In this study, cold-set protein gel based on an emulsifying step followed by acid (glucono-d-lactone)-induced gelation of pre-heated whey protein isolate (WPI) was developed as delivery system to control flavor release. Effects of WPI content, oil content and emulsifier type on the kinetics of gelation, gel properties were investigated. Flavor compounds with different physicochemical properties were incorporated into the gel system, and flavor release was tracked by GC headspace analysis. Change of WPI content from 3 to 6 wt% led to increase in the storage modulus (G’) of the gel, but did not show significant influence on gelation time. Texture analysis indicated that fracture stress, fractures strain and stiffness of the gel were positively correlated with protein content. Increase of oil content (5-20 wt%) in the emulsion resulted in decrease in gelation time, and increase in G’ of the gel. Gel with higher oil content tended to have higher stiffness. When small molecule emulsifiers (tween 20 and span 85) were added into the emulsion, gelation took longer time and gel presented lower G’ and stiffness. Moreover, significant higher volume of water was released from the gel during storage, indicating poor water holding capacity. GC analysis showed that changes in WPI content and oil content greatly influenced release rate and air-gel partition coefficient of the flavors. Compared to ungelled emulsions, flavors had lower release rates in the gelled emulsion, suggesting barrier property of the gel network. It also revealed that flavors had different release behavior in gels with different textural properties but same composition. The results of this study showed that emulsion filled protein gel could delay flavor release, which could find potential applications in some functional foods, e.g. fat-reduced food.
Principal investigator: Dr. Song Miao song.miao@teagasc.ie
