| In this study,rice and waxy corn starches were used as raw materials,and the starches were modified with octenyl succinic anhydride(OSA),and then treated by dry heat treatment to obtain composite modified starches.Fourier transform infrared spectroscopy,differential scanning calorimeter,scanning electron microscopy and rapid visco analyzer were used to characterize the physicochemical properties and digestion properties of the composite modified starches.Composite modified rice and waxy corn starches were used as particulate stabilizers,sunflower seed oil was used as the oil phase to construct Pickering emulsion.The effects of composite modified rice and waxy corn starches on emulsion stability were investigated by using tools such as laser particle size analyzer,confocal laser scanning microscope and rheometer.The effects of environmental factors(starch concentration,oil phase volume fraction,system p H,Na Cl addition and sucrose addition)on the stability of Pickering emulsions stabilized by composite modified rice starch particles were studied.A food-grade emulsion delivery system loading with curcumin was constructed by using the modified rice starch particles as stabilizers,and the loading rate,storage stability and bioavailability of curcumin in the system were studied.This study provides theoretical guidance and technical support for the preparation of new food-grade particle emulsifiers and the construction of starch-based emulsion delivery systems.The main research contents and conclusions are as follows:(1)Using rice and waxy corn starches as raw materials,the starches were hydrophobically modified by OSA to obtain hydrophobically modified rice and waxy corn starches,then the composite modified starches were prepared by two dry heat methods: 180°C electric dry heat treating(Electric Dry Heat,EDH)for 20 min,40 min,60 min and roast dry heat treating(Roast Dry Heat;RDH)for 20 min,40 min,60 min.Scanning electron microscope,Fourier transform infrared spectrometer,differential scanning calorimeter,and rapid visco analyzer were used to characterize the physicochemical properties and digestion properties of the composite modified starches.The digestive properties of the dual modified starches were studied by in vitro digestibility method,and the hydrophobicity of starch was studied by measuring the three-phase contact angle of modified starches.The results showed that the native rice starch was polygonal with well-defined edges,the natural waxy corn starch was round or oval,and a few granules were irregular.The OSA modification had no obvious damage to starch granules.The starch retained granular structure after oven drying at180°C for 20 and 40 min.However,with the extension of the dry heat treatment time,some holes appeared on the starch surface,and some starch granules were eroded and even some granules were obviously broken for the samples baked at 180°C for different time dry heat treatments.Dry heat treatment and OSA modification did not change the starch crystal type,but decreased the relative crystallinity of the starches(p < 0.05).Both OSA modification and dry heat treatment could reduce starch gelatinization temperature and enthalpy(p < 0.05).In vitro digestion results showed that OSA modification reduced the RDS content of starches,but dry heat treatment improved the digestive properties of starches(p < 0.05).(2)Composite modified rice and waxy corn starches were used as emulsifiers,and sunflower oil was used as the oil phase,we constructed the oil-in-water Pickering emulsion.The emulsifying properties of the composite modified starches were investigated by recording the volumes of the emulsion,measuring the particle sizes of the emulsion and the rheological properties of the emulsion.The interfacial properties of the emulsions were observed by confocal laser scanning microscope and optical microscopy.The results showed that the emulsion stabilized by starch dry heating in the electric hot oven at 180℃ had better physical stability than the emulsion stabilized by starch dry heating in the baking oven at 180℃.And with the extension of dry heating time,the droplet sizes of emulsion gradually decreased,and the storage stability was significantly improved(p<0.05).The results of confocal laser scanning microscope showed that the composite modified starches were evenly wrapped on the surface of the oil droplets,preventing the aggregation of the oil droplets,thereby stabilizing the emulsion.After storage at room temperature for 300 d,the starch particles of emulsions stabilized by EDH and RDH were still tightly adsorbed on the surface of the oil droplets,except for the reduction of starch granules around the droplets of emulsion stabilized by RDH-60,which indicated that the emulsion could be stabilized by the composite modified starch granules.(3)The Pickering emulsion was constructed with dual modified rice starch(RDH-40)as the particle emulsifier,the environmental factors(starch concentration,oil phase concentration,system p H,Na Cl addition and sucrose addition)on emulsion stability were studied by recording cream volumes and measuring droplet sizes.The results showed when the starch concentration increased in the range of 0.5% to 4.0%,the droplet sizes decreased from 97.69 μm to 84.11 μm,and the cream volume and viscosity of the emulsion increased gradually.Confocal laser scanning microscope observation found that with the increase of starch concentration,the amount of starch wrapped around the oil droplets gradually increased,and the wrapping became tighter.When the oil phase concentration increased in the range of 25% to 67%,the particle sizes of the emulsion gradually increased,the cream volume of the gradually increased,and the amount of starch wrapped around the oil droplets gradually decreased.When the oil phase concentration was 75%,no emulsion was formed.The effect of p H on the physical stability of the emulsion was as follows: when the p H was 7.0,the stability of the emulsion was the best.With the decrease of p H value(1.0 ―7.0),the stability of emulsion gradually deteriorated,while the emulsion stability increased significantly when p H value was 11.0.This may be because the partial gelatinization of starch under strong alkali conditions,so the emulsion was stabilized by both starch granular and starch macromolecular,which improved the emulsion stability.After adding Na Cl or sucrose,the cream volumes of the emulsion slightly decreased,while the droplet sizes gradually increased,which indicating the emulsion stability decreased.(4)The OSA modified starch(OS-starch)and RDH-40 were used as particulate stabilizers,sunflower oil as oil phase,food-grade emulsion delivery systems loading with curcumin were constructed.The oil phase of dissolving curcumin and emulsion stabilized by Tween 20 were used as controls,the curcumin loading rate,storage stability and digestive properties of the emulsion were measured to explore the ways and mechanisms to improve the bioavailability of curcumin.The results showed that the emulsion stabilized by RDH-40 had better physical stability than the emulsions stabilized by Tween 20 and OS-starch.Under the storage condition of 30 d at room temperature in the dark,the curcumin content in pure oil,emulsion stabilized by Tween20,emulsion stabilized by OS-starch and emulsion stabilized by RDH-40 lost 8.6%,50.6%,40.5%,9.6%,respectively.Under the storage condition of 30 d at 40 °C in the dark,the curcumin content in pure oil,emulsion stabilized by Tween 20,emulsion stabilized by OS-starch and emulsion stabilized by RDH-40 lost 4.9%,54.3%,36.4%,and 15.4%,respectively,which indicated that the emulsion stabilized by RDH-40 had better curcumin loading effect and protective effect.The results of free fatty acid released during emulsion digestion showed that the emulsion stabilized by RDH-40 had a faster oil release rate during digestion,which was helpful for the release and absorption of curcumin in the small intestine,so the bioavailability of curcumin was improved(24.19%). |
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