Figure 1.
Figure 2.
Figure 3.
Detailed encapsulation methods, materials, proportions, and stability, release profile, and functionality of encapsulated essential oils
| Method | Suitable materials | Stability | Release profile | Functionality | Reference |
|---|---|---|---|---|---|
| Spray-drying | Maltodextrin, Arabic gum, whey protein, gelatin, lecithin | High stability under optimized drying conditions; protects from light and oxygen; moderate thermal/humidity stability | Controlled release depending on wall material; suitable for long-term storage | Cost-effective; improves shelf-life, preserves bioactivity, enhances photostability | Aguiar et al. (2020) |
| Freeze-drying | Maltodextrin, trehalose, gelatin, trehalose, polysaccharides | Retains volatile compounds but may lose some due to freezing | Gradual release over time | Preserves essential oils during storage; suitable for heat-sensitive compounds | Sousa et al. (2022) |
| Extrusion methods | Alginate, chitosan, carrageenan | Moderate (pH-sensitive) | Controlled release based on polymer properties | Produces uniform particles; suitable for large-scale production | Chiriac et al. (2021); Asbahani et al. (2015) |
| Solvent evaporation | Poly(lactic-co-glycolic) acid (PLGA), ethyl cellulose, poly-ε- caprolactone (PCL) | High stability with minimal degradation; sensitive to solvents | Sustained release due to polymer matrix | Controlled release; targets methanogens; protects essential oils from external factors; enhances antioxidant capacity | González-Reza et al. (2020) |
| Complex coacervation | Gelatin-gum Arabic, chitosan-alginate | High pH/thermal stability; stable against environmental factors like light and oxygen | Controlled release through polymer degradation | Improves bioavailability, masks odor and taste | Muhoza et al. (2022); Sousa et al. (2022) |
| Ionic gelation | Alginate, chitosan, pectin | Stable in mild processing conditions | Rapid release in aqueous environments | Simple and fast process; protects sensitive compounds | Yammine et al. (2024); Chiriac et al. (2021) |
| Emulsion-based | Alginate, cyclodextrins, lecithin | Stable in emulsified form; low oxidative stability | Release depends on emulsion stability | Suitable for hydrophilic and hydrophobic compounds | Lu et al. (2016); Sousa et al. (2022) |
| Co-extrusion and gelation | Alginate-chitosan multilayers | High (multilayer protection) | Delayed (lower gastrointestinal) | Targeted delivery; reduces rumen bypass | Homayouni-Rad et al. (2024); How et al. (2022) |
Materials employed in the encapsulation of essential oils to mitigate methane emissions in ruminants
| Material | Type | Encapsulation methods | Key benefits | Limitations | Reference |
|---|---|---|---|---|---|
| Maltodextrin | Polysaccharide | Spray-drying, freeze-drying | Cost-effective, high solubility, improves shelf-life, preserves bioactivity | Hydrophilic; may have limited protection in aqueous environments | Fernandes et al. (2014) |
| Arabic gum | Polysaccharide | Spray-drying, coacervation, complex coacervation | Emulsifying properties, stabilizes volatile compounds | Limited thermal stability, expensive | Fernandes et al. (2014); Al-Hamayda et al. (2023) |
| Whey protein | Natural polymer | Spray-drying, coacervation | High encapsulation efficiency, biodegradable | Sensitive to pH and heat | Xiao et al. (2022) |
| Alginate | Natural polymer | Extrusion, ionic gelation | pH-sensitive, controlled release, suitable for sensitive compounds | May have rapid release in certain conditions | Benavides et al. (2016); Sousa et al. (2022) |
| Chitosan | Natural polymer | Co-extrusion, extrusion, ionic gelation, coacervation | Improves bioavailability, enhances stability | pH-dependent release (insoluble at neutral pH) | Arias et al. (2021); Negi and Kesari (2022) |
| Gelatin | Natural polymer | Coacervation, spray-drying, freeze--drying | Thermo responsive, biocompatible, high stability, protects from light and oxygen | Requires cross-linking for stability; may not be suitable for all essential oils | Sousa et al. (2022) |
| Trehalose | Disaccharide | Freeze-drying | Protects essential oil volatiles, stabilizes during drying | High energy input required | Domian et al. (2015) |
| Poly (lactic-co-glycolic) acid (PLGA) | Synthetic polymer | Solvent evaporation | Biodegradable, controlled release, improves bioavailability | Expensive, may require specific processing conditions | Blasi (2019) |
| Ethyl cellulose | Synthetic polymer | Solvent evaporation | High mechanical strength, sustained release | Hydrophobic; may have limited biodegradability | Julaeha et al. (2023); Sousa et al. (2022) |
