Abstract:

This study aimed to prepare reference materials for Shigella by a freeze-drying method. Orthogonal array design
was applied to choose the optimal formulation of lyoprotectant that provided maximum protection efficiency. Chicken powder was
used as the substrate for reference materials, which was mixed proportionally with the lyoprotectant and freeze-dried after addition
of the fresh bacterial solution with a predetermined number of cells. The reference materials had a characteristic value (bacterial
count) of 530 CFU/bottle with an uncertainty of 24 CFU/bottle. At −20 and 4 ℃ the freeze-dried samples could be stored for 12
months with good stability of the characteristic value. At 25 ℃,the storage life of the freeze-dried samples was 9 months, during
which the characteristic value remained stable. However, at 60 ℃, the stability was poor.

Key words: Shigella sonnei, reference materials, matrix, chicken