Physico—chemical modifications of liposome structures through interaction with surfactantsy‡

The liposome-surfactant interaction has been studied in this paper through the disrupting effect caused by surfactant molecules on large unilamellar vesicles prepared by reverse-phase evaporation. This process leads, in the end, to the rupture of such structures and to the solubilization of the phospholipidic components, via mixed surfactant-phospholipid micelle formation. This phenomenon is described by a three-stage model and characterized by two parameters: the highest surfactant/phospholipid ratio that can exist in a vesicle (R_{e sat}) and the lowest surfactant/phospholipid ratio required to keep the lipid and surfactant in the form of mixed micelles (R_{e sat}). These parameters have been determined by spectrophotometry and ³¹P NMR spectroscopy, obtaining results in a good agreement with both techniques. The surfactants tested have been: sodium dodecyl sulfate (SDS), sodium laurylether sulfate (SLES), N-hexadecyl-trimethylammonium bromide (HTAB), octylphenol series (8–20 EO) and alkylbetaines(C-10, C-12 and C-14). Different R_{e sat} and R_{e sol} values have been obtained for each of the surfactants. This has permitted a study of the solubilizing capacity versus the phospholipidic bilayer of the different surfactants as a function of their structure.     

Cold crystallization studies on PET/PEN blends as revealed by microhardness

The cold crystallization of amorphous films of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) blends, with different composition, prepared by co-precipitation from solution followed by melt-pressing for 2 min at 280°C and quenching in ice-water, was followed by measuring the microhardness, H, in real time as a function of crystallization temperature and time. An analytical model was derived, relating properties of the individual components to the blend microhardness based on an Avrami-type equation to account for the crystallization of the components upon heating. Fitting of the model to the experimental results revealed a two-step hardening process of the blends. The degree of transesterification of the blends, can be estimated with this model. Finally, a removal of the physical ageing, inducing a decrease in H of PET in the blend, was observed upon heating above its glass transition temperature. This revised version was published online in November 2006 with corrections to the Cover Date.     

RETENTION OF D-LIMONENE DURING FREEZE DRYING OF ORANGE JUICE

Retention of d-limonene during freeze drying of citrus juices from several sources was investigated as a multi-phase problem. Reconstituted to 25 and 10° Brix, commercial frozen concentrates show high retention (between 90 and lOO%), whereas fresh-squeezed juice shows a relatively low retention (about 30%), comparable to that found previously for synthetic emulsions. Retention data for pasteurized fresh juice after substantial agitation and for never-concentrated, commercial pasteurized juices show an intermediate value (between 60 and 70%). Presence and stability of cloud are shown to correlate closely with improved d-limonene retention in commercial frozen concentrates. On this basis, a simple model is developed which predicts the retention level for this type of juice in the asymptotic region. The results for the other types of juice studied are interpreted with the aid of microscopic determinations of oil droplet size and the model derived for synthetic emulsions.     

Effect of long‐chain inulin on the texture profile and survival of Lactobacillus paracasei ssp. paracasei in set yoghurts during refrigerated storage

The effects of adding inulin at 20 g/L as a fat replacer and probiotic bacteria on the physicochemical and textural characteristics of yoghurt were studied. The ability of long‐chain inulin to improve the probiotic (Lactobacillus paracasei ssp. paracasei) bacteria viability in yoghurt was investigated. The addition of inulin made the texture (firmness, cohesiveness, adhesiveness and gumminess) of skimmed yoghurt similar to that of whole yoghurt, demonstrating the role of inulin as a fat replacer. However inulin increased syneresis and did not influence the viability of probiotic bacteria in the yoghurts. The addition of probiotic bacteria in yoghurts improved syneresis and increased firmness and gumminess.     

Experimental evaluation of fatigue crack initiation from corroded hemispherical notches in aerospace structural materials

A test program was developed and executed to evaluate the influence of corroded hemispherical notches on the fatigue crack initiation process in aluminium 7075‐T7351, 4340 steel and D6AC steel. Surface enhancements such as shot peening and laser shock peening were also incorporated as part of the test effort with the intent of assessing any improvements in fatigue performance. The aluminium specimens exhibited a relative insensitivity to the surface enhancements for crack initiation in pits ranging from 0.3 to 2.0 mm, and localized yielding was only a factor for smaller pits operated at an elevated load ratio. Residual stresses created by the surface enhancements as well as localized yielding improved the crack initiation behavior from the base of the pits for both the 4340 and D6AC steel specimens. This behaviour was evident at high and low load ratios. In particular, laser shock peening induced residual stresses produced a significant increase in the crack initiation stress even when localized yielding was not a factor.