Analysis of Aromatic Compounds

Most food flavour precursors exist in water-soluble form within natural raw materials, whilst a small proportion is distributed within the lipid components of food.

Consequently, it would be incomplete to limit flavour analysis and research solely to the organic eluates from food raw materials. Appropriate separation methods must be selected to isolate all flavour components as completely as possible from the tissue cells of natural raw materials, in order to fully reflect the flavour characteristics inherent to the food itself.

Selecting an appropriate method to extract flavour compounds from food and prepare samples suitable for qualitative and quantitative analysis is the primary step in food flavour analysis and a key technique in flavour research.

The use of online mass spectrometers enables real-time analysis of aroma compounds; the results provided by these instruments can enhance research, flavour development and quality control within the food and flavouring industries, whilst also facilitating online process monitoring.

Aromas and their perception influence purchasing decisions. It is therefore essential for the industry to understand our sense of smell and taste – for example, when drinking a cup of coffee or savouring a piece of chocolate – at the very moment flavour molecules interact with our receptors.

The flavour and taste of food can also change over time, depending on factors such as raw materials or production processes. However, to maintain brand consistency, the quality of a food’s aroma must remain consistent.

The ProC-TOF online mass spectrometer is an accurate, highly sensitive, ready-to-use technology that enables rapid characterisation of food and monitoring of processes in the food science, technology and agricultural industries, without the need for any sample preparation.

Flavour is one of the key factors by which consumers perceive and evaluate food; it is a complex combination of taste, aroma, and even visual, cultural and psychological aspects.

Strictly speaking, aroma is related to the types and concentrations of volatile organic compounds that come into contact with the nasal cavity before and during the consumption of food. Depending on the type of food, aromatic compounds may include esters, alcohols, terpenoids, organic acids and organosulphur compounds.

Nasal gas analysis can directly quantify the aroma compounds perceived by consumers, helping to translate the consumer experience into information that scientists can study and use to improve products.

Real-time online detection technology is used to analyse the exhaled air from volunteers’ nostrils in real time, thereby helping to understand how aroma compounds change over time during consumption, and further elucidating the non-linear relationship between the types and concentrations of these compounds and consumers’ sensory perceptions.

Chromatography, particularly gas chromatography–mass spectrometry (GC-MS), is not suitable for nasal analysis due to its slow processing speed and high species selectivity.

As coffee beans emit a wide variety of VOCs, which to a certain extent determine the coffee’s aroma, flavour and colour, high-resolution mass spectrometry has been applied to monitor the coffee bean roasting process and analyse coffee aromas. Identification

Volatile organic sulphides (VSCs) have multiple and complex effects on the taste and flavour of food. For example, dimethyl sulphide (DMS) and methyl mercaptan (MeSH, which imparts a Cheddar cheese flavour) are commonly used flavouring agents at appropriate concentrations.

Dimethyldisulphide (DMDS) and dimethyl trisulphide (DMTS), on the other hand, require rigorous testing and control, as these two compounds have an unpleasant odour and a low human taste threshold.

Methyl mercaptan and dimethyl sulphide (DMS) are prone to oxidation upon heating and/or exposure to the environment, resulting in the formation of DMDS and DMTS¹. Conversely, the high reactivity of organosulphur compounds necessitates analytical methods capable of effectively eliminating side reactions that may occur during sample collection, storage and pre-treatment.

At the same time, the ultra-high sensitivity and extremely wide linear range of the latest generation of mass spectrometers enable the detection of trace levels (pL/L (ppt)) of organosulphur compounds that may be present in natural environments.

Wine

An online mass spectrometry detection platform identifies and quantifies phenolic off-flavours caused by Brettanomyces yeast in wine.

Wine yeast (scientific name Brettanomyces), commonly known as ‘Brett’ yeast, often proliferates on the surfaces of fruit skins and oak barrels.

During wine fermentation, Brettanomyces can impart unpleasant flavours to the wine, typically in the form of volatile phenolic compounds such as 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG).

If the concentration of these compounds exceeds a certain threshold, they can impart an odour to the wine reminiscent of animal faeces. Therefore, from the perspective of both producers and consumers, it is particularly important to strictly control the concentration of such compounds in wine.

Aromatic compounds in beer

The qualitative and quantitative analysis of trace aroma compounds in beer relies on the rapid response and high sensitivity of mass spectrometers.

The distinctive flavours of alcoholic beverages (such as beer and red wine) stem from the terpenes and other aromatic compounds they contain.

Currently, the ProC-TOF online mass spectrometer is utilised for the online monitoring of volatile organic compounds (VOCs), including beer aroma compounds, owing to its rapid response and high sensitivity.

However, mass spectrometry methods still face certain challenges when detecting trace volatile organic compounds in alcoholic beverages. Firstly, the high concentration of ethanol in alcoholic beverages can cause the detector response to become supersaturated, thereby reducing the measurement accuracy of other low-concentration VOCs. Secondly, the method has limited ability to distinguish between isomers, such as monoterpenes and sesquiterpenes.

To enable the quantitative analysis of trace isomeric VOCs, a fast gas chromatograph (fastGC) has been configured at the front end of the mass spectrometer, thereby achieving effective separation of isomers.

At the same time, ethanol elutes before other analytes in the gas chromatograph, thereby enabling the precise quantitative analysis of aroma compounds in alcoholic beverages.

The ProC-TOF online mass spectrometer can be applied to the following foods and flavourings:

Hot drinks: coffee, tea

Cold drinks: fruit juices, flavoured waters, carbonated drinks

Alcoholic beverages: beer, wine, vodka, whisky

Dairy products: milk, hard cheese, mozzarella, mascarpone, yoghurt, panna cotta, butter, whey

Vegetables: chillies, tomatoes, herbs, garlic, onions, pulses, soya beans, broccoli, sweet peppers, rice

Fruit: apples, strawberries, raspberries, blackberries, blueberries, gooseberries, bananas,

Seasonings: saffron, pepper, herbal extracts, truffles

Meat: poultry, pork, ham, Wagyu beef, beef

Snacks: chewing gum, chocolate, biscuits, sweets, cereal bars

Fats: sunflower oil, olive oil, palm oil, coconut oil, fish oil, animal fats

Bread, yeast

Cooking fumes, frying fumes