| Blueberry anthocyanins have many physiological and health-benefical properties,which can be used in food,pharmaceutical and cosmetic industries.However,blueberry anthocyanins have low stability.Microencapsulation was used to improve their stability in this thesis.Meanwhile,it is important to study the interaction between blueberry anthocyanins and human serum albumin.Therefore,the interaction between blueberry anthocyanins and human serum albumin wasinvestigated in this study.The encapsulation process of anthocyanins was modeled and optimized.The thermal degradation kinetics of resulting anthocyanin powders after optimized was studied.Furthermore,anthocyanin powders were subjected to a simulated gastrointestinal digestion in vitro and the releasing properties were evaluated.In addition,the evolution of physicochemical proeprties of anthocyanin powders during 4-month storage at different temperatures was studied.The main results are shown below:(1)The interaction between blueberry anthocyanin and human serum albumin was investigated by UV-visible spectroscopy and fluorescence spectroscopy.The results suggested that ACN had a strong ability to quench the fluorescence of HSA in a static manner.The calculated thermodynamic parameters revealed that electrostatic forces and hydrophobic effects played an important role in the interaction between ACN and HSA.UV-visible spectroscopy and fluorescence spectroscopy revealed that the secondary structure of HAS was changed,a-helix became loose and the environment of tryptophan residues in HSA may changed in the prescence of anthocyanins.Moreover,the spectral overlap integral(J)between the donor emission and the acceptor absorption,the distance(r0)between donor and acceptor in anthocyanin-HSA were calculated at different temepraures,using the equations from Forster nonradiative energy transfer theory.The J and r0 values were 6.83x10-15cm3·L-mol-1 and 3.12nm at 288K,6.86×10"15cm3·L·mol-1 and 3.18nm at 298K and 6.87×10-15cm3·L·mol-1 and 3.22nm at 308K.The data also replied that energy probably transferred from HSA to CAN.The Forster nonradiative energy transfer may contribute to the quenching of intrinsic fluorescence.(2)Four wall materials,including maltodextrin(DE-21),β-cyclodextrin,whey protein isolate and gum Arabic were combined according to simplex lattice design.Blueberry anthocyanins were encapsulated using the resulting formulations.Encapsulation efficiency(EE)and encapsulation productivity(EP)were selected as the indexs to evaluated encapsulation effect.All the data about EE and EP were modeled by neural network technology(ANN)and the formulation composition was optimized by genetic algorithm(GAM).Four optimum formulations were generated by the ANN-GAM approach.In all the optimum formulation,WPI had the highest content.Using the optimum formulations,the EP values were higher than 97%and the EE values exceed 82%.It suggested that it was reliable to use ANN-GAM approach to optimize the formulation.Next,the basic physical and chemical properties of four optimized encapsulated powder were determined.It was found that there were no significant differences in moisture content,aw,and hygroscopicity(p>0.05),whereas the differences in bulk density,RE in water,color(L*,a*,b*)mean particle size(μm),Tg,monomeric anthocyanins(cyanindin-3-O-glucoside,malvidin-3-O-glucoside,peonidin-3-O-glucoside)were significant(p<0.05)among all the samples.According to the results of SEM morphologies and X-ray,it was found that the four samples using optimum formulations showed rough surfaces with irregular shrinkage.Due to the glassy structures,anthocyanins entrapped can be protected against oxidation and heating.(3)The thermal degradation kinetics of encapsulated anthocyanin powders using optimized formulations were studied at 80 ℃ and pH 3.6 and 7.0.Compared with the anthocyains without encapsulation,the degradation rate constant(k)decreased significantly(p<0.05),while the half life(t1/2)increased markedly after encapsulation.In the simulated gastrointestinal digestion system,there were no significant differences(p>0.05)in total anthocyanins content released by four optimized encapsulated powders.However,the total phenolic content released by four optimized encapsulated powders were significantly different in simulated gastric fluid at pH 2.5(p<0.05).In simulated intestinal fluid,the total phenolic and total anthocyanins contents of four optimized encapsulated powders were significantly different(p<0.05).ABTS and FRAP antioxidant capacities were determined to evaluate the changes of antioxidant capacities of encapsulated powders.With the increase of pH value,antioxidant capacities of encapsulated powders increased in simulated gastric fluid.However,the antioxidant capacities of encapsulated powders significantly reduced in simulated intestinal system(p<0.05).(4)The best optimized encapsulated powders from ANN-GAM approach were chosen as the experimental object,then stored at room temperature,4℃ and-18℃,respectively for four months.The physical chemical properties were analyzed monthly.The results revealed that there were no significant differences in moisture content,aw,hygroscopicity,solubility of F4 encapsulated powders during storage(P>0.05).However,with the incease of storage time,cake of degree and bulk density showed a gradual increasing trend,although the differences among them were insignificant(P>0.05).It was also found that the glass transition temperature Tg decreased during storage.Interestingly,there was no peak in the DSC spectrum of samples stored for more than 4 months.During the storage,total anthocyanins,total phenolics,color change(L*,a*,b*)of encapsulated powders showed a decreasing trend(p>0.05),while antioxidant capacities measured by ABTS and FRAP methods decreased significantly(p<0.05).Moreover,with the extension of storage time,encapsulation efficiency did not change significantly,whereas encapsulation productivity,release in water and monomeric anthocyanins of encapsulated powders decreased gradually(P<0.05). |
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