Abstract: In order to obtain a low-cost fermentation medium for recombinant chymosin strain Chy1 in a large scale, the effects of glucose, corn syrup, yeast extract and urea concentration on chymosin production by recombinant chymosin strain Chy1 were explored by single factor tests. The results indicated that the effects of glucose, corn syrup, urea and yeast extract on chymosin production were significant. The optimal fermentation medium was optimized by uniform design tests to be glucose of 45 g/L, corn syrup of 17 g/L, yeast extract of 6 g/L and urea of 12 g/L. Under these optimal conditions, the activity of chymosin can reach up to 342.86 SU/mL, which exhibited a 1.22 fold enhancement when compared with original medium. This optimal fermentation medium provided a basis for massive chymosin production by recombinant chymosin strain Chy1 with high efficiency and low cost.

Key words: chymosin, recombinant strain, uniform design methodology, low-cost medium