Metabolic Characteristics Of Oxygen-enriched Fermentation Of Sodium Gluconate And The Construction Of Its Kinetic Models

Sodium gluconate(SG)fermentation by Aspergillus niger in China is now in a world leading level.However,oxygen tranfer cannot been improved any further with normal air aeration,which is now becoming the bottleneck of SG fermentation.With inlet oxygen concentration up to 32%in a 5-L fermentator,the fermentation time was shortened from 20.1 h to 15.5 h,and the OUR level was increased from 57.15±1.77 mmol/L/h to 81.01±1.25 mmol/L/h.Thus,both the production rate and yield was significantly enhanced.Larger KLa values and more dispersed morphology were obtained in oxygen-enriched fermentations,which were the main causes of higher SG production rate.According to the result of metabolic flux analysis,flux distributions in fermentations with oxygen concentration of 25%were favorable to the synthesis of SG formation.In the growth phase,85%of the glucose was utilized for SG production when the enriched oxygen was employed,and this proportion was only 79%in nature air fermentations.During the stationary phase for SG production,this proportion was increased to 89.3%and 93%respectively in the control(nature air)and oxygen-enriched(25%)fermentations.Pool sizes of metabolites in oxygen-enriched fermentations was shrinked compared to that of air fermentation.The redistribution of metabolic flux and the drastical decrease of the by-product,citrate from 1.36 g/L to 0.34 g/L,made the major contributions to the increase of SG production rate.In combination with online physiological parameters,kinetic models of oxygen-enriched fermentation of SG by A niger were constructed.The mycelial growth was expressed as:X=0.930e0.402t/1.020+0.580e0.403t(R2=0.9927).Owing to the significant physiological diversities of the cells between the growth and stationary phase,piecewise equations were introduced to depict the process of product synthesis and glucose consumption.The equations for product synthesis:P=0.101X+40.08 ln(1.02+0.58e0.402t)-7.12(R2=0.9991)(0?t?8);P=2.06t(OUR-45.29)(R2=0.9976)(8?t?tT).The equations for glucose consumption:S=342.5-17.45X-37.08 ln(1.02+0.58e0.402t)(R2=0.9979)(0?t?8);S=326.6-17.36X-3.251n(1.02+0.58e0.402t)-1.74 t(OUR-45.29)(R2=0.9964)(8?t?tT).Where tT is the terminal point of the fermentation,and OUR is the average oxygen uptake rate of the stable phase in oxygen-enriched fermentation.The models constructed in this paper can excellently predict the experimental results as shown in the verification experiments.