Preparation Of Chitooligosaccharides By Enzymatic Hydrolysis Of Chitosan And Its Quality Control

Chitooligosaccharides (COS) is a kind of oligosaccharides with many unique biological activities. It has great application prospects in food, medicine, agriculture and environmental protection areas. Preparation of COS by enzymatic hydrolysis is an ideal preparation method. But the substrate concentration in enzymatic hydrolysis is generally low, usually no more than 5%. It leads to the high cost in hydrolysis, purification, concentration, and drying. In this paper, a new technology of preparation of COS by enzymatic hydrolysis under high substrate concentration was studied. The main contents are as follows:Chitosan was pretreated by high-shear dispersion device which was used to reduce dissolution time and increase substrate concentration in reaction system. This innovation reduced the level of energy consumption and production costs. By examining the influence of temperature, pH, enzyme dosage, substrate concentration, and reaction time on degradation, the optimal degradation conditions were obtained: temperature 45℃, pH4.5, enzyme dosage 8U/g, substrate concentration <10%, degradation time 6h.Fractionation and purification of COS under high material concentration were studied. The optimal operating parameters of UF membrane (MWCO10kDa) were: operating pressure 0.25MPa~0.3Mpa, operating temperature room temperature, and solid content 5% to 10%. The static and dynamic adsorption experiments showed that 717 basic anion exchange resin could effectively remove residual acetic acid and pigments in hydrolyzate. The decolorization rate was 47.4%, the optimal flow rate was 2BV/h, and the leakage was at 8BV.The spry drying was investigated and the optimal spray drying conditions were: solid content 25% ~ 30%, inlet air temperature 180℃, feed rate 55mL/min. The contents of reducing sugar, total sugar and free amino groups, antioxidant properties, color and solubility of spray-dried product was almost the same as that of vacuum freeze-dried product. However, its energy consumption was much lower than that of the freeze-drying and it was more suitable for industrial production.20L scale experiment was carried out. Product yield reached 66.5%, and it was 16% higher than that of preparation under low substrate concentration. Comparisons of contents of free amino groups, reducing power, antibacterial activity were made between COS prepared by enzymatic and chemical methods. The results indicated that COS prepared by enzymatic method possessed higher contents of free amino groups, reducing power, antibacterial activity. Quality standards of COS prepared by enzymatic hydrolysis was proposed and contents of free amino group and reducing sugar were firstly set as key quality standards.