High-pressure Short-duration Steaming of Soybean Significantly Enhances the Degradation Rate and Reduces the Content of Secondary Precipitates of Soy Sauce
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Abstract:
Secondary precipitates affect the appearance and commercial value of soy sauce adversely. Therefore, to investigate ways to minimize secondary precipitates in soy sauce, the content of secondary precipitate protein and the amount of secondary precipitates in soy sauce made from soybean prepared using high-pressure and short-duration steaming (0.54 MPa/14 min) were compared with the same parameters in soy sauce made from soybean prepared using low-pressure and long-duration steaming (0.24 MPa/18 min) as a control. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight/time-of-flight tandem mass spectrometry were used to analyze the secondary precipitate proteins and secondary precipitates in the soy sauces. The B3 subunit of glycinin G4 (20 ku) and the A1a subunit of glycinin G1 (35 ku) were the main protein components of the secondary precipitates. The B3 subunit content in soy sauce prepared using the soybean steamed at high pressure for a short time (hereinafter, the sample) was 65.38% lower than that of the control, whereas the A1a subunit in the sample was completely degraded. The secondary precipitate content in the sample was also reduced, by 72.69% relative to the control level. Additionally, the application of high pressure and a short time to steam the soybean enhanced the rate of utilization of proteins in the raw materials by 9.37% and led to the following increases in the soy sauce: amino acid nitrogen: 14.14%; total nitrogen: 10.74%; total sugars: 22.36%; reducing sugars: 27.87%; and salt-free solids: 12.38% (p<0.05). Therefore, the adoption of high pressure and a short duration for the soybean steaming process can significantly enhance the rate of secondary precipitate protein degradation, reduce the content of secondary precipitates, and increase the content of taste compounds in soy sauce, leading to simultaneous improvements in the appearance and taste of the product.
