人肠道微生物对海带岩藻聚糖硫酸酯及其寡糖的降解利用

HUMAN GUT MICROBES DEGRADE AND UTILIZE FUCOIDAN AND ITS OLIGOSACCHARIDES FROM LAMINARIA JAPONICA IN VITRO

采用人肠道微生物体外厌氧发酵技术,研究人肠道微生物对不同分子量岩藻聚糖硫酸酯的降解利用。分别将五个志愿者的肠道微生物接种到以高分子量和低分子量岩藻聚糖硫酸酯为唯一碳源的培养基中,酵解48h后,采用TLC和PAGE分析分子量变化,PMP-HPLC分析单糖组成变化,GC分析短链脂肪酸的生成情况。结果发现:在人肠道微生物体外降解岩藻聚糖硫酸酯的体系中,岩藻聚糖硫酸酯寡糖和低分子量组分(10—20k Da)含量显著降低,而且酵解产物的单糖组成没有变化,说明被人肠道微生物彻底降解利用;而人肠道微生物对高分子量岩藻聚糖硫酸酯(>20k Da)的降解和利用度很低,产物的半乳糖和甘露糖的比例明显下降。低分子量和高分子量岩藻聚糖硫酸酯在酵解后均生成短链脂肪酸乙酸、丙酸和丁酸,但在高分子量岩藻聚糖硫酸酯发酵液中还生成了支链脂肪酸(异丁酸、异戊酸)和戊酸。研究结果表明,人肠道微生物能够彻底降解利用复杂的海带岩藻聚糖硫酸酯寡糖和低分子量组分,但是对高分子量岩藻聚糖硫酸酯的降解率很低。单糖分析说明人肠道微生物能够降解和利用多糖中的所有单糖,产生有利于肠道健康的短链脂肪酸,但是只有低分子量岩藻聚糖硫酸酯能够抑制支链脂肪酸生成。

To investigate the degradation and utilization of fucoidan from Laminaria japonica of different molecular weights with human gut microbiota,we sampled human gut microbiota from five volunteers in vitro.High-and low-molecular-weight fucoidan（coded HMWF and LMWF,respectively） were fermented with the microbiota in anaerobic culture system in vitro for 48 h.TLC and PAGE were used to analyze the degradation of fucoidan.PMP-HPLC and GC were used to analyze the monosaccharide composition and short chain fatty acids in fermentation product,respectively.Results show that the content of oligosaccharides and low-molecular-weight fucoidan（10—20k Da） decreased markedly,while the monosaccharide composition of degradation products remained unchanged,indicating that the LMWF could be degraded entirely and utilized by human gut microbiota in anaerobic culture system in vitro.However,only small amounts of HMWF（20k Da） could be degraded to oligosaccharides,and the proportions of galactose and mannose in the fermentation product decreased significantly.GC analysis showed that both LMWF and HMWF could be degraded to acetic acid,propionic acid and butyric acid（short-chain fatty acids）.Branched-chain fatty acids（isobutyric acid and isovaleric acid） and valeric acid could be detected in HMWF medium only.Therefore,human gut microbiota can degrade and utilize complex fucoidan oligosaccharides and low-molecular-weight fractions from L.japonica in anaerobic culture system in vitro;however,it could be difficult to degrade a large-molecular-weight fucoidan with human gut microbiota.All sugars in the fucoidan oligosaccharides and large-molecular-weight fucoidan could be utilized by the microbiota to produce short-chain fatty acids,which is good for intestinal tract health.However,only LWMF could inhibit the produce of branched-chain fatty acids with human gut microbiota.