Effect of storage time on the mechanical and microstructural properties of bigels based on xanthan gum and castor oil

Abstract

As biphasic systems bigels are formed by hydrogels and organogels. Given their characteristics, they have been studied in food, pharmaceutical and cosmetic applications for bioactives delivery. The rheological characteristics and amount used of the individual structured systems influence the final properties; thus, the objective of this work was to evaluate the effect of the proportion of castor oil organogel, the concentration of organogelator, and the storage time in the mechanical and microstructural properties of bigeles. Bigels were prepared from structured castor oil organogels with monoacylglycerides at concentrations of 6% (MOG) and 6.5% (HOG) wt/wt, and hydrogels with 2% wt/wt xanthan gum (HG) at three organogel/hydrogel ratios 15 of 85, 30 of 70, and 45 of 55. Bigels were characterized by optical microscopy with polarized light filter, centrifugal stability, texture, and rheology for 60 days. The increase in the proportion of organogel favors the mechanical response (k, G₀, and firmness) of bigels. The high viscosity of castor oil slows down the structuring of organogel droplets, showing an improvement in its mechanical properties after 15 days of its preparation. The increase in the organogelator concentration is significant in the bigels with 30% and 45% proportions of organogel in the rheological tests. By using HOG in the formation of bigels, higher values for G₀ and k were obtained, as well as higher centrifugal stability compared with bigels formed from MOG. The rheological and microstructural behavior of bigels can be modified according to their application by varying the proportions of organogel/hydrogel and the concentration of the organogelator.