Whereas some ingredients are created through rigorous work in the lab, botanicals have slowly generated over the course of natural history. Botanical ingredients are increasingly valued by today’s consumers and manufacturers—due to willingness to go back to the source adding naturality but also linked to the perceived benefits of botanicals around emotions and healthy halo—but they’ve played an active role in taste, nutrition and health for centuries, from the ritual of drinking flavourful herbal tea infusions to the use of flowers, roots and herbs to treat illnesses.
Although there are several traditional and trusted methods for extracting botanical ingredients, technological advances have driven process innovations, including extraction methods that are more sustainable and efficient than before and may even produce high-quality products. We take a deep-dive into extraction technologies, with input from Li Pan, PhD, Kerry Research Scientist-Taste Innovation; Wangbao Gan, PhD, Kerry Technology Director; and Zeynep Ilkbahar, Kerry Global Taste Regulatory Lead.
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Traditional botanical extraction processes
To turn a solid plant into a soluble compound, active ingredients have typically been added to a liquid such as water and/or alcohol then separated or blended. The resulting botanical products can be used in food and beverage products ranging from soft drinks, alcoholic beverages, hard seltzers and ice creams to great confectionary products.
Here are some of specific techniques for creating different botanical formulations:
- Tincture: Raw materials such as leaves, roots, seeds and flowers are added to a room temperature blend of ethanol and water. After a defined period, the solids and liquids are separated, and the remaining liquid is the tincture.
- Infusion: Here too, raw materials such as leaves, roots, seeds and flowers are added to a blend of ethanol and water, but the mixture is heated. After a defined period, the solids and liquids are separated, and the remaining liquid is the infusion.
- Distillate: To make a distillate, we start with a tincture then run a distillation process, capturing the vapor from the heated liquid. Our scientists then fractionate the liquid—repeatedly heating and condensing the liquid—which can yield a purer final product, known as a distillate, which is then blended.
- Extract: Create an infusion, separating the liquid and solid then re-run them through the infusion process. The resulting concentrated paste or liquid is the extract. It may then be supported on a carrier like glycerine, triacetin or propylene glycol.
New Botanical Extraction Technologies on the Horizon
Although the above techniques are proven ways to create quality botanical extracts, pressures about safety, sustainability and cost are driving the industry to find greener approaches to extracting biomasse compounds from natural resources. For example, new extraction and fractionation technologies have been developed so that target nutrients, functional components and flavour ingredients are extracted and enriched while contaminants, off-notes, and other undesirable components are removed.
The below recently developed technologies, which are categorized under the headings "Extraction Method", "Fractionation and Separation" and "Drying Technologies", are involved in different stages of botanical extract preparation. Although not all technologies are widely available, many of the promising ones may soon be used by Kerry in the botanical process.
Conventional solvent extraction is still widely applied in the food industry, with new technologies improving extraction efficiency and quality, lowering the cost and using more sustainable techniques. Extraction methods for preparing botanical extracts are based on the differences in physical or/and chemical properties of the mixture, such as molecular size, polarity and electrical charges of different ingredients.
- Freeze-Thaw Assisted Extraction
The freeze-thaw method is regarded as a sustainable technique for the decomposition of plant tissue and cell membrane. The freeze-thaw pretreatment is able to increase the degree of cell membrane permeabilization greatly, thus improving the efficiency of the following extraction. This technology has been proved to have potential at improving the yield.
- Pressurized Hot Water Extraction (PHWE)
Water extraction is one of the cleanest and green technologies, although traditional water extraction often lacks efficiency and selectivity. PHWE is an extraction technology that uses super-heated water with a temperature above its atmospheric boiling point (100°c/273k, 0.1MPa), but below its supercritical threshold (374°c/647k, 22.1MPa), as the extraction solvent. PHWE has been mainly used to extract relatively polar extracts.4
- Intensification Methods Assisted by Ultrasonication and Microwaves
Ultrasound and microwave-assisted extraction offer several advantages such as efficient cell wall disruption. Microwave-assisted extraction (MAE) involves the utilization of microwave radiation to heat the sample-solvent mixture, making the solvent more accessible in the sample and accelerating the partitioning process. Ultrasound assisted extraction (UAE) uses high frequency (20 kHz) pulses to generate local hotspots at macroscopic scale with high shear stress and temperature by producing cavitational bubbles, which burst at the surface of the plant sample matrix, induces the destruction of plant cell walls and facilitates the mass transfer of active compounds into the solution. In comparison with conventional methods, ultrasound and microwave-assisted extraction offer not only efficient cell wall disruption, but also use less solvent and less time5.
