The impact of ultrasound duration on the structure of β-lactoglobulin

Sunset Yellow Dye Induces Amorphous Aggregation in β-Lactoglobulin at Acidic pH: A Multi-Techniques Approach

Protein aggregation is of two types: (i) amorphous and (ii) amyloid fibril. Several extrinsic factors (temperature, pH, and small ligands) stimulate protein aggregation in vitro. In this study, we have examined the role of sunset yellow (SY) on the β-lactoglobulin (BLG) aggregation at pH 2.0. We have used spectroscopic (turbidity, Rayleigh light scattering (RLS), far-UV CD) and microscopic (transmission electron microscopy [TEM]) techniques to describe the effects of SY on BLG aggregation. Our results showed that BLG aggregation is dependent on SY concentrations. Very low concentrations (0.0–0.07 mM) of SY were unable to induce aggregation, while SY in the concentrations range of 0.1–5.0 mM induces aggregation in BLG. The kinetics of SY-stimulated aggregation is very fast and monomeric form of BLG directly converted into polymeric aggregates. The kinetics results also showed SY-induced BLG aggregation disappeared in the presence of NaCl. The far-UV CD and TEM results indicated the amorphous nature of SY-induced BLG aggregates. We believe that our results clearly suggest that SY dye effectively stimulates BLG aggregation.

Fabrication and characterization of quercetin loaded casein phosphopeptides-chitosan composite nanoparticles by ultrasound treatment: Factor optimization, formation mechanism, physicochemical stability and antioxidant activity

Ultrasound treatment was used to successfully prepare Quercetin (Qu)-loaded Casein phosphopeptides (CPP)/chitosan (CS) nanoparticles. Compared with the control, the above ternary nanoparticles with the smallest size (241.27 nm, decreased by 34.32%), improved encapsulation efficiency of Qu (78.55%, increased by 22.12%) when prepared under following conditions: ultrasonic frequency, 20/35/50 kHz; the power density, 80 W/L; the time, 20 min, and the intermittent ratio, 20 s/5s. Electrostatic interactions, hydrogen bonding, and hydrophobic interactions were the main driving forces for nanoparticles formulation, which were strengthened by ultrasound treatment. The compact, homogeneous and spherical composite nanoparticles obtained by sonication were clearly observed by scanning electron microscope and atomic force microscope. The environmental stability (NaCl, pH, exposure time, storage time, and simulated gastrointestinal digestion) and antioxidant activity of the ternary nanoparticles were remarkably enhanced after ultrasonic treatment. Furthermore, the ternary nanoparticles prepared by ultrasound exhibited excellent stability in simulated gastrointestinal digestion. The above results indicate that ultrasound not only increases the loading of the nanoparticles on bioactive substances but also improves the environmental stability and antioxidant activity of the formed nanoparticles. Ultrasound-assisted preparation of nanoparticles loaded with bioactive substances could be well used in the functional food and beverage industry.

Effect of ultrasonic pretreatment monitored by real-time online technologies on dried preparation time and yield during extraction process of okra pectin

BACKGROUND

Ultrasonic pretreatment is a novel physical method that can be used in the extraction process of okra pectin. Real-time online monitoring technologies were introduced in time and frequency domains when okra was pretreated. Preparation time of dried okra and yield of okra pectin were studied; and physicochemical properties of okra pectin were analyzed at the optimum ultrasonic parameter.

RESULTS

Results showed that ultrasonic intensity of sweeping-frequency ultrasonic (SFU) pretreatment was stronger than that of fixed-frequency ultrasonic pretreatment (FFU). SFU pretreatment (60 ± 1 kHz) at 30 min had a strong ultrasonic voltage peak of 0.05387 V and signal power peak of -6.62 dBm. The preparation time of dried okra was 160 ± 14.14 min in the pretreated group, 44.83% lower than control without SFU pretreatment. The intercellular space was 56.03% higher than control. Water diffusion coefficient increased from 1.41 × 10^-9 to 2.14 × 10^-9  m²  s^-1 . Monobasic quadratic equations were developed for the monitored ultrasonic intensity and pectin yield. Compared to control, extraction yield (16.70%), pectin content (0.564 mg mg^-1 ), solubility (0.8187 g g^-1 ) and gel strength (30.91 g) were improved in the pretreated group. Viscosity decreased, and values of G' and G″ crossing at 63 rad s^-1 revealed the viscoelastic behavior and the beginning of viscous behavior with a sol state.

CONCLUSION

Decrement of dried preparation time and increment of yield were achieved by ultrasonic pretreatment during the extraction process of okra pectin, and the relationship of ultrasonic intensity monitored by real-time online technologies and yield was given. © 2021 Society of Chemical Industry.

