Insight into the role of droplets in quinoa starch-based Pickering high internal phase emulsion for enzymatic hydrolysis reaction

Pickering high internal phase emulsion has emerged as potential platforms for biocatalytic reactions. Herein, native quinoa starch was used as the emulsifier to form a stable Pickering HIPE with an internal phase up to 80 %. The catalytic performance of lipase loaded in HIPE was evaluated for the enzymatic hydrolysis of hexyl hexanoate. Compared with the typical Pickering emulsion, biphasic, and monophasic systems, the Pickering HIPE system displayed higher conversion (83.54 % at 1440 min) and specific enzyme activity (1.41 U/mg), thus emphasizing the crucial role of microdroplets and large interface area created by both the starch particles and high internal phase volume. Subsequently, HIPEs with different starch concentrations were fabricated to further understand the catalysis behavior happening at compartmentalized microdroplets and interfaces. The microstructural, interfacial, and rheological properties of the HIPEs were systematically determined to explain the correlation between emulsion properties and catalytic efficiency. High starch concentration reduced the droplet size and increased the interfacial area, thus shortening the mass transfer distance and enlarging the reaction area. Meanwhile, the increased surface coverage and viscosity led to poor accessibility and limited mass movement. This trade-off made the maximum conversion be obtained at 2 wt% concentration. The study provides novel information about the role of emulsion droplets in the catalytic performance of lipase in starch-based HIPE.