Mild Ultrasound Turns Fragile Meat Protein–Polysaccharide Complexes Into Stable Matrices

Food scientists have shown that the dose of a polysaccharide can quietly decide how much benefit ultrasound delivers to a protein mixture. In a study published in Food Production, Processing and Nutrition, researchers prepared binary complexes of sarcoplasmic protein (SP) extracted from fresh meat and Lycium barbarum polysaccharide (LBP), a bioactive polysaccharide from goji berry, at incorporation levels from 0% to 5%. Although every mixture received the same nominal ultrasonic settings, the effective, in-situ cavitation intensity differed from sample to sample, and that hidden variable ultimately determined whether the complexes held together or fell apart.

The motivation was straightforward. Sarcoplasmic proteins are an underutilized by-product of meat processing, and pairing them with LBP is attractive because the polysaccharide brings documented biological activity and modification potential. But the authors note that adding LBP triggers serious stability problems, including phase separation and weak intermolecular interactions that damage the structural integrity of the composites and accelerate system degradation. Ultrasound-assisted processing has shown promise against exactly this kind of instability, because acoustic cavitation generates shear forces and shock waves that can homogenize mixtures, expose reactive regions, and strengthen non-covalent contacts between proteins and functional components without chemical additives.

To prepare the complexes, the team minced fresh meat at 4.0 °C, homogenized it with ultrapure water, filtered the supernatant protein, and stirred in LBP at mass ratios of 0%, 1%, 2%, 3%, 4%, and 5% before adjusting the SP concentration to 20 mg/mL. Each mixture was then sonicated for 15 minutes at 20 kHz and 180 ± 20 W/L with a 6 mm probe in 3-second on/off cycles, while an ice bath kept the temperature between roughly 0 and 4 °C. The resulting samples were labeled LBP-SP0 through LBP-SP5 according to their polysaccharide content, and all procedures were run in triplicate.

A key insight of the work is that the nominal ultrasound dose is not the dose the molecules actually experience. Because a high LBP concentration raises the viscosity and surface tension of the aqueous solution, it hinders the propagation of ultrasonic energy and weakens acoustic cavitation. Conversely, too little polysaccharide leaves SP molecules directly exposed to intense shock waves and shear, risking excessive protein denaturation. The researchers quantified the real in-situ sono-process intensity with a crystal violet decolorization method, which relies on the hydroxyl radicals generated during cavitation bubble collapse to bleach the dye, with absorbance tracked at 580 nm.

The measured intensities told a non-linear story. The control LBP-SP0 system reached 67.73%, while the sonicated groups measured 46.90% (LBP-SP1), 54.53% (LBP-SP2), 60.48% (LBP-SP3), 65.92% (LBP-SP4), and 62.26% (LBP-SP5). Intensity climbed from 1% to 4% LBP, peaking in the LBP-SP4 group, then dropped back to a mild level at 5% LBP, where molecular crowding and elevated viscosity dampened cavitation. The authors interpret the LBP-SP5 reduction not as diminishing returns but as a favorable shift from excessive to mild sonication, and they classify LBP-SP1 and LBP-SP2 as relatively low-intensity groups, LBP-SP5 as mildly treated, and LBP-SP4 as excessively sonicated.

Stability testing with a LUMisizer multiple light scattering instrument made the consequences visible. As storage time extended from 0 to 1200 seconds, the clarity index of every sample rose, reflecting gradual sedimentation of composite particles that clears the supernatant. The untreated control showed the fastest rise along with visible precipitation and liquid-layer separation, whereas LBP-SP5 rose slowest and looked nearly homogeneous. After a plateau beyond 3000 seconds, the final clarity index ranked LBP-SP0 highest, followed by LBP-SP4, LBP-SP3, LBP-SP2, LBP-SP1, and finally LBP-SP5, the most stable. Quantitatively, mild sono-processing improved the system stability of LBP-SP0 by 42.01%.

