Improved umami flavor of soy sauce by adding enzymatic hydrolysate of low-value fish in the natural brewing process

There is a demand for natural soy sauce product rich in umami substances to reduce the addition of monosodium glutamate (MSG). This work aimed to develop a new type of seafood soy sauce by adding fishy removed enzymatic hydrolysate of low-value fish in the fermentation of low-salt solid-state soy sauce to improve its umami taste. The conditions were optimized to obtain low-value fish hydrolysate for seafood soy sauce preparation. Compared with the traditional soy sauce, the seafood soy sauce showed improved aroma, umaminess and aftertaste. Two more organic acids (OAs) and approximately a 20% OAs content increase were detected in the seafood soy sauce. The contents of amino acid nitrogen (AAN) and total nitrogen (TN) were also improved and reached the national first-grade soy sauce standard. The free amino acids (FAAs) content in fermented seafood soy sauce was much higher than that of traditional soy sauce. It was noted that the content of umami FAAs in the fermented seafood soy sauce was more than seven times that of the traditional soy sauce. Consequently, adding enzymatic low-value fish hydrolysate as raw materials in the fermentation improved the flavor and quality in the soy sauce.