Effects Of Exogenous Lactic Acid Bacteria On The Anti-colon Cancer Activities Of Fermentation Products Of Dietary Fibers In Vitro

Resistant starch(RS),xylooligosaccharides(XOS)and inulin(IN),three dietary fibers can be fermented by the intestinal microflora,to product short chain fatty acids(SCFAs)with health benefits.Lactic acid bacteria(LAB),especially probiotics,can degrade these dietary fibers and moderate the balance in intestinal microflora,enhance the production of SCFAs(mainly acetate,propionate and butyrate),which are helpful for the gut health.In particular,the production of butyrate with anticancer activity is benefit for the prevention of colon cancer.The influence of exogenous LAB on the colonic fermentation of dietary fibers and the anticancer activities of the fermentation products to colon cancer cells were studied.The health adults' fecal extrat as intestinal microflora was used to ferment these dietary fibers in vitro at 37 °C for 24 h and 48 h,fellowed by detection of acetate,propionate,butyrate and lactate.After that,one of ten exogenous strain cultures was added into the fermentation systems to assess production of the four acids.At last,growth inhibition and apotosis induction of the fermentation products to colon cancer cells(HCT-116 cells)were elevated by the cell experiments.Gas chromatography(GC)and spectrophotometer(SP)methods were applied to detect the contents of acetate,propionate,butyrate and lactate in the fermentation products.The results showed that:(1)when fermentation time increased,the contents of acetate,propionate and butyrate were increased while the contents of lactate increased firstly but decreased after then;and the relationships between organic contents and fermentation time were not be infuenced by the addition of exogenous LAB strains.(2)before the addition of exogenous LAB strains,more propionate generated in the fermentation products of RS,more actate and less lactate produced in the fermentation process of XOS,and more butyrate produced in the fermentation systems of IN.(3)after adding the exogenous strains cultures,the contents of acetate and butyrate in the fermentation products of RS,XOS and IN were enhanced by 8-10 strains;the content of propionate in the fermentation products of RS and IN were enhanced by 5-10 strains,however,only 2 strains increased the content of propionate in the fermentation products of XOS.At the time point of 24 h,lactate was increased more by strains and then decreased at a high degree at 48 h.Thus,these results suggested that most of exogenous LAB strains enhanced the accumulation of SCFAs and the conversion of lactate in the fermentation products of RS,XOS and IN.CCK-8 was used to elevate the cell proliferation inhibition of the fermentation products,and results are listed as below:(1)without the addition of exogenous LAB strains,the proliferation inhibition of the fermentation products of RS,XOS and IN was 35.4-41.6%,66.2-67.5% and 61.4-65.7%,respectively.However,when strains cultures were added into the fermentation systems,the proliferation inhibition was 42.4-91.1%,63.4-82.4% and 48.5-91.1%,respectively.In total,most of strains cultures enhanced the cell proliferation inhibition of the fermentation products of three dietary fibers.(2)Results of correlation analysis and confirmation trials both pointed out that the cell proliferation inhibition of the 20 fermentation products of each dietary fiber was mainly contributed by butyrate(but not acetate and propionate),while lactate in fermentation products was unfavorable as it could decrease proliferation inhibition.DNA-Ladder and flow cytometry were applied to reveal the cell apoptosis induction of the fermentation products of RS,XOS and IN with the addition of exogenous LAB strains,and results are listed as below:(1)the selected fermentation products based on the results of the growth inhibition experiments,could induce the cells into apoptotic cells,and DNA ladder formed.The potency of fermentation products on induction of cell apoptosis was also similar with the effects of cell proliferation inhibition.It was meaned that fermentation products inhibited proliferation of HCT-116 cells by inducing apoptosis.(2)Standard butyrate solutions induced cells apoptosis in dose-dependent manner,and potency of butyrate on cell apoptosis induction was also similar with the potency of cell proliferation inhibition.Thus,the results revealed that the butyrate in fermentation products directly influence the anti-colon cancer activity of the fermentation products.In conclusion,the beneficial collaborative effect between exogenous LAB strains and intestinal microflora could accelerate the production of organic acids during the fermentation of dietary fibers,especially butyrate,which is essential to enhance the anti-colon cancer activity of fermentation products of dietary fibers.More important,the research provides some scientific evidence for the combination of three dietary fibers and LAB strains applied in functional foods with the prevention of colon cancer.