A stepwise micro-DSC study of Small, Large and Giant Unilamellar Vesicles prepared as pure and mixed systems of DMPC, DPPC, DSPC and DOPC was performed, achieving the preparation of final model membranes whose phospholipid compositions represent the 75% in terms of the phospholipids tails and the 50% headgroups of the Insulin Secretory Granules (vesicles located in the pancreatic Langerhans β-cells and which are responsible for insulin and amylin storage and secretion in response to nutrient intake). Moreover, the effect of Free Fatty Acids, whose levels are recurrently altered in diabetic and/or obese subjects, on the thermodynamic stability of the final membranes was eventually investigated. The results allowed to discriminate each single thermodynamic contribution among the main factors that dictate the overall thermodynamic stability of these complex unilamellar systems evidencing mainly entropic effects hierarchically summarized as phospholipid unsaturations > phospholipid tail length > membrane curvature. The effect of the Free Fatty Acids highlighted a strong stabilizing effect on the membranes as well as more pronounced phase segregations in the case of saturated acids (palmitic and stearic), whereas the opposite effect was observed in the case of an unsaturated one (oleic).
Thermal treatments are widely applied to gluten-free (GF) flours to change their functionality. Despite the interest in using pulses in GF formulations, the effects of thermal treatment at the molecular level and their relationship with dough rheology have not been fully addressed. Raw and heat-treated red lentils were tested for starch and protein features. Interactions with water were assessed by thermogravimetric analysis and water-holding capacity. Finally, mixing properties were investigated. The thermal treatment of red lentils induced a structural modification of both starch and proteins. In the case of starch, such changes consequently affected the kinetics of gelatinization. Flour treatment increased the temperature required for gelatinization, and led to an increased viscosity during both gelatinization and retrogradation. Regarding proteins, heat treatment promoted the formation of aggregates, mainly stabilized by hydrophobic interactions between (partially) unfolded proteins. Overall, the structural modifications of starch and proteins enhanced the hydration properties of the dough, resulting in increased consistency during mixing.
PEGylated proteins are widely used for therapeutic applications, therefore a fundamental understanding of the conjugates' structure and their behaviour in solution is essential to promote new developments in this field. In the present work, myoglobin-poly(ethylene glycol) conjugates were synthesized and studied by using differential scanning calorimetry and UV-visible spectroscopy to obtain information on the bioconjugates' thermodynamic stability, also focusing on the PEG's role on the solvent-protein surface interaction. The overall results of this study indicated a thermal destabilization of the proteins that follows the extent of the bioconjugation without, however, compromising the native structure which remains functional. Moreover, the myoglobin PEGylation prevented the post-denaturation aggregation phenomena and enhanced the protein thermal reversibility. The thermodynamic interpretation of the data indicated that the bioconjugation influences the solvent-exposed protein surface difference between native and denatured state, contributing to the interpretation of the overall protein modification and functionality.
The influence of free fatty acids
(FFAs) on the nisin–membrane
interaction was investigated through micro-DSC and fluorescence spectroscopy.
A simple but informative model membrane was prepared (5.7 DMPC:3.8
DPPS:0.5 DOPC molar ratio) by considering the presence of different
phospholipid headgroups in charge and size and different phospholipid
tails in length and unsaturation level, allowing the discrimination
of the combined interaction of nisin and FFAs with the single phospholipid
constituents. The effects of six FFAs on membrane stability were evaluated,
namely two saturated FFAs (palmitic acid and stearic acid), two monounsaturated
FFAs (
cis
-unsaturated oleic acid and
trans
-unsaturated elaidic acid) and two
cis
-polyunsaturated
FFAs (ω-6 linoleic acid and ω-3 docosahexaenoic acid).
The results permitted assessment of a thermodynamic picture of such
interactions which indicates that the peptide–membrane interaction
does not overlook the presence of FFAs within the lipid bilayer since
both FFAs and nisin are able to selectively promote thermodynamic
phase separations as well as a general lipid reorganization within
the host membrane. Furthermore, the magnitude of the effects may be
different depending on the FFA chemical structure as well as the membrane
lipid composition.
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