High‐intensity ultrasound improves threadfin bream surimi gelation at low NaCl contents

Abstract

Effects of high‐intensity ultrasound (HIU) treatments on gelation of threadfin bream (Nemipterus spp.) surimi at various NaCl contents (0.5, 1, and 2% NaCl) were investigated. Protein extractability at 0.5% NaCl was increased with the ultrasonic intensity (p < 0.05). At all tested NaCl contents, reactive sulfhydryl group (SH) content and surface hydrophobicity of the surimi pastes were increased after HIU treatments and were accompanied by a decrease in the Ca2+‐ATPase activity and total SH content, indicating a greater extent of unfolding and conformational changes induced by HIU at higher NaCl contents. Textural properties and color of the surimi gels at 0.5% NaCl were improved concomitant to an increase in ultrasonic intensity (p < 0.05), whereas HIU treatments resulted in inferior gels at 1 and 2% NaCl. Scanning electron microscopy (SEM) revealed that HIU resulted in a more orderly gel network at 0.5% NaCl. Fourier transform infrared (FT‐IR) spectroscopy indicated that the α‐helix content of the surimi gels was decreased as the ultrasonic intensity and NaCl content increased, confirming that structural changes induced by HIU were more profound at higher NaCl contents. The results suggested that HIU technology can be applied to improve only the 0.5% NaCl surimi gel. Practical Application High‐intensity ultrasound (HIU) improved surimi gel containing 0.5% NaCl due to an increase in protein extractability and protein conformational changes. It is likely to lay a theoretical foundation for utilization of HIU technology in production of surimi‐based products at low/reduced salt levels.

Improvement of gelation properties of silver carp surimi through ultrasound-assisted water bath heating

“…In fact, this increase in β-sheet content reflected an enhancement of the number of hydrogen bonds which could maintain stable protein conformation and strengthen the intermolecular forces between proteins so as to form an ordered gel network structure [14] , [40] . Similar results were reported by Tang et al [32] who concluded that surimi gels of threadfin bream at 2% NaCl content had less α-helix but more β-sheet, thus confirming that high NaCl level induce a higher degree of unfolding in proteins. Xiong et al [2] reported that the protein secondary structures in bighead carp surimi gels presented a higher β-sheet content at 3% NaCl addition compared with 0.5% NaCl addition.…”

“…Gao et al [25] reported that the deformation and breaking force of surimi gels were promoted as the NaCl content increased from 0% to 5%, and these results were consistent with ours. Similarly, Tang et al [32] also concluded that the gel strength of surimi with 0.5% NaCl addition was lower than that with a 2.0% NaCl addition.

Fig.

…”

“…4 , a reduction of roughly 4% or 5% of the α-helix content was observed at high salt concentration, while β-sheet and β-turn contents displayed an opposite trend, no matter what kind of treatment. This indicated that high salt condition helped to induce more protein unfolding [32] , which promoted structural transformations from α-helix to β-sheet structure [39] . In fact, this increase in β-sheet content reflected an enhancement of the number of hydrogen bonds which could maintain stable protein conformation and strengthen the intermolecular forces between proteins so as to form an ordered gel network structure [14] , [40] .…”

“…Xing et al [14] came to similar conclusions that HIU treatments could decrease the α-helix content and increase the amount of other secondary structures. This is because proteins can have better unfolding behavior after ultrasonic treatment as it can facilitate the cross-linking and aggregation of proteins, thus contributing to the formation of compact gel networks and good gel properties during the heating process [32] . However, it was also observed that gels from the U + U group had lower β-sheet content and more random coil content compared with the U + W group.…”

“…2 ). Ultrasound, in facilitating the exposure of more active groups, promoted interactions between protein molecules, and contributed to the formation of more compact gel networks [32] . In this context, a study by Li et al [45] revealed that ultrasound induced a more orderly aggregation of chicken breast protein, thereby forming denser and organized gel networks.…”