by Melissa Barrett April 13, 2018
This blog is a follow up to Protecting your Product – Preservatives
In the previous post we discussed what preservatives are, what they aren’t, when to use them and when you can get away without using them.
This time we will be looking at how preservatives work, the different types available, natural vs synthetic and how to ensure your preservatives are safe and effective in your formulations.
Last time we learned that preservatives prevent the growth of unwanted microbes in our products and thus keeping them safe and effective – but how do they do this?
Generally, preservatives have two main mechanisms of action:
Microbicidal: actively killing microbes and ideally their spores
Microbistatic: inhibits the growth and multiplication of microbes
Different preservatives achieve this in different ways but generally it is through one or more of the following actions: interference with the cell membranes, enzymatic function, protein structure or cellular metabolic processes.
Preservatives can be further categorised according to the microbes they target. Some are best used against bacteria and some are best used against yeasts and moulds. These two types need to be used together to prevent the growth of all types of harmful microbes.
For example Sodium Benzoate works well against bacteria but performs poorly against yeast and mould. Typically it will be in used in conjunction with Potassium Sorbate which is effective against yeast and moulds but ineffective against bacteria.
Thankfully it is now common to get one product which combines the two types – these products are referred to as broad spectrum preservatives.
Preservatives either natural or synthetic are not particularly nice compounds – they either kill or inhibit the growth of cells and so have the potential to do harm if used incorrectly.
In general, conventional synthetic preservatives tend to be more effective across a wider range of conditions than natural or nature-identical preservatives. It is worth noting that all approved preservatives are considered safe in your finished product when used correctly.
Those who are making claims about having all-natural ingredients or wanting to certify their product as organic you may find you are restricted with what preservatives you can use.
All preservatives will have their limitations, typically we need to be concerned with the following:
Inclusion rate: the amount of preservative used will greatly affect how well it performs in your product. The general rule of thumb is that we try to use the least amount required to effectively preserve the product as all preservatives have the potential to cause irritation. Generally, the inclusion rate will be provided as a range e.g. 0.5 – 2%. When working out how much to use make sure you consider all factors that affect preservative performance see Formulation & Manufacturing considerations below…
pH: the pH of your formula can dramatically affect the performance of the preservative. Always adjust the pH of your formula to within the range required for your preservation system. Tip: pH can drift over time by +/- 10% so ensure you adjust pH accordingly
Temperature: some preservatives cannot tolerate hot temperatures and must be added during the cool down phase of manufacture. Also, if you intend to sell you product in a country where the temperature is likely to go above 40°C then ensure you use a preservative that can tolerate such temperatures.
Solubility: knowing whether a preservative is soluble in oil or water is crucial both for determining a suitable ingredient for your product but also for working out your manufacturing process.
Ingredient selection: Certain ingredients will increase the risk of your product growing microbes and so how you preserve your formula should reflect this. Plant matter (such as seeds or natural exfoliators), plant oils, vitamins, actives, sugar, honey, glycerine, extracts, clays etc all have the potential to either contain microbes or feed microbes.
Certain ingredients in your formulation can directly affect the ability of your preservative to do its job. A good example of this is surfactants – a high surfactant load will affect many preservatives. Conversely, some ingredients can help the activity of your preservatives. The lesson here is to research your ingredients and their compatibility with one another.
Raw material handling: How you and your supplier handle and store raw materials can greatly affect the amount of microbes you introduce to your product. The less microbes you introduce the less preservative you might need so always ensure storage areas and packaging are clean and suitable.
Manufacturing hygiene: A clean workspace and using clean materials will make a huge difference to the amount of microbes that are introduced to a product during manufacture. Ensure all equipment is sanitised and appropriate personal hygiene practices are followed.
Packaging: Packaging type will have a great impact on the stability of your product and the amount of preservation it will require. Open top jars for example will need more preservation as they are repeatedly exposed to the air and user’s fingers. On the other hand, packaging like airless pumps may require less as there is no contact with the user or the air.
Testing: We are often asked “if I add X amount of preservative to my product – what will the shelf life be?” Unfortunately, it is not that simple. The only way to effectively determine the shelf life of your product is to have it tested. There are independent labs set up to do this and if you are serious about selling your product then we advise using one of them.
So, in conclusion, preservatives themselves are not scary but learning how to use them can be and not using them will be even scarier! Remember, always handle any ingredients with care and make sure you are informed before you start using it.
Next up we will discuss something that follows nicely on from preservatives – Antioxidants.
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