Preparation And Biological Activities Of Agar Oligosaccharides

In recent years,the chemical modification of marine polysaccharides,which lead to preparation of derivatives with high biological activities and low toxicity,has attracted more and more attention. Agar oligosaccharide of low molecular weight was degraded by gracilaria agar with the method of mild acidic hydrolysis , and the technology was optimized by response surface.The agar oligosaccharide pyridine sulfation was degraded by the method of chlorosulfonic acid-preparation,and the technology was optimized by orthogonal test.In addition, the vitro antioxidant activity of agar oligosaccharide and agar oligosaccharide pyridine sulfation was investigated.The effect of agar oligosaccharide on water preservation and moisture was described. It will provide basic datas to the area of food, biology, medicine and cosmetic.The main tasks and conclusions of this paper are as follows:1. In order to study the relationship between the condition of hydrolysis and the yield of hydrolysis rate, three factors were chosed to optimized the yield of hydrolysis rate using the method of Response Surface, they were concentration of hydrochloric acid, ratio of solid to liquid and hydrolysis time. Regression equation, Y= 81.5933+0.7175X1+1.8938X2+2.7313X3-3.1567X12-3.3042X22-3.3092X32-0.6625X1X2+0.0475X1X3-0.8000X2X3, was fitted by multiple linear regressing. From the regression equation, among the three factors, the effect on the yield of hydrolysis rate was concentration of hydrochloric acid > ratio of solid to liquid > hydrolysis time. The validating test was carried under the three factors level, and the result showed that there was no significant difference between the test-value and the forecasting-value(P>0.05).Oligosaccharide fractions were isolated by gel permeation chromatography and the structure of fraction was studied by using negative-ion electrospray ionization-mass spectrometry(ESI-MS), and 1H and 13C-NMR spectrometry. Results showed that the structure of agar oligosaccharide was not changed widely during hydrolysising.2. Three common sulfated way in agar oligosaccharide with sulfur trioxide-dimethylformamide, concentrated sulfuric acid or chlorosulfonic acid–pyridine were compared, taking the content of sulfate group in esterified products and productivity as index. And the treatment of chlorosulfonic acid–pyridine was proved to be the best way to prepare sulfated agar oligosaccharide as a result. Orthogonal test was designed to optimize the reagent ratio, reaction time and reaction temperature. The best esterification technology was as follows: the ratio of chlorosulfonic acid to pyridine was 1:2, reaction time was 4h, reaction temperature was 60℃.With the optimal technology, the content of esterified agar oligosaccharide was 26.1% and the productivity was 68.3%.3. Application of different antioxidant models have been employed to aquire the antioxidant activity of agar oligosaccharides and their sulfated derivatived oligosaccharides in vitro research. The results showed that sulfated derivatives agar oligosaccarides have a higher antioxidant activity compared with agar oligosaccharides in differnrt models: Scavenging capacity of derivatized agar oligosaccharides by superoxide anion has been greatly improved with its IC50 value at approximately 0.18mg/mL while its underivatized products at 0.37mg/mL and the mixture much higher than 0.37mg/mL. Therefore under the same concentration, the Scavenging capacity with the superoxide anion O₂^·- followed in the order that: sulfated derivatized agar oilgosaccharides > agar oligosaccharides > mixture of the Agar oligosaccharides. The results of free radical scavenging capacity of the oganic DPPH showed that sulfated derivatized agar oilgosaccharides,agar oligosaccharides and mixture of the agar oligosaccharides ineffectively scavenge the free ridical DPPH, with the maximum scavenging rate 16.13%, 17.33% 24.92% respectively. The results of scavening capacity of the hydroxyl radical (·OH)showed that sulfated derivatized agar oilgosaccharides,agar oligosaccharides and mixture of the agar oligosaccharides all have scavenging capacity and the scavenging capapcity has a certain correlation between the concentration and scavenging capacity. The results of scavenging reductive capicity of three samples showed that sulfated derivatized agar oilgosaccharides,agar oligosaccharides and mixture of the agar oligosaccharides all have a certain reductive capacity, agar oligosaccharides and sulfated derivatized agar oilgosaccharides have a higher reductive capapcity than mixture of agar oligosaccharides under the same concentration.4. Preliminary study of the fresh-keeping and water- keeping effect of agar oligosaccharide on aquatic products processing was conducted. the yield of weight increasing after being soaked, drip loss, cooking loss, textural properties salt-soluble protein content and Ca²⁺-ATPase activity were performed on shrimp meat, tilapia fillets and oysters which were treated with different precursor solutions. the fresh-keeping and water-keeping effect of agar oligosaccharide on aquatic products were markedly better than the blank ,water and polymannuronate (P<0.05).