Soybean whey (SW) is a by-product generated from the production of soybean protein isolates (SPI) from defatted soybean. SW is not commercially utilized and is discarded as industrial waste in Japan. Here, we examined whether SW could improve the physical properties of salmon, a protein-rich food. Salmon fillets were soaked in water (WT), citric acid-NaOH solution (CN), or SW before baking. The effects of presoaking with each solution on the qualities of baked salmon fillets were compared. We confirmed that SW contained numerous soluble proteins and carbohydrates in descending order of content, namely, sucrose, stachyose, and raffinose. Additionally, the mineral component ratios of SW closely resembled those of soymilk rather than SPI. Presoaking in SW caused a significantly higher yield rate and lower hardness of salmon fillets than presoaking in WT and CN. Although the salmon fillet moisture content only tended to be increased by SW presoaking when compared to CN presoaking, it was significantly increased when compared to WT presoaking. The results of sensory test showed that salmon fillets presoaked in SW were significantly softer with higher moisture and had a deeper orange color than those presoaked in WT and CN. However, they did not differ in smell. In all evaluations, except of smell, the salmon fillets presoaked in SW were significantly preferred as compared to those presoaked in WT and CN. These results suggested that SW can protect salmon against heat-induced quality reduction. In conclusion, SW could be used for improving the physical properties of protein-rich foods.
