Study On The Production Of Monacolin K By Submerged Fermentation Of Monascus Ruber 9901 In Bioreactors

The production of Monacolin K(MK) by Monascus sp. in submerged fermentation has reached a high level in shake flask, due to the relatively mature fermentation process and conditions. The key to achieve the industrialization is the large-scale bioreactor fermentation, which is based on the small and medium-sized scale-up experiments, in order to find out the regulation mechanisms of mycelial growth and metabolism production of Monascus sp. Hence, in order to understand the relationship among fermentation conditions, mycelial morphology and the production of MK by submerged fermentation of M. ruber 9901, a series of experiments were carried out in 5 L to 1500 L bioreactors. Four parts of experiments were carried out herein, including the study of the effects of culture and fermentation conditions on mycelial morphology, the effects of culture and fermentation conditions on MK yield; the relationship between mycelial morphology and MK yield and how to improve MK yield by adjusting culture and fermentation conditions.In the shake flask fermentation, the conditions of spore inoculum, rotation speed, medium composition and inoculum concentration were optimized by single factor experiment, in order to obtain the pellet-based seed liquid. The major morphology of M. ruber 9901 was mycelia after inoculation for 48 h, and then a small amount of pellet formed. The pellet diameter reached the maximum of 1680 μm after fermentation of 192 h and the proportion of pellet was 62%. The yield of MK was up to 1460 mg?L-1, which was 47% higher than that of the original.In 5 L to 50 L bioreactors, the conditions of inoculant ball size, seed, inoculum concentration, ventilation rate, rotation speed, time for the variable temperature and dissolved oxygen level were optimized by single factor experiment. In 5 L bioreactor, the final MK yield was up to 485 mg?L-1, which was 38% higher than that of the original, which using the second order of pellet with 1500 μm as the seed culture. In 30 L bioreactor, the suitable conditions were as follow: inoculum concentration 8%, the ventilation rate 1.5 v?v-1?m-1, the rotational speed 350 r?min-1(impeller tip speed ut 1.64 m?s-1), under which the pellet diameter was 2157 μm and the proportion of pellet was 41%. The final MK yield was up to 737 mg?L-1, which was 61% higher than that of the original. In the 50 L bioreactor, the suitable conditions were as follow: changing temperature from 30 ℃ to 25℃ after inoculation for 60 h, maintaining the dissolved oxygen level at 50%, under which the pellet diameter was 2309 μm and the proportion of pellet reached 53%. The yield of MK was up to 912 mg?L-1, which was 51% higher than that of the original. During scale-up submerged fermentation of M. ruber 9901, it was found that the formation of more and larger pellet in broth was beneficial for improving the production of MK by M. ruber 9901.In 200 L-1500 L bioreactors, the conditions of changing temperature, rotation speed and the agitator type were optimized. In the 200 L bioreactor, the suitable conditions were as follow: changing temperature from 30℃ to 25℃ after inoculation for 24 h, rotation speed 200 r?min-1(ut 1.75 m?s-1), under which the pellet diameter was 2451 μm and the proportion of pellet reached 67%. The yield of MK was up to 1672 mg?L-1, which was 87% higher than that of the original. In the 1500 L bioreactor, the suitable conditions were as follow: increased rotation speed from100 r?min-1(ut 1.82 m?s-1) to 180 r?min-1(ut 3.27 m?s-1) after inoculation for 24 h, curved six-blade impeller as both upper and lower impeller, under which the pellet diameter was 2209 μm and the proportion of pellet reached 52%. The production of MK by M. ruber 9901 was up to 1168 mg?L-1 in the 1.5 T stirred bioreactor.