Preparation Process Optimization And Property Analysis Of Esterified κ-carrageenan

Kappa-Carrageenan(κ-carrageenan)is a hydrophilic colloid with wide application value in the field of food industry.But there are some disadvantages like easy shrinkage and dehydration,high gelation temperature and so on and cannot meet the requirements of multi-function and high-performance of some products.In order to expand its use range and application performance,κ-carrageenan was esterified with maleic anhydride(MAH),glutaric anhydride(GA)and octenyl succinic anhydride(OSA)as esterification agents in this paper.The structure of κ-carrageenan was changed by esterification reaction and adding new functional groups,and the physico-chemical and gel properties of esterified κ-carrageenan were further analyzed.The main research contents and results of this paper are as follows:First of all,the process conditions for maleic acid esterified carrageenan(MC)were optimized by single factor test.Under the reaction time was 3.5 h,the reaction temperature was 30℃,the concentration of MAH was 8.0%,the concentration of carrageenan was 7.5%,the range of pH was 8-8.5,the degree of substitution(DS)reached the value of 0.032.Infrared spectroscopy(FT-IR)showed that the peaks of MC at 1734 cm-1 and 1576 cm-1 had obvious ester carbonyl and carboxyl absorption characteristics.The viscosity test results showed that the introduced branched chains after MAH esterification hindered the interwinding of molecular chains,so the viscosity of MC decreased by 39.9%compared with native κ-carrageenan(NC).Scanning electron microscope(SEM)results showed the gel network structure of MC was damaged to a certain extent with the gel strength decreased by 47.4%.Rheological analysis showed that the intermolecular forces of carrageenan weakened after MAH esterification,MC was more difficult to form gel network structure and the gel network was easier to disintegrate at high temperature.So the elastic modulus and viscosity modulus of MC fluid decreased significantly,and the solidification and melting temperatures decreased by 7.6℃ and 5.3℃respectively.Thermogravimetric analysis showed that the thermal stability of MC was decreased and the dissolving temperature decreased by 3.5℃.SEM results also showed that the surface of MC particles was rougher.Secondly,the technological conditions for the preparation of glutaric acid esterified carrageenan(GC)were as follows:the carageenan concentration was 7.5%,the glutaric anhydride concentration was 4.0%,the reaction time was 2 h,the reaction temperature was 30℃,the range of pH was 8-8.5,DS was up to 0.077.FT-IR results showed that the absorption characteristic peaks of ester carbonyl and carboxyl groups appeared in curve of GC at 1734 cm-1 and 1576 cm-1,and the peaks increased with the increase of DS.Rheological analysis showed that the conformational transition temperature of GC was in advance,and the solidification temperature and melting temperature decreased by 5.8℃ and 7.9℃ respectively compared with NC.After the GA esterification,the gel network structure and the internal molecular structure of GC were damaged to a great extent,so the gel strength decreased by 72.8%and the content of 3,6-AG decreased by 32.4%.Due to ester formed by GA and other hydrophobic groups grafted on carrageenan molecules,the emulsification and emulsification stability were improved by 22.5%and 28.7%respectively.Thirdly,the effects of different reaction conditions on the DS of octenyl succinateκ-carrageenan(OC)esterified by OSA were studied.The results showed:the pH range was 8.0-8.5,the OSA concentration was 3.5%,the reaction temperature was 40℃,the carrageenan concentration was 5.0%,the reaction time was 3 h,DS was up to 0.083.FT-IR results of OC showed that there were significant ester carbonyl and carboxyl absorption characteristics at 1734 cm-1 and 1576 cm-1 and the peaks became more obvious with the increase of DS.Rheological analysis showed that after OSA esterification,the intermolecular forces of carrageenan became weaker,the elastic modulus and viscosity modulus of OC fluid decreased significantly and the solidification and melting temperatures also decreased compared with NC.The gel network structure of OC was also partially destroyed,and the gel strength decreased with the increase of DS,with a decrease of 41.0%.Due to the weakening of the intermolecular force and the destruction of the structure of OC,the sulfate content,3,6-AG content and viscosity of esterified carrageenan in different DS decreased to different degrees.After the grafted of OSA long carbon chain group on carrageenan,on the one hand the distance between the molecular chains was increased,on the other hand the intermolecular forces was weakened and the gel network structure bacame looser.So the transparency increased with the increase of DS,with a maximum increase of 16.5%.