Abstract:

The production of Douchi, a Chinese traditional fermented soybean product, was replicated in the laboratory on a small scale in order to study the biochemical changes associated with the ripening process. Douchi was made by mucor SP. fermenting uncracked, undehulled and cooked soybean seeds and followed by a 42-d ripening at 45 to 48 ℃. Changes in proximate compositions (moisture, ash, crude lipid, dietary fiber, carbohydrate and energy), total nitrogen, non-protein nitrogen, nitrogen soluble index, amino nitrogen, water soluble nitrogen, free amino acid concentration, in vitro digestibility of protein, total titratable acid, and browning index of Douchi with different length of ripening time were analyzed. Results showed that ash content increases over the ripening process, while dietary fiber and carbohydrate significantly diminish. A sharp increase and a slight decline in total titratable acid are detected at the beginning (0 to 8 d) and end (32 to 42 d) of ripening, respectively. Total nitrogen keeps stable, while non-protein nitrogen, nitrogen soluble index, amino nitrogen, water-soluble nitrogen, free amino acid concentration, and in vitro digestibility of protein increase throughout the ripening process, which results in enhancemant of nutritional value of product.

Key words: Douchi, proximate composition, nitrogenous consitiuents, browning, ripening, digestibility