| In this paper, oxidized octenyl succinate anhydrate starch of low viscosity had been prepared with cassava starch as raw material, octenyl succinic anhydride (OSA) as esterification agent and NaClO as oxidant by one-step method in aqueous systems. The effect of reaction temperature, pH, reaction time, the amount of NaClO and OSA on the degree of oxidation and the degree of substitution had been taken consider of comprehensively with single factor method, which to make decisions for the optimum conditions of preparation. At the same time, the gelatinization properties and emulsifying properties of native starch, monoesterification octenylsuccinate starch and oxidized-octenyl succinate dual modified starch were compared, and the structures of them were tested by FTIR, XRD, SEM, DSC, et al. What’s more, microcapsules had been prepared with oxidized-octenyl succinate dual modified starch as wall material and olive oil as core material by spray-dring. In consideration of the effects which were inlet air temperature, air flow, core wall ratio and the amount of wall material on microencapsulation embedding rate. Besides, the structures and release properties of microcapsule were studied.The study of oxidized-octenyl succinate dual modified starch preparation by one-step method showed that the degree of substitution(DS) and the degree of oxidation(DO) had different variation according to the changes of reaction conditions, which the DS and DO first increased and then decreased when the reaction temperature or pH value increased; the DS first increased and then decreased but DO substantially constant increased to a certain extent when the reaction time increased; the DS first increased and then decreased but DO increased when the amount of NaCIO increased; the DS increased but DO substantially constant when the amount of esterification agent increased. The preparation process was simplified and the production cycle was shortened by one-step method, and the optimum conditions were decided, which the reaction temperature was 35 "C, the system pH was 9.0, reaction time was 3 h, NaCIO added amount was 2%, OSA added amount was 8%.Furthermore, the study of gelatinization properties and emulsifying properties of oxidized-octenyl succinate dual modified starch showed that the degree of substitution and the degree of oxidation had a decisive role in those properties. The dual modified starch which prepared by one-step method had a low viscosity characteristics, and the viscosity of the dual modified starch reduced significantly along with the degree of oxidation increases (DO> 0.15%); meanwhile, the dual modified starch had low gelatinization temperatures and the thermal stability and cold stability of starch paste viscosity increased significantly and emulsifying properties improved, but the retrogradation, transparency, and freeze-thawing stability were between native starch and monoesterification octenylsuccinate starch. The HLB values of oxidized octenyl succinate anhydrate starch were between 13.0-13.6, which can be used as an excellent emulsifier in O/W type emulsion. With the degree of oxidation and the degree of substitution of dual modified starch increased, emulsion stability enhanced. What’s more, octenylsuccinate starch ester groups and carboxyl groups in the oxidized octenyl succinate anhydrate starch molecules had been confirmed by FTIR spectra, and the XRD and SEM showed that dual modified starch after oxidation and esterification reactions remained the same crystal structure, and gelatinization temperature decreased by DSC analysis, which was easier gelatinated.Besides, the study of olive microcapsules preparation by spray-drying showed that oxidized octenyl succinate anhydrate starch of low viscosity was not only an excellent emulsifier in O/W type emulsion, but also a favourable wall material, while spray-drying operating conditions of microcapsules preparation improved and there were no need to add other emulsifiers, which embedding effects were better than monoesterification octenylsuccinate starch, gum arabic, gelatin and P-cyclodextrin. Simultaneously, the optimum parameters were decided when dual modified starch DO was 0.0842% and DS was 0.0229, which inlet temperature was 180℃, feeding rate was 17 mL/min, the amount of air flow was 9 L/min, homogeneous time was 8 min, core wall ratio was 1:3, the concentration of wall materials was 9% and without other additional emulsifiers. In these conditions, the maximum of embedding rate can be reach 89.68%. Moreover, the quick release ability of the microcapsules was good in aqueous phase, and the highest core material release rate can be reach 96.43% in 5 minutes. Complementary, the microcapsules were regular, circular and distributed evenly, and the smallest average particle size was 22.51 μm. |
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