Structural changes by dehydration of cherry tomatoes (Lycopersicon esculentum) packed in bags based on thermoplastic corn starch/talc nanoparticles composites

LÓPEZ, OLIVIA; CASTILLO, LUCIANA E; GARCÍA, MARIA ALEJANDRA; BARBOSA, SILVIA ELENA; VILLAR, MARCELO

Praga

Congreso; 18th International Microscopy Congress (IMC 2014); 2014

Universidad de Praga

Fruits are dehydrated to enhance storage stability, minimize packaging requirement and reduce transport weight [1]. The aim of this work is to evaluate the feasibility of using packages based on thermoplastic starch/talc nanocomposites to dehydrate cherry tomatoes (Lycopersicon esculentum), evaluating their cells structural changes. Tomatoes were packed within bags ofthermoplastic corn starch (TPS) with 0 and 5% w/w talc. Tomatoes were sorted for uniform size, color, and without physical damage. To decrease fruits initial microbial charge, half of them were dipped in chlorinated water (250 ppm Cl2) before being packaged. Packaged samples were stored (50% RH-25ºC) for 2 months. Samples were removed from bags, weighted and conditioned. Cubic samples were immersed in glutaraldehyde to preserve their cellular structure. Samples were rinsed with phosphate buffer before post-fixation step by immersing them in osmium tetroxide; then they were washed with bidistilled water, dehydrated usingacetone, and dried until the critical point. Finally, samples were examined in a JEOL JSM-35 CF electron microscope and mean cell diameters (Dc) were determined by considering around 100 cells using AnalySis Pro 3.0 software program. Samples suffered alterations in their color and volume due to natural dehydration (Fig. 1). Macrostructural changes were induced by microstructural modifications. Fresh tomatoes tissue has a well-organized structure of rounded cells and intercellular spaces (Fig. 2a). Dehydration caused reduction in tomatoes volume due to large moisture gradients that induced microstructural stresses, collapsing capillaries and decreasing intercellular contact [2]. Both visual observation and SEM demonstrated the lack of microbial activity in all dehydrated samples. Lost weight for tomatoes packed in TPS and TPS-talc bags was 92 and 69%, respectively. Dc for samples within TPS was lower than thosecorresponding to tomatoes packed in TPS-talc bags (Fig. 2b and 2c). Lost weight is in good agreement with Dc and it is attributed to the higher capacity to retain water of TPS-talc bags compared to TPS ones. Talc enhances films barrier properties due to it hinders vapor diffusion.Chlorine treatment caused a higher damage in cell tissues (Fig. 2c and 2d). Despite chlorine affected tomatoes structure, lost weight was similar than those corresponding to unchlorinated ones. Dc corresponding to chlorinated samples could not be determined due to tissue destruction and cells collapse. In conclusion, bags based on TPS/talc nanocomposites were suitable to dehydrate naturally tomatoes cherries without affecting fruits microbial quality.