduction"

Chlorella sp., which has unique nutrition components and biological activity, is widely applied in many fields, such as health care products, food, biological bait, biological fuel, feed addition, carbon dioxide fixation and sewage disposal. Aiming at the problems existing in cultivation ways, a novel platform technology named Heterotrophic-Dilution-Photoinduced sequential cultivation was invented successfully in our laboratory to achieve high-density and high-quality culture of chlorella. This technology has been scaled up to 65t fermenter--400 m2 runway pond. But an important problem is to control the total amount of bacteria (TAB)in chlorella powder. So far, the research on the control of total number of bacteria in producing process of chlorella powder has not been reported in literatures. Thus, this study focused on the variation of TAB in process of production based on "Sequential Heterotrophy-Dilution-Photoinduction" (SHDP) and the control of TAB was not systematic studied relatively.Firstly, the variation of TAB in induced chlorella liquid in different season was investigated. The results showed that TAB increased with the fast growth rate in summer, and remained unchanged in winter. Induced water which was sterilized by NaClO solution had no effects on total bacteria amount in chlorella liquid. At last, TAB increased to 108 CFU/mL after induction. In addition, a certain number of bacteria (105 CFU/mL) can be introduced to chlorella liquid from air in induced process.Secondly, according to the variation of TAB in chlorella mud in centrifugal process, it was found that TAB increased up to 2-3 times after centrifugation. The orders of magnitude about TAB have not been changed, thus bacteria were not introduced to chlorella mud in the centrifugal process. According to the changes of physical and chemical indicators in chlorella mud in process of cooling storage, it was confirmed that cooling storage can prevent chlorella mud deterioration. In addition, qualified chlorella mud cannot be achieved by different sterilization means, such as microwave sterilization, pasteurization, and instantaneous high temperature sterilization.Lastly, the results of the TAB in spray drying process showed that 99 percent of bacteria in chlorella mud can be killed in this process. But for chlorella mud with a high content of bacteria, it was hard to achieve qualified chlorella powder after drying spray. Thus, the effects of different sterilization methods on total bacteria amount in chlorella powder were investigated in this study, such as oven heating, high speed ion irradiation and high speed electron irradiation. And the results showed that high speed ion irradiation can effectively control the total bacteria amount in chlorella powder.The above results not only set a solid foundation to control the TAB in the industrial production of chlorella powder, but also have important reference value for controlling TAB in production process of other microalgae powders.