A whiff of microencapsulation of flavour and fragrances by spray drying

It’s time to wake up and smell the roses. In this post, capture the fragrance, avoid the thorns by gaining some tips on how to use spray drying for microencapsulation of flavour and fragrances. Learn about the benefits of microencapsulation, how to select a carrier material and important factors affecting the emulsification step. Read on and enjoy the smell of success in preserving your flavour and fragrances.

My daughter visited last weekend and we sat in the garden enjoying an unusually warm autumn day. I had hung the laundry outside to dry in the sun and the pleasant scent of cleanliness tickled our noses whenever the wind blew in our direction. We also had to laugh a little remembering one strange phase that my daughter went through during her pre-teen years. She would scream and yell that her clothes, fresh off the drying rack, smelled horrible and all her friends would laugh at her. The drama lasted until we demonstrably switched laundry detergents and my daughter finally calmed down.

Our lives wouldn’t be much without our senses. I can’t even keep them off the blog! Just look back at a previous blog post, where I wrote about how to satisfy your sense of taste by creating magical flavours using rotary evaporation. Funnily, it’s not the first time laundry has been featured on the blog either. A nice laundry drying discussion with my father-in-law led to a blog post on how shell freezing can speed up manifold freeze drying.

But our sense of smell is also incredibly powerful and deserves some attention. It’s about time that both flavour and fragrances got some time here on the blog. I say, we’ve talked about creating flavour already, let’s talk about how to preserve flavour. And I’ve got a great way to do this: mainly through microencapsulation of flavour and fragrances by spray drying!

The main reason we use encapsulation is to protect a sensitive compound in a solid matrix against damage from the surrounding environment during shelf life. Encapsulation is also useful for the sustained, controlled or targeted release of encapsulated products.

But do we really need to encapsulate flavour and fragrances? The short answer is yes.

Flavor and fragrance compounds used in food and cosmetic industries are rather volatile liquids that are often thermally and chemically labile, sensitive to air, light and irradiation. An effective approach for protection of these precious compounds is encapsulation of flavour and fragrances into carrier matrices.

In fact, you probably already know some of the commonly used encapsulated flavour and fragrances: fish oil, sunflower oil, vegetable oil, peppermint oil, limonene oil, walnut oil, chia oil, d-limonene phytosterols, and sulfur aroma, just to name a few.

And the reason I suggest encapsulating flavour and fragrances is because of the many advantages using a spray dryer offers:

  • Prolonged shelf-life
  • Controlled or delayed release
  • Protection against the environment
  • Covering of unpleasant or unwanted tastes and smells
  • Protection of the volatile compound from undesirable interactions

There are various techniques you can use to produce microcapsules, including spray drying, fluidized bed, extrusion, freeze drying, co-crystallization and coacervation, as well as organic phase separation. I want to focus on spray drying for several reasons. The method is simple in operation, highly reproducible, low in production costs and easy to scale-up. Because of this, encapsulation of flavour and fragrances by spray drying is the preferred choice of many formulators.

With this method, typically multiple-core microcapsules are produced, where the core material is dispersed throughout the carrier to form the protection shell.

I don’t want to get into too many specifics on spray drying, as I’ve covered spray drying basics on the blog before and if you want more details, take advantage a great free spray drying guide. Instead, I’d like to focus on how you can apply the method to flavour and fragrances.

Let’s first look at how you can choose the carrier material.

A variety of carriers or matrix materials are available for encapsulation. Your carrier should have properties such as water solubility, film forming and emulsification abilities, low viscosity, low hygroscopicity, low costs, a bland taste and high stability.

Common carrier materials include:

  • Carbohydrates: maltodextrin, pectin, sucrose, cellulose (e.g.: Hydroxypropyl methylcellulose(HPMC) ), gum arabic, cyclodextrins, modified starches (e.g.: Hi-CAP100, N-LOK, CAPSUL, ENCAPSUL855, CRYSTAL TEX 627, CIEmCAP12633, CIEmCAP12634, CIEmCAP12635 and others
  • Proteins: whey protein concentrate (WPC), whey protein isolate(WPI), soy protein, caseinates
  • Others: skimmed milk powder (SMP), gelatin, wax

Now that you’ve chosen your carrier material, let’s discuss the actual emulsification process. A key step in the encapsulation of flavour and fragrance is the preparation of the initial feed emulsion. This step determines the retention of volatiles and encapsulation efficiency of the active compound. So let us devote some time to perfecting our emulsification conditions.

Factors affecting emulsification

1. Solids concentration/carrier material – The effect of solids concentration depends on the type of core material (in our case the flavor or fragrance) to be encapsulated. Research shows that increasing the concentration of carrier material increases the encapsulation efficiency and retention of the core material. Possibly, increasing the solids content reduces the time needed to form a semi-permeable membrane at the surface of the drying particle. A fast formation of the solid surface could be associated with low levels of surface oil content, as there is less opportunity for the core material droplets to come onto the particle surface.

2. Viscosity – The viscosity you use to spray dry the initial feed emulsion with your flavour and fragrances should be lower than 300 mPa. You might be tempted to use high viscosities because they prolong the atomization process and help form semi-permeable membrane rapidly. High viscosities suppress the internal circulations and oscillations of droplets, decrease the surface oil and improve retention. However, if the viscosity exceeds a certain threshold, the effect on retention becomes negligible due to larger exposure during atomization and difficulties in droplet formation.

3. Emulsion stability – Pay attention that your emulsion remains stable during the whole spray drying period. You could use the creaming index to analyze the emulsion stability. Consider using protein-polysaccharide complexes as stabilizers. These complexes can generate higher droplet density, reduce the density difference between oil and aqueous phases and decrease the driving force that causes phase separation.

4. Initial emulsion droplet size – I use the Sauter mean for statistical calculations of the initial emulsion droplet size. The final dried product specifications, including particle size, encapsulation efficiency, surface oil and volatile retention are usually influenced by the emulsion droplet size. For example, research has shown that encapsulation efficiency increases as emulsion decreases, as small emulsion droplets seem to be included and embedded more efficiently within the final microcapsules. Similarly, research has demonstrated that peppermint essential oil is better retained in smaller emulsion particles than in larger ones. We should consider that flavour could evaporate more easily from large emulsion particles during atomization. Flavour compounds that are highly volatile or soluble might suffer greater losses during spray drying. In general, a narrow droplet size distribution is beneficial to the spray drying process.

Are you still with me? I think I have a lot more to cover on this topic, including spray drying parameters, actual examples and further discussions on using spray drying for preservation of flavour and fragrances. But I don’t want things to get too long and stinky here, so I will continue with this topic in a future post. If you happen to want more in the meanwhile, I can recommend a brand-new webinar on spray drying of pharmaceutical compounds! And I promise I won’t keep you waiting long for part 2 of this post. Smell you later!

Till next time,

The Signature of Bart Denoulet at Bart's Blog