| Debranched starch（DBS）,a typical enzyme-modified starch,has excellent load capacity due to the linear structure and strong self-assembly retrogradation ability,which allows small molecules be effectively loaded on DBS by interacting with it.This has enabled DBS to be widely used in food and pharmaceutical applications.To further enhance the application potential of DBS,chemical modifications have been applied to improve the physicochemical properties of debranched starches.However,chemical modifications may involve residual issues of chemical reagents and the safety of the product is debatable.It has been shown that non-starch polysaccharides can effectively improve the gelation and retrogradation properties of starch,therefore,non-starch polysaccharides complexing with DBS have a good research prospect for optimizing the starch properties.In this study,the debranched waxy maize starch（DWMS）was prepared by the pullulanase debranching method,and its physical and chemical properties were characterized.Subsequently,the effect of Mesona chinensis Benth polysaccharide（MCP）on the gelation,rheology and microstructure of DWMS was investigated,and the interaction mechanism between MCP and DWMS was analyzed based on the experimental results.Finally,DWMS and MCP were compounded to construct curcumin（Cur）-loaded microcapsules,and the microcapsules were characterized and in vitro gastrointestinal release assays were performed to investigate their potential as sustained release carriers.The main research contents and results are as follows:（1）DWMS was prepared from waxy maize starch（WMS）treated with pullulanase（58°C,8 h）.And the structural characteristics of waxy maize starch before and after debranching were characterized.The results of starch chain length distribution showed that the molecular degree of polymerization（DP）in WMS was almost higher than 100DP（98%）.After debranching,DWMS mainly consisted of linear short chain starch（70%<100 DP）.The gelatinization experiment results showed that DWMS exhibited extremely low viscosity throughout the process.The results of particle size and zeta potential tests showed that the particle size（16.7μm to 4.7μm）and zeta potential（53.3m V to 27.9 m V）of DWMS were significantly lower than those of WMS.DWMS has higher solubility and lower swelling capacity than WMS.The crystalline type of WMS starch completely changed,and the A-type starch of WMS was transformed into B-type after debranching.The thermodynamic test results showed that the thermal stability of DWMS was lower than that of WMS,and the initial degradation temperature of DWMS molecules decreased.（2）The effects of MCP on the texture,rheology and microstructure of DWMS gels were studied,and their interaction mechanism was also explored in this chapter.DWMS-MCP composite gels were prepared by compounding different concentrations of MCP（0%,0.5%,1%,3%and 5%,w/w）with DWMS（5%,w/v）.The results of texture and rheological properties showed that the gel strength and hardness of 1%MCP gel were significantly higher than those of other groups.The results of low-field NMR showed that the T2 value of DWMS-MCP gel system decreased with the increase of MCP content.However,compared with other samples,DWMS-1%MCP gel had the highest strong binding water content(A21,4.6±0.7 g/100 g)and the lowest weak binding water content(A23,94.2±0.8 g/100 g).Combining with the results of inverted fluorescence microscope,the mechanism may be:low concentration of MCP can interact with DWMS,to form a stronger gel network than DWMS,resulting in better alignment of molecular chains and rearranging into a more orderly structure.However,excessive addition of MCP led to the self-aggregation of MCP,and the phase separation between DWMS and MCP hindered the orderly rearrangement of starch,thereby damaging the orderly structure and gel stability.（3）The effect of MCP on short-term regeneration characteristics of DWMS was explored.The results showed that the short-term regeneration（1 day）of DWMS can be divided into two stages.In the first stage（0–4 h）,the gel hardness of DWMS increased rapidly.However,in the second stage（4–24 h）,the gel hardness of DWMS increased slowly.During the short-term regeneration process,low concentrations of MCP（0.5%and 1%）can increase the gelation rate,but high concentrations of MCP（3%and 5%）reduced the gel strength.XRD results showed that the relative crystallinity（RC）of DWMS gel increased with the increase of storage time,especially in the first stage.However,the crystallinity increased slightly in the second stage,indicating that the rapid regeneration of DWMS mainly occurred in the first 4 h.The effect of MCP on the crystallinity of DWMS was consistent with the change of gel strength.The results of SEM and particle size test showed that the second stage of short-term retrogradation of DWMS seemed to be dominated by the aggregation of starch granules.（4）The effect of MCP on the release performance of microcapsules was further investigated by constructing Cur-loaded microcapsules with DWMS and MCP as wall materials.With the increase of MCP,the embedding efficiency and loading capacity of microcapsules for Cur gradually increased,which was consistent with the decrease of crystallinity and the change trend of particle size.This is because the addition of MCP increases the hydrophilic groups in the system,and Cur can be embedded better in the microcapsules by increasing the absolute value of zeta potential.The results of infrared spectroscopy showed that DWMS,Cur and MCP interacted by hydrogen bonds to form microcapsules,further achieving the embedding of drugs.X-ray diffraction results showed that Cur hindered the short-term retrogradation and recrystallization of DWMS,and reduced the relative crystallinity of microcapsules.The relative crystallinity decreased more obviously with the addition of MCP.Microcapsules showed good DPPH scavenging ability,and with the increase of embedding rate and MCP,the antioxidant capacity increased gradually.In vitro gastrointestinal release experiments showed that all microcapsules released slowly in simulated gastric and intestinal fluid,and the release rate of microcapsules in intestinal fluid was significantly slower than that in gastric fluid.This may be due to the low p H of gastric fluid,which facilitated the degradation of starch in an acidic environment. |