- Supercritical Fluid Extraction (SFE)
Supercritical fluid extraction (SFE) has become one of the most promising green extraction techniques to date. SFE utilizes supercritical fluids—which exhibit properties between liquid and gas above their critical points—as extraction solvents. So far, CO2, which has a low critical point (73 atm and 31°C) and allows for a relatively mild operation condition, is the most commonly used supercritical fluid. Besides the advantages of being clean, safe and cost effective, the most outstanding advantage of SFE over traditional extraction procedures is that the efforts needed for the post-extraction clean-up steps are dramatically reduced. Today, SFE on a large scale is mainly used for decaffeination and the production of hop extracts. However, there is a growing interest for other industrial applications such as the extraction of aroma and oil from fruits and spices as well as flavonoids and terpenes from functional botanicals.6
Fractionation and Separation
Further fractionation and separation is sometimes needed to produce products containing target ingredients with higher purity. Often selected based on the different chemical or physical properties of various ingredients, common technologies used for separation including chromatographic techniques, liquid-liquid extraction, centrifuge, distillation and membrane filtration. Supercritical fluid extraction, as mentioned in the previous section, is also been used for separation since it can be used for extraction on solid raw material, but also conduct fractionation for liquid extracts. The below points mainly focus on chromatography, membrane filtration and liquid-liquid extraction.
- Column Chromatography
Chromatographic procedures are the most selective, the most diverse, and the most widely used techniques in the fractionation of extracts. The separation principle of chromatography based on the molecules varying in size, charge, polarity and solubility. In the food industry, various macroporous polymeric resins are the most common chromatography used for scale-up processes, especially in juice production, fermentation and dairy. Resin chromatography has been successfully applied for debittering, demineralization and decolorization as well as for removing toxins and pesticides and recovering pigment, polyphenols, proteins and starches with high qualities. Although this process has high selectivity when compared to other separation methods, the limited scale-up capacity of chromatography is a disadvantage. To improve this deficiency, highly engineered process implementing chromatographic separation such as Simulated Moving Bed (SMB) process and Sequential Multi Column Chromatography (SMCC) have been developed in past decades, which dramatically improve chromatography production and cut costs.7
- Membrane Filtration
As a processing and separation method, membrane filtration is a green technology gaining wide application in the food industry. The pressure-driven membrane processes include microfiltration, ultrafiltration, nanofiltration and reverse osmosis according to the pore size of the membrane. With different pore sizes (or molecular weight cut-off, MWCO) of membranes, the separation of components with a large range of particle sizes is feasible. However, the membrane separation principle is not only based on the pore sizes, but also the charge of the molecules and their affinity for the filtering membrane. This makes membrane separation more complicated but also provides more flexibility for application. Membranes have some advantages over traditional technologies. For example, the scale-up systems are highly automated and intuitive, and allow operation at room temperature. Small MWCO filtrations can also be used to remove extra solvents without thermal treatment as in a traditional evaporate process.8
- Continuous Countercurrent Column
Liquid–liquid extraction, also known as solvent extracting, is a well‐established separation technique that separates components by utilizing an unequal distribution of the components between two immiscible liquid phases. Mixer-setters, Centrifugal Contactors and Continuous Countercurrent Column are major scale-up operations based on this technology. In a Continues Extraction Column process, the dispersed drops move counter currently against the flow of the second (continuous) phase, then the solute rich stream is collected either from the top or bottom depend on if the extract solvent is heavier or lighter than the carrier solvent.9
Sometimes, botanical extracts, especially aqueous extracts, need to be dried into a solid form for a longer shelf life. The optimized and well controlled drying process can produce a high quality product with the lowest losses of active ingredients and flavors while maintaining microbial safety. Well-known dry technologies in the food industry such as spray drying, vacuum belt drying and drum drying won’t be reviewed here. Instead, more advanced drying technology including freeze drying, microwave-vacuum drying and infrared drying technologies are briefly introduced.
