| Tuber indicum was first named by the samples collected by Cook&Massee in India,but it is mainly distributed in China,and it is also the most common and most widely distributed truffle species with the largest yield in China.T.indicum not only has rich nutrients and unique fragrance,but also exhibit biological functions,such as antioxidant and anti-fatigue activities.In this thesis,T.indicum originated from Yunnan was used as the raw material to study the effects of hot air drying(AD),vacuum drying(VD)and vacuum freeze drying(FD)on the quality of truffles.The drying T.indicum by FD were selected to separate and purified T.indicum polysaccharides,and study the anti-fatigue mechanism of T.indicum polysaccharides and its effects on gut microbiota community.The main research results are as follows:1.Different drying methods were adopted to dry the fresh T.indicum slices,and the effects of the drying methods on the physicochemical qualities,nutrients retention and microstructures of T.indicum were evaluated;the effects of the drying methods on the volatile flavor compounds of T.indicum were also compared;the contents of soluble sugar,sugar alcohol,free amino acids,flavor nucleotides and organic acids in T indicum were analyzed.Equivalent unami concentration(EUC)was used to evaluate the umami of T.indicum.The results showed that FD products have the highest L value and the lowest a value,and can favorably maintain the product color;AD products have the highest browning degree;FD products have the lowest hardness and high brittleness;AD products have high hardness and low brittleness.The rehydration rate and rehydration rate of FD products are significantly higher than those of the other two kinds of products(P<0.05),and there was no significant difference:in rehydration ratio and rehydration rate between AD products and VD products(P>0.05).Drying no significant effect on the total protein content of T.indicum(P>0.05),the remaining quantities of vitamin C and reducing sugar of FD and VD products were significantly higher than those of AD products(P<0.05),the remaining quantity of total flavonoids of FD products was significantly higher than that of AD and VD products(P<0.05).SEM observation of the microstructure showed that FD products display an alveolate loose structure,while AD and VD products have compact organization structure and obvious contraction.The contents of volatile components,such as eight carbon compounds,aldehydes,esters and ketones,decreased after drying process of fresh T.indicum,and alkanes,heterocyclic compounds and sulfur-containing volatile components are generated.The composition of volatile flavor components of FD products is most similar to that of fresh T.indicum.In addition,E-nose can distinguish fresh T.indicum from drying products,and the results are consistent with those of GC-MS.Drying method has different effects on soluble sugar,free amino acids,organic acids and flavor nucleotides.FD products contain 121.56 mg/g of soluble sugar,2.31 mg/g of flavor nucleotides,133.53 mg/g of organic acids and 12.89 g MSG/100g d.b of equivalent umami concentration(EUC).There was no significant difference in the content of free amino acids between the three products.Taking into account the retention rates of the physic and chemical quality,nutritional ingredients and volatile and non-volatile flavor substances of the drying products,FD is the most fit drying method for T.indicum.2.T.indicum crude polysaccharides were obtained through the extraction process of response surface optimization(enzymatic time,enzymolysis temperature,enzymolysis pH,enzyme dosage).DEAE-52 cellulose ion-exchange chromatography and Sephadex G-100 gel chromatography were utilized for the further separation and purification,and a final T.indicum polysaccharide named EPT was obtained.The structure of the EPT was identified by chemical and physical analysis.Results showed that under the enzymatic extraction process condition of response surface optimization of T.indicum polysaccharides,the optimal technological condition for enzymatic extraction of T.indicum crude polysaccharide was as follows:enzymatic time was 4.58 h,enzymolysis temperature was 52.25?,enzymolysis pH was 2.48 and the ratio of enzyme to distilled water was 0.82%.Under the above conditions,the highest yield of T.indicum polysaccharides was 3.87%,and the sugar content of the crude polysaccharides was 30.51%.Three components of T-1,T-2 and T-3 were seperated via DEAE-52 cellulose ion-exchange chromatography.Through the antioxidant activities evaluation,it was found that the T-3 component has the most significant effect in eliminating free radicals of DPPH,OH and O2-·.Then T-3 was further separated and purified by Sephadex G-100 column chromatography to get the EPT eventually.It was found that EPT contains 98.3%of carbohydrate,2.46%of Uronic acid,90.87%of purity of EPT and 0.52%of sulfate.HPLC analysis showed that EPT was composed of three kinds of monosaccharide of arabinose,glucose and galactose,with the molar percentages of 0.99%,95.88%and 3.13%,respectively.Moreover,EPT is linked by ?-glucosidic bond.The results of ultraviolet spectrum and infrared spectrum scanning showed that no nucleic acids or protein were detected in EPT.Moreover,EPT displays the characteristic absorption peaks of polysaccharose substances,which means that EPT belongs to furanose.3.The animal model vas used to study the anti-fatigue and gut microbiota regulation effects of EPT in mice.The results showed that the T.indicum powder and EPT can significantly enhance and prolong the exhaustive swimming time of mice,3 g/kg·d of EPT could prolong the exhaustive swimming time of mice from 11 minutes in control group to 15 minutes.Besides,T.indicum powder and EPT could significantly increase the content of liver glycogen and muscle glycogen,enhance the regulating effect of exercise and energy metabolism,improve the activity of lactic dehydrogenase,reduce the concentration of creatine kinase,eliminate lactic acids generated by haustive exercise,enhance the activities of antioxidant enzymes in endogenous cells,including catalase,superoxide dismutase and glutathione peroxidase,reduce the content of hydroxyl radicals and the concentration of malondialdehyde in serum,and improve the anti-fatigue ability of mice by elhancing the activity of mitochondria complex.3 g/kg·d of EPT exerted the most significant influence on the anti-fatigue related indexes of mice.Furthermore,T.indicum powder and EPT could affect the gut microbiota structure.And exerted less influence on the composition of the enteric microorganism in classification levels of phylum,family and genus,but displayed significant influence on the level of OTU.T.indicum powder and EPT could affect different species of intestinal flora significantly,and the intestinal flora was related to intestinal inflammation and anti-fatigued function.In addition,through correlation analysis,it was verified that the change of intestinal flora abundance is correlated with anti-fatigued function. |
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