Amino acid profiles of sufu, a Chinese fermented soybean food

Abstract

Sufu is a Chinese soybean cheese-like product obtained by solid-state fungal fermentation and ripening of tofu. The resulting “pehtze” is salted, followed by maturation in brine. Total (TAA) and free amino acid (FAA) profiles were determined during consecutive stages of sufu manufacture, i.e., tofu, pehzte (fungal fermented tofu), salted pehtze and in white, red and grey sufu, ripening in dressing mixtures of different salt content (8%, 11%, and 14% w/w). TAA in tofu, pehtze and salted pehtze totalled 547, 551 and 351 mg/g dry matter, respectively. FAA increased from total 1.3 to 15.6 mg/g dm in pehtze after fermentation of tofu by Actinomucor elegans and to 11.9 mg/g dm in salted pehtze. During ripening up to 80 days, total FAA in red sufu increased from 28 to 88 mg/g (8% salt), 28–63 mg/g (11% salt) or 26–42 mg/g (14% salt). In white sufu the levels of FAA were generally higher and the effect of salt was less inhibitory. Levels of FAA in white sufu increased in 80 days from 33 to 104 mg/g (8% salt), 27–92 mg/g (11% salt) and 19–73 mg/g (14% salt). The pattern of essential amino acids compared favourably with those of eggs and cow's milk. While FAA increased during ripening of red and white sufu, the ratio of each amino acid remained essentially constant, and glutamic acid, leucine, aspartic acid, alanine, phenylalanine and lysine were found in large quantities. However, in grey sufu the ratio was different, with large proportions of leucine, alanine, isoleucine, valine and phenylalanine found after ripening.