Dynamics and energetics of bovine lactoferrin and phenylmethane dyes interaction followed by surface plasmon resonance.

Although toxic and dangerous, Phenylmethane (PhM) dyes have a variety of medicinal functions. To optimize the use of these dyes, it is essential to understand their interaction mechanism with proteins. Through surface plasmon resonance, we investigated the kinetics and thermodynamics of interaction between bovine lactoferrin (BLF) and PhM dyes at pH 7.4, which allowed elucidate the effect of the dyes' functional groups on the binding process. Negative ΔG° revealed that at thermodynamic equilibrium the formed [BLF-PhM]° complex was more stable than the free BLF and PhM molecules. The increase in the number of methyl groups in the PhM structure led to an increase in the rates of association (ka) and dissociation (kd) and the binding constant (Kb). A similar effect was observed when comparing methyl violet B (MVB) and methyl violet 6 B (MV6B), in which the charged MV6B structure promoted an increase in the ka, kd, and Kb values. By contrast, an increase in the number of phenyl groups (2-3 rings) led to a decrease in the Kb values. The [BLF-PhM]° formation was entropically driven, indicating that hydrophobic interactions are critical for stabilizing these complexes These results are beneficial for understanding the molecular dynamics of protein-dye interactions.

The kinetics of formation of resveratrol-ß-cyclodextrin-NH2 and resveratrol analog-ß-cyclodextrin-NH2 supramolecular complexes.

The determination of the kinetics of inclusion processes is significant for the application of inclusion complexes as carriers for bioactive molecules. We determined the kinetic parameters of inclusion between modified ß-cyclodextrin (ß-CD-NH2) and the polyphenols resveratrol (RES) and its structural analog (RESAn1), using the real-time analysis of surface plasmon resonance. The association and dissociation rate constants (ka and kd) showed that RESAn1 inclusion and its dissociation from ß-CD-NH2 were faster than a similar process for RES ( [Formula: see text]  = 3.10∙104 ± 0.14 M-1s-1, [Formula: see text] =1.87∙103 ± 0.11 M-1s-1; [Formula: see text] =0.39 ± 0.02 s-1, [Formula: see text] =0.30 ± 0.02 s-1, at 25 °C). The activated complex formation was also affected by the structural differences between the polyphenols, as showed by the activation energies of the association step ( [Formula: see text] 14.81 ± 0.64 kJ∙mol-1, [Formula: see text] -15.01 ± 0.75 to 82.35 ± 4.47 kJ∙mol-1). These effects of polyphenol structural differences are due to the desolvation process of interacting molecules. These results elucidate the role of small group to the dynamics of the molecular inclusion of ß-CD.

Characterization of starch-based bioplastics from jackfruit seed plasticized with glycerol.

Biodegradable films based on starches from different botanical sources exhibited physicochemical and functional properties which were related with the starch characteristics. However, had inadequate mechanical properties and were hard and brittle. In this research, jackfruit seed starch plasticized with glycerol were developed and characterized. The starch and glycerol concentrations ranged from 2 to 6% w/w and 20 to 60 g/100 g starch, respectively. Bioplastics were obtained by the casting method and characterized in terms of color, mechanical properties, solubility, water vapor permeability (WVP), morphology and free energy of the hydrophobic interaction. Electronic micrographics showed the presence of some intact starch granules. The bioplastics were hydrophilic and those of 6% starch and 40% glycerol were the most hydrophilic ([Formula: see text] = 41.35 mJ m-1). The solubility of the films presented a direct relationship with the starch concentration ranging from 16.42 to 23.26%. Increased opacity and color difference were observed with increasing starch concentration. The WVP ranged from 1.374 × 10-3 to 3.07 × 10-4 g m/day m2 which was positively related with the concentration of starch and glycerol. Tensile strength, percent elongation and Young's Modulus indicated that the jackfruit starch and glycerol provided a film with good mechanical properties. The results replaced that jackfruit starch can be used to develop films, with low opacity, moderate WVP and relatively high mechanical stability, by using glycerol in the gelatinized starch dispersions.

Work of adhesion of dairy products on stainless steel surface.

The adhesion of the solids presents in food can difficult the process of surface cleaning and promotes the bacterial adhesion process and can trigger health problems. In our study, we used UHT whole milk, chocolate based milk and infant formula to evaluate the adhesion of Enterobacter sakazakii on stainless steel coupons, and we determine the work of adhesion by measuring the contact angle as well as measured the interfacial tension of the samples. In addition we evaluated the hydrophobicity of stainless steel after pre-conditioning with milk samples mentioned. E. sakazakii was able to adhere to stainless steel in large numbers in the presence of dairy products. The chocolate based milk obtained the lower contact angle with stainless steel surface, higher interfacial tension and consequently higher adhesion work. It was verified a tendency of decreasing the interfacial tension as a function of the increasing of protein content. The preconditioning of the stainless steel coupons with milk samples changed the hydrophobic characteristics of the surfaces and became them hydrophilic. Therefore, variations in the composition of the milk products affect parameters important that can influence the procedure of hygiene in surface used in food industry.