| Lotus root（Nelumbo nucifera）is the rhizome of the lily plant,which can be eaten or used medicinally,widely distributed in all parts of China,the annual output is huge.Lotus root residue is the byproduct of lotus root juice processing,which has not been exploited and utilized.It is known that lotus root residue is still rich in dietary fiber,phenolic substances,vitamins and minerals,especially dietary fiber,which is called the seventh major nutrient element,accounts for more than 30%of dry weight of lotus root residue.Dietary fiber has many biological activities such as maintaining digestive system health,enhancing immunity,lowering cholesterol and blood pressure,lowering blood sugar and anti-cancer,which are closely related to human health.At present,there are many studies on the extraction of dietary fiber,however,the study on the extraction of SDF from lotus root dregs by subcritical water is rarely reported.Based on this,the aim of this paper was to extract SDF from lotus root dregs by subcritical water and characterize its structure,on this basis,preliminarily study its effects on intestinal microflora in mice.The main results are as follows:（1）The SWE and antioxidant activity of SDF from lotus root dregBased on single factor experiments,orthogonal design was used to optimize the SWE process of SDF from lotus root dregs.The antioxidant activity of SDF in lotus root dregs was preliminarily evaluated by determining the reduction ability and the scavenging rate of DPPH·and ABTS·+.The optimum technological parameters of SWE were:10%of HCl（v/v）、extraction temperature 140℃、extraction time 16 min、the liquid-solid ratio:20:1（mL/g）,under these conditions,the yield of SDF was40.8%increased by 16%compared with hot water extraction.Under the range of 15mg/mL,the reduction ability,DPPH·and ABTS·+scavenging rate of SDF from lotus root dregs increased gradually with the increase of SDF concentration,when the concentration reached 5 mg/mL,the scavenging rates of DPPH·and ABTS·+were38.23%and 27.93%,respectively.The SWE method is superior in terms of extraction time and extraction yield.（2）Isolation,purification and preliminary structural characterization of SDF from lotus root dregs.Crude SDF from lotus root dregs were gradually separated and purified by DEAE-52 and Sephadex G-50 cellulose column,obtaining one homogeneous fraction SDF-A2,with the total sugar content 93.82%.SDF-A2 was characterized by combing HPLC、FT-IR spectroscopy、AFM and chemical analysis,results showed that the average molecular weight（MW）of SDF-A2 was 3730 Da,it was composed of d-glucose and d-galactose;its molar ratio was 49:1,the main chain was composed of glucose and the branched chain is composed of glucose and galactose;the results of Periodate oxidation and Smith degradation showed that d-glucose as the main chain was connected with 1→3 glycosidic bond;d-glucose and d-galactose as the branched structure were connected with 1→、1→2、1→6、1→2,6、1→4 or 1→4,6 glycosidic linkages.FT-IR spectroscopy showed the existence ofα-type glycosidic linkages in SDF-A2;the triple helix structure did not exist in SDF-A2;existing in the form of intermolecular aggregates.（3）Effects of SDF from lotus root dregs on intestinal microflora in miceThe result of the anti-digestibility of SDF against artificial human gastric acid andα-amylase showed that the maximal hydrolysis degree were 2.67%and 4.98%respectively,under 5%,suggesting that SDF from lotus root dregs could not be hydrolyzed by gastric acid andα-amylase,had relatively high stability and digestive tolerance.Feeding mice the SDF from lotus root dregs experiment showed that SDF of lotus root dregs could promote the proliferation of Bifidobacterium and Lactobacillus beneficial bacteria in intestinal tract of mice and inhibit the proliferation of Enterobacter and Clostridium perfringens harmful bacteria;it could regulate the increase of short chain fatty acid（acetic acid,butyric acid）and lactic acid content in intestinal tract of mice;it could increase antioxidant enzymes in serum of mice in high dose group.In conclusion,SDF from lotus root dregs can actively regulate intestinal microorganisms,promote the growth of beneficial microorganisms and inhibit the reproduction of harmful microorganisms. |