| Poly-ε-caprolactone (PCL) | Synthetic polymer | Solvent evaporation | Slow degradation, long-term release | May require organic solvents for processing | De Ávila et al. (2017); Chiriac et al. (2021) |
| Polysorbate (Tween 80) | Surfactant | Emulsion-based | Enhances essential oil solubility, stabilizes nanoemulsions | Oxidative instability; requires antioxidants | Baranauskaite et al. (2021); Sousa et al. (2022) |
| Lecithin | Lipid-based | Emulsion-based, spray-drying | Natural emulsifier, improves bioavailability | Sensitive to pH and temperature | Sánchez-Osorno et al. (2023) |
| Vegetable hydrogenated fatty acids | Natural matrix | Emulsion-based, microencapsulation | Cost-effective, protects lipophilic essential oils; effective rumen by-pass, protects essential oils from ruminal degradation | Prone to oxidation over time; may require specific processing conditions | Amin et al. (2021) |
Summary of in vitro and in vivo studies on the use of encapsulated essential oils for methane emission reduction in ruminants
| Encapsulated essential oil | Encapsulation method | Test system | Ruminant species | Dose | Observed effect | Reference |
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| Blend of essential oils | N/A | in vivo | beef steers | 150 mg/kg DM |
| Alemu et al. (2019) |
| Blend of essential oils (cinnamaldehyde, eugenol, carvacrol, and capsicum oleoresin) | Fat matrix | in vivo | sheep | 0, 200, and 400 mg/kg dietary DM |
| Soltan et al. (2018) |
| Blend of essential oils (cinnamaldehyde, named Olistat-Cyn, Olistat-G, and Olistat-P) | Fat matrix | in vitro | cows | 1.0 g |
| Amin et al. (2021) |
| Blend of essential oils | N/A | in vitro | dairy cow | 0, 50, 100, 200, 300, 400, and 500 mg/L |
| Ahmad (2023) |
| Blend of essential oils | N/A | in vitro | sheep | 0, 400, 800 μg/kg DM |
| Ahmed et al. (2014) |
| Fruit peel phytonutrient | Spray-drying with chitosan | in vitro | cows | 0, 2, 4, and 6% DM |
| Phupaboon et al. (2024) |
| Blend of essential oils | Fat matrix | in vivo | dairy cows | 1.2 g/cow/day |
| Tondini et al. (2024) |
| Lemongrass and man gosteen peel phytogenic compounds | Ionic gelation | in vivo | steers | 0, 1, 2, 3, and 4% of substrate |
| Prachumchai et al. (2024) |
| Pepper blend | N/A | in vivo | bullocks | 0, 200, and 400 mg/kg of concentrate |
| Giacomelli et al. (2023) |
| Phytogenic blend | N/A | in vivo | steers | 300 mg/kg of concentrate |
| Brunetto et al. (2023) |
| Yucca schidigera extract | Nano-encapsulation | in vitro | N/A | 0.25, 0.5, and 1 mL/g DM |
| Botia-Carreño et al. (2024) |
| Acacia tannin extract | Gum Arabic-maltodextrin microparticles | in vitro | sheep | N/A |
| Adejoro et al. (2019 b) |
| Blend of essential oils | N/A | in vivo | bulls | 150 mg/kg DM |
| Martins et al. (2018) |
| Phytonutrient of Wolffia globosa | Spray-drying using chitosan | in vitro | dairy cows | 0%, 2%, 4%, and 6% of total DM substrate |
| Muslykhah et al. (2024) |
Overview of encapsulation techniques with their physical and chemical mechanisms (Adapted from Yammine et al_, 2024 and Li et al_, 2025)
| Technique | Type | Process description | Advantages | Disadvantages |
|---|---|---|---|---|
| Spray-drying | Physical | Essential oils are atomized into fine droplets and rapidly dried using heated air. Protective wall materials (e.g., polysaccharides) can be applied to enhance stability. |
|
|
| Freeze-drying | Physical | Involves freezing followed by sublimation of water under reduced pressure. The technique helps preserve essential oils but may result in some loss due to temperature sensitivity and volatility. |
|
|
| Extrusion methods | Physical | Essential oils are processed through an orifice under controlled conditions. Techniques include: hot-melt extrusion, melt injection, centrifugal/co-extrusion, electrostatic spinning, and particle formation from gas-saturated solutions. |
|
|
| Solvent evaporation | Physical | A four-step process involving dissolution of core and shell materials, emulsification, solvent removal to solidify microcapsules, and final drying. |
|
|
| Complex coacervation | Chemical | Occurs through interactions between oppositely charged biopolymers, leading to phase separation. The polymer-rich phase is collected to encapsulate essential oils. |
|
|
| Ionic gelation | Chemical | Involves ionic crosslinking of biopolymers, where essential oils are incorporated and trapped within the polymer matrix. |
|
|
| Emulsion-based encapsulation | Chemical | Two immiscible liquids are mixed, forming dispersed droplets that serve as carriers for essential oils within a stable emulsion system. |
|
|
| Co-extrusion and gelation | Chemical | Droplets are generated through controlled vibration and fall into a gelling solution, effectively encapsulating volatile bioactive compounds. |
|
|