| Longan(Dimocarpus longan Lour.)is a typical summer fruit in southern China,and it is a medicine and food homologous plant.As fresh longan is not resistant to storage,70% of longan fruit is sold in fresh for season,and the rest is sold in dry form.Traditional Chinese medicine and modern science consider that the immunomodulatory activity of dried longan,also known as longan,is more significant than fresh longan.In our prophase research,we have confirmed that polysaccharide was the main bioactive compounds in longan pulp,which has the significantly immunomodulatory activity in vitro and in vivo.At present,researches on polysaccharides in mainly focus on two aspects.For one aspect,it is concerned about how to improve the extraction process of longan polysaccharides and the utilization rate of longan;For another,the structure-activity relationship between the bioactivity of longan polysaccharide is also concerned.Therefore,when optimizing the extraction process to improve the extraction rate,attention also should be paid to the effect of the extraction process on the structural changes of longan polysaccharide,and further clarify the effect of the structural changes on the bioactivity of longan polysaccharide.The main methods,results and conclusions in this study are presented as follows.1.Optimization of superfine grinding and enzymatic assisted extraction technology of longan polysaccharideThe dried longan was prepared by heat pump drying with fresh longan,and then dried longan was dried the second time after alcohol soaking for removing the small molecular component,and the dried longan dried(water content 10.72%)after two times drying was used as the experimental longan material.The extraction rate of Polysaccharides from Longan was taken as an evaluation index to optimize the superfine grinding and enzymatic assisted extraction process.First,five process control factors: time for superfine grinding,enzyme dosage,material to liquid ratio,pH value,extraction temperature and time for extraction were tested by single factor experiment.Base on the single factor results,according to the Box-Benhnken center combination principle,the response surface was optimized considering three factors: time for superfine grinding,enzyme dosage and time for extraction.The model was established by the response surface optimization.Combined with the results of single factor experiment and response surface experiment,the optimum extraction conditions of longan polysaccharide were determined as follows: pH value was 5,extraction temperature was 50?,superfine grinding for 2min,dosage of cellulase was 140U/g,extraction time for 90 min,and at this condition,the extraction rate of longan polysaccharide was 38.99%.The size of longan pulp decreased by 40%,which has theoretical guiding significance for control and optimization of superfine grinding process in actual production.2.The effect of superfine grinding and enzymatic assisted extraction technology on the physicochemical properties of longan polysaccharideThe traditional hot water extraction technology and superfine grinding assisted extraction technology were used as control together with superfine grinding and enzymatic assisted extraction technology,all of three kinds of processes above were processes,followed whit the concentration,deproteinization,ultrafiltration,alcohol precipitation and freeze drying processes,and the product was named as LP,LP-S and LP-SE respectively.The results showed that the yield of LP-SE was 3.28% which was 200% and 90% higher than LP and LP-S respectively.There was no significant difference in the monosaccharide composition,neutral sugar and protein of three kinds of longan polysaccharides,while the reducing sugar of LP-SE was higher than LP and LP-S,and uronic acid was lower than LP and LP-S significantly.The structure of three kinds of longan polysaccharides was determined by infrared scanning(FTIR),Advanced Polymer Chromatography(APC),Zeta Particle Potential Analyzer,Scanning Electron Microscope(SEM),iodine-potassium iodide reaction,and Congo red reaction.The results showed that the three kinds of longan polysaccharides were all acid piran heteropolysaccharide with ? and ?-D configuration.The molecular weight and particle size showed that the molecular weight and particle size of LP-SE decreased significantly,and the results of SEM and Congo red showed that there were more reticular and spiral structure in LP.The reticular and spiral structure in LP-S and LP-SE was significantly destroyed and reduced.The results of solubility and rheological properties showed that compared with LP and LP-S,solubility and fluidity of LP-SE increased significantly,viscosity and gel properties of LP-SE decreased significantly.3.The effect of superfine grinding and enzymatic assisted extraction technology on the bioactivity activities of longan polysaccharideTaking LPS as control,the immunomodulatory activity of stimulating the macrophages to secrete NO,TNF-?,IL-6 and IL-1? was compared between LP,LP-S and LP-SE.The results showed that the cells toxicity of the three kinds of longan polysaccharides was low,and LPSE had the strongest immunomodulatory activity of stimulating the macrophages to secrete the cytokines.Taking LP,LP-S and LP-SE as carbon source,and glucose,FOS as the control,the probiotic activity of three kinds of longan polysaccharides to six strains of probiotics was investigated.The results showed that LP-SE had significant proliferation activity of Lactobacillus plantarumsubsp,Lactobacillus bulgavicus,Lactobacillus casei and Leuconostoc mesenteroides,and LP had significant proliferation activity of Lactobacillus fermentum.Taking LP,LP-S and LP-SE as carbon source,inulin and the monosaccharides composed of and longan polysaccharide as the control,the fermentation characteristics of three kinds of longan polysaccharides on intestinal feces bacteria was investigated.The results showed that all the three kinds of longan polysaccharides could be utilized by feces bacteria,and promote the proliferation of fecal bacteria,and stimulate the secretion of short chain fatty acids.Compared with the other two kinds of longan polysaccharides,the speed of LP-SE fermentation was the fastest,besides,the effect of regulating the bacterial population ratio of LP-SE was the best,furthermore,the content of short chain fatty acids produced of LP-SE during fermentation was the most. |
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