Effect Of Dynamic High-pressure Micro-fluidization On The Rheological Properties And Conformation Of Yeast Mannans

As a species of yeast, saccharomyces cerevisiae is rich in China, howere, the recovery of its by-products is less, it was used as feed or directly discharged as waste, generally. This is not only pollute the environment, but also waste natural resources. Yeast mannans exit in the outside of the yeast cell wall, and they have been reported with anti-bacterial, anti-inflammatory, enhance immunity and other activities. Study of yeast mannans can improve the added value of the yeast cell wall, also,promote the industry applications of polysaccharide.As a new processing technology, dynamic high-pressure micro-fluidization(DHPM) has been applied in the preparation of yeast mannans,while the effect of the process on yeast mannan has not been thoroughly studied. Thus, in order to to solve the above problem, we developed a method including hot water extraction and compound enzymolysis to prepare yeast manans with different purity from yeast cell wall. First, we compared the rheological properties of yeast mannans with different purity, then, investigated the rheological properties, structure and conformation of the sample with the highest purity before and after DHPM treatment.By water extraction and alcohol precipitation, papain treatment, pronase treatment, we get the YM1,YM2, YM3 samples, the purity increased sequentially. At the range of 0.1-100 1/s, η of YM1, YM2 decreased gradually with increasing shear rate, while unchanged of YM3, under the same shear rate, ηof the first two samples were higher than the third one. In the range of 5-85 ℃, η of the three samples decreased as the temperature rised, among them, YM2 exhibited the weakest viscosity-temperature dependence; Under the constant temperature mode, apparent viscosity of YM1 and YM2 decreased with the shear rate increased, the non-newtonian index of them were in the range of 0.23-0.30 and 0.35-0.41 respectively, thus, the non-newtonian of YM1 is stronger than the YM2; the non-newtonian index of YM3 is 0.914 under 5 ℃, in line with pseudoplastic fluid characteristics. When salts were initially added to the ionfree solution, η of the three samples decrease and further addition of ions to the system resulted in less impact on viscosity. The G’ of YM2 is always higher than YM1 within the range of scanning frequency, their gel structure is destroyed when the frequency is above 10 1/s. As the purity of YM improved, the solution changed from pseudoplastic fluid into newtonian fluid.The Higiro’s 1 and Higiro’s 2 plots obtained by capillary viscometry gave an intrinsic viscosity [η]of 0.166 and 0.131 dl/g, and the [η] first increased and then decreased with the pressure increased.These yeast mannan solutions showed Newtonian flow behavior at all the tested concentrations. The apparent viscosity of yeast mannan solutions decreased continuously with increase in temperature(25 °C to 85 °C) at a given shear rate. The viscosity did not change within the p H values of 4.0 to 10.0;however, it increased when the p H decreased from 4.0 to 2.0. The concentration of Na Cl and KCl up to100 m M did not affect the viscosity of yeast mannan solutions significantly. The viscosity decreased with addition of Ca Cl2 up to 10 m M and would stay constant above this concentration. Compared with the untreated sample, the viscosity of the solution decreased with the pressure increased.Surface of yeast mannas gradually becomes loose and porous with the pressure increased, from dense flakes aggregation to a network structure of loose and porous sponge. The DHPM treatment did not affect the infrared scanning spectrum of the yeast mannans. The conformational parameters derived from Mark-Houwink and Flory equations([η] vs Mw and Rg vs Mw) were 0.15 and 0.39 respectively,suggested a sphere conformation of yeast mannan. The Mw of untreated, with 50, 100, 150 and 200 MPa treated samples were 1.27×105, 1.28×105, 1.26×105, 1.16×105, 1.12×105 g/mol respectively,polydispersity index were 1.126, 1.102, 1.086, 1.067, 1.101, 1.115 respectively, values of Mark-Houwink parameters were all less than 0.3, Flory parameters were all less than 0.4. The above results provide the theoretical basis for its functional design and process-control.