Stability of curcumin encapsulated in solid lipid microparticles incorporated in cold-set emulsion filled gels of soy protein isolate and xanthan gum

The objective of this study was to investigate the feasibility of producing cold-set emulsion filled gels (EFG), using soy protein isolate (SPI) and xanthan gum (XG) and incorporating curcumin-loaded solid lipid micro particles (SLM). For this purpose, the formulation G(xG) (15%, w/v SPI, 0.1%, w/v XG and 5 mM CaCl2) was selected for the production of EFG. A comparative study on the rheological and microstructural properties of non-filled gels and EFG revealed that SLM stabilized with Tween 80-Span 80 behaved as active fillers in the gel matrix, increasing the Young's modulus from 1.1 to 2.3 kPa, and also increasing the values of storage and loss moduli. The incorporation of SLM also affected the microstructural organization of the systems. Whereas unfilled gels presented a microstructural organization similar to that of interpenetrated networks, EFG exhibited a microstructure with clear phase separation. The stability of encapsulated curcumin in EFG was monitored using a colorimetric test and it was confirmed that the bioactive component showed a high stability for 15 days. After that period, the color started to change, indicating a decrease in curcumin concentration. The instability of curcumin was probably related to structural alterations of the EFG, which led to decreases of hardness after 7 days of storage at 10 degrees C, and to the collapse of the structures after 30 days. Although formulation improvements are required, the results indicate that the encapsulation of curcumin in SLM incorporated in EFG is a potential alternative for the replacement of yellow artificial dyes in gelled food products.