Study On The Technology And Mechanism Of Agar Modified By Hydrogen Peroxide

Agar is a kind of seaweed polysaccharide with gelling ability.Due to its gel reversibility and high hysteresis,agar has a wide range of applications in food and medicine.However,at present,the only index of agar is gel strength,and the other indexs such as whiteness and transparency were of poor quality,which cannot meet the need of rapid development,especially in the food and pharmaceuticals industries.In this study,the agar was modified with hydrogen peroxide by controlling certain reaction conditions,and the high quality agar with low sulfate and high whiteness were prepared,which enriched the agar species and made it more potential application value.Firstly,the modified agars were prepared using hydrogen peroxide in ethanol solution under appropriate pH conditions.Results showed that the maximum gel strength of the modified agar was 1068 g/cm2,which increased by 30.9%compared with that of raw agar(816 g/cm2),and the minimum sulfate content of the modified agar was 0.21%,which decreased by 73.4%compared with that of raw agar(0.79%).Moreover,the viscosity,ash content,molecular weight,gelling temperature,melting temperature and dissolving temperature all decreased,whereas the whiteness and transparency increased after modification.Fourier transform infrared spectroscopy revealed that the modified agar displayed differences at 931,1071,1156,and 1250 cm-1.Scanning electron microscopy also showed that the particles of the modified agar were still intact,and the surface was smooth.Thermogravimetric analysis demonstrated that the modified agar presented better thermal stability than raw agar.These findings indicated that the spatial structure of agar treated with hydrogen peroxide changed,which improved the quality in viscosity,gel strength and whiteness of modified agar compared with that of raw agar.Secondly,the modified agars were prepared using hydrogen peroxide in ethanol solution under appropriate temperature conditions.The results showed that sulfate content,3,6-anhydro-L-galactose content and weight-average molecular weight of the modified agars all decreased compared with the raw agar.In addition,the modified agar existed a certain amount of carboxyl and carbonyl groups.Those results indicated that the agar could be desulfurized,degraded and oxidized by hydrogen peroxide.It could be seen from the infrared scanning that the absorption peak of the modified agar was weakened at 931 and 1250 cm-1 compared with the raw agar,and the absorption peaks at 1071 and 1156 cm-1 were also significantly different,which indicated that the structure of the modified agar had changed.Thermogravimetric analysis showed that the modified agars presented better thermal stability than raw agar.Compared with the raw agar,the gel strength of modified agar increased whereas the viscosity decreased.Finally,the agar was bleached by hydrogen peroxide.The optimal technological conditions of agar bleaching were determined by single factor optimization experiments.A batch of high white agar was prepared under the optimization conditions,and the physical and chemical properties was compared with the raw agar.Then,the high whiteness agar was applied to soft candy.The results showed that the optimal bleaching process conditions were as follows:60%of the ethanol concentration,60℃ of the reation temperature,11 of the reation pH,2 h of the reation time,20%of the total mass of agar powder of H2O2 addition amount,1:6 of the ratio of material to liquid.The whiteness of agar under the optimum conditions was 74.4%,which increased by 31.7%compared with that of raw agar(56.5%).The transparency was increased from 56.8%to 64.4%,and the gel strength was decreased from 1338 g/cm2 to 1228 g/cm2.Compared with the soft candy made from the raw agar,the soft candy made from the high whiteness agar not only had better color,but also had higher elasticity and brittleness.