| As a precursor of vitamin A,?-carotene(BC)has many important physiological functions and can be used as natural colorants and dietary supplements.However,BC,a fat-soluble vitamin,is easy to be degraded during production and processing,which limits its application in the field of food.The polysaccharide-phenolic acid covalent complexes,as a new kind of wall materials,can be employed to improve the stability and water solubility of BC.Therefore,in this project,curdlan and ferulic acid(FA)were studied.The effects of alkali-neutralization treatment on the solution behavior,structure and functional characteristics of curdlan were discussed.Meanwhile,the preparation,structural characteristics,functional characteristics and in vitro antioxidant activity of the FA-grafted curdlan conjugates were investigated.On this basis,the emulsifying characteristics of the FA-grafted curdlan conjugates and their impacts on the stability of BC were evaluated.The main results are as follows:(1)Effects of alkali-neutralization treatment at different concentrations on the solution behavior,structural characteristics and rheological properties of curdlan were investigated by using macromolecular characterizations and microscopic techniques as well as polymer dilute solution theroy.Results showed that curdlan treated by alkali-neutralization in aqueous solutions underwent a transformation from ordered triple helix structures to loose triple helix structures and finally to random coils,accompanied with increased water solubility and reduced intrinsic viscosity and molecular weight.At the same time,alkali-neutralization treatment had important influences on the microstructure,crystallinity,thermal property and rheological property of curdlan,but unchanged its chemical structure.(2)The FA-grafted curdlan conjugates were successfully prepared by free radical mediated grafting method.The optimal process conditions obtained by single factor experiments and orthogonal test design were as follows: 5 mg/mL 25 mL curdlan solution,250 mg FA,50 mg ascorbic acid,5 mol/L hydrogen peroxide and 12 h.At the optimal condition,the highest grafting ratio of the FA-grafted curdlan conjugate was 98.62 ? 1.21 mg FA/g.(3)The physicochemical properties,structural characteristics,microstructure,functional characteristics and in vitro antioxidant activity of the FA-grafted curdlan conjugates were investigated by means of the combination of physics and chemistry and microscopic techniques,which compared with those of native curdlan and FA.The results showed that the grafting ratios of FA-grafted curdlan conjugates,that are Cur-g-FA and Cur-D-g-FA,were 99.30 ± 1.19 mg FA/g and 102.93 ± 1.63 mg FA/g,respectively,in the presence and absence of salt.FA was grafted onto the C-6 and C-4 positions of the curdlan through covalent linkages in the form of ester bonds,and the presence of salt had a negative effect on the grafting ratio and structural characteristics of the grafted conjugates.Moreover,compared with the curdlan,grafting reaction caused the reducation in the crystallinity,thermal stability and rheological properties of Cur-g-FA and Cur-D-g-FA,but considerably enhanced their antioxidant activities in vitro,which were positively correlated with the grafting ratios.(4)The emulsifying property,emulsifying stability and Zeta potential of the Cur-D-g-FA-prepared emulsions were all evidently improved with the increase of Cur-D-g-FA concentration,but the particle size of the emulsions was decreased.The Cur-D-g-FA-prepared emulsions exhibited elastic behavior at higher concentration and had good oxidation stability compared with that of the emulsion prepared by curdlan treated by alkali-neutralization.Furthermore,the emulsion prepared by 0.8% Cur-D-g-FA showed good physical stability(ion strength,pH and temperature)and storage stability to BC.In vitro gastrointestinal digestion assay revealed that BC within the Cur-D-g-FA-prepared emulsion showed a good bioaccessibility. |
PDF Full Text Request