Hydrosols as natural antimicrobials for food applications

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Unlocking the Potential of Hydrosols: Transforming Essential Oil Byproducts into Valuable Resources

Publication . Almeida, Heloísa H.S.; Fernandes, Isabel P.; Amaral, Joana S.; Rodrigues, Alírio; Barreiro, M.F.

The global demand for sustainable and non-toxic alternatives across various industries is driving the exploration of naturally derived solutions. Hydrosols, also known as hydrolates, represent a promising yet underutilised byproduct of the extraction process of essential oils (EOs). These aqueous solutions contain a complex mixture of EO traces and water-soluble compounds and exhibit significant biological activity. To fully use these new solutions, it is necessary to understand how factors, such as distillation time and plant-to-water ratio, affect their chemical composition and biological activity. Such insights are crucial for the standardisation and quality control of hydrosols. Hydrosols have demonstrated noteworthy properties as natural antimicrobials, capable of preventing biofilm formation, and as antioxidants, mitigating oxidative stress. These characteristics position hydrosols as versatile ingredients for various applications, including biopesticides, preservatives, food additives, anti-browning agents, pharmaceutical antibiotics, cosmetic bioactives, and even anti-tumour agents in medical treatments. Understanding the underlying mechanisms of these activities is also essential for advancing their use. In this context, this review compiles and analyses the current literature on hydrosols’ chemical and biological properties, highlighting their potential applications and envisioning future research directions. These developments are consistent with a circular bio-based economy, where an industrial byproduct derived from biological sources is repurposed for new applications.

2024Journal article

Open access

Disclosing the potential of Cupressus leylandii A.B. Jacks & Dallim, Eucalyptus globulus Labill., Aloysia citrodora Paláu, and Melissa officinalis L. hydrosols as eco-friendly antimicrobial agents

Publication . Almeida, Heloísa H.S.; Crugeira, Pedro Jorge Louro; Amaral, Joana S.; Rodrigues, Alírio; Barreiro, M.F.

Antimicrobial resistance is a major global health concern, threatening the effective prevention and treatment of infections caused by microorganisms. These factors boosted the study of safe and green alternatives, with hydrosols, the by-products of essential oils extraction, emerging as promising natural antimicrobial agents. In this context, four hydrosols obtained from Cupressus leylandii A.B. Jacks & Dallim, Eucalyptus globulus Labill., Aloysia citrodora Paláu and Melissa officinalis L. were studied. Their chemical composition comprises neral, geranial, 1,8-cineole, terpinen- 4-ol, and oplopanonyl acetate, compounds with recognised antimicrobial activity. Concerning antimicrobial activity, significant differences were found using different hydrosol concentrations (10–20% v/v) in comparison to a control (without hydrosol), showing the potential of the tested hydrosols to inhibit the microbial growth of Escherichia coli, Staphylococcus aureus, and Candida albicans. A. citrodora hydrosol was the most effective one, inhibiting 90% of E. coli growth and 80% of C. albicans growth, for both hydrosol concentrations (p < 0.0001). With hydrosol concentration increase, it was possible to observe an improved antimicrobial activity with significant reductions (p < 0.0001). The findings of this work indicate the viability of reusing and valuing the hydrosols, encouraging the development of green applications for different fields (e.g., food, agriculture, pharmaceuticals, and cosmetics).

2024Journal article

Open access

Solid dispersions as effective curcumin vehicles to obtain k-carrageenan functional films for olive oil preservation

Publication . Rezende, Stephany; Santamaria-Echart, Arantzazu; Almeida, Heloísa H.S.; Marcet, Ismael; Carpintero, Maria; Rendueles, Manuel; Lopretti, Mary; Dias, Madalena M.; Barreiro, M.F.

Synthetic packaging materials offer cost efficiency and performance but pose environmental risks. This study explores sustainable alternatives by developing k-carrageenan (KC) films functionalized with curcumin, using solid dispersions (SDs) to improve curcumin's compatibility, addressing the challenge of incorporating hydrophobic functionalities into hydrophilic film matrices. Films with varying curcumin content (1–20 wt%; KC1- KC20) were compared to a base film without curcumin (KC0) regarding water solubility, vapor permeability, water contact angle, and tensile properties. Compared to KC0, KC10 (10 % curcumin-SDs) exhibited improved water resistance, with solubility decreasing from 82.89 % to 77.18 %, while maintaining vapor permeability (2.96 × 10􀀀 10 g⋅m/s⋅m2⋅Pa). KC10 demonstrated enhanced tensile properties, with a 12.51 % increase in tensile modulus (241.47 MPa), a 3.86 % increase in stress at break (3.50 MPa), and a 4.42 % increase in strain at break (2.36 %). Furthermore, it exhibited potent antioxidant activity without releasing curcumin into a simulated fatty medium (non-migratory active protection mechanism), effectively preserving olive oil by limiting lipid oxidation to a peroxide value (PV) of 14 mEq. O2/kg oil, compared to 20 mEq. O2/kg oil in unprotected samples under accelerated conditions. It demonstrated significant antimicrobial activity with bacterial reductions of 95.4 % (Escherichia coli) and 90.6 % (Listeria monocytogenes), surpassing KC0. In conclusion, k-carrageenan films functionalized with curcumin SDs are promising and sustainable alternatives to synthetic packaging materials.

2025Journal article

Open access

Biosynthesis of antioxidant xanthan gum by Xanthomonas campestris using substrates added with moist olive pomace

Publication . Crugeira, Pedro Jorge Louro; Almeida, Heloísa H.S.; Marcet, Ismael; Rendueles, Manuel; Pires, Marcella Golini; Rafael, Helder Martins; Rodrigues, Ana Isabel G.; Santamaria-Echart, Arantzazu; Rafael, Helder; Barreiro, M.F.; Golini Pires, Marcella

Moist olive pomace (MOP) is a high moisture content by-product of the olive oil industry. Managing this recalcitrant residue (transport, storage, and drying) is a priority demanding investment in finding alternative valorisation routes. In this context, the biosynthesis of xanthan gum (XG) incorporating MOP in the substrate (0.0 %, 5.0 %, 10.0 %, 15.0 %, 20.0 %, 25.0 %, 30.0 % and 50.0 %) to induce bacterial stress was attempted. XG biosynthesis yield was quantified, and the product was characterised by structural analysis (FTIR), thermal behaviour (TG), rheology and antioxidant capacity. Relative to the control (sample with no added MOP), a significant increase in XG biosynthesis was found for concentrations up to 30.0 % MOP. In particular, for XG produced with 15 % MOP, a 50.91 % (p < 0.0001) increase was achieved, together with 395.78 % for viscosity. In general, XG produced with MOP presence showed antioxidant activity, a value-added property, especially for applications in the food, pharmaceutical and cosmetic areas. The results indicated that the stress imposed by the MOP induced a microbial response leading to XG production increase, structural and viscosity modifications, and antioxidant properties incorporation. Overall, this work points out a new MOP application contributing to the sustainability of the olive oil productive chain from a biobased circular economy perspective.

2023Journal article

Open access