Abstract:

Objective: To determine the values of total volatile basic nitrogen (TVB-N), trimethylamine, hydrogen sulfide
and biogenic amines derived from the decomposition of proteins in sufu and Douchi and consequently ensure the safety of
fermented soybean products. Methods: The above parameters were measured according to the Chinese national standards
(GB/T 5009.44—2003, GB/T 5009.179—2003, and GB/T 16489—1996) and previously published methods, respectively.
Results: The values of TVB-N, total biogenic amine, putrescine, trimethylamine, and hydrogen sulfide of Douchi were 8.20–
372.72 mg/100 g, 15.67–2 057.56 mg/kg, ND–276.03 mg/kg, 0.26–10.43 mg/100 g and 1.22–27.27 mg/kg, respectively,
while those of sufu were 95.33–652.94 mg/100 g, 11.38–2 406.95 mg/kg, 11.38–1 147.32 mg/kg, 0.42–4.31 mg/100 g and
0.27–3.72 mg/kg, respectively. Conclusions: Sufu and Douchi are rich in TVB-N, TMA, H2S and BAs, which adversely affect the
eating quality of products. TVB-N, putrescine, total biogenic amines and trimethylamine are preliminarily considered as indicators
of sufu spoilage whereas spoilage indicators for Douchi are TVB-N, total biogenic amines and trimethylaminecan. The limit
standards for these indicators could be determined by taking the production process into account.

Key words: Douchi, sufu, protein decomposition products, tolal volatile basic nitrogen (TVB-N), trimethylamine, hydrogen sulphide, total biogenic amine, putrescine