Agar Extracation From Gracilaria And Modification By Maleic Anhydride And Its Application

Agar is a natural hydrophilic polysaccharide with the ability of gel and gel stability which can be used as thickener,emulsifier,suspending and gelling agent.It has a large range of applications especially in foods,cosmetic,medical and biological fields.In the alkali-extracted process,the loss of colloids,low yield,high pollution and the low transparency limited the application of agar.Thus,to provide a guidance for improving agar yield and reducing the loss in production,the internal changes were analyzed in Gracilaria under the different extraction processes(alkali,enzyme and enzyme-assisted extraction processes).Then,the agar was modified with maleic anhydride by wet method to improve the transparency under the premise of ensuring the index of the agar,and provided ideas for the preparation of the agar derivatives.At last,the modified agar was used as wall material to prepare microcapsule for the sake of extending the application range of agar and its derivatives.Firstly,the internal changes and loss rate of Gracilaria,yield and physicochemical of agar were studied during differernt extraction processes(alkali,enzyme and enzyme-assisted extraction processes).The results showed that cellulase hydrolyzed the cell wall of Gracilaria during the enzyme treatment.After alkali-treatment,the cell wall of Gracilaria was destroyed with a outflow of colloids.At the same time,the step of alkali-treatment can cleave sulphate ester at C-6 of theι-galactose with simultaneous formation of 3,6-AG,thereby improving the gelling properties.Acid and bleaching treatment will further soften the tissue of Gracilaria,and facilitate the extraction of agar.In the whole extraction process,the surface of the Gracilaria was gradually destroyed which can be observed by the removed,thick cell wall and the colloidal cortical cells were exposed.In the Alkali-extraction process,the loss rate of Gracilaria was63.0%,the agar yield was 12.3%,and the gel strength was 760.6 g/cm~2.Compared with the alkali-extraction process,the enzyme-extraction process showed the high sulfate content(3.4%)and yield(28.5%)with coincidentally,the low gel strength(358.1 g/cm~2)and loss rate of Gracilaria(22.6%).The loss rate of Gracilaria was decreased(45.9%)and the yield of agar was increased(20.3%)in the enzyme-assisted process.After 3%alkali-treatment,the sulfate content was decreased(1.9%)and the gel strength was increased(695.7 g/cm~2).The whiteness,transparency,solution,gelling and melting temperature of the agar obtained by the alkali-extraction process were higher than those of the enzyme-extraction and enzyme-assisted processes.The agar viscosity(18~20 cP)obtained by the three extraction processes was higher than that of the native agar(9.3 cP).Secondly,agar was modified by maleic anhydride to obtain a highly transparent agar.Then,the optimum preparation process and properties of maleic anhydride modified agar(MAHG)were determined and analyzed.The results showed that:maleic anhydride addition was 2%,pH was 7-7.5,temperature was 30℃,agar concentration was 9%,reaction time was 1 h,continued reaction time was 0 h.The transparency increased from 51%to 79%with a gel strength 867.4g/cm~2;the property of swelling and emulsifying was improved.In addition,the 3,6-AG,sulfate,gelling,melting and dissolution temperature of MAHG were decreased slightly.The FTIR test showed that maleic anhydride and agar esterified successfully.The TG test showed a decline of thermal stability and a improvement of water retention of MAHG.Finally,the microcapsules was prepared using MAHG and soybean oil by the sharp hole-solidification bath.The optimum preparation process and physicochemical index of the microcapsules were determined and analyzed,and the results showed that:1.5%MAHG(wall material),8 mL soybean oil(core material)and 60℃drum wind drying.The microcapsules droplet size of MAHG was 0.14 cm,the oil loading rate was 56.3%,and the encapsulation efficiency was 99.1%.The DHA was microencapsulated simultaneously and compared with the emulsion stability of different core materials.The MAHG-DHA microcapsules was obtained,and its droplet size was 0.15 cm,oil loading rate was 62.2%,encapsulation efficiency rate was99.2%.The result of accelerated oxidation 7 d-test showed that the microcapsules peroxide value of MAHG-DHA(67.4 mmoL/kg)was significantly lower than that of non-microencapsulated DHA(860.1 mmoL/kg),suggesting that the storage stability of MAHG-DHA microcapsules was improved significantly.