Membrane Application in Soy Sauce Processing

Membrane technology is playing an important role in improving the quality of soy sauce and ensuring the biosafety of soy sauce. With microfiltration (MF) and ultrafiltration (UF), the turbidity and count of aerobic microorganisms in the product of soy sauce could be significantly reduced, while the nutrients could be retained, thus refined soy sauce with prolonged shelf life and enriched flavor could be produced. With nanofiltration (NF) membrane technology, low-salt soy sauce is produced with raw soy sauce containing high NaCl concentration. Due to the high osmotic pressure induced by the high concentration of NaCl in soy sauce, a three-step operation of dilution, concentration, and diafiltration is found to be the suitable operation mode for low-salt soy sauce production. In processing soy sauce by membrane technology, membrane selection, and optimization of operating conditions determine the performance of membrane separation process, and the quality of soy sauce products. Raw soy sauce is very complicated, containing bacteria, bacteria debris, proteins, polysaccharides, amino acids, and inorganic salts. Membrane fouling, resulting in low operating efficiency and even system failure, constitutes a major problem in wider applications of membrane technology in soy sauce industry. Fouling is controlled to some extent by selecting appropriate membranes and optimizing process parameters. © 2010 Elsevier Ltd. All rights reserved.