Investigation On Properties Of High Methoxylated Pectin As A Biological Delivery Vehicle

With the increasing demand of consumers for food nutrition and function,bioactive substances are becoming more and more popular among consumers.To solve the problem of biologically active substances being unstable due to environmental factors and easily damaged in the digestive tract of organisms,they can be embedded in biological delivery carriers,and orally delivered to specific parts of the body for release and function.Among the biomolecular delivery carriers,both proteins and lipids are susceptible to hydrolysis and destruction by digestive enzymes,but polysaccharides tend to have better resistance to digestion and can be used as colon-targeted delivery carriers.Pectin belongs to polysaccharide.The ultra-high methoxylated pectin(UHMP)obtained through esterification modification has an esterification degree of over 90%,and its high interfacial activity makes it have good emulsification properties,making it a potential biological delivery carrier material.Based on this,in this thesis,the emulsions with UHMP as emulsifier were subjected to simulated gastrointestinal digestion and simulated colonic fermentation to investigate the digestion mechanism,delivery efficiency and intestinal impact of the emulsions.The emulsions were further prepared into easily stored microcapsules to investigate their physical properties and re-solubilization performance.Firstly,the UHMP and UHMP emulsion were subjected to simulated gastrointestinal digestion.The samples were digested in the simulated gastric solution(p H=2,37 ℃,containing pepsin)with stirring for 1 h,and in the simulated intestinal solution(p H=7,37℃,containing pancrelipase and bile salts)with stirring for 2 h.The results showed that the molecular structure of UHMP could remain stable in the simulated gastric digestion,and the molecular weight and reducing end content of UHMP did not change significantly before and after digestion.In the simulated intestinal digestion,the esterification degree of UHMP decreased from 90.60% to 51.04% due to the hydrolysis of the ester bond on galacturonic acid(Gal A)by pancrelipase,and the molecular weight was slightly reduced.Laser confocal observation showed that UHMP emulsion droplets underwent hydrophobically aggregation in simulated gastric solution with high charge density,and the aggregating pectin were distributed on the droplet surface to protect the droplets.In simulated intestinal solution,neutral p H and surfactant bile salts led to the redispersal of emulsion droplets.Interfacial substitution of bile salts,hydrolysis of oil phase by pancreatic lipase and reduction of interfacial activity of UHMP due to de-esterification contributed to the destabilization and breakage of emulsion.The stability of the emulsion during digestion was positively correlated with the pectin concentration in the concentration range of 1% to 3%(w/v),presumably because the interfacial adsorption layer of the emulsion became thicker with increasing pectin concentration and more resistant to bile salt substitution.The free fatty acid release rate of UHMP emulsions during intestinal digestion(7.33%～11.15%)was significantly lower than that of citrus pectin emulsions at the same concentration(15.48%～18.25%),and the free fatty acid release rate decreased with the increasing pectin concentration.UHMP could effectively protect the emulsion-embedded material during digestion,resulting in a retention rate of70.15%.Secondly,to deliver tributyrin(TB)into the colon and exert its effect,the UHMP emulsions encapsulated with TB were subjected to dynamic simulated colonic fermentation,and the effects of the emulsions on the growth and metabolism of intestinal flora were determined using a biomimetic colonic bioreactor.Compared with the control group(SO emulsion),the TB-embedded UHMP emulsion significantly promoted the production of butyric acid in the fermentation system and showed the potential effect of reducing the production of the harmful metabolite ammonia nitrogen.The butyric acid content in the TB emulsion group reached 10.58 mmol/L at 24 h of fermentation,while the butyric acid content in the SO emulsion group was only 3.04 mmol/L.At 48 h of fermentation,the ammonia nitrogen content in the TB emulsion group increased by 51.34%,significantly lower than98.52% in the SO emulsion group The ammonia nitrogen content in the TB emulsion group increased by 51.34% at 48 h of fermentation,which was significantly lower than that in the SO emulsion group(98.52%),indicating that TB is expected to be a butyric acid supplement to the colon and improve the intestinal microecology.Analysis of intestinal flora composition by thermogram and STAMP differences showed that TB emulsion tended to promote the growth of butyric acid-producing genera(e.g.Clostridium,Lachnospiraceae and Blautia),and SO emulsion better promoted the growth of propionic acid-producing genera(e.g.Phascolarctobacterium and Parabacteroides),suggesting the potential efficacy of TB emulsions in improving host energy metabolism and alleviating inflammation through butyric acid supplementation.Finally,the physicochemical properties of microcapsules made by spray drying of UHMP emulsions were investigated.The TB microencapsulated products obtained by spray drying had a moisture content of less than 5%,a bulk density higher than 0.45 g/m L,and thermal stability at a processing temperature of 250°C.The surface of the particles was smooth and dense,and the wall material was distributed with small emulsions.The unpleasant odor of TB was reduced to 16.09% of the original,and the protection effect was good.The state of 3% UHMP re-soluble emulsion was closest to the original emulsion.The droplet distribution of 3% UHMP re-soluble emulsion was homogeneous and stable,and the polymer dispersibility index was 0.140 ± 0.070.The average particle size of the droplet of the re-soluble emulsion(472 nm)was slightly larger than that of the original emulsion(451 nm).Optical microscopy and laser confocal observation showed that the stability of the re-soluble emulsions during simulated gastrointestinal digestion was also positively correlated with the UHMP concentration.The results of this study provide a theoretical basis for the subsequent application development of TB emulsions.