Chemical and Textural Properties in Commercial Fermented Soybean Curds of Sufu

A survey aiming to find out the chemical and textural properties of commercial fermented soy bean curd called sufu was conducted. Sixteen brands of plain sufu produced in the Northern or the Southern part of China were collected and examined for their crude protein, crude fat, texture profiles, free amino acids, and free fatty acid contents. Twenty-one free amino acids were extracted and derivatized using a commercial kit followed by separation and analyzed by the gas chromatography-mass spectrometry (GC-MS). Similarly, ten free fatty acids were extracted using alumina, eluted, separated and analyzed. The content ranges of crude fat and protein were 22～36% and 31～38%, respectively. In texture profile analysis, ranges of the texture parameters were 131～493 g (hardness), 0.4～0.5 (cohesiveness), -137 to -50 gs (adhesiveness), 0.6～1 (springiness), 47～220 g (gumminess) and 32～177 g (chewiness). Twenty-one different free amino acids, especially alanine, glycine, α-aminobutyric acid, valine, leucine, allo-isoleucine, aspartic acid, glutamic acid and lysine in large amount, as well as ten fatty acids in total, notably linoleic acid (9-octadecanoic acid), oleic acid (9,12-octadecadienoic acid), linolenic acid (9,12,15-octadecadienoic acid), hexadecanoic acid and octadecanoic acid were found. This information provides important quality reference ranges for product developers and manufacturers to optimize and produce the plain sufu.