Optimization of cell mass production of the probiotic strain Lactococcus lactis in batch and fed-bach culture in pilot scale levels

Lactococcus lactis is highly efficient probiotics microorganism with wide range of benefits on human health. This study was conducted to design and establish industrial platform for high cell density cultivation of this novel probiotic strain, L. lactis (WICC-B25). During bioreactor cultivation of lactic acid bacteria in industrial scale, there are two main problems during process namely: low cell growth rate and high lactate production. These both together resulted in low cell mass production. Therefore, this study was focused on cultivation parameters optimization for high cell mass production with minimal lactate formation in shake flask and bioreactor levels. Cell growth was studied in 16-L stirred tank bioreactor under controlled and uncontrolled pH conditions. The maximal cell mass of about 5.6 g L was obtained after 14 h cultivations under uncontrolled pH condition. This value was almost 35% higher than those cell mass obtained in pH controlled culture. Based on this data, fed-batch cultivation strategy was developed using mixed substrate feeding solution (containing all medium component) and mono-feeding (using glucose alone). For both cultures, fed was adjusted to constant rate of 3 g L h and, DO was cascaded to agitation speed to prevent the drop of DO to value less than 30% saturation as oxygen is limited factor for high cell mass production. Culture of mono-glucose feeding yielded the maximal cell mass of about 20 g L after 30 h. On the other hand, the cell mass obtained in mixed substrate feeding culture was only 8.4 g L. Thus, we can conclude that fed-batch cultivation under uncontrolled pH, mono-glucose feeding and DO stat of 30% is suitable cultivation strategy for high cell mass production of L. lactis in bioprocess industry.