Study On High Density Culture Process And Releasing Strategies Of Growth Inhibitors Of Aroma-producing Lacticaseibacillus Casei TCS

Lacticaseibacillus casei is a widely used lactic acid bacteria,which can be used as an auxiliary starter to enhance flavor of fermented dairy products.High-density culture is the basis of developing high-efficient freeze-drying starter,high-density culture strategies should be established to guide the industrial production.This paper focused on an aroma-producing L.casei TCS as the research object.Firstly,the optimal culture medium composition is determined using artificial neural network-genetic algorithm.Secondly,the cell growth kinetic model,the product synthesis kinetic model and the substrate consumption kinetic model were studied in batch culture,to explore the effects of acid inhibition,salt stress and substrate inhibition on the growth of L.casei.A set of high-density culture strategy of L.casei TCS was established by combining chemical neutralization,ion exchange and fed batch method.It provides a theoretical basis for the research and development of a high-yield aroma starter.The main conclusions of the paper are as follows:(1)The fermentation medium were optimized using artificial neural network-genetic algorithm.The results showed that the high density medium of L.casei TCS was composed of glucose 35 g/L,peptone 62 g/L,sodium acetate 5 g/L,sodium triammonium citrate 2 g/L,dipotassium phosphate 3 g/L,tween-80 1 g/L,anhydrous magnesium sulfate 0.3 g/L,manganese sulfate monohydrate 0.2 g/L,sweet corn juice 24 g/L.ANN-GA has good fitting and prediction performance.The R~2 and RMSE of the model are 0.9656 and 0.0216 respectively.The error between the experimental value and the prediction value is small,so it is suitable for the optimization of L.casei TCS fermentation medium.At 37℃,the number of viable bacteria reached 9.66 lg CFU/m L,which was 4.2 times that of MRS medium.(2)L.casei TCS was cultured in 5 L fermenter with optimized medium.The optimal inoculum was 4%,and the optimal initial p H value was 7.0.The changes of viable bacterias,lactic acid contents and glucose contents with time were determined.Three kinetic models of fermentation were established by nonlinear fitting with MATLAB,and the function expressions were obtained.The results showed that the growth of bacteria was in accordance with Logistic model,the production of lactic acid and the consumption of glucose was in accordance with the partially coupled Piret-Luedeking model.The R~2 values of the three models were 0.9998,0.9990,0.9992,and the RMSE values were 0.0156,0.1689,0.1545,respectively.The models could accurately reflect the dynamic changes of the fermentation process.(3)The growth of L.casei TCS was mainly affected by acid inhibition,salt stress and substrate inhibition.Through chemical neutralization,the acid inhibition was relieved by adding lye in the fermentation process,but the osmotic pressure increased and the number of viable bacteria decreased.Adding weak basic anion exchange resin IRA-67 to the medium stage of logarithmic growth could effectively adsorb lactic acid,which could maintain the p H of the system between 5.0 and 5.5,prolong the growth period of the bacteria and avoid the inhibition of the increasing osmotic pressure on the growth.Furthermore,an opportune feed supplement at the late fermentation stage relieved the substrate inhibition.The results showed that the number of viable L.casei TCS was 9.3 times of that without optimization,reaching 10.01lg CFU/m L.