Susana Aucejo

Water effect on the morphology of EVOH copolymers

The effect of water on the morphology of four ethylene vinyl alcohol copolymers (EVOH) with different ethylene contents was studied by differential scanning calorimetry (DSC). EVOH film samples equilibrated in controlled atmospheres at different relative humidities (RH) and 23°C were analyzed. Under dry conditions, the glass transition temperature (Tg) was unaffected by copolymer ethylene content. As RH increases, Tg decreases. It seems that the presence of water within the polymer matrix results in plasticization of the polymer. Tg varies from around 50°C (dry) to below room temperature. EVOH copolymers are glassy polymers when dry and rubbery polymers at high RHs. Fox and Gordon–Taylors equations well describe Tg depletion at low water uptake, although severe water gain results in a considerable Tg decrease, which is not predicted by these theories. Melting temperature, Tm, and enthalpy, ΔHm, were also analyzed. When dry, Tm decreases as ethylene content increases. No significant water effect was found on either Tm or ΔHm. Hence, crystallinity seems to be unaffected by water presence.

Solubility of alcohols in ethylene‐vinyl alcohol copolymers by inverse gas chromatography

Sorption isotherms of alcohols in EVOH copolymers were determined by inverse gas chromatography below and above the glass transition temperature. The sorbates studied were : methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol, and t-butanol. From the sorption isotherms, Henrys law solubility coefficients (S) were evaluated and correlated to size, condensability, and OH position in the molecule as well as on temperature. Molecular dimension was an important factor, affecting the solubility via two contrary effects : molecular size and condensability. When comparing alcohols of the same size, primary alcohols were sorbed more than secondary alcohols and these more than tertiary alcohols at every temperature in the study. At low temperatures, the larger the size the greater the solubility, contrary to what was observed at high temperatures. Temperature effect on solubility was also tested applying Vant Hoffs equation. Since S behaved differently below and above T g for every sorbate two values of the enthalpy of solution were obtained, positive above T g and negative below T g .

Characterisation and antimicrobial activity of active polypropylene films containing oregano essential oil and Allium extract to be used in packaging for meat products

ABSTRACT Cooked ham is more prone to spoilage than other meat products, making preservation a key step in its commercialisation. One of the most promising preservation strategies is the use of active packaging. Oregano essential oil (OEO) and Proallium® (an Allium extract) have previously been shown to be useful in polylactic acid (PLA)-active films for ready-to-eat salads. The present work aims to study the suitability of polypropylene (PP) films containing OEO and Proallium® in the preservation of cooked ham. Concerning the technological features of the studied material, no significant changes in the mechanical or optical properties of PP films containing the active substances were recorded in comparison to the PP film without extracts. However, films containing both active substances were more flexible than the control film and less strong, highlighting the plasticisation effect of the natural extracts. Moreover, physical properties changed when active substances were added to the film. Incorporation of 4% Proallium® affected the transparency of the film to a higher extent compared to 8% OEO, undergoing decreases in transparency of 40% and 45%, respectively. Moreover, only the film containing the highest amount of OEO (8%) significantly decreased the thickness. Both active substances showed antibacterial properties; however, Proallium®-active films seemed to be more effective against Brochothrix thermosphacta than PP films containing OEO, with all percentages of Proallium® killing the bacterial population present in the ham after 60 days. In addition, materials containing the lowest Proallium® content exhibited higher acceptability by consumers in the sensory analyses with 63–100% willing to purchase, better even than the control package (56–89%). In fact, 2% of Proallium® obtained the best results in the odour study performed by the panellists.