The Study On The Preparation Of Low Molecular Weight Hyaluronic Acid

Hyaluronic acid(HA) is a kind of biological polymer of great biocompatibility, which is widely used in medical and cosmetic fields because of its good moisture-holding and lubricating property. In recent years, it has been discovered that orally-taking low-molecular weight HA (LMW-HA) can increase the content of endogenous HA and promote the synthesis of high-molecular HA in vivo, so it is of excellent immunity-strengthening and anti-aging function. The preparation methods and technological conditions of LMW-HA were studied in this paper, so as to develop its application in the field of food and health products.Physical, chemical, enzymic and physical-chemical methods have been chosen to degrade HA in this research. The results were as follows: the three oxidizing degradation methods of HA, H₂O₂+Cu²⁺, H₂O₂+ascorbic acid+ succinic acid and NaClO systems, could bring about a striking degrading effect, and the molecular weight was low after degrading(25,000). In the physical-chemical methods, the system of ultrasound+NaClO brought about a better degrading effect, with the molecular weight of HA decreasing to 10,000. HA could not be degraded by pectase, cellulase and lysozyme. The structure of basic composing units of HA had no noticeable change after being degraded by the above-mentioned methods. Generally, H₂O₂+ascorbic acid system was considered as the best way to degrade HA.The optimum conditions of degrading HA by hydrogen peroxide+ascorbic acid system were: H₂O₂:Vc=2:1,pH4.0,temperature55℃,reaction time 15min,additive amount of hydrogen peroxide 2.0 mmol/gHA. The initial molecular weight and concentration of HA was important for HA degradation: the higher the initial molecular weight was, the higher the molecular weight was after degrading and the greater the molecular weight changed, the greater the initial concentration was, the lower the molecular weight was after degrading. In order to decrease the viscosity of the reaction system and to increase the initial HA concentration, a pretreation method was used: humid HA solid sample was heated for 30min in 121℃. The initial concentration of HA was enhanced from 0.5% to 4%.The ultrafiltration technology was used for separating low molecular weight HA. Different low molecular weight HA was well separated after fractionating HA solution by PES with capture molecular weight being 30000, 10000,5000in order, four components with homogeneous molecular weight were obtained by HPLC detection, their molecular weights as follows:32095, 19436, 9548, 1132⁴315.For different PES membrane, the recovery of HA was above 92%, the total recovery after three times'ultrafiltration process was 86%. Dormancy dilution was used in ultrafiltration, the operation conditions were:â–³P₃₀₀₀₀=0.15MPa,â–³P₁₀₀₀₀=0.15MPa,â–³P₅₀₀₀=0.20MPa, room temperature; pH4.0; the HA concentration 1%.Ultrafiltration solution was deposited by 4% calcium acetate and 80% acetone after vacuum concentration, in these deposition conditions, the recovery of HA was 70.5% for 5000 PES membrane's penetrating fluid.