Freezing and drying of pink grapefruit-lycopene encapsulated in Ca(II)-alginate beads containing galactomannans

Abstract

Lycopene extracted from pink grapefruit was encapsulated on Ca(II)-alginate beads with the addition of trehalose and galactomannans to improve its stability against freezing and drying. Three galactomannans of different physicochemical properties were studied since their inclusion affects both loading efficiency and release of lycopene in wet beads; however, there is no information about their performance during freezing and dehydration operations. The remaining lycopene and its stability towards isomerization were analyzed in beads subjected to continuous freezing, freezing/thawing cycles and vacuum- and freeze-drying. Isothermal crystallization studies were conducted by LF-NMR and related to beads formulation and lycopene stability. In the absence of excipients, lycopene was severely affected by all the treatments, retaining less than 20% of the original content. Alginate beads containing trehalose with guar gum protected more than 80% of the lycopene regardless of the employed freezing or drying methods. These beads concomitantly showed higher solid fraction than the other two galactomannans-containing systems, displaying guar gum ability to associate water. On the other hand, the addition of vinal gum affected lycopene stability (between 40 and 60% were recovered after treatments), even compromising the positive effect of a well-established cryoprotectant as trehalose. Thus, the addition of secondary excipients should be carefully conducted. The differences among galactomannans could be related to the substitution degree of the polymer chains, affecting the overall systems interactions. These results can contribute to excipients selection for the encapsulation of labile biomolecules in Ca(II)-alginate beads subjected to freezing and drying.