pH-based processing strategy: principles, design, and applications (2023-Now)

Introduction

The pH-based processing strategy is a straightforward yet effective approach for inducing structural changes in plant-derived components. By altering their structural arrangement, this method can significantly modify their physicochemical properties, enhancing their functionality in various applications. Conventionally, few studies were focused on the investigation on how the pH-based process alters the structures of plant-derived components.

• pH-induced structural changes

The structural properties of bioactive compounds play a crucial role in determining their solubility, stability, and encapsulation efficiency in food systems. For example, curcumin is typically present in a crystalline form that limits its solubility and bioavailability in aqueous environments. Recently, we observed that the a pH-based process (alkali-acid treatment) can significantly induce the structural changes of crystalline curcumin (Figure 1). Remarkably, curcumin aggregates formed through pH treatment can be efficiently encapsulated into emulsions, even at high concentrations (1 mg/mL). Microscopy analysis revealed that the pH-induced process disrupts curcumin’s crystalline structure, transitioning it into a more dispersible form.

Figure 1. The pH-based versus direct approaches for incorporating hydrophobic curcumin crystals into emulsion systems (such as nanoemulsions).

Our molecular dynamics simulations highlighted the pH-induced structural changes. For instance, a significant portion of the hydrophobic domain revealed that curcumin molecules were predominantly stabilized through hydrophobic interactions in water, with minimal hydrogen bond formation within curcumin molecules. Instead, the curcumin molecules at interface favor the hydrogen bonds with water molecules. Therefore, our simulation results support that this alkali-acid pretreatment significantly alters the structure and interactions of the crystalline curcumin.

Figure 2. Interfacial behavior of the curcumin cluster in water.

Reference

Gong, X.; Suryamiharja, A.; Zhou, H.* pH-induced structural changes of crystalline curcumin enhance its encapsulation in emulsions. ACS Food Science & Technology 2024. DOI: https://doi.org/10.1021/acsfoodscitech.4c00595.

• Formulation of phenolic compound-loaded nanoparticles from raw plants

We hypothesize that the structure of other plant-derived components, such as proteins and acidic polysaccharides, can also undergo significant alterations through this approach. For instance, our research has demonstrated that a similar process can be employed to directly formulate phenolic compound-loaded nanoparticles from raw plant materials.

Figure 3. The potential pH-induced structral changes of plant-derived components via an alkali-acid treatment.

Reference

Gong, X.; Wang, M.; Zhou, H.* Harnessing pH for sustainable and effective synthesis of phenolic compound-loaded nanoparticles directly from raw plants. Food Chemistry 2025, 467, 142327. DOI: https://doi.org/10.1016/j.foodchem.2024.142327.

• Upcycling polyphenols from plant byproducts into foods

Our research utilized this pH-based process for upcycling polyphenols from plant byproducts, transforming waste materials such as fruit peels and seeds into valuable functional food ingredients. For example, we have use the pH-based process to upcycle the polyphenols from peanut skin into the nanoemulsions as a model food system, which suggests that this processing strategy can effectively maximize the utilization of polyphenols from plant byproducts.

Reference

Gong, X.; Wang, M.; Lu, P.; Zhou, H.* An improved pH-driven method for upcycling polyphenols from plants or byproducts into foods. Foods 2024, 13 (23), 3945. DOI: https://doi.org/10.3390/foods13233945.