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The formation of beta-lactoglobulin (BLG)/sodium polystyrene sulfonate (PSS) complexes decelerates the change in the surface properties of the mixed solutions with the surface age and increases the steady-state dilational surface elasticity in a narrow PSS concentration range. At the same time, the changes in the surface properties are accelerated in the dispersions of BLG fibrils with and without PSS due to the influence of small peptides coexisting with fibrils. A decrease in the peptide concentration as a result of the dispersion purification leads to slower changes in the surface properties at low PSS concentrations. The increase in the polyelectrolyte concentration results in an increase in the steady-state surface elasticity due to the fibril/PSS complex formation and in very slow changes in the surface properties if the polyelectrolyte exceeds a certain critical value. The latter effect is a consequence of the formation of large aggregates and of an increase in the electrostatic adsorption barrier. The consecutive adsorption of BLG fibrils and PSS leads to the formation of regular multilayers at the liquid–gas interface. The multilayer properties change noticeably with an increase in the number of layers from four to six in agreement with previous results on the multilayers of PSS with an oppositely charged synthetic polyelectrolyte, presumably due to the heterogeneity of the first PSS layer. The dynamic elasticity of the multilayers approaches 250 mN/m, indicating that they can effectively stabilize foams and emulsions.

The adsorption layers of cupin-1.1, one of the two evolutionary conserved β-barrel domains of vicilin─the garden pea storage globulin─at the liquid-gas interface were studied by a few methods of the surface chemistry. The kinetic dependencies of the surface pressure of cupin-1.1 solutions in 8 M urea overlap in a single master curve if the surface pressure is plotted as a function of the normalized time. The analysis of the master curve allows separation of a few adsorption steps including the induction period, the regions of the diffusion-controlled and barrier-controlled adsorption kinetics, and a plateau region of slow adsorption. Another master curve can be constructed from the dependencies of the dynamic surface elasticity on surface pressure. This curve has some similarities with the corresponding results for recently studied cupin-1.1 spread layers on the surface of urea solutions and gliadin adsorption layers. There are also important distinctions with the master curve for adsorption layers of cupin-1.1 in the system without denaturants. This difference can be connected with the formation of larger and more rigid aggregates in pure water than the aggregates in urea solutions.

The dynamic surface properties of native κ-casein solutions and aqueous dispersions of its fibrils differ significantly from the corresponding properties of the systems with globular proteins. The dependence of the dynamic surface elasticity of κ-casein solutions on surface pressure has a local maximum, indicating partial displacement of macromolecules from the proximal region of the surface layer to the distal one. This dependence becomes monotonic for fibril dispersions, similar to the results for dispersions of globular protein fibrils, but unlike the latter case, the surface elasticity close to the steady state reaches values that are approximately four times higher than the data for native protein solutions at the same concentrations.

The dynamic surface properties of aqueous dispersions of α-lactalbumin (ALA) amyloid fibrils differ noticeably from the properties of the fibril dispersions of other globular proteins. As a result, the protocol of the application of ALA fibrils to form stable foams and emulsions has to be deviate from that of other protein fibrils. Unlike the fibrils of β-lactoglobulin and lysozyme, ALA fibrils can be easily purified from hydrolyzed peptides and native protein molecules. The application of the oscillating barrier method shows that the dynamic surface elasticity of ALA fibril dispersions exceeds the surface elasticity of native protein solutions at pH 2. ALA fibrils proved to be stable at this pH, but the stability breaks at higher pH levels when the fibrils start to release small peptides of high surface activity. As a result, the dynamic surface properties of ALA coincide with those of native protein solutions. The ionic strength strongly influences the adsorption kinetics of both fibril dispersions and native protein solutions but have almost no impact on the structure of the adsorption layers.

The properties of adsorbed layers of protein fibrils differ significantly from the properties of fibril spread layers on an aqueous subphase. If the dependencies of the dynamic surface elasticity on surface pressure of Lysozyme (LYS) and β-lactoglobulin (BLG) aqueous dispersions proved to be close to the results for native protein solutions, LYS and BLG spread layers on the surface of 0.1 M NaCl solution exhibited the surface elasticity more than two times higher than the values for protein solutions with the same NaCl concentatration, presumably due to lower surface concentrations of hydrolysed peptides in the latter case. The properties of fibril spread and adsorbed layers and also their morphology, unlike the surface properties of protein solutions, depend noticeably on the ionic strength of the aqueous bulk phase. This dependence is stronger in case of LYS layers, which are also more prone to the formation of macroscopic and mesoscopic surface aggregates as compared with BLG layers., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The spread layers of lysozyme (LYS) microgel particles were studied by surface dilational rheology, infrared reflection-absorption spectra, Brewster angle microscopy, atomic force microscopy, and scanning electron microscopy. It is shown that the properties of LYS microgel layers differ significantly from those of ß-lactoglobulin (BLG) microgel layers. In the latter case, the spread protein layer is mainly a monolayer, and the interactions between particles lead to the increase in the dynamic surface elasticity by up to 140 mN/m. In contrast, the dynamic elasticity of the LYS microgel layer does not exceed the values for pure protein layers. The compression isotherms also do not exhibit specific features of the layer collapse that are characteristic for the layers of BLG aggregates. LYS aggregates form trough three-dimensional clusters directly during the spreading process, and protein spherulites do not spread further along the interface. As a result, the liquid surface contains large, almost empty regions and some patches of high local concentration of the microgel particles.

Experimental data for tridecyl dimethyl phosphine oxide (C 13 DMPO) adsorption layers at the water/air interface, including equilibrium surface tension and surface dilational viscoelasticity, are measured by bubble and drop profile analysis tensiometry at different solution concentrations and surface area oscillation frequencies. The results are used to assess the applicability of a multistate model with more than two possible adsorption states. For the experiments with single drops, the depletion of surfactant molecules due to adsorption at the drop surface is taken into account. For the assessment, the same set of model parameters is used for the description of all obtained experimental dependencies. The agreement between the proposed model and the experimental data shows that for the nonionic surfactant C 13 DMPO, the description of the adsorption layer behavior by three adsorption states is superior to that with only two adsorption states.

American Foulbrood (AFB) is a contagious and severe brood disease of honey bees caused by the spore-forming bacterium Paenibacillus larvae . The identification of honey bee colonies infected by P. larvae is crucial for the effective control of AFB. We studied the possibility of identifying the infection levels by P. larvae in honey bee colonies through the examination of powdered sugar samples collected in the hives. The powdered sugar was dusted on the top bars of honeycombs and collected from a sheet paper placed at the bottom of the hive. Three groups of honey bee colonies were examined: Group A1 - colonies with clinical symptoms of AFB ( n = 11); Group A2 - asymptomatic colonies located in apiaries with colonies showing symptoms of AFB ( n = 59); Group B - asymptomatic colonies located in apiaries without cases of the disease ( n = 49). The results showed that there was a significant difference in spore counting between Groups and that the spore load in sugar samples was always consistent with the clinical conditions of the colonies and with their belonging to AFB-affected apiaries or not. Based on the obtained results the cultural examination of powdered sugar samples collected from hives could be an effective tool for the quantitative non-destructive assessment of P. larvae infections in honey bee colonies., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Bassi, Galletti, Carpana, Palminteri, Bosi, Loglio and Carra.)