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. 2025 Sep:120:107469.
doi: 10.1016/j.ultsonch.2025.107469. Epub 2025 Jul 18.

Mechanism of ultrasonic-alkali-thermal modification for enhancing the emulsifying properties of rice protein and its stability in high-internal-phase emulsions

Lijie Zhu  1 , Haiqiang Liao  1 , Kun Zhuang  1 , Shangyuan Sang  2 , Lei Chen  1 , Xianhui Chang  1 , Qi Zhang  1 , Qingyun Lv  1 , Xiuying Liu  3 , Xinqi Liu  4 , Wenping Ding  5
Affiliations

Mechanism of ultrasonic-alkali-thermal modification for enhancing the emulsifying properties of rice protein and its stability in high-internal-phase emulsions

Lijie Zhu et al. Ultrason Sonochem. 2025 Sep.

Abstract

Rice protein, as a hypoallergenic plant protein, faces limitations in food industry applications due to the poor emulsification of its native form. In this study, rice protein was subjected to ultrasonic, alkali-thermal, and combined ultrasonic-alkali-thermal treatments. Experimental results revealed that the ultrasonic-alkali-thermal combined treatment significantly reduced the particle size to 129.67 nm. Structural analysis showed an increase in random coil content within the secondary structure, indicating a transition from ordered to disordered conformation. Contact angle measurements demonstrated improved intermediate wettability of the modified protein. The high-internal-phase emulsion prepared with ultrasonic-alkali-thermal treated rice protein exhibited enhanced stability, with the Turbiscan Stability Index as low as 0.39, reduced emulsion particle size (14.17 μm), and elevated storage moduli. These findings collectively suggest that the ultrasonic-alkali-thermal treatment is an effective strategy for enhancing the emulsifying properties of rice protein.

Keywords: Alkali-thermal; Emulsification property; High-internal-phase emulsion; Rice protein; Ultrasound.

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Conflict of interest statement

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
(A) The influence of different modification methods on the zeta potential of rice protein. (B) The influence of different modification methods on the particle size of rice protein. (C) The influence of different modification methods on the solubility of rice protein. (D) The influence of different modification methods on the emulsifying performance of rice protein. Note: Different letters between the results denote statistically significant differences (p < 0.05). Rice protein (RP), Alkali-thermal treatment (AH), 200 W ultrasonic treatment (U2), 600 W ultrasonic treatment (U6), 200 W ultrasonic-alkali-thermal treatment (UAH2), 600 W ultrasonic-alkali-thermal treatment (UAH6).
Fig. 2
Fig. 2
(A) Ultraviolet spectra of different modified rice proteins. (B) Fluorescence spectra of different modified rice proteins. (C) Effects of different modification methods on the surface hydrophobicity of rice proteins. Note: Different letters between the results denote statistically significant differences (p < 0.05). Rice protein (RP), Alkali-thermal treatment (AH), 200 W ultrasonic treatment (U2), 600 W ultrasonic treatment (U6), 200 W ultrasonic-alkali-thermal treatment (UAH2), 600 W ultrasonic-alkali-thermal treatment (UAH6).
Fig. 3
Fig. 3
(A) Effects of different modification methods on the interfacial tension of rice protein. (B) Effects of different modification methods on the contact Angle of rice protein. (C) Gel electrophoresis profiles of different modified rice proteins. Note: Rice protein (RP), Alkali-thermal treatment (AH), 200 W ultrasonic treatment (U2), 600 W ultrasonic treatment (U6), 200 W ultrasonic-alkali-thermal treatment (UAH2), 600 W ultrasonic-alkali-thermal treatment (UAH6).
Fig. 4
Fig. 4
SEM images of different modified rice proteins. Note: Rice protein (RP), Alkali-thermal treatment (AH), 200 W ultrasonic treatment (U2), 600 W ultrasonic treatment (U6), 200 W ultrasonic-alkali-thermal treatment (UAH2), 600 W ultrasonic-alkali-thermal treatment (UAH6).
Fig. 5
Fig. 5
(A) Effects of different modification methods on the particle sizes D43 of rice protein-stabilized emulsions. (B) Effects of different modification methods on the particle size distribution of rice protein-stabilized emulsions. (C) Effects of different modification methods on the emulsion potential of rice protein-stabilized emulsions. (D) Changes in TSI values of rice protein-stabilized emulsions within 1 h by different modification methods. Note: Different letters between the results denote statistically significant differences (p < 0.05). Rice protein (RP), Alkali-thermal treatment (AH), 200 W ultrasonic treatment (U2), 600 W ultrasonic treatment (U6), 200 W ultrasonic-alkali-thermal treatment (UAH2), 600 W ultrasonic-alkali-thermal treatment (UAH6).
Fig. 6
Fig. 6
(A) Effects of different modification methods on the energy storage modulus and loss modulus of rice protein-stabilized emulsions. (B) Effects of different modification methods on the apparent viscosity of rice protein-stabilized emulsions. (C) Macroscopic static images of rice protein-stabilized emulsions at 0 days and 7 days (from left to right: RP, AH, U2, U6, UAH2, UAH) 6). Note: Rice protein (RP), Alkali-thermal treatment (AH), 200 W ultrasonic treatment (U2), 600 W ultrasonic treatment (U6), 200 W ultrasonic-alkali-thermal treatment (UAH2), 600 W ultrasonic-alkali-thermal treatment (UAH6).
Fig. 7
Fig. 7
(A) Emulsion laser confocal images of rice protein stabilization by different modification methods. (B) Emulsion optical microscope images of rice protein stabilization by different modification methods. Note: Rice protein (RP), Alkali-thermal treatment (AH), 200 W ultrasonic treatment (U2), 600 W ultrasonic treatment (U6), 200 W ultrasonic-alkali-thermal treatment (UAH2), 600 W ultrasonic-alkali-thermal treatment (UAH6).
See this image and copyright information in PMC

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