Lecithin microemulsion gels: A NMR study of molecular mobility based on line widths

Microemulsion gels obtained from solutions of lecithin in organic solvents (in particular isooctane) in the presence of a small amount of water are studied by NMR line width measurements. The ‘H, 13C, and slP resonances of the lecithin molecule are investigated as a function of added water w, (w, = [HzO]/ [LEC]). The line width of the 31P resonance increases sharply at the w, value that induces the maximal viscosity (w, = 3), and similar to the viscosity, the 1H resonance of the -N+(CH& polar head, as well as the l3C resonances of the -CH2CH2N+ group, shows a maximum in their line width (i.e. a minimal molecular mobility) around w, = 3. Conversely, at this w, the mobility of water does not appear to be particularly restricted; actually an effect is noticed only by the addition of the first molecule, which induces a significant increase of mobility both in the polar head of the phospholipid moiety and in the water itself. More in general, the molecular details obtained by NMR data are compared with the data obtained by other chemical physical techniques that are only sensitive to the macroscopic molecular structure. The bulk of data indicates that (i) the highly flexible, transient network constituting the gel consists of entangled polymer rodlike lecithin reverse micelles, (ii) such a network structure is formed continuously upon addition of water rather than in an all-or-nothing transition, (iii) solvent and water mobility do not correlate with macroscopic gel viscosity, whereas there is a clear correlation between viscosity and stiffening of the phosphorus atom, (iv) during water addition and gel formation significant change in mobility of specific lecithin groups occur, and (v) in particular, the first added water molecule induces a conformational change of the lecithin polar head

Gelatin edible coatings with mint essential oil (mentha arvensis): film characterization and antifungal properties

In this work, mint essential oil (MEO) was added into gelatin films and antifungal activity was evaluated. Five concentrations of MEO (0, 0.06, 0.13, 0.25, 0.38, 0.50% (g/g gelatin)) were incorporated into gelatin solutions. The films were prepared by casting and characterized for their barrier properties, mechanical resistance, morphology, thermal and antifungal activity. The addition of oil into the solution slightly improved water vapor barrier, increased thickness and opacity, decreased transparency and modified thermal and mechanical properties of films. With addition of oil above 0.38%, the films were effective against the growth of Botrytis cinerea and Rhizopus stolonifer, indicating an inhibitory activity. Thus, gelatin-based edible films incorporated with MEO showed to be an effective way to inhibit microbial growth on the film surface5694045405617.289/2009-8FAPESC - Fundação de Amparo à Pesquisa e Inovação do Estado de Santa Catarin