Episode 100: An investigation into freeze-drying and spray-drying effects on peptides

There is no post like post number 100 to try something new on Bart’s Blog. Today, I go on a journey of reminiscence, but I dedicate the 100th blog post to a fresh new idea. I summarize for you the findings of an interesting research paper I recently read. So if you are ready to get to the bone of freeze drying versus spray-drying effects on bioactives, in particular the peptide profile of a plant protein hydrolysate, give it a try and read on.

Dear readers, I simply can’t believe it, but I am sitting down to write the blog’s 100th post! My goodness, what a journey it has been from circuses to lifeguards to nightmares to music to sports to movies to gardening to oh, so much food, and so much wine!

Oh right! And some science in-between! Well, you know very well that we cover chromatography, rotary evaporation, freeze-drying and spray-drying topics here and I hope we continue to do so in the next 100 posts to come.

As it is a bit of a special (okay, very special) post, I’ve decided to do things a bit differently than usual. I would like to share with you findings from a very interesting research paper I read recently and, as I consider to be appropriate, to dedicate the post to our newcomer: spray drying.

First off, here is the paper:

https://www.mdpi.com/2227-9717/9/3/425/htm

Second off, let me tell you all the exciting things they find out about freeze-drying and spray-drying effects on bioactive peptides and why you should care in the first place.

High-protein ingredients have increased in popularity due to their nutritional and functional benefits upon consumption. However, processing of these protein ingredients and the enzymatic hydrolysates derived from them can be problematic, particularly during drying, as this step can induce protein denaturation and peptide aggregation.

Spray drying and freeze drying are common methods used to convert an ingredient into a powdered version of itself to:

  • Increase product stability
  • Facilitate more efficient transport options
  • Improve product shelf life thanks to reduced water activity

I’ve explained how spray drying and freeze drying work in a previous blog post. But I will summarize these techniques once more here:

How it worksBenefitsLimitationsRecommended Applications
Spray DryingTransforms a solution or dispersion from a liquid to a dry state, where a liquid suspension is atomized into a chamber with hot dry air, evaporating the droplets and resulting in fine particles with low moisture content- Rapid
- Simple
- Create particles with defined particle size
- Possibility to encapsulate the ingredient to protect it from the environment
- Relatively inexpensive		- Can lead to loss of key actives
- Can cause loss of nutritional benefits that exist in the raw source
- Can damage heat-sensitive proteins
- Can be technically challenging		Preferred for low cost and higher scale production throughput
Freeze dryingWater is removed by sublimation from a frozen state und reduced pressure. Helps retain stability of physiochemical and biological activities of peptides- Comparably more costly
- Long process
- Requires less surveillance and management		For applications where product stability is a concern and smaller product volumes are required

Other considerations include physical and chemical attributes such as solubility, taste, density, colour, and others, which need to be assessed for freeze-drying and spray-drying effects to best align with the desired end-product formulation.

Now, in the paper I wanted to review for you,

The authors use peptidomic and machine learning techniques to see if the drying approach for a plant protein hydrolysate could influence peptide profile and subsequent predicted functionality.

The authors wanted to investigate the freeze-drying and spray-drying effects not just on physical attributes and protein content, but also on peptide content. Bioactive peptides are an integral part of the functionality of an active ingredient. Specific activities attributed to natural peptides include anti-aging, anti-cancer, anti-inflammatory, anti-oxidant, cholesterol lowering and other characteristics. Many peptides have been shown to possess more than one bioactivity.

Interestingly, the authors did not find many great differences in the peptide profile and functionality of spray-dried and freeze-dried preparations.

  • They do point out several variances they note in their own research and existing scientific work with regards to freeze-drying and spray-drying effects on preparations, including:
  • Slightly darker colour in spray dried sample
  • Some reports of heat-induced protein aggregation with increasing drying temperatures in spray drying (lower number of peptides)
  • Increase in peptides with Asp, His and Lys amino acids in freeze-drying preparations versus spray-drying preparations (as expected due to previous reports that Lys is particularly susceptible to damage during spray drying)
  • A slight trend towards longer, higher molecular weight, and more positively charged peptides with freeze-drying preparations (may lend itself to the consideration that freeze drying is a gentler process than spray drying)
  • Peptides exclusive to the spray-drying preparations had a greater proportion of negatively charged peptides compared to freeze-drying preparations (could contribute to the increased solubility typically associated with spray-dried powders)
  • Peptides exclusive to freeze-drying preparations carry a slightly less negative charge of 0.24, which when combined with increased peptide length, molecular weight and physical characteristics may contribute to the reduced solubility associated with lyophilized powders
  • A 1.74% increase in hydrophobicity predicted with spray drying when bioinformatics approach was used – could be related to slight, but non-significant increases in hydrophobic amino acids (Ala, Met, Phe, Pro, Try and Val) in peptides exclusive to spray-drying preparations
  • Anti-inflammatory bioactivity is predicted to be comparable for both spray-drying and freeze-driyng applications

So there you have it, a nice little comparison, yet again, of freeze-drying and spray-drying effects, but this time on bioactives and focused on peptides.

If you are interested in more information on working with proteins and peptides, download a free application review on purification of proteins and peptides.

Did you enjoy this type of post? Let me know in the comments so I know if I should do this with you sometime in the future again!

Till next time,

The Signature of Bart Denoulet at Bart's Blog