Thermogravimetric analysis reinforced that ranking. All groups degraded most dramatically between 50 and 250 °C, but the final residual mass fraction followed the sequence LBP-SP5 > LBP-SP3 > LBP-SP2 > LBP-SP1 > LBP-SP0 > LBP-SP4, with LBP-SP5 clearly the most thermally resistant. The maximum mass-loss peaks, tracked by derivative thermogravimetry, appeared at 150.0 °C for the control and at 152.4, 146.0, 144.4, 131.4, and 145.8 °C for LBP-SP1 through LBP-SP5 respectively. The authors attribute the divergent decomposition behavior to the different effective cavitation intensities acting on each system, since tightly crosslinked composite structures demand more thermal energy to dissociate.

Microscopy connected those bulk measurements to structure. Transmission electron microscopy showed predominantly spherical particles in every sample, but the low-intensity groups LBP-SP1 and LBP-SP2 formed loose, poorly defined aggregates with blurred boundaries, while the excessively sonicated LBP-SP4 group produced discrete, evenly dispersed spherical particles that, despite their regular appearance, failed to build a stabilizing three-dimensional network. In contrast, mild processing in LBP-SP5 yielded compact spherical nanoparticles representing well-assembled SP-LBP aggregates. Atomic force microscopy added three-dimensional detail, showing relatively uniform height across the LBP-SP5 sample, and scanning electron microscopy, together with elemental mapping in which nitrogen ranged from 18.55% in the control down to 11.51% in LBP-SP5, tracked the surface microstructural changes.

Spectroscopy explained the mechanism at the molecular level. Circular dichroism showed that 1% or 2% LBP left secondary structures essentially unchanged, but a pronounced decline in α-helix content appeared from 3% LBP onward, indicating progressive disruption of the protein’s compact structure that facilitates binding with LBP. Surface hydrophobicity measurements using an ANS fluorescent probe revealed the standout result: the LBP-SP5 group’s hydrophobicity rose 59.27% above the control, evidence that mild sonication induced controlled unfolding that exposed previously buried hydrophobic residues. Those patches then drove hydrophobic interactions with LBP and the assembly of integrated aggregates. Tryptophan and three-dimensional fluorescence spectra showed quenching at low LBP levels, rising intensity at 2–3%, and a notably higher TDF peak for LBP-SP5 than for the excessively sonicated LBP-SP4, which the authors read as tryptophan residues becoming embedded in a protective hydrophobic core within the well-assembled aggregates. FT-IR amide A band shifts, peaking between 3277 and 3350 cm⁻¹ across the samples, further linked hydration behavior to the observed stability differences.

The overall picture is that LBP concentration tunes the ultrasonic microenvironment, which in turn governs protein conformation, intermolecular interactions, morphology, and colloidal stability. Too little polysaccharide provides insufficient binding sites; too much delivered intensity over-unfolds the protein into isolated particles that cannot network. At 5% LBP, the viscosity-mediated damping of cavitation created exactly the controlled, moderate sonication needed to convert fragile LBP-SP complexes into stable functional matrices. The authors note that their supplementary tests also showed LBP addition raised the DPPH radical scavenging rate of the SP matrix by 73.58% relative to pure SP at 5 mg/mL, though the core contribution of this study remains the demonstration that effective ultrasound intensity, not the instrument setting alone, is the variable to control when designing protein-polysaccharide assemblies for food applications.

Subject of Research: How varying Lycium barbarum polysaccharide concentrations modulate in-situ ultrasonic intensity, structure, and colloidal stability of meat sarcoplasmic protein complexes

Article Title: Effects of sono-process intensities on structural characteristics and stability of meat sarcoplasmic protein binary complexes

Article References: Chen, J., Chen, J., Zhang, M., Cao, S., Lin, X., Huang, Z., Zang, M., & Wang, D. (2026). Effects of sono-process intensities on structural characteristics and stability of meat sarcoplasmic protein binary complexes. Food Production, Processing and Nutrition, 8(1), Article 74. https://doi.org/10.1186/s43014-026-00430-8

Image Credits: AI Generated

DOI: 10.1186/s43014-026-00430-8

Keywords: ultrasound, sarcoplasmic protein, Lycium barbarum polysaccharide, protein-polysaccharide complexes, colloidal stability, cavitation, surface hydrophobicity, circular dichroism, thermogravimetric analysis, transmission electron microscopy, food processing, meat by-products