Influence of solid lipid nanoparticle/xanthan gum coatings on compositional and enzymatic changes in guava (Psidium guajava L.) during ripening

The objective of this work was to evaluate the effect of solid lipid nanoparticle/xanthan gum (SLN/XG) coatings on the changes in ascorbic acid (AA) and pectin methylesterase activity (PME) during the ripening of guava fruit. Mature green ‘Media China’ guavas (116 °hue angle) were chosen for this study. SLN were obtained by the hot homogenization method and then blended with XG to prepare film-forming dispersions. The SLN concentrations used in the coatings were 65 and 75 g L^-1, and they were compared to control samples. The film-forming systems were applied by dipping the guavas and then storing them at 10°C and 85% relative humidity (RH) for 32 days. The SLN film-forming systems were stable when particle size was 276 nm. The polydispersity index was below 0.3 and the zeta potential (ζ) was >|25| mV. The best results were obtained with the SLN concentration of 65 g L-1 since the guavas treated with it showed the lowest range of AA loss (34%). Additionally, at this concentration, guava cell wall hydrolysis, as monitored by PME activity, was delayed, showing a maximum activity peak at day 32, compared to the control samples, which presented the maximum on day 18. However, the higher SLN content (75 g L^-1) produced physiological damage in the fruit: AA loss was 40%, and the maximum activity peak for PME occurred on day 22, though the green color of those samples remained unchanged during storage. According to these results, SLN/XG coatings with 65 g L-1 of SLN act as a gas exchange barrier that helps extend the shelf life of guavas to almost 5 weeks.