Biochemical changes of traditional Chinese-type soy sauce produced in four seasons during processing

Traditional Chinese-type soy sauces were prepared in four seasons. Weather information (temperature, humidity and index of weather degree) was recorded during processing, and biochemical changes during the ageing of the soy sauce were evaluated. Results showed that microbiological counts, protease activity, total nitrogen, formaldehyde nitrogen, total titratable acid, reducing sugar, molecular weight distribution and free amino acids changed significantly during processing. Peptides of 3–5 kDa were the main fraction in all soy sauces. Leucine, arginine, glutamic acid, lysine and isoleucine were dominant individual free amino acids. These indices were different among soy sauces prepared in four seasons. There were obvious correlation between biochemical indices of soy sauce and environmental factors. The results are helpful to select appropriate processing technology to improve soy sauce quality.