Abstract
Supercritical CO2 (SC-CO2) extraction offers a sustainable method for obtaining solvent-free oils rich in bioactive molecules, valuable for nutraceutical and functional food products. However, the limited stability of certain extract components can hinder their application.
This study explores α, β, and γ cyclodextrins (CDs) as emulsifiers to enhance SC-CO2-extracted tomato oil (TO) stability. TO/CD emulsions with high oil volume fractions (φ) of 60 %, 65 %, 70 %, and 75 % were prepared using the three types of CDs. Only α-CDs formed gel-like, stable emulsions up to φ = 70 %. Confocal microscopy revealed that increasing φ led to morphological changes, including reduced droplet size, decreased roundness, and larger coalescence zones, affecting stability and functionality. Emulsions at φ 60 % showed optimal performance with reduced phase separation, high viscosity, smaller droplet size, and lower coalescence.
The stability of carotenoids and tocopherols was evaluated under heat (50 °C) and UV-C exposure to simulate accelerated aging and sterilization. Emulsions improved carotenoid stability at elevated temperatures compared to bulk TO. Tocopherols were highly stable in bulk TO and moderately stable in TO/α-CD emulsions. Under UV-C exposure, TO/α-CD emulsions enhanced carotenoid and tocopherol stability for up to 9 h, compared to pure TO.
Further analysis with α-CDs and synthetic glyceryl trioctanoate (GTO) at φ = 60 %, 65 %, and 70 % replicated the concentrations of lycopene and α-tocopherol in TO. These results suggest that TO/α-CD emulsions can serve as stable, high-quality ingredients for nutraceutical and functional food applications.
Highlights
- α-Cyclodextrins (α-CD) stabilize SC-CO2-extracted tomato oil (TO) emulsions up to 70 %.
- TO/α-CD emulsion with φ = 60 % showed optimal thermal and UV-C stability of bioactives.
- Confocal microscopy confirmed optimal stability with smaller droplets at φ = 60 %.
Introduction
Tomato (Solanum lycopersicum L.) is one of the most widely consumed vegetables worldwide, both in fresh and processed forms. It is an excellent source of bioactive compounds, including carotenoids (α- and β-carotene, lycopene), ascorbic acid (vitamin C), tocopherols (vitamin E), and phenolics (e.g., quercetin, kaempferol, naringenin, caffeic acid, ferulic acid, and chlorogenic acid). These bioactives contribute significantly to human nutrition, providing well-documented health benefits, including antioxidant, anti-inflammatory, and anticancer properties (Ali et al., 2020; Laayouni et al., 2023).
Among these bioactive compounds, lycopene and tocopherols are particularly notable due to their powerful lipophilic antioxidant activities. Lycopene, the primary carotenoid responsible for the characteristic red pigmentation of tomatoes, is one of the most effective dietary antioxidants, although it lacks provitamin A activity. Its broad spectrum of bioactive properties includes anticancer, antidiabetic, antimicrobial, anti-allergenic, and antithrombotic effects, making it a promising candidate for innovative applications across diverse industries, including functional foods, pharmaceuticals, advanced food packaging, and cosmetic formulations (Di Sano et al., 2022; Imran et al., 2020; Liang et al., 2019; Saini et al., 2020; Sakemi et al., 2020; Zhu et al., 2020). Both in vitro and in vivo studies have demonstrated that lycopene is capable of mitigating oxidative stress-induced metabolic dysfunctions and associated pathologies, including inflammation, obesity, and diabetes mellitus (Shafe et al., 2024).
Lycopene naturally occurs in 72 isomeric forms, with approximately 90 %–98 % in the all-[E]-lycopene configuration (Koe & Zechmeister, 1952). However, its molecular structure—characterized by eleven conjugated and two non-conjugated double bonds—makes it highly susceptible to isomerization and degradation upon exposure to heat, light, and oxygen. This leads to the formation of [Z]-isomers, such as 5-[Z], 9-[Z], 13-[Z], and 15-[Z] lycopene, along with other cleavage products like apocarotenoids. As a result, such structural alterations compromise lycopene’s visual appeal, antioxidant efficacy, and nutritional value, highlighting the need for strategies aimed at enhancing its stability during storage and processing. Moreover, the inherently poor water solubility of lycopene poses additional challenges to its bioavailability and functional performance, necessitating the development of advanced extraction and encapsulation techniques (Sampaio et al., 2019).
Tocopherols, a class of phenolic antioxidants, play a critical role in inhibiting lipid autoxidation by scavenging free radicals and reacting with singlet oxygen. In vegetable oils, α-tocopherol specifically mitigates the effects of singlet oxygen during sensitized photoxidation. Beyond their function as Vitamin E, tocopherols operate independently or in synergy with other antioxidants to protect cells from oxidative damage caused by free radicals, thereby reducing the risk of chronic conditions such as cardiovascular diseases and certain cancers. Additionally, tocopherols contribute to skin health by preventing UV-induced damage and promoting wound healing (Bermúdez et al., 2018).
Tocopherols, a class of phenolic antioxidants, play a crucial role in protecting lipids from oxidative damage by scavenging free radicals and interacting with singlet oxygen. Beyond their well-known function as vitamin E, tocopherols operate both independently and synergistically with other antioxidants to protect cells from oxidative stress, thereby reducing the risk of chronic diseases such as cardiovascular disease and certain cancers. Additionally, tocopherols promote skin health by preventing UV-induced damage and enhancing wound healing (Bermúdez et al., 2018). In vegetable oils, tocopherols help mitigate the effects of singlet oxygen during sensitized photooxidation. Given these beneficial properties, tocopherols are extensively used in the food industry, both as natural extracts and synthetic forms, to extend the shelf life of vegetable oils and maintain the quality of fat-containing food products, particularly during storage and processing.
