This Application Note describes the fast and highly sensitive detection of trace-level aroma compounds in the headspace gas above fresh strawberries. Sampling is carried out using an easy-to-use microchamber system, with analysis by thermal desorption (TD) and gas chromatography/time-of-flight mass spectrometry (GC/TOF MS). Compound identification is further enhanced by the use of TargetViewTM software, allowing rapid screening against a large commercial library and a smaller customised library of sulfur compounds.
Food aroma profiles typically contain components over a wide range of concentrations, though very often the most odour-active compounds are only present at trace levels. In such situations all aspects of the sampling and analysis methods need to be optimised for detection and identification of the widest range of analytes. The aroma of strawberries is one of the most complex of all fruits, and has received a good deal of attention in recent years1–3, especially from the point of view of identifying the olfactory components that characterise different strawberry varieties. In this Application Note we describe the use of a multi-hyphenated microchamber- based analytical setup that offers the low detection limits necessary for the identification of these key volatiles, while not compromising on the flexibility, speed, and ease-of-use that is critical in food analysis.
Markes’ Micro-Chamber/Thermal ExtractorTM 4 is a stand- alone sampling accessory for dynamic headspace sampling of organic vapours from a wide variety of materials, including foodstuffs. Operation is simple, with short sampling times (typically <60 minutes) and the capability to analyse up to four or six samples at once, depending on the model chosen. The sample is placed in one of the inert-coated microchambers, which can be heated (Figure 1). Air or inert gas passes into the microchamber at a constant flow rate, sweeping the headspace vapours directly ontoa sorbent-packed tube, ready for the thermal desorption stage (see below). This continuous flow results in the collection of large volumes of headspace vapours from across the volatility range, thereby significantly increasing sensitivity and ensuring that the sample is representative of the entire odour/aroma profile under the temperature conditions selected.
Sampling and subsequent analysis of the strawberry samples described here combines four powerful technologies. Dynamic headspace sampling flushes the organic vapours from the strawberry onto a sorbent- packed tube, while thermal desorption concentrates these vapours and delivers them into the GC in a narrow band of carrier gas for optimum sensitivity. Analysis uses inherently sensitive time-of-flight mass spectrometry, and compound-identification software speeds up data processing by rapidly and automatically detecting and confirming the identity of headspace components.
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