The difference of secondary structure (a) (b) and tertiary structure (c) of protein of large yellow croaker with different freezing treatments, immersion freezing (IF), single-frequency UAF (SUAF) at 20 kHz, 28 kHz and 40 kHz, dual-frequency UAF (DUAF) at 20/28 kHz, 20/40 kHz and 28/40 kHz, multi-frequency UAF (MUAF) at 20/28/40 kHz. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)