Several techniques have been explored for lycopene and tocopherols extraction, including solvent-based methods, microemulsion techniques, and supercritical fluid extraction (Yadav et al., 2024). Supercritical carbon dioxide (SC-CO2), in particular, has emerged as an environmentally friendly, non-toxic, and efficient green technology. SC-CO2 operates under conditions of optimal diffusibility and high solubility for lipophilic compounds while being easily separable from the final product (Katherine et al., 2008). Although CO2 is non-polar, the addition of co-solvent systems, such as ethanol-water mixtures, enhances its efficiency for extracting both polar and non-polar bioactives, ensuring higher yields and broader applicability. Studies have consistently demonstrated that SC-CO2 is highly effective for obtaining high-quality oils, rich in lipophilic bioactives, from tomato matrices (Lenucci et al., 2010; Pellicanò et al., 2020). However, preserving the stability of all-[E]-lycopene and other health-promoting compounds in oil during storage and food processing remains a significant challenge (Durante et al., 2020).
To overcome these threats, encapsulation technologies have been developed to protect bioactive compounds from environmental degradation while enhancing their solubility, bioavailability, and controlled release. These systems include emulsions, pickering emulsions, micelles, liposomes, nanoparticles, and electrospun fibers, among others (Franco & Jimenez, 2025; Wang et al., 2024). Smart release systems responsive to environmental triggers, such as pH, temperature, or light, have also emerged as innovative solutions for enhancing the functional performance of encapsulated bioactives (Iuele et al., 2025).
Oil-in-water (O/W) emulsions are widely used to stabilize tocopherols by encapsulating them in the oil phase, reducing their exposure to oxygen and light, which significantly slows oxidative degradation (Yang et al., 2015). The addition of emulsifiers and co-antioxidants, such as ascorbic acid, in O/W emulsions enhances the physical and oxidative stability of tocopherols, making them effective for use in food, cosmetic, and pharmaceutical applications (Huang et al., 1995). O/W emulsions are particularly promising for encapsulating and delivering hydrophobic bioactives like lycopene. These systems protect bioactives from oxidation and thermal degradation while enhancing their dispersibility and uptake in aqueous environments (McClements, 2012). However, the instability of emulsions, due to phenomena like coalescence and phase separation, can limit their practical use. To address this, there is growing interest in natural stabilizers that ensure both safety and environmental sustainability.
Cyclodextrins (CDs), a family of safe and biocompatible cyclic oligosaccharides derived from starch, have garnered significant attention as effective natural stabilizers for emulsions. Classified into three main types—α-CD (six glucose units), β-CD (seven glucose units), and γ-CD (eight glucose units)—these molecules form inclusion complexes or larger coating structures (e.g., cyclodextrinosomes) with hydrophobic compounds, enhancing their stability and solubility. Among the different types of CDs, α-CDs have shown particular promise for stabilizing O/W emulsions containing lycopene-rich tomato oils. Studies by Durante et al. (Durante, et al., 2016, 2020) demonstrated that α-CD-stabilized emulsions delayed carotenoid degradation and improved bioactive retention, although all-[E]-lycopene remained more susceptible to oxidation compared to crude TO. In these studies, TO was encapsulated with α-CDs in a molar ratio of approximately 0.56:1 (mol TO/mol α-CDs, considering the TO essentially composed of tryglycerides with average molecular weight of 865 g/mol), and a total oil volume fraction (φ) of 0.05 was used.
Building upon these findings, the present study further investigates the stability of bioactive compounds in CDs-stabilized emulsions of TO, focusing on all-[E]-lycopene, [Z]-lycopene isomers, and α- and β-tocopherols under thermal (50 °C) and UV-C treatments. TO was emulsified at φ of 60 %, 65 %, 70 %, and 75 %, with 100 g/L α-CD aqueous solutions, to evaluate the effects of encapsulation on bioactive compound stability. Emulsions with β-CD and γ-CD were also prepared, but did not show satisfactory phase stability compared to those obtained with α-CD. The structural properties of these emulsions were characterized using optical and confocal microscopy, providing insights into droplet morphology, interfacial layer formation, and dispersion stability. By exploring innovative stabilization strategies and their impact on bioactive retention, this research aims to advance the development of sustainable, functional lycopene delivery systems with broad applications in food and pharmaceutical industries.
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Materials
All-[E]-lycopene standard (HPLC purity >98 %) and β-carotene were obtained from CaroteNature (Lupsingen, Switzerland). Food-grade cyclodextrins (CDs, CAVAMAX® W6) were generously provided by IMCD Italy SpA (Milan, Italy). High-purity carbon dioxide (CO2, 99.995 %) for supercritical fluid extraction (SC-CO2) was sourced from Mocavero Ossigeno (Lecce, Italy). Alpha- and beta-tocopherol standards (α-T and β-T), glyceryl trioctanoate (GTO purity ≥95 %), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and all the other high-performance liquid chromatography (HPLC) grade solvents were purchased from Sigma-Aldrich (Milan, Italy).
Francesco Milano, Riccardo Tornese, Vincenzo De Leo, Monica De Caroli, Livia Giotta, Miriana Durante, Marcello Salvatore Lenucci, α-Cyclodextrins for stability enhancement of bioactive-rich tomato oil extracted with supercritical CO2: Emulsion performance under thermal and UV-C treatments, Food Bioscience, Volume 68, 2025, 106768, ISSN 2212-4292, https://doi.org/10.1016/j.fbio.2025.106768.
