Preparation And Characterizaion Of Dual-modiifed Starches With Hydroxypropyl And Octenyl Succinate Anhydride

The preparation of dual-modified tapioca starch was studied by two kinds of reactionsequences respectively, one of which was esterification with octenyl succinate (OS) firstly andetherification with hydroxypropyl (HP) later, and the other one contrary. Thephysical–chemical characters of the dual-modified starches and the application of lowviscosity dual-modified starches as microcapsule wall materials were researchedsystematically. In the following, detailed processes and results of the study were presented.The preparation of dual-modified starches, esterified with octenyl succinate anhydridefirstly and etherified with hydroxypropyl later (the product was called OSA-HP for short),was studied. The results were showed that, the propriate concentration range of octenylsuccinate anhydride (OSA) was3%~5%, which of propylene oxide (PO) was10%~15%. Thedegree of substitution of octenyl succinate groups (DSOSA) showed signifcant increase, whilethe molar degree of substitution of hydroxypropyl groups (MSHP) was reduced, when theconcentration of OSA was increased, indicating that the etherification at step two wasnegatively impacted by the esterification at step one under the process of esterification withOS firstly and etherification with HP later. The DSOSAshowed no signifcant change, while theMSHPwas signifcantly improved, when the concentration of PO was increased, indicatingthat the etherification at step two had little impact on the esterification at step one under theprocess of esterification with OS firstly and etherification with HP later.The preparation of dual-modified starches, etherified with hydroxypropyl firstly andesterified with octenyl succinate anhydride later (the product was called HP-OSA for short),was also studied. The results were showed that, the propriate concentration of OSA was3%~5%, which of PO was10%~15%. The MSHPshowed signifcant increase, while the DSOSAwas signifcantly reduced, when the concentration of PO was increased, indicating that theesterification at step two was negatively impacted by the etherification at step one under theprocess of etherification with HP firstly and esterification with OS later. The MSHPwasreduced, while the DSOSAshowed signifcant increase, when the concentration of OSA wasincreased, indicating that the etherification at step one had a certain negative impact on theetherification at step one under the process of etherification with HP firstly and esterification with OS later.The dual-modification process, etherification with HP firstly and esterification with OSlater, was considered as the optimal selection by the comparison of products effect of the twomodification sequences. The degree of substitution of functional groups was higher, thereaction agents could be in full use, and the production cost was controlled in this way.Compared with native starch and single modified starch, the physical–chemicalcharacters of the dual-modified starches were influenced by etherification level andesterification level respectively. The results were showed that, surface morphology and shapeof the dual-modified starches were changed drastically, and more suffered along with thehigher levels of etherification and esterification. The successful introduction of OS groupswas proved by the appearance of some characteristic absorption peaks in FT-IR. Thecrystalline type was not changed, while the relative crystallinity showed slight decrease, whenthe levels of etherification and esterification were higher. The apparent viscosity wasincreased along with the higer level of esterification, but reduced along with the higer level ofetherification. The dual-modified starches had lower gelatinization temperature (about50℃)and slower retrogradation, which were reduced along with the higher levels of etherificationand esterification. The transparency, anti-retrogradation and emulsibility showed signifcantincrease, and were improved when the levels of etherification and esterification were higher.The emulsion stability could remain above30%even afrer96h.The application of low viscosity dual-modified starches as microcapsule wall materialswas studied. The results were showed that, the low viscosity HP-OSA had higher emulsionstability and rheology, while the microcapsule products showed better embedding effect whenusing the OSA-HP as wall material (its surface oil content was2.67%, retention of oil was79.8%), but the embedding effect of microcapsule made by some OSA starch products frommatket was better.