| Starch and protein are important components in food systems.Adding an appropriate amount of protein to starch system to form a mixture or complex system can achieve multiple goals of changing the physicochemical and functional properties of starch.Dry heating modification is a physical modification method.Compared with chemical modification,this method possesses advantages in safety,green,pollution-free and simple in production process,and has mostly used for the modification of polymers liked to starch and protein.In this study,rice starch(RS)and whey protein isolate(WPI)were used as the main raw materials to prepare dry heated WPI composite rice starch under different dry heating time.The physicochemical properties of dry heated WPI composite rice starch and the interaction mechanism between RS and WPI during the dry heating process were studied.On the basis of the above studies,from the perspective of enhancing the hydrophobic properties of the modified starch and reducing its particle size,p H shifting and ball milling technologies were used to optimize the emulsifying ability of the modified starch.Finally,an ideal starch-based solid particle emulsifier was successfully constructed and the its stabilizing mechanism of Pickering emulsion was further discussed.Furthermore,the effects of preparation conditions on the properties of Pickering emulsion stabilized by the ideal starch-based solid particle emulsifier were investigated,and then the stability of loading ?-carotene was studied by constructing Pickering emulsion gel.The main results are as follows:(1)Dry heated WPI composite rice starch was prepared from rice starch and whey protein isolate.The results of scanning electron microscopy(SEM)and laser particle size analyzer showed that the modified starch had particle agglomeration during the dry heating process.The longer the dry heating time was,the more obvious the agglomeration was and the larger the average particle size was.Differential scanning calorimetry results showed that dry heating treatment in the presence of WPI significantly decreased the gelatinization temperature of RS but without affecting the gelatinization enthalpy change.The results of X-ray diffraction and FT-IR showed that the long-range and short-range ordered structure of the modified starch decreased with the extension of dry heating time,which indicated that dry heating treatment could destroy intermolecular and intramolecular hydrogen bonds of starch.The contact angle and oil absorption of modified starch increased with the extension of dry heating time,indicating that dry heating treatment enhanced its hydrophobicity,which was related to the exposure of the hydrophobic groups of endogenous protein and exogenous protein(from WPI)of starch induced by dry heating.(2)Five dry heated WPI composite rice starches were prepared by adjusting the p H(p H3.0,5.0,6.5,9.0 and 11.0)of the composite system.The physicochemical properties of five modified starches and the characteristics of their stabled Pickering emulsions were comparatively detected by instrumental analysis.The results showed that in the p H range of the experiment,dry heating had no impact on the chemical structure of WPI composite rice starch,but had a certain degree of damage to its short-range ordered structure.The damage degree under acidic p H was higher than that under alkaline p H.Dry heating can cause particle aggregation and an increase in contact angle of WPI composite rice starch to different degrees.A higher degree of particle aggregation and a moderate increase in contact angle were happened under the condition of p H 5.0 close to the isoelectric point of WPI.But under the p H condition deviating from the isoelectric point,the particle aggregation degree and contact angle increased with the increase of p H.The dry heating WPI composite rice starches prepared at various p H conditions had a certain ability to stabilize Pickering emulsion.Among them,the starch samples at p H 6.5,p H 9.0 and p H 11.0 had good emulsifying effects.Although each emulsion had a certain degree of creaming,the change of emulsion creaming during 30 d storage was not obvious.Microscopic observation revealed that the emulsion had a spherical three-dimensional structure,and the dry heated WPI composite rice starch played a stabilizing role in the Pickering emulsion by adsorbing on the oil-water interface and filling in the droplet gap.(3)The planetary ball milling was used to refine the dry heated WPI composite rice starch(RW-6h,composite system p H 9,dry heating at 130°C for 6 h).The effects of milling time,milling speed and feeding amount on the physicochemical properties and emulsifying ability of RW-6 h were investigated.The results showed that with the increase of milling time,milling speed and the decrease of feeding amount,the particle integrity of RW-6h decreased,the broken starch particles and theirs aggregates increased,the hydration ability increased,the average particle size of the sample decreased,and the emulsifying ability increased first and then decreased.Taking the emulsification index as the evaluation index,the ball milling conditions were further optimized by three-factor and three-level orthogonal experiment.The results showed that the optimal ball milling conditions were ball milling time 2.5 h,ball milling speed 280 rpm,and feeding amount 10 g.Under this condition,the volume average particle size and crystallinity of the ball milled starch sample(RW-6h-BM)was 8.15 ?m and0%,respectively.The emulsifying index of the stabled Pickering emulsion was 95.45%,and and the volume average particle size of the emulsion droplets was 19.16 ?m.(4)The Pickering emulsion was prepared using starch sample RW-6h-BM obtained under the optimal ball milling process as a particle emulsifier.The influence of preparation conditions including c,?,p H and ionic strength on the characteristics of the emulsions were studied.The Pickering emulsion gel was constructed by adjusting the preparation conditions.On this basis,the stability of ?-carotene loaded on the emulsion gel was studied.The results showed that with the increase of c,the droplet size of Pickering emulsion decreased,the stability of emulsion increased,the apparent viscosity and storage modulus(G')also increased gradually,however,when the c was too low(< 1.67%)or too high(> 15%),the emulsification effect was poor,and phenomenon of “oiling out” is likely to occur.RW-6h-BM could stabilize the emulsion in a wide range of p H(4?9)and Na Cl concentration(0?500 m M).When the system had no Na Cl and the environmental conditions were acidic or neutral,RW-6h-BM showed the best emulsifying effect.Under the corresponding conditions,the emulsions had relatively high apparent viscosity and G'.When c was 11.67 %,p H was 5,Na Cl concentration was 0 m M,? was 40.0 % and 42.86%,Pickering emulsion gel could be formed by emulsifying of RW-6h-BM.The accelerated oxidation rate of ?-carotene loaded by the emulsion gel decreased by 89.61 % compared with that of ?-carotene without embedding.The results indicated that the Pickering emulsion stabilized by RW-6h-BM could be used as an excellent carrier for structured oil and loading liposoluble components. |
PDF Full Text Request