Cold gelation of curcumin loaded whey protein aggregates mixed with k-carrageenan: Impact of gel microstructure on the gastrointestinal fate of curcumin

This study aimed to design mixed hydrogels composed of whey protein aggregates (WPA)/k-carrageenan with a tailored microstructure to protect curcumin within the upper gastrointestinal tract and deliver it to the colon. Curcumin was loaded in WPA and followed by cold gelation of the aggregates in the presence of k-carrageenan. The Microstructure of the hydrogels varied from homogenous to protein continuous or k-carrageenan continuous depending on the k-carrageenan concentration (0.0, 0.1 and 0.55%, w/w). The physical stability of curcumin toward precipitation during gelation of curcumin-loaded WPA was significantly improved after k-carrageenan addition. The higher capacity of k-carrageenan containing gels to curcumin entrapment was attributed to curcumin embedment inside of the rich-protein microdomains (called microgels), higher viscosity of the gel pre-solutions contained k-carrageenan and the shorter gelation time of the corresponding gels. Moreover, it was found about 31% of the loaded curcumin was released in the simulated gastrointestinal tract for pure WPA gels, while after addition of 0.55% k-carrageenan to WPA gels, more than 87% of loaded curcumin were delivered to the colon. Besides, 33% of curcumin degraded after the gastrointestinal digestion, while for WPA gels containing 0.1% and 0.55% k-carrageenan it was only 9.6% and 3.5%, respectively. The results were attributed to the protective effect of k-carrageenan to protein during in vitro digestion so that the access of digestive enzymes into the hydrogels was limited resulting in a reduction of gel matrix erosion and curcumin release. Therefore, curcumin remained bound to the protein and was not damaged during digestion until it reaches the colon.