Nanoparticulation of enzymatically cross-linked whey proteins to encapsulate caffeine via microemulsification/heat gelation procedure

A co-surfactant free microemulsion was formulated with sunflower oil, span 80 and whey protein solution and used as nanoreactor to generate caffeine-enveloping capsules through heat gelation of protein. Transglutaminase-induced cross-linking of proteins prior to microemulsification decreased the mean diameter from 478 to 318 nm for core-free particles and from 232 to 118 nm for capsules. As well, the lower limit of capsules size decreased from 78 nm to 45 nm due to enzymatic cross-linking. Scanning electron microscopy showed that morphology of particles and capsules was not completely spherical which was attributed to the protrusion of protein molecules out of aqueous droplets during gelation. The enzymatic treatment yielded in particles with higher glass transition temperature due to the reinforced structure of particulate gel. Fourier transform infrared spectroscopy confirmed the structural changes in proteins by heat and establishment of covalent cross-linkages by the enzyme action manifested by a band at 1078 cm⁻¹.