Materials nanocomposits a partir de whiskers de cel•lulosa i matriu polimèrica de cautxú

De acuerdo con los objetivos generales del proyecto y plan de trabajo previsto, para esta anualidad, se obtuvieron fibras y microfibras de celulosa a partir de dos fuentes: celulosa vegetal de pino y eucalipto y celulosa bacterial. Las microfibrillas han sido utilizadas como material de refuerzo para la fabricación de materiales compuestos a partir de caucho natural, policaprolactona y polivinil alcohol. Las muestras se fabricaron mediante la técnica de "casting" en medio acuoso y temperatura ambiente. Las muestras fueron caracterizados en sus propiedades mecánicas, físicas y térmicas. Se observó que, en general, la adición de las microfibrillas de celulosa en las matrices poliméricas provoca una mejora sustancial en las propiedades mecánicas del material en comparación con el polímero sin reforzar. Los resultados pueden resumirse de la siguiente manera: 1.Fabricación de materiales compuestos a base de caucho natural y fibras de celulosa. Se obtuvieron fibras y nanofibras de celulosa que fueron modificadas químicamente y usadas como refuerzo en matriz de caucho. Los resultados mostraron mejora de propiedades mecánicas del material, principalmente en los materiales compuestos reforzados con nanofibras. 2. Obtención de whiskers de celulosa y su utilización como material de refuerzo en una matriz de policaprolactona. Se obtuvieron whiskers de celulosa a partir de pasta blanqueada. La adición en una matriz de policaprolactona produjo materiales compuestos con propiedades mecánicas superiores a la matriz, con buena dispersión de los whiskers. 3. Obtención de fibras de celulosa bacterial y nanofibras de celulosa, aislamiento y utilización sobre una matriz de polivinil alcohol. Se obtuvo celulosa bacterial a partir de la bacteria Gluconacetobacter xylinum. Además se fabricaron nanofibras de celulosa a partir eucalipto blanqueado. La celulosa bacterial como material de refuerzo no produjo importantes mejoras en las propiedades mecánicas de la matriz; en cambio se observaron mejoras destacables con la nanofibra como refuerzo.

Use of antimicrobial biodegradable packaging to control Listeria monocytogenes during storage of cooked ham

The antimicrobial effect against L. monocytogenes of biodegradable films (alginate, zein and polyvinyl alcohol) containing enterocins was investigated. Survival of the pathogen was studied by means of challenge tests performed at 6 °C during 8 and 29 days, for air-packed and vacuum-packed sliced cooked ham, respectively. Air packaging was tested with two concentrations of enterocins (200 and 2000 AU/cm2). Control air-packed cooked ham showed an increase of L. monocytogenes from 104 to 107 CFU/g after 8 days. By contrast, packaging with antimicrobial films effectively slowed down the pathogen's growth, leading to final counts lower than in control lots. Air-packaging with alginate films containing 2000 AU/cm2 of enterocins effectively controlled L. monocytogenes for 8 days. An increase of only 1 log unit was observed in zein and polyvinyl alcohol lots at the same enterocin concentration. Vacuum packaging with films containing enterocins (2000 AU/cm2) also delayed the growth of the pathogen. No increase from inoculated levels was observed during 15 days in antimicrobial alginate films. After 29 days of storage, the lowest counts were obtained in samples packed with zein and alginate films containing enterocins, as well as with zein control films. The most effective treatment for controlling L. monocytogenes during 6 °C storage was vacuum-packaging of sliced cooked ham with alginate films containing 2000 AU/cm2 of enterocins. From the results obtained it can concluded that antimicrobial packaging can improve the safety of sliced cooked ham by delaying and reducing the growth of L. monocytogenes.

Physical performance of biodegradable films intended for antimicrobial food packaging

Antimicrobial films were prepared by including enterocins to alginate, polyvinyl alcohol (PVOH), and zein films. The physical performance of the films was assessed by measuring color, microstructure (SEM), water vapor permeability (WVP), and tensile properties. All studied biopolymers showed poor WVP and limited tensile properties. PVOH showed the best performance exhibiting the lowest WVP values, higher tensile properties, and flexibility among studied biopolymers. SEM of antimicrobial films showed increased presence of voids and pores as a consequence of enterocin addition. However, changes in microstructure did not disturb WVP of films. Moreover, enterocin-containing films showed slight improvement compared to control films. Addition of enterocins to PVOH films had a plasticizing effect, by reducing its tensile strength and increasing the strain at break. The presence of enterocins had an important effect on tensile properties of zein films by significantly reducing its brittleness. Addition of enterocins, thus, proved not to disturb the physical performance of studied biopolymers. Development of new antimicrobial biodegradable packaging materials may contribute to improving food safety while reducing environmental impact derived from packaging waste.