Volatiles from food
Aroma profiling and detection of off-odours
Analysis of food has long been important in order to evaluate its composition, monitor changes upon processing or cooking, and to identify the components that provide them with desirable (or undesirable) characters.
Of the vast array of food components, volatile organic compounds (VOCs) are arguably the most important, because they give rise to aroma and thus are fundamental in making food enjoyable to eat.
However, profiling the VOCs giving rise to food aroma is a challenge for the analyst because aromas often contain many VOCs at a wide range of concentrations. In addition, the distinctive aroma of a particular foodstuff frequently results from one or two trace-level compounds with a disproportionately high odour-activity.
In recent years, however, improvements in analytical techniques have opened up the area of food volatiles to detailed investigation, and big advances are now being made in understanding the role of VOCs in food. Current activity – both in research and industry – is focused in three main areas:
- Aroma profiling – Understanding the factors that give rise to the aroma differences between similar foods, including how these are governed by genetic differences.
- Food safety – Understanding the origin of VOCs giving rise to off-odours or taints, as well those that can be used as indicators of food deterioration (shelf-life) or contamination from the materials used in packaging.
- Food consistency and quality – Ensuring production-line consistency of products from batch to batch.
In all these situations every aspect of the sampling and analysis protocol needs to be optimised in order to detect and identify the the widest range of analytes. Markes offers a range of solutions for the sampling and analysis of volatiles from food.
What Markes can offer
Thermal desorption systems
Sampling vapours onto sorbent tubes, with analysis by thermal desorption (TD), is widely used for food aroma profiling and off-odour detection. This is because it provides the high level of concentration enhancement needed for detailed chemical analysis by standard analytical tools, complementing sensory information obtained by olfactometry. It also involves minimal sample preparation and is readily automated, and is so a convenient alternative to conventional sample preparation methods.
In addition, Markes’ UNITY-xr and TD100-xr thermal desorbers are particularly well-suited to the challenges of food aroma and odour analysis, for the following reasons:
- The short, inert flow path ensures compatibility with reactive compounds such as mercaptans, amines, and oxygenated species, which often have very low odour thresholds.
- The cryogen-free focusing trap allows selective elimination of unwanted, high-concentration interferents including water, ethanol and acetic acid, which might otherwise compromise detection of trace-level target compounds.
- The backflush operation of the focusing trap allows use of multi-bed sorbent tubes, enabling simultaneous analysis of very volatile and semi-volatile compounds from a single sample.
Sample preparation and automation
Markes' Centri sample automation and preconcentration platform incorporates all the capabilities of tube-based TD systems, while also offering automated sampling and trap-based analyte focusing using headspace, SPME and HiSorb high-capacity sorptive extraction.
Trap-based focusing on Centri boosts sensitivity in all sampling modes, and opens
up options for water management and sample re-collection for repeat
Alternatively, systems are available for on-line sampling and near-real-time sampling, while small volumes of concentrated samples are conveniently captured on TD tubes using Markes’ Easy-VOC or Markes’ ACTI-VOC.
|Detecting compounds in complex matrices || |
Aroma profiling of foods often requires detailed interrogation of complex chromatograms, to confirm the presence (or absence) of key target components, such as trace-level odour-active or taint compounds. It is also often necessary to determine the non-target compounds present, for instance when comparing similar products.
Markes’ TargetView software can help reduce the amount of time spent on these tasks. Through a combination of ‘intelligent’ background compensation, compound deconvolution and library matching, it does away with the need to manually process complex GC–MS profiles, producing a simple report that lists the analytes found in the sample.
- For examples of the use of Centri to analyse volatiles from foods and beverages, see the range of Centri application notes.
- For a description of use of Markes’ Micro-Chamber/Thermal Extractor and TD-100 thermal desorber for the rapid aroma profiling of...
...bacon, see Application Note 095.
...cheese, see Application Note 101. This example employs BenchTOF and TargetView for analysis.
...strawberries, see Application Note 104. This example employs BenchTOF and TargetView for analysis.
- For more examples of the use of TD-based methods for the analysis of the flavour and fragrance profiles of foodstuffs and consumer products, see Markes’ TD Applications Guide: Food and drink and TD Applications Guide: Fragrance and odour profiling.
- For a study into peach volatiles using the UNITY thermal desorber, see: J. Cano-Salazar, M.L. López, C.H. Crisosto and G. Echeverría, Volatile compound emissions and sensory attributes of ‘Big Top’ nectarine and ‘Early Rich’ peach fruit in response to a pre-storage treatment before cold storage and subsequent shelf-life, Postharvest Biology and Technology, 2013, 76: 152–162.
- For a paper describing the application of the ULTRA-UNITY system to distinguish between fresh and rancid oatcakes, see: C. Cognat, T. Shepherd, S.R. Verrall and D. Stewart, Comparison of two headspace sampling techniques for the analysis of off-flavour volatiles from oat based products, Food Chemistry, 2012, 134: 1592–1600.