High internal phase Pickering emulsions stabilized by natural deep eutectic solvents: The freeze-thaw stability and cryopreservation capability

Water-in-oil (W/O) high internal phase emulsions (HIPEs) enhance the utilization of functional components but have limited freeze-thaw (F/T) stability. This study employed natural deep eutectic solvents (NADESs) as the internal phase instead of water to prepare W/O HIPEs stabilized by oleanolic acid (OA). The impact of the presence of NADESs on the F/T stability of OA-based HIPEs was investigated. Three NADESs were chosen: Pro: Sor (1:1), Pro: Glu (1:1), and Pro: Glu (5:3). Compared with HIPE-Water, the particle size and macroscopic changes of HIPE-NADESs did not change significantly with the increase of F/T cycles. Both differential scanning calorimetry (DSC) and low field-nuclear magnetic resonance (LF-NMR) proved that HIPE-NADESs were protected from ice crystal damage, and the free water of HIPE-NADESs moved toward the bound and immobilized water. The rheology confirmed that the interfacial films of HIPE-NADESs became thicker, and HIPE-NADESs formed strong gel networks that restricted the mobility of droplets. In addition, compared with HIPE-Water, the survival rate of probiotics embedded in HIPE-NADESs was increased by 11.40 times after freezing. This finding presents a novel approach and justification for enhancing the F/T stability of W/O emulsions. • W/O HIPEs with excellent freeze-thaw stability were prepared by NADESs as the internal phase. • HIPE-NADESs are protected from ice crystal damage during 3 freeze-thaw cycles. • HIPE-NADESs form strong gel networks that restricted the mobility of droplets and the interfacial film becomes thicker. • NADESs-based HIPEs significantly improve the survival rate of Bifidobacteria after cryopreservation.