Ultrasonic pre-treatment modifies the pH-dependent molecular interactions between β-lactoglobulin and dietary phenolics: Conformational structures and interfacial properties

There is a need to understand the ultrasound-induced changes in the interactions between proteins and phenolic compounds at different pH. This study systematically explored the role of high-intensity ultrasound pre-treatment on the binding mechanisms of β-lactoglobulin (β-LG) to two common phenolic compounds, i.e., (-)-epigallocatechin-3-gallate (EGCG) and chlorogenic acid (CA) at neutral and acidic pH (pH 7.2 and 2.4). Tryptophan fluorescence revealed that compared to proteins sonicated at 20% and 50% amplitudes, 35%-amplitude ultrasound pre-treatment (ULG-35) strengthened the binding affinities of EGCG/CA to β-LG without altering the main interaction force. After phenolic addition, ULG-35 displayed a similar but a greater extent of protein secondary and tertiary structural changes than the native protein, ascribed to the ultrasound-driven hydrophobic stacking among interacted molecules. The dominant form of β-LG (dimer/monomer) played a crucial role in the conformational and interfacial properties of complexes, which can be explained by the distinct binding sites at different pH as unveiled by molecular docking. Combining pre-ultrasound with EGCG interaction notably increased the foaming and emulsifying properties of β-LG, providing a feasible way for the modification of bovine whey proteins. These results shed light on the understanding of protein-phenolic non-covalent binding under ultrasound and help to develop complex systems with desired functionality and delivery.

Physicochemical properties and digestion mechanism of starch-linoleic acid complex induced by multi-frequency power ultrasound

The effects of multi-frequencies (mono: 20 kHz, 40 kHz, 60 kHz; dual: 20/40 kHz, 40/60 kHz, 20/60 kHz, and tri: 20/40/60 kHz) on physicochemical properties and in vitro digestibility of arrowhead starch-linoleic acid (AS-LA) complexes were evaluated. The complexing index and FTIR analyses showed that sonication treatment might be helpful in the formation of AS-LA complexes in an ultrasound frequency-dependent manner. The SEM micrographs revealed that the various ultrasonication frequencies caused dense network structure in AS-LA complexes. The XRD showed a V-type crystalline structure with increased crystallinity. Compared with arrowhead starch, a decrease in rapidly digestible starch , and an increase in resistant starch contents of AS-LA under various ultrasound frequencies was due to arrowhead starch and linoleic acid molecular interactions, which inhibited the further binding abilities. As a non-thermal technology, ultrasound could be effectively employed to prepare starch-lipid complexes with significant potential in functional foods and drug delivery systems.

Effects of ultrasound-assisted sodium bisulfite pretreatment on the preparation of cholesterol-lowering peptide precursors from soybean protein

In order to take full advantage of the gastrointestinal digestive function, the effects of S-type ultrasound-assisted sodium bisulfite (UASB) pretreatment on the preparation of cholesterol-lowering peptide precursors derived from soybean protein were investigated and the structural characterizations of pretreated proteins were explored. UASB pretreatment with the operational mode of mono-frequency ultrasound at 28 kHz, ultrasonic power density of 200 W/L and ultrasonic time of 50 min exhibited the highest cholesterol-lowering activity (56.90%) of soybean protein hydrolysates (SPH) after simulated gastrointestinal digestion, which increased by 87.17% compared to the control. Under these conditions, the peptide content of SPH after simulated gastrointestinal digestion was not significantly different (p > 0.05) compared to the control. Further FTIR analysis showed that UASB pretreatment increased β-turn and β-sheet content and decreased α-helix and random coil content. The changes in the surface hydrophobicity and microstructures of soybean protein indicated that UASB pretreatment loosened soybean protein structure and exposed more hydrophobic groups. SDS-PAGE indicated that the restriction sites changed after UASB pretreatment. In conclusion, UASB pretreatment is an efficient method for the preparation of cholesterol-lowering peptide precursors.

Improving the Solubility and Digestibility of Potato Protein with an Online Ultrasound-Assisted PH Shifting Treatment at Medium Temperature

Ultrasonic (US) treatment was combined with pH shifting (pHS) and mild thermal (40 °C) (T40) treatment (US/T40/pHS) to improve the solubility of potato protein. The effects of the ultrasonication frequency, ultrasonication time, and incorporation sequence on the solubility of potato protein were investigated. The results showed that online US/T40/pHS treatment resulted in higher solubility of potato protein and enhanced free amino group release during in vitro digestion. The solubility of potato protein treated with online US/T40/pHS at a mono-frequency of 40 kHz for 15 min increased by 1.73 times compared with the control (p < 0.05). The digestibility rate increased by 16.0% and 30.8% during gastric and intestinal digestion, respectively, compared with the control (p < 0.05). It was demonstrated that online US/T40/pHS treatment significantly changed the secondary and tertiary structures of potato protein according to the results of circular dichroism and internal fluorescence. SDS-PAGE, particle size, and atomic force microscopy (AFM) showed that structural changes led to the formation of large soluble aggregates. The results suggested that the improvement in the solubility and digestibility of potato protein treated with online US/T40/pHS may be due to the formation of large soluble aggregates, which are more hydrophilic and sensitive to digestive enzymes.