Heat-treated lacquer seed protein isolate as an efficient emulsion stabilizer enhances curcumin protection and delivery via a 'gastric shield-intestinal release' mechanism

Abstract

Lacquer tree seed protein isolate (LSPI) is a plant protein with high nutritional value but is often underutilized as animal feed or discarded, leading to waste. We previously showed that heat treatment is more effective than enzymatic or alkaline modification for improving LSPI's emulsifying properties. In this study, LSPI subjected to heat treatment at different temperatures was used to prepare emulsions for delivering curcumin. These emulsions protected curcumin through a ‘gastric shield-intestinal release’ mechanism, with 120 °C (LPSI-120) identified as the optimal protein treatment temperature. Emulsions stabilized by LSPI-120 achieved a maximum curcumin encapsulation efficiency of 90.7%, representing a 25% improvement over emulsions stabilized by untreated LSPI. Heat treatment strengthened the interfacial protein load, mitigating co-oxidation of lipids, protein, and curcumin during storage. As a result, LSPI-120 retained 59.4% of curcumin after 12 d, 1.28-fold higher than the untreated LSPI emulsion. Furthermore, heat-treated LSPI improved the effectiveness of delivery by reducing gastric coalescence, maintaining interfacial integrity, and increasing viscosity. LSPI-120 emulsions exhibited a 62% reduction in gastric coalescence and in viscosity up to 1,381 MPa·s, along with pronounced shear-thinning behavior under intestinal conditions. Ultimately, LSPI-120 emulsions enabled maximal free fatty acid release (22.1 μmol/mL) and curcumin bioaccessibility (43.3%). These findings demonstrate that heat-treated LSPI can serve as a sustainable and functional delivery material, simultaneously enhancing nutraceutical bioavailability and supporting agricultural by-product valorization.

Keywords

Plant protein / Lacquer seed protein isolate / Emulsion / Curcumin encapsulation / Bioaccessibility

Author contributions

The authors confirm their contributions to the paper as follows: supervision: Meng YH, Han YH; investigation: Zhu WB, Gong T, Yang XY; project administration: Meng YH, Zhang CQ; data curation: Zhu WB, Yang XY; methodology: Hu CY, Shi LS; validation: Zhu WB; writing original draft: Zhu WB, Gong T; writing, review and editing: Meng YH, Hu CY. All authors reviewed the results and approved the final version of the manuscript.

Data availability

The datasets are available from the corresponding author on reasonable request.

Acknowledgments

This work was supported by the Guidance Fund for Technology Innovation of Shaanxi Province (2020QFY08-06) and the 2020 Team Innovation Project from the Fundamental Scientific Research Special Capital Fund of the National Universities, China (GK202001008).

Conflict of interest

The authors declare that they have no conflict of interest.

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