Emulsified lipids are prevalent in processed foods, most commonly as oil-in-water emulsions. These require emulsifiers to stabilize the immiscible oil and water phases. Despite this stabilization, emulsions are thermodynamically unstable, susceptible to several destabilization mechanisms, including Ostwald ripening (OR). OR is particularly significant in emulsions containing oils with relatively high water solubility, such as essential oils or short-chain triacylglycerols. In OR, smaller oil droplets dissolve into the aqueous phase and redeposit onto larger droplets, leading to a net increase in average droplet size. This can accelerate other destabilization mechanisms like coalescence and creaming, reducing shelf life. This study focuses on mitigating OR in oil-in-water emulsions. One approach is using ripening inhibitors—hydrophobic substances that, when mixed with polar oils, counteract the curvature effect driving OR through an entropy of mixing effect. These inhibitors also act as weighting agents, reducing creaming. The rate of Ostwald ripening is described by an equation considering interfacial tension, oil molar volume, diffusion coefficient, oil solubility, gas constant, and temperature. Emulsifiers influence OR by altering interfacial tension, while aqueous phase additives affect it by changing the continuous phase viscosity and thus the diffusion coefficient. The study examines the impact of emulsifier type and various water-soluble additives (glucose, maltose, glycerol, propylene glycol) on OR in model oil-in-water emulsions, considering their relevance to concentrated beverage emulsions containing high levels of water-soluble additives.

Existing literature extensively covers Ostwald ripening in emulsions. Studies have explored the use of ripening inhibitors, such as triglycerides, to retard droplet growth by reducing the density contrast between the oil and water phases. The impact of different emulsifiers on OR has also been investigated, focusing on the relationship between interfacial tension and droplet growth. Research has examined the influence of various additives on emulsion stability, but a comprehensive understanding of the combined effects of emulsifier type and specific water-soluble additives on OR remains limited. This gap highlights the need for a study systematically investigating the interactions between these factors to develop more stable emulsion-based systems.

The study used Tween 60 and Brij S20 as model surfactants with similar hydrophobic tails (C18 alkane chains) but different hydrophilic heads (Tween 60 has three shorter polyoxyethylene chains, Brij S20 has one long one). *n*-decane was used as the model oil, with corn oil added as a ripening inhibitor at varying concentrations (0, 5, 10, 20, 30% w/w). Water-soluble additives (glucose, maltose, glycerol, propylene glycol) were incorporated into the aqueous phase at different concentrations (0, 5, 15, 30% w/v). Emulsions were prepared by homogenizing oil and aqueous phases using a high-shear blender and a microfluidizer. The pH was adjusted to 3 or 7. Droplet size was measured using a laser diffraction particle size analyzer. OR rates were calculated based on the Lifshitz-Slyozov-Wagner theory. Viscosity of aqueous phases was measured using a sine wave vibro-viscometer, and interfacial tension was measured using a pendant drop tensiometer. Statistical analysis using Duncan's multiple range test was performed (p<0.05).

Increasing corn oil concentration in the oil phase significantly reduced Ostwald ripening rates, effectively inhibiting it at ≥20% (w/w). Glucose, maltose, and glycerol all inhibited OR in emulsions without corn oil, with the effect increasing with concentration. Propylene glycol showed a contrasting effect, accelerating OR in Brij S20-stabilized emulsions but not in Tween 60-stabilized ones. The addition of glucose and maltose continued to inhibit OR even in the presence of corn oil (5% w/w), while glycerol's effect was lost. In emulsions without corn oil, Brij S20-stabilized emulsions showed higher OR rates than Tween 60-stabilized ones, potentially due to differences in interfacial layer properties. However, in the presence of corn oil, this trend reversed. The addition of water-soluble additives generally decreased interfacial tension, particularly for Tween 60, and increased aqueous phase viscosity, both factors expected to reduce OR. Propylene glycol's effect on OR rate appeared linked to its ability to modify surfactant properties, particularly influencing the interfacial layer characteristics of Brij S20.

The findings demonstrate that both hydrophobic (corn oil) and hydrophilic (glucose, maltose, glycerol) additives can effectively inhibit Ostwald ripening, but their mechanisms differ. Corn oil acts as a compositional ripening inhibitor, while the hydrophilic additives likely influence OR by increasing aqueous phase viscosity and, in some cases, decreasing interfacial tension. Propylene glycol's behavior highlights the complex interplay between additive type, emulsifier structure, and interfacial properties. The observed differences between Brij S20 and Tween 60 emulsions suggest that the structure of the surfactant's hydrophilic head group significantly impacts the emulsion's response to additives. These findings have important implications for designing more stable emulsion-based food and beverage products, particularly those containing polar oils, by carefully selecting appropriate emulsifiers and water-soluble additives.

This study provides valuable insights into controlling Ostwald ripening in oil-in-water emulsions. The effectiveness of both hydrophobic and hydrophilic additives, alongside the significant impact of emulsifier type, has been established. Future research should explore the underlying molecular mechanisms of propylene glycol's interaction with different surfactants at the oil-water interface and investigate a broader range of additives and oil phases to further optimize emulsion stability.

The study used model oils (*n*-decane and corn oil) and surfactants. Extrapolating these findings to complex food systems containing multiple components may require further investigation. The influence of other factors, such as temperature and storage conditions, on the long-term emulsion stability was not fully explored. The study focused on non-ionic surfactants, and the results may not generalize to other surfactant types (ionic surfactants).