High cell density culture(HCDC)could decrease the fermentation size,benefit the downstream separation process,shorten the total production period,and decrease the equipment investment.Nowadays,HCDC has been attracted the attentions in the biochemical engineering fields,and widely applied in the food additives production.Some limited factors including substrates,inhibitory compositions,dissolved oxygen concentration and broth rheological properties has the direct influence on the outputs of HCDC.Selection of a favorable fermentor including typical stirred or airlift bioreactors,and recently-developed membrane or dialysis bioreactors is another critical factor for HCDC,and the operation strategies including the feedback control on the basis of the DO-stat,pH-stat,CO2 emission,substrateconcentration or respiratory quotient,and the non-feedback control also affect HCDC process significantly.This review summarized the recent research progress in the limited factors,bioreactors and operation control strategies of the high cell density culture,presented the examples of its application in the food additives production including astaxanthin,lipase,phytase,docosahexaenoic acid,α-acetolactate decarboxylase and L-lactic acid,and finally predicted the prospects of high cell density culture technology.

The 2-keto-D-gluconic acid(2-KGA) in fermentation broth was determined by polarimetry.Some factors affecting the determination of 2-KGA were investigated in detail,such as the concentration of the test solution,the temperature of the test solution and the pH of the test solution.It was found that the test solution content in 2.5~5.00 g 2-KGA per 100 mL,pH in the acidic range,more accurate measurement results could be achieved.The relevant phenomena were discussed according to the relevant principles of organic chemistry.

A continuous fermentation process of 2-keto-D-gluconic acid(2KGA)production from rice starch hydrolysate was developed using Pseudomonas fluorescens JD1202.The effects of starting point of continuous fermentation,dilution rate and feeding glucose concentration on 2KGA production were investigated.Results showed that the dilution rate and feeding glucose concentration had a significant effect on 2KGA production performance.When the dilution and media composition were at a stable level,the fermentation can start at any point,there had no significance of the concentrations of cell,substrate and product.The optimal operating factors were obtained as:0.065 h-1of dilution rate and 170.0 g/L of feeding glucose concentration.Under these conditions,the steady state produced 2KGA at the concentration of 130.34 g/L,average volumetric productivity of 8.47 g/L h and the fermentation conversion rate of 89.46%.In conclusion,this efficient continuous fermentation process by the strain Pseudomonas fluorescens JD1202 is competitive for industrial production 2KGA from rice starch hydrolysate.