MICROWAVE ASSISTED EXTRACTION 101: WHAT, HOW, AND WHY

RAPID, HIGH YIELD, AND ENERGY EFFICIENT EXTRACTION

The goal of extraction in the food and fragrance industry is to separate valuable compounds from raw materials, like lavender oil from lavender, while preserving specific physical-chemical and organoleptic properties of the compounds, like taste, smell, and color. Traditional extraction techniques have been used for hundreds of years, but often suffer from low yields, long processing times, and energy inefficiencies. To address these challenges, novel extraction techniques like microwave assisted extraction (commonly abbreviated as MAE) are gaining in popularity to deliver faster processing times, higher yields, and greater energy efficiency.

WHAT IS MICROWAVE ASSISTED EXTRACTION?

At it’s core, microwave assisted extraction uses microwave energy to volumetrically heat polar molecules within a sample, leading to compounds diffusing into the solvent. It starts with a microwave generator converting electric energy into microwave energy. From there, the microwave energy is directed to a chamber via waveguides.

Inside the chamber, the microwave energy selectively targets polar molecules within the sample, causing them to rapidly rotate to align with the changing field direction. This rotation converts microwave energy to thermal energy by generating heat through friction between molecules, rapidly increasing the temperature. As a result, the water matrix vaporizes and the cell walls and/or plasma membranes break, diffusing the plant compounds into the solvent. The mixture can then be separated or filtered to remove the solvent or plant matter, creating an extract (like orange extract). Alternatively, it can remain in the solvent to create a diluted extract or flavored solvent (like orange infused oil).

THE IMPORTANCE OF SOLVENT CHOICE

Like all extraction techniques, it’s important to choose a solvent that will produce a high quality product with optimal yields. With microwave assisted extraction, solvent choice is important due to how different solvents interact with microwave energy – particularly in terms of their polarity and ability to absorb microwave energy.

NON-POLAR SOLVENTS

Since microwave energy targets polar molecules, non-polar solvents (i.e. solvents that don’t contain polar molecules like oils) are generally transparent to microwave energy. Meaning microwave energy will pass through the solvent with minimal heating, instead primarily targeting the polar molecules within the plant tissue.

For instance, when a mixture of plant material and non-polar solvent is subjected to microwave energy, only the polar molecules within the plant cells are heated. These heated compounds will then diffuse into the relatively cool, non-polar solvent. This selective heating approach can minimize thermal degradation of both the solvent and the target compounds. Quite a useful technique for extracting heat-sensitive compounds.

POLAR SOLVENTS

On the other hand, polar solvents (i.e. solvents that contain polar molecules like water or ethanol) readily absorb microwave energy, leading to rapid and uniform heating of both the solvent and the plant tissue. In this case, microwave energy heats the entire mixture (solvent and plant tissue) causing polar molecules in both components to absorb energy and increase in temperature. This can result in faster extraction because the entire mixture is heating but also means that the extract is collected in a relatively hot solvent, which may not be ideal for temperature-sensitive compounds.

BENEFITS OF MICROWAVE ASSISTED EXTRACTION

IMPROVED EXTRACTION YIELD

Compared to traditional extraction methods, microwave assisted extraction could improve the yield of secondary metabolites and aroma compounds. This is because microwave energy vaporizes the water matrix within cells, which can lead to the cell walls and/or plasma membranes breaking. Since majority of the secondary metabolites and aroma compounds are in the cell walls or cytoplasm, the cells breaking can shorten the path for diffusion, making it easier for the plant compounds to be released into the solvent.

RAPID 

Microwave assisted extraction is generally much quicker than traditional extraction methods because microwave energy selectively targets polar molecules within the sample, leading to rapid volumetric heating (core-to-surface heating). For instance, it can take roughly 30 to 90 minutes, depending on the plant material, solvent, and desired end product. Whereas traditional techniques usually involve emitting energy (like steam) into a chamber, a lengthy surface to core heating process that can take hours. 

ENERGY EFFICIENT 

Microwave assisted extraction is more energy efficient than traditional techniques because microwave energy selectively targets polar molecules. This allows for most of the energy to be transferred to the molecules, with little lost to the surrounding environment. Whereas traditional extraction techniques usually emit energy (like steam) into a chamber with no way to selectively heat.  As a result, energy is often wasted heating up the surrounding environment (like the chamber walls or air) and non-relevant plant tissue. 

CONCLUSION: SPEED UP PRODUCTION WITHOUT SACRIFICING QUALITY  

Microwave assisted extraction offers a powerful alternative to traditional extraction techniques, often delivering improved yields, higher efficiency, and faster processing. By selectively targeting polar molecules within plant materials, microwave assisted extraction can cause rapid diffusion of plant compounds while preserving important sensory and chemical properties of the compounds. This makes it an ideal candidate for applications in the food and fragrance industry like creating infused oils or oil concentrates. As demand for faster and more efficient processes grow, microwave assisted extraction is a great opportunity to speed up production without sacrificing on quality. 

Contact us to learn more about microwave assisted extraction.