Gum tragacanth-whey protein isolate cryo- and xerogels for entrapment and controlled release of silymarin

Silymarin (SM) is a flavonoid mixture that has been extensively studied owing to its proven anti-diabetic effects. In the present study SM-loaded gum tragacanth-whey protein isolate cryo- and xerogels were prepared and their physico-chemical, textural, mechanical and microstructural properties were analyzed by Fourier transform infrared spectroscopy (FTIR), texture analyzer, N2 adsorption-desorption technique and scanning electron microscopy. Moreover, swelling rate of gels and their SM release profile were investigated in acidic and basic conditions. The results indicated that cryogels were highly porous incorporating a network of interconnected open pores. In contrary, xerogels microstructure was quite compacted with internal closed and isolated pores. The addition of gum tragacanth markedly improved physic-chemical, textural, mechanical and morphological properties of the gels, while silymarin increased porosity and weakened the mechanical strength and morphological characteristics of the gel networks. SM loading also decreased the swelling ratio of gels. These macroscopic changes were linked to molecular interactions amongst gum tragacanth, whey protein isolate and silymarin as confirmed by FTIR spectra. The results of release measurements revealed that cryogels lost 80% of their silymarin content during exposure to acidic and basic condition, but xerogels strongly retained it within their matrix and underwent only a 30% loss. Both types of gels showed the highest release rate in phosphate buffer solution compared to acidic pH. Data fitting with release kinetics models indicated that the dissolution mechanism was controlled by Korsmeyer-Peppas model.