- Freeze Drying
Freeze drying, also known as lyophilization, is a drying process in which the liquid medium (usually water) in samples is crystallized at a low temperature and then sublimated from the solid state directly into the gaseous state. Compared to conventional drying technologies, the key advantages of freeze drying include the retention of morphological structures as well as the biological and chemical properties and high recovery of volatile and heat sensitive components. Despite the unbeatable advantages, freeze-drying is still considered as one of the most expensive drying processes because of the high energy consumption and high costs on both operation and maintenance. Today, freeze-drying is used in a wide range of common food products include fruit and vegetables, instant coffee and dairy products.11,10
- Microwave Vacuum Drying
Microwave vacuum drying is a dehydration process that combine microwave radiation energy and vacuum. The microwave radiation can heat the samples rapidly by converting the electromagnetic energy to thermal energy. However, the vacuum reduces the boiling point of water, keeping the product temperature low, as well as creating a pressure gradient that enhances the drying rate. In comparison to freeze-drying, it is more economical, as drying progress is much faster and thus allows a higher throughput for the same plant dimensions.12
- Infrared Drying
Infrered (IR) radiation using wavelengths that range from 2.5 to 200 μm represents a new method applied to various thermal processing operations in the food industry. The use of IR radiation for dehydrating foods has many advantages. Besides taking less time and energy, the drying process can be precisely controlled and the temperature is distributed uniformly in the drying system, which greatly improve the quality of finished products. It has also been found that thermal processing using infrared can increase the levels of antioxidants and phenolic compounds of the extract from natural resource such as peanut shell, grape and citrus, when implemented in solvent extraction process, such microwave and ultrasonication.13
- Yan Jiao, et al., Effect of Freeze-Thaw Pretreatment on Extraction Yield and Antioxidant Bioactivity of Corn Carotenoids (Lutein and Zeaxanthin). Journal of Food Quality, 2018 |Article ID 9843503 | https://doi.org/10.1155/2018/9843503
- Huixia Zhu, et al., Freeze–thaw repetition as an auxiliary method to promote efficient separation of hemicellulose from poplar. Green Chemistry, January 2020, 22(21) DOI: 10.1039/C9GC03792F
- R. Vali Aftari, et al., Antioxidant activity optimisation of Spirulina platensis C-phycocyanin obtained by freeze-thaw, microwave-assisted and ultrasound-assisted extraction methods. Quality Assurance and Safety of Crops & Food. 2017, 09(1): 1-9 DOI https://doi.org/10.3920/QAS2015.0708.
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- M. Vinatoru, et al., Ultrasonically assisted extraction (UAE) and microwave assisted extraction (MAE) of functional compounds from plant materials. Trends in Analytical Chemistry, 2017, 97:159-178
- Andrea Capuzzo. Supercritical Fluid Extraction of Plant Flavors and Fragrances Molecules 2013, 18: 7194-7238; doi:10.3390/molecules18067194
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- Jack D. Law and Terry A. Liquid-Liquid Extraction Equipment Doi: http://www.cresp.org/NuclearChemCourse/monographs/11_Law_Liquid-liquid%20extraction%20equipment%20jdl_3_2_09.pdf
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- Sándor Ferenczi, et al., Evaluation of Microwave Vacuum Drying Combined with Hot-Air Drying and Compared with Freeze- and Hot-Air Drying by the Quality of the Dried Apple Product. Periodica Polytechnica Chemical Engineering, 2014, 58(2), 111-116
- Salam A. Aboud, et al., A Comprehensive Review on Infrared Heating Applications in Food Processing. Molecules, 2019, 24, 4125
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