Once a standard in the industry, natural flavours are only now making a comeback. But what defines a flavour as ?natural? and how can compounding methods expand a flavourist?s palette? Philip Ashurst, PhD, reports
In today?s climate of increasing consumer interest in foods and beverages that can be described as natural, there is growing demand for flavours that can be similarly described. Natural flavours, however, are actually not new, and many of the earliest essences in widespread use would have merited this description. For example, a lemonade essence purchased in the 1950s would almost certainly have been derived from natural lemon oil and possibly enhanced with natural citral obtained through a distillation process.
Today, however, natural flavours are closely defined in food legislation. Important differences in what may or may not be described as ?natural? do arise between different markets and can have an impact on the development of particular flavours.
The flavour industry also recognizes (and uses) other descriptions that may be applied to particular natural flavours. For example, FTNF (from the natural fruit) is sometimes applied to flavours where the aroma substances are wholly derived from the fruit indicated by the flavour. The term WONF (with other natural flavours) is used to describe flavours where the aroma chemicals come from natural sources other than that suggested by the description of the flavour.
Natural flavours are usually, but not necessarily, liquid, and are usually simple compounded flavours and essences obtained by washing essential oils. Compounded flavours are made by mixing appropriate quantities of aroma chemicals in a suitable vessel with an approved food solvent.
Many manufacturers take the view that the solvent, which for most flavours is significantly greater in quantity than the total amount of aroma chemicals, takes the status of the aroma substances. However, if the solvent is ethanol, there are no particular difficulties in obtaining a natural (ie, non-synthetic) source of the solvent. Another important solvent is propylene glycol, which is not a natural product.
When a natural flavour is to be made by the process of partitioning an essential oil in solvent, it may, depending on the solvent, be possible to use a mixture of materials of natural origin. However, most manufacturers and users do not concern themselves with the status of the solvent(s) provided they are of appropriate quality.
The chemical substances that contribute to the aromas of natural products — fruits, fruit juices and other foods — are varied. The Dutch TNO organisation regularly updates its Volatile Compounds in Food publication, which currently lists at least 7,000 different substances found in some 400 foodstuffs.
Creative flavourists often define flavouring substances in terms of their organoleptic characteristics rather than their chemical formulas, and these are often grouped into 16 sensory areas that are sometimes described as the ?flavour wheel.? The characteristics of these 16 flavour areas and the types of aroma chemicals that demonstrate these are shown in Table 1.
Individual foods can be used to provide sources of all the individual aroma substances, although these are often present in the food in very low concentrations. The more important sources of natural aroma chemicals are essential oils, simple plant extracts, fermentation products, fruit juices, plant exudates and dairy products. Well-established physical processes have been developed whereby such sources can provide concentrates from which individual chemical compounds — the basic aroma chemical building blocks — can be isolated.
The quantities in which individual substances occur in many foods are, however, extremely small, as shown in Table 2. Since many, if not most aroma chemicals have taste thresholds in the parts per billion (and certainly parts per million) range, the consequence of this is that to extract pure individual aroma chemicals from their natural food source can be extremely time consuming and expensive.
For this reason, many natural aroma chemicals are used as mixtures, such as the aroma volatiles fraction that can be obtained during the process of concentrating a fruit juice. These volatile fractions can be a very important source of the basis of a natural flavour — especially those that merit the FTNF distinction.
Natural sources of aroma chemicals (or their precursors) where individual substances are present in economically significant quantities are invariably not actual foods (or beverages) but are materials used as ingredients. An example is vanilla beans, rich in vanillin, or pimento berries, which contain essential oils with a significant content of eugenol and isoeugenol. Ingredients such as these are widely used to provide the starting point for a wide range of natural aroma chemicals. Other true natural ingredients that can be obtained readily and affordably include a range of simple alcohols and fatty acids as well as aldehydes and ketones. Interaction between these components is the basis for the production of a huge range of further aroma chemicals.
The issue that concerns many in the flavour industry today is the interaction of natural chemicals. The simple question is whether a reaction involving natural chemicals to produce a further substance renders the substance natural. For example, every ?A? level chemistry student knows that ethanol (in wine, for example) will readily oxidise to acetic acid and that where ethanol and acetic acid remain in contact in an acid environment (such as wine), some ethyl acetate will form to create ?natural ethyl acetate.? However, if this process is carried out in a laboratory or factory environment with natural ethanol and acetic acid, the resulting ethyl acetate is regarded by some food legislation as not natural. EU countries require that for a flavour to be described as ?natural,? it must be made from flavouring substances that are obtained ?by physical, enzymatic or microbiological processes.? Other jurisdictions appear to take a different view based on the origin of the component substances.
Natural flavours of 20-30 years ago would have been typically based on materials such as fruit juice volatiles, essential oils (especially citrus) and even concentrated fruit juices. Such starting materials were often (and indeed still are) fractionated by simple liquid-liquid extraction processes and then enhanced by the more limited range of true natural aroma chemicals that can be readily obtained by solvent extraction (vanillin), distillation (citral) or microbiological fermentation (diacetyl). The resulting products would then typically be dispersed into an appropriate solvent.
Today, there is a very wide range of aroma chemicals available that enables flavourists to make natural flavours by simple compounding techniques that are directly analagous to the way nature-identical aroma chemicals have always been made. Nature-identical aroma chemicals (in UK definition) are chemically identical (at least at the molecular level) to their natural analogies but made by chemical synthesis.
The sheer range of natural aroma chemicals together with their price and availability raises interesting questions about their origins. There are many grey areas concerning how individual natural substances are actually prepared, and although many of today?s natural aroma chemicals undoubtedly meet the spirit of the UK/EU definition, there will be those that do not.
Putting aside the issue of natural components, there are special areas of concern that relate to natural flavours. They usually have higher raw material costs and, certainly for the more traditional natural flavours, were often significantly weaker in strength than their synthetic counterparts. Depending on the methods by which individual natural components were obtained, the purity of these substances can often be lower than the synthetic analogue and there may be the possibility of significant contaminants.
Quality control of all flavours is a blend of the objective (physical properties, gas chromatographic trace, etc.) and the subjective but extremely important organoleptic assessment. The quality control of natural flavours is no different except that it is now increasingly possible to introduce authenticity testing (at least to simpler natural flavours) to determine whether the principal aroma chemicals are indeed truly natural. The ultimate test for ?naturalness? could now be argued as sub molecular compliance of stable isotope ratios of individual carbon, hydrogen and oxygen molecules in the aroma substance(s) with the ratios found in authentic natural materials.
A few specialist laboratories are now building databases of such information — particularly relating to substances such as vanillin and benzaldehyde (almond) that not only make authentication of the substance possible but also its origin. Such testing is inevitably expensive and for most manufacturers the rules appear to be simple:
- Check the legislation of the country of origin of your natural aroma chemicalsand that of the country of use of the flavour.
- Work with proven and reliable sources of raw material.
- Insist on the availability of raw-materials audit trails.
It is clear that the demand for natural flavours will continue to increase and that there will be greater pressure from flavour manufacturers, food producers and law enforcers for these important ingredients to meet all the local requirements to comply with the description of ?natural.?