Impact of ultrasound-assisted single washing process on tilapia mince: Biochemical changes, structural modifications, and gel formation

Ultrasound (US)-assisted single washing was applied to reduce water usage in tilapia mince washing during surimi production. The mince-to-water ratio of 1:2 in US-assisted washing was compared with ratios of 1:2 and 1:3 in conventional washing (CW-2 and CW-3, respectively). Screening of US power revealed the greatest effect at an intensity of 3.19 W/cm² on mince whiteness (p < 0.05), without damage to protein polypeptide chains, and no extensive biochemical changes. Subsequently, the mince was subjected to various US exposure times of 1, 3, and 5 min (US-1, US-3, and US-5, respectively) at 3.19 W/cm², maintaining the same total washing time of 10 min across all treatments. US-assisted washing increased myofibrillar protein loss compared with that with CW, as indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the loss increased with longer exposure time-from 7.57 % in US-1 to 12.76 % in US-5. The US-1-washed mince exhibited the highest Ca²⁺-ATPase activity and reactive sulfhydryl (SH) content, even higher than that of CW-3 (p < 0.05). Random coil structures decreased in US-5, while other secondary structures did not change significantly. Tertiary structure analysis using Raman spectroscopy revealed comparable tyrosine and tryptophan exposure in US-1, US-3, and CW-3, which may contribute to the increased breaking force and distance through higher extent of hydrophobic interactions in their corresponding surimi gels compared with CW-2 and US - 5 (p < 0.05). Oxidation of SH groups and hydrophobic interactions increased in US-3 and US-5 (p < 0.05). US-1 was identified as the optimal condition for a single washing of tilapia mince to reduce water usage with minimal negative effects on protein.