Microemulsification–cold gelation of whey proteins for nanoencapsulation of date palm pit extract

Abstract

Cold gelation of whey proteins is a promising method to produce biopolymeric particles entrapping heat-sensitive nutraceuticals at ambient conditions. An aqueous phase composed of heat-treated whey protein isolate (WPI), date palm pit aqueous extract powder, glucono-δ-lactone (GDL) and calcium chloride was microemulsified in a mixture of sunflower oil and sorbitan monooleate. The partial hydrolysis of GDL to gluconic acid resulted in cold gelation of whey proteins inside the nanodroplets of microemulsion which afterwards were precipitated by centrifugation. Heat-treated WPI, extract free particles and extract-loaded capsules had mean sizes of 23, 304 and 230 nm, respectively. Fourier transform infra-red spectroscopy revealed the partial conversion of Amid I band in native WPI to Amid II band in particles and capsules, as well, formation of disulfide bonds. Extract-loading donated a more spherical morphology to particles but did not influence their thermal behavior examined by differential scanning calorimetry. A controlled release character was suggested for nanoparticles based on the phenolics content measurement released from extract-loaded nanoparticles.