Freeze drying has a deleterious effect on the viability of microorganisms. In front of this difficulty, the present study adopts response surface methodology to optimize the chemical compositions of protective agents to seek for maximum viability of Bifidobacterium longum BIOMA 5920 during freeze-drying. Through the compara- tive analysis of single protectant, the complex protective agents show better effect on the Bifidobacterium viability. Human-like collagen (HLC), trehalose and glycerol are confirmed as significant factors by Box-Behnken Design. The optimized formula for these three variables is tested as follows: HLC 1.23%, trehalose 11.50% and glycerol 4.65%. Under this formula, the viability is 88.23%, 39.67% higher in comparison to the control. The viable count is 1.07×10 9 cfu·g-1 , greatly exceeding the minimum viable count requirement (10 6 cfu·g-1 ).
A new type of collagen mimetic peptide, （PKG）n（POG）2n（DOG）n, with charged-domain ends had been designed and successfully prepared in this work, which self-assembled into collagen-like triple helices homotrimers. The collagen-like homo- trimers underwent higher level of self-assembly via static electrical interaction between positive and negative domains. Transmission electron microscope （TEM） examinations showed three typical morphologies of homotrimer assembly, which were defined as film, bicontinuous and fibril morphology in this paper. The film was formed in the initial stage and gradually transformed to bicontinuous or fibril morphology to improve stability of the assemblies or decrease surface energy. Furthermore, mechanism of assembly process was proposed based on TEM observations and theoretical analyses of packing equation.
Ying SHI Song WANG Xiu-Mei WANG Qiang CAI Fu-Zhai CUI Heng-De LI
