Effects and Mechanisms of Ultrasonic and Papain Treatment on Texture Properties of the Abalone (Haliotis discus hannai) Meat

<i>Haliotis discus hannai</i> meat has a firm texture that makes it difficult to chew and swallow, so tenderizing is necessary. Ultrasonic treatment and papain enzyme processing are used to reduce the hardness of abalone meat. This study tests physicochemical indicators and protein changes to assess meat quality and protein alterations. The maximum reduction in hardness of raw meat reached 60.58%, while heat-treated abalone meat achieved 61.13%, with free water and bound water converting to immobile water. The L* value of the meat decreased, while the a* and b* values increased. In raw meat, the content of TCA-soluble peptides increased with increasing treatment intensity. However, in heat-treated meat, this peptide content decreased with rising temperature. Muscle fiber filament breaks and pore numbers increased. The BPB binding content showed a negative correlation with the percentage of α-helix. Total sulfhydryl and free amino groups in raw meat decrease with increasing treatment intensity; both parameters in cooked meat decrease with rising temperature. Changes in tertiary protein structure cause alterations in fluorescence intensity, with secondary structure shifting from α-helix to β-sheet conformation. The results suggested that ultrasonic and papain treatments can induce structural alterations in proteins. This leads to protein cleavage and depolymerization, collectively resulting in softening of abalone meat texture and redistribution of internal moisture. These processes result in softening of abalone meat and redistribution of internal moisture. This study provides a theoretical basis for developing abalone tenderizers.