Abstract:

Walnut meal, a by-product left after pressing walnuts for oil, contains rich protein and its nutritional value is high.
Polypeptide production from cold-pressed walnut meal by liquid-state fermentation of Bacillus subtils natto was investigated
in this study. The effects of fermentation time, feed concentration, initial pH, inoculum amount, and fermentation temperature
on the content of polypeptide and the degree of hydrolysis (DH) were studied, and these fermentation parameters were
optimized by single-factor experiments and Box-Behnken response surface methodology. Results showed that the optimum
fermentation parameters were determined as follows: fermentation time, 84 h; feed concentration, 8 g/100 mL; initial pH
value, 8.0; inoculum amount, 11% and fermentation temperature, 33 ℃. The maximum content of polypeptide and DH of
2.58 mg/mL and 37.5%, respectively were simultaneously obtained under these optimized conditions.

Key words: walnut meal, Bacillus subtils natto, liquid-state fermentation, polypeptide, process optimization