Invertase stability in alginate beads: Effect of trehalose and chitosan inclusion and of drying methods

The purpose of present work was to analyze the effect of trehalose and chitosan on invertase activity preservation in wet and dried alginate beads, by taking advantage of the well known trehalose protective effect of labile compounds during drying and chitosan improvement on mechanical properties of alginate beads. The beads were subjected to different drying methods (freeze-drying, vacuum and forced air circulation drying) and to a mild thermal treatment (50 °C). The size and morphology of the beads were analyzed by optical microscopy and by scanning electron microscopy. The size of the beads was affected by drying at an extent which depended more on the drying method than on the beads composition. Freeze-drying allowed better maintenance of the diameter and circularity of the beads, which showed smoother surface and smaller pores than those generated by vacuum or air drying. The inclusion of chitosan in the gelation media improved enzymatic activity recovery after beads generation; this fact was attributed to a higher mechanical resistance provided by the interaction between alginate and chitosan. There was no effect of trehalose inclusion during this step. Interactions between alginate and chitosan, as well as the effect of trehalose presence were manifested in the FT-IR spectra, and on the increase of alginate decomposition temperatures as detected by DSC. In the alginate beads the enzymatic activity was not enough protected from the damage caused by drying or by heat treatment. The thermal stability of invertase in the dried beads was independent on the type of drying employed, being mainly affected by beads composition. Although trehalose was not effective to prevent enzyme functionality damage during beads generation, it was essential for achieving adequate invertase protection during freezing, drying (freeze-, vacuum or air drying) and thermal treatment.

► We study invertase stability in alginate beads with trehalose and chitosan addition. ► Beads were subjected to different drying methods and to thermal treatment. ► The size of the beads depended more on the drying method than on formulation. ► Chitosan improved enzymatic activity recovery after beads generation. ► Trehalose was essential for invertase stability along drying and thermal treatment.