The Study Of Technology On Fermentation Coupling With Foam Separation Producing Nisin

Nisin is a polypeptide bacteriocin produced by Lactococcus lactis subsp.lactis. It iswidely used as a preservative in food industry. However, high cost for fermentation andlow yield limit its wide application. For improving the yield of nisin, therefore, this paperfurther investigated fermentation coupling with foam separation for nisin production basedon previous works in our research group and the influence of Ca2+and95%ethanol onfermentation by L.lactis and bioassay of nisin in broth was also discussed.Firstly, two technologies of fermentation coupling with foam separation were designedon the basis of the pH-controlled batch fermentation of L.lactis. Namely, foam separationwas conducted during8-11h and6-12h of fermentation with the gas flow of60mL/minand30mL/min, respectively, and sterile air and nitrogen were individually used asexperimental gas in the two technologies. The results showed the second technology waspreferred to the first and achieved a higher enrichment of nisin and lower cell enrichment,which benefit to fermentation coupling with foam separation producing nisin. Moreover,nisin production continued to increase after foam separation completion in the twofermentation technologies compared to the control group and the maximum total nisinactivity (4657IU/mL) was achieved when online foam separation was carried out using airof30ml/min between6h and12h, which was improved by36.2%compared to that of thecontrol group (3420IU/mL).In the next place, fermentation coupling with foam separation by immobilized L.lactiswas studied. Firstly, the effect of immobilized L.lactis on its fermentation under controlledpH was researched. The stability of the immobilized L.lactis and the ability to produce nisinwere then investigated in repeated batch fermentation process and the best batch offermentation was confirmed, under which fermentation coupling with foam separation byimmobilized L.lactis was carried out. The results were presented as follows.(1) Nisinactivity in broth began to keep stability at12h of fermentation, which was2h later thanthat of fermentation by free L.lactis.(2) The stability of immobilized L.lactis was better,having a lower amount of cells in the broth, in the first four batch fermentation. Nisinproduction kept stable during2-5batch of fermentation with an average activity of2726IU/mL, which was82%of that of fermentation by free L.lactis.(3) In fermentationcoupling with foam separation by immobilized L.lactis, the amount of cells entrained infoam decreased by75.3%, compared to that in fermentation of the free L.lactis and the totalnisin activity (3678IU/mL) reached79.0%of that obtained from fermentation coupled withfoam separation by free L.lactis. Finally, effects of Ca2+and95%ethanol on free-pH fermentation of L.lactis andbioassay of nisin in broth were investigated. The results presented that nisin activity wasimproved at various concentrations of Ca2+and different amount of addition of95%ethanol.However,95%ethanol had mainly an effect of the nisin bioassay in the broth, by which itimproved the nisin activity while Ca2+improved the ability of the cell to yield nisin toimprove nisin activity.