Water-In-Oil Pickering Emulsions Stabilized by Water-Insoluble Polyphenol Crystals

Abstract

In recent years, there has been a resurgence of interest in Pickering emulsions because of the recognition of the unique high steric stabilization provided by particles at interfaces. This interest is particularly keen for water-in-oil (W/O) emulsions because of the limited range of suitable Pickering stabilizers available. We demonstrate for the first time that W/O emulsions can be stabilized by using crystals from naturally occurring polyphenols (curcumin and quercetin particles). These particles were assessed based on their size, microstructure, contact angle, interfacial tension, and ζ-potential measurements in an attempt to predict the way that they act as Pickering stabilizers. Static light-scattering results and microstructural analysis at various length scales [optical microscopy, confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM)] confirmed that the quercetin particles has a nearly perfect crystalline rod shape with a high aspect ratio; that is, the ratio of length to diameter ( L/ D) was ca. 2.5:1-7:1. On the other hand, the curcumin particles ( d = 0.2 μm) had a polyhedral shape. Droplet sizing and CLSM revealed that there was an optimum concentration (0.14 and 0.25 wt % for quercetin and curcumin, respectively) where smaller water droplets were formed ( d ≈ 6 μm). Interfacial shear viscosity (η ) measurements confirmed that a stronger film was formed at the interface with quercetin particles (η ≈ 25 N s m) rather than with curcumin particles (η ≈ 1.2 N s m) possibly because of the difference in the shape and size of the two crystals. This study provides new insights into the creation of Pickering W/O emulsions with polyphenol crystals and may lead to various soft matter applications where Pickering stabilization using biocompatible particles is a necessity.

Effects of tea polyphenol ester with different fatty acid chain length on camellia oil‐based oleogels preparation and its effects on cookies properties

“…The contact angle between the Tp-ester and the water (θ w ) or the oil (θ o ) of each Tp-ester was determined with a contact angle meter (OCA 15EC; Dataphysics instrument company, Filderstadt, German) (Zembyla, Murray, & Sarkar, 2018). Each Tp-ester was pressed into circular slices with a width of 1 cm and a height of 1 mm, using a tablet press with a 5-ton pressure die.…”

“…Tp-laurate had the lowest θ o (17.6°), but no significant differences (P > 0.05) in that of the other three Tp-ester were found (Figure 1). The θ w value of four Tp-esters, ranging from 26.1°to 109.3°, was listed in descending order: Tp-stearate > Tp-myristate Tp-palmitate > Tp-laurate, suggesting that Tp-stearate (θ w > 90°) mainly exhibits hydrophobic and preferentially resides in the oil phase and so tends to stabilize W/O emulsions; Tp-myristate and Tp-palmitate (θ w close to 90°) can be wetted in the oil or water phase and so are able to stabilize oil droplets dispersed in water; and Tp-laurate (θ w < 30°) has extremely big hydrophilicity and lipophilicity and so can be completely dispersed in the water phase or oil phase (Zembyla et al, 2018). Variations in the contact angles of these Tp-esters may be mainly due to the variations in their molecular characteristics, such as fatty acid chain length.…”

“…The camellia oil, stained red by Nile red, was distributed in the form of globular droplets in all the samples, and the size of oil droplets decreased with the increase of fatty acid chain length ( Figure 2B). We speculated that the variation in the oil droplets size was attributed to the difference in the length of the fatty acid chain of Tp-ester particles, which had different wettability at the interface, identifying that the particles are preferentially located in the water or in the oil phase (Zembyla et al, 2018). The adsorption capacity at the oilwater interface of Tp-laurate particles is so weak that the formed thin layer can hardly trap oil droplets (Meng, Qi, Guo, Wang, & Liu, 2018); but, in the presence of the hydration of citrus pectin, the small oil droplets can condense and wrap into large droplets (Figure 2 [b1]).…”

“…Pickering mechanism (Figure 1), meanwhile, in the presence of the hydration of citrus pectin, the fine and small oil droplets easily formed and evenly dispersed in the system (Figure 2 [b2 and b3]) . Tp-stearate particles themselves tend to accumulate at the water−oil (W/O) interface, which forms a steric barrier protecting the emulsion droplets against coalescence and contributing to the compact oil droplets (Figure 2 [b4]) (Zembyla et al, 2018). A positive relationship between the hardness of dried products and the fatty acid chain length of the Tp-ester particles was found ( Figure 2C).…”

Synthonic Modeling of Quercetin and Its Hydrates: Explaining Crystallization Behavior in Terms of Molecular Conformation and Crystal Packing

“…[16][17][18] Due to this vast range of biological effects, having antioxidant, anti-inflammatory, anti-bacterial and anti-hypertensive properties as well as the ability to inhibit the growth of human cancer cell lines, quercetin finds use in the nutraceutical industry and as food supplement or ingredient. [19][20][21][22][23][24][25] The molecular structure of quercetin can be observed in Figure 1. 17,[26][27][28] Quercetin can exist as anhydrous (QA), monohydrate (QMH) and dihydrate (QDH) forms.…”