Novel food-grade water-in-water Pickering emulsions stabilized by cellulose nanocrystals with long-term stability and slowing down starch digestibility

Abstract

Construction of water-in-water (W/W) emulsions based on thermodynamic properties of natural macromolecules better aligns with the growing demand for healthy food and innovative food structure designs. In this work, W/W Pickering emulsions with excellent storage stability (30 days) stabilized by cellulose nanocrystals (CNCs) were constructed to slow down starch digestibility, in which amylopectin (AMP) was the dispersed phase and hydroxypropyl methylcellulose (HPMC) was the continuous phase. The stability of AMP/HPMC Pickering emulsions demonstrated a significant concentration-dependent relationship with CNCs, showing enhanced stabilization at higher CNCs concentrations. With increasing CNCs concentration, the particle size of the AMP/HPMC Pickering emulsion decreased from 5.85±2.29 μm to 2.87±0.92 μm. Moreover, AMP/HPMC Pickering emulsions showed remarkable environmental stability (pH stability and ionic strength stability), and the droplet sizes were maintained consistently across various conditions, with alterations only observed under extremely alkaline environments (pH=11). During in vitro digestion, the accessibility of digestive enzymes to AMP was hindered by the interfacial barrier formed by CNCs at the two-phase interface, resulting in a significant reduction in glucose release, effectively slowing down starch digestibility. This work would advance the construction and development of the novel starch-based W/W Pickering emulsions, and provide innovative insights for investigating its application in slow-digestible food systems and even low glycemic index (GI) food.

Highlights:

Introduction

The global burden of diabetes has experienced a substantial and concerning escalation during the past three decades, emerging as a major public health challenge worldwide (B. Zhou et al., 2024). The 2021 International Diabetes Federation (IDF) Global Diabetes Map showed that the predicted number of people with diabetes worldwide by 2030 is 642 million. Slowing down starch digestion to reduce postprandial blood glucose (PBG) is one of the effective strategies for preventing diabetes (T. Xu et al., 2021). Previous researches had shown that modification of starch could regulate the digestion rate of starch (Chi et al., 2021; Petropoulou et al., 2020). However, starch modification by chemical, physical, and enzymatic methods had many limitations, such as the use of a large number of chemical reagents, high equipment requirements, and high production costs (Geng et al., 2023; Lopez-Silva et al., 2020; Zailani et al., 2022). In addition, the diversity and palatability of prepared food might be sacrificed by the modification of starch, which was not desired for those who paid more attention to the food taste. Therefore, without changing the structure of starch, the addition of a protective layer to the starch surface was a feasible strategy to slow down the rate of starch digestion by food microstructure design concepts (Li et al., 2023).

Emulsion system was constructed by the incompatibility of two-phase solutions. The dispersed phase was encapsulated in the system, which was protected by the continuous phase. It was an excellent system for protecting starch and preventing its contact with digestive enzymes. The increasing consumer preference for low-oil and oil-free food formulations has propelled water-in-water (W/W) emulsions to prominence in food science research, owing to their unique biphasic architecture achieved through thermodynamic incompatibility of aqueous polymer solutions, which eliminates the requirement for oil phases (J. F. Chen et al., 2019; Grinberg & Tolstoguzov, 1997; C. Zhou et al., 2023). In addition, W/W emulsions have significant advantages in encapsulation and delivery of bioactive ingredients, modulation of food microstructure, enrichment and separation of proteins or polysaccharides by virtue of good biocompatibility and macromolecular crowding effects (Beldengrün et al., 2018; Gonzalez-Amado et al., 2021; J. F. Chen et al., 2019; Xie et al., 2023). In recent years, in addition to dextran/poly(ethylene oxide) (DEX/PEO) and dextran/poly(ethylene glycol) (DEX/PEG) systems, polysaccharides and proteins solution were employed to construct food-grade W/W emulsions systems (Beldengrün et al., 2020; Lei et al., 2022; Wang et al., 2023). Owing to their abundant natural sources and renewability, starch was a popular candidate as one of the phases for the construction of W/W emulsions (Hazt et al., 2020; Luo et al., 2025; Machado et al., 2021). By employing waxy corn starch (WCS) as the dispersed phase, Chen (J. F. Chen et al., 2018) successfully constructed W/W emulsions, which utilized water-water interface and external water phase to hinder the accessibility of digestive enzymes to starch. This provided a new perspective to construct W/W emulsions using different polysaccharides to slow down starch digestion.

However, the low interfacial tension between the two phases of W/W emulsions and the thick and ill-defined interface resulted in poor stability (Esquena, 2016; Yan et al., 2023). Furthermore, conventional small molecule surfactants could not be conducted to stabilize W/W emulsions, which had a thick interfacial layer. Preparation of W/W Pickering emulsions stabilized by solid particles was a good strategy to improve their stability and better application in the food field, such as polysaccharide particles, protein particles, and protein microgels (J.-F. Chen et al., 2019; Lei et al., 2022; Machado et al., 2021; Qian et al., 2022). Cellulose nanocrystals (CNCs) are nanoscale solid particles prepared using cellulose as a raw material, which are widely utilized as Pickering stabilizers due to their good aspect ratio, excellent mechanical properties, and biodegradability (Bai et al., 2020; Peddireddy et al., 2016a; Ruan et al., 2023). Compared with other methods, CNCs prepared by ammonium persulfate (APS) oxidation have more environmentally friendly and better biocompatibility. In addition, carboxylate groups are generated through APS oxidation reaction to enhance the structural stability of CNCs and the dispersibility of CNCs in aqueous system, which is conducive to the stabilization in W/W emulsion systems (Nie et al., 2024a; Pratiwi et al., 2023).

In this work, W/W emulsions were constructed using amylopectin (AMP) and hydroxypropyl methylcellulose (HPMC), and CNCs prepared by ammonium persulfate (APS) oxidation method were added to improve the stability of emulsions system. AMP/HPMC Pickering emulsions were prepared by adjusting the concentration of the two phases in the system and characterized by an inverted fluorescence microscope, droplet size measurements, and viscosity measurements. The effects of the concentration of the two-phase substances and the concentration of CNCs on AMP/HPMC Pickering emulsions have been studied. The pH stability and ionic strength stability of AMP/HPMC Pickering emulsions have been observed to evaluate the resistance ability to the external environment. Finally, simulated digestion of AMP/HPMC Pickering emulsions with AMP as the dispersed phase was conducted to analyze changes in glucose release. The objective of this study is to prepare AMP/HPMC Pickering emulsions using CNCs to slow down starch digestion, thereby laying a theoretical foundation for developing slow-digestible starch-based foods through W/W emulsions.

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Materials and reagents

Amylopectin (from maize, CAS: 9037-22-3), Hydroxypropyl methylcellulose (50 mPa·s, CAS: 9004-65-3) with 28-30% methoxy and 7.0-12% hydroxypropyl, and Fluorescein 5(6)-isothiocyanate (CAS: 27072-45-3) were purchased from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Calcofluor white stain was purchased from Sigma-Aldrich Trading Co., Ltd. (Shanghai, China). Dibutyltin dilaurate was purchased from Macklin Biochemical Co., Ltd. (Shanghai, China). Cotton linter cellulose…

Chunling Nie, Pengrui Wu, Yefan Niu, Zhihong Song, Xindi Wei, Zhonghui Shen, Yijun Liu, Jianguo Wang, Novel food-grade water-in-water Pickering emulsions stabilized by cellulose nanocrystals with long-term stability and slowing down starch digestibility, Food Hydrocolloids, 2025, 111507, ISSN 0268-005X, https://doi.org/10.1016/j.foodhyd.2025.111507.