Chitosan-gellan gum polyelectrolyte hydrogel beads containing tea tree oil microcapsules: Preparation, characterization and application

Encapsulation can be applied for essential oil protection, increasing the probability of its application in food preservation. In this study, tea tree oil (TTO) microcapsule powder (MP) was prepared by a spray-drying approach with soy protein isolate (SPI) and fructooligosaccharide (FOS) as wall materials and were subsequently further encapsulated by chitosan (CH) and gellan gum (GG) via a polyelectrolyte complex coacervation approach. The hydrogel beads prepared with a GG mass ratio of 25% presented the best appearance and the densest internal structure. FTIR and Raman spectral analyses demonstrated the generation of hydrogen bonds between CH and GG. Thermogravimetric analysis confirmed that complex coacervates formed by CH and GG as wall materials can improve the thermal stability of TTO. Owing to the excellent barrier properties of the hydrogel beads, the hydrogel beads maintained high DPPH and ABTS free radical scavenging activities after storage. Moreover, the sustained release of TTO hydrogel beads has potential for preserving fresh-cut banana. These discoveries indicate that hydrogel beads can be used as ideal carriers of essential oils such as TTO and may be used in food preservation in the future.