Dealing with soy sauce precipitation at submicron-/nano-scale: An industrially feasible approach involving enzymolysis with protease and alkaline conditions

This study proposes an industrially feasible approach to handle the heating-induced soy sauce precipitates (SSPs) during soy sauce production. Protein (32.59%; containing a large amount of hydrophobic amino acid) and sugar (26.86%) were found to be the main composition of SSPs, and high content of mineral elements were also discovered in SSPs. A pH adjustment to 8-12 along with an enzymolysis step with alkaline protease seemed beneficial for this purpose while offering opportunities to manipulate the soy sauce quality. The pH adjustment decreased SSPs particle size from micron-scale to submicron- or nano-scale, and improved significantly the efficiency of SSPs protein enzymatic hydrolysis and protein recovery (up to 80%). The enzymolysis with alkaline protease enabled the generation of pyrazines while affecting the contents of phenols, alcohols, furans, pyrroles and sulfur-containing compounds. Interactions occurred between amino acids and sugars, among volatiles, and between volatiles (like aldehydes) and other monomers under such alkaline conditions. This study presents an efficient approach that is of practical significance to dealing with SSPs in soy sauce production and reuse of SSPs.