Tracking down aroma — food process applications

Aroma analysis is a valuable addition to the quality assurance of products.

The different questions that can be answered by aroma analysis are as varied as the range of aroma compounds themselves. Does a product has an untypical unknown smell? Does the product still possess the typical aroma at the end of its shelf life? How can internal sensory panels be reliably trained for product-specific off-flavours? But, the term ‘aroma’ should be defined first.

What is aroma?

The technical term ‘aroma’ solely describes volatile compounds which can be perceived olfactively, by the human sense of smell. Commonly known aroma impressions such as smoke, vanilla and coffee generally consist of a multitude of individual aroma compounds. Aroma perception is a part of the organoleptic perception, which is formed by the aroma, taste and trigeminal impressions.

In contrast to the aroma, the taste of a product is perceived gustatory via the human taste organ and the trigeminal impressions via the fifth cranial nerve (trigeminal nerve). This interaction gives the overall organoleptic impression, known as flavour.

Organoleptic perception is formed by the perception of aroma, taste and trigeminal impressions. For a larger image, click here.

How is aroma perceived and detected?

The volatile compounds of the aroma are perceived at the olfactory receptors of the nose. The volatile compounds can be received via the nose itself or via the throat. Only a small number of volatile compounds are aroma-active compounds — only about 5% in food.

In addition, these aromatic substances are usually only found in very low concentrations, which are nonetheless sufficient to stimulate the olfactory receptors of the human nose.

Organoleptic perception is formed by the perception of aroma, taste and trigeminal impressions.

The sensitivity of the instrumental detectors of the analytical equipment often fails to keep up with the human nose. The determination of the individual components of an aroma is therefore carried out using the combined measurement principle of gas chromatographic separation and the subsequent detection via the human nose at the sniffing-port, a technique known as gas chromatography olfactometry (GC-O). The results determined in total give a product’s spectrum of aroma compounds.

The  aroma  expert  determines  the  different  aroma  within  a  product  by  using  the  sniffing-port,  whereas  the  gas  chromatograph separates them. (Source: aromaLAB)

Why analyse the spectra of aroma?

The following practical examples provide an overview of the most common questions:

• There is a shortage of raw material and/or raw material prices rise significantly and there is a need to determine the level to which a specific raw material can be reduced within the recipe, while still maintaining the quality of the product’s aroma.
• The supplier is no longer able to deliver a certain raw material at the usual quality and there is a need to determine the extent to which the new quality of the raw material influences the quality of the product’s aroma.
• The use of added aroma is to be reduced within the context of providing ‘clean labelling’ and there is the need to determine the reduced level at which the quality of the product’s aroma can still be maintained.
• During a new product development, a storage test is used to determine up to which point in time the product’s aroma will retain the desired quality.
• Prior to changing the production process/technology, there is a need to determine to what extent the change in conditions will influence the quality of the product’s aroma.
• A particular recipe of unknown composition is to be examined to determine the main components of its aroma.

In general, the consumer will have a negative perception of the aroma if:

1. the typical aroma of the product is missing or the perception is too low;
2. there is an inappropriate mixture of aroma compounds (recipe);
3. there are perceivable off-flavours.

Off-flavours generally occur during the transport of raw materials, in the event of changes in recipes, changes in production parameters, followed by the introduction of new packaging, changes in storage conditions and during the transport of the goods to the customer.

What are the benefits of aroma analysis?

The analytical data form the basis for further clarifications and the deducing of internal measures. Targeted conclusions can only be drawn about the cause of the off-flavours once the characteristics of the aroma fingerprint are known. The most frequent causes are of a microbiological or chemical nature (Table 1).

Abnormal aroma	Odour	Most common causes	Matrix
Geosmin	mouldy, beetroot	microorganisms (Streptomyces)	cocoa mass
2,4,6-Trichloroanisolestale	cork taint	microbial modification of chlorinated substances in the bark of the cork oak	wine
5 3-Methyl-2-buten-1-thiol	skunky	sunlight	beer
Various unsaturated aldehydes eg, (Z)-non-2-enal, (Z)-dec-2-enal, (E,Z)-nona-2,4-dienal, (E,E)-deca-2,4- dienal and trans-4,5-epoxy-(E)-2-decenal	fatty, metallic	sunlight	PET bottles mineral water
4-Vinyl-2-methoxyphenol	clove	degradation of 4- hydroxy-3-methoxycinnamic acid	orange juice
p-Cresol	like a cowshed	malfermentation	white pepper

Table 1: Overview of the most common off-flavours by matrix. (Sources: aromaLAB;Pixabay)

The downstream possibility to synthesise the off-flavour is particularly helpful in the daily work. The standardised off-flavour can be used for training purposes and for the early detection of deviations in odour.

Off-flavours often occur in isolated cases and the recognition and evaluation of the situation is usually difficult in everyday work life. With the aid of off-flavour standards, processes within the framework of deviation management can be standardised.

As a result, trained personnel are able to directly recognise off-flavours upon the receipt of the goods, during the production process or the quality assurance routine and can act in accordance with predefined measures. The assignment of odour-related deviations during the process facilitates rapid intervention and avoids and/or reduces production errors and costly product recalls.

This article has been reprinted with permission from aromaLAB.