The Nisin Produced By Streptococcus Thermophilus Microcapsule Fermentation Coupling With Separation

Nisin, a kind of small molecule peptides, was produced by Lactococcus lactis or Streptococcus lactis. It has been used widely in the food industry as a kind of natural green food preservatives, for the performance of inhibiting the growth of G+ bacteria and Bacillus, but non-toxic side effects on the human body. Our group have studied a thermophilic streptococcus 6032 liquid core microcapsules to ferment the Nisin, which was prepared by the extrusion method using the sodium alginate(A) and chitosan(C) as wall materials. Others have studied the foam separating technics to produce Nisin. However, there are rare reports on the nisin production by thermophilic streptococcus 6032 liquid core microcapsules fermentation coupling with foam separation. The present study was designed to couple the Nisin fermenting and foam separating, which could relieve the feedback inhibition by on-line separation the Nisin, and achieve the continuous fermentation.The main research contents and results of this paper were as follows:(1)The extrusion method was employd to prepare the ACA Streptococcus thermophilus 6032 liquid core microcapsules. Based on the results of single factor experiment, the response surface method was further utilized to optimize the conditons of the preparation process. The optimal technological conditions were the chitosan dissolution time 2h, stirring speed 236r/min, the temperature 33.7℃ and dropping rate of 4.9mL/min. The potency reached to 5242.00IU/mL, and the absorbance OD60o was 0.182 when using the ACA Streptococcus thermophilus 6032 liquid core microcapsule to ferment Nisin. The cell microcapsules were observed under the 40 times of optical microscope and the inverted microscope. They were mostly spherical and the same in size, particle diameter was about 790um, film thickness was about 22.5um.(2)In order to lay the basis of the nisin production by the ACA Streptococcus thermophilus 6032 liquid core microcapsules fermentation coupling with foam separation, the conditions of the ACA Streptococcus thermophilus 6032 liquid core microcapsules fermentation and foam separation were optimized. ①Through Response Surface Methodology, the optimal conditions for fermentation were the initial pH of 6.1, the culture temperature of 28.7℃and the fermentation time of 20h. Under these conditions, the nisin potency reached to 5460.00IU/mL and the breakage rate of microcapsules was 0.71%. The optimization results of the content of culture medium for the foam separation were the sodium chloride content of 1.50%, the calcium chloride content of 1.45% and the corn steep liquor content of 24.50%. Then the nisin potency was 5798.23IU/mL and the enrichment ratio of Nisin arrived at 7.4.② The suitable foam separation mode coupling with fermentation for Nisin producing was investigated between pumping air and adding NaHCO3. The pumping air mode was more suitable for foam separating than the mode of producing CO2 by adding the saturated NaHCO3 solution. The optimal conditions for the pumping air separation Nisin were screened by orthogonal method. The results showed that the height of foam layer 11 cm, the temperature 34℃, pH 7.0, the separation time 60min and the ventilation rate 0.15L/min. Under these conditions, the enrichment ratio of Nisin was 8.4, the recovery rate was 83.89%, and the cell enrichment ratio was 0.221%.(3)The process of Nisin producing by Streptococcus thermophilus 6032 liquid core microcapsule fermenting coupling with foam separating was researched. The optimal process of foam separation process was selected as the control group. Base on the pH-controlled Nisin bath fermenting coupling with foam separating, during 14-22 h and 18-20h of fermenting process the gas was pumped in at 0.05L/min and 0.10L/min. Two technologies was compared, then the better one was selected. The fermenting coupling with foam separating to produce Nisin results showed that two kinds of fermenting technologies were better than the unventilated group. The second technology was superior to the first one, for its higher enrichment of nisin and lower cell enrichment, when the enrichment ratio of Nisin was 13.44, the maximum Nisin potency reaches to 7960.16IU/mL, which was increased by 25.22% compared to the control group.