48 May / June 2019
Rapid Determination of Strawberry Flavour Integrity using Static Headspace-Selected Ion Flow Tube Mass Spectrometry
by Kalib J.M. Bell, Vaughan S. Langford Syft Technologies Ltd, 3 Craft Place, Christchurch 8024, New Zealand
Automated, direct headspace analysis using selected ion flow tube mass spectrometry (SIFT-MS) provides rapid and economic screening of flavour mixes. By coupling the SIFT-MS analysis with multivariate statistical analysis, rapid determination of ingredient flavour quality can be achieved without needing to resort to expert data interpretation. In this paper, classification of different batches of various strawberry flavour mix types of unknown, proprietory compositions is achieved with analysis times of less than one minute per sample. This approach has quality control applications for the food industry.
Introduction
Unintended use of an out-of-specification flavour mix in foods, beverages or nutritional formulations can lead to reduced consumer confidence and product losses. However, traditional screening using a trained sensory panel is expensive. Viable instrumental alternatives for determining acceptance are few due to various practical limitations:
• The gold-standard VOC analysis methods - gas chromatography (GC), gas chromatography-olfactometry (GC-O), and liquid chromatography (LC) - are slow and can struggle with the diversity of compounds in flavours. They also require significant sample preparation, including derivatisation for the short- chain aldehydes and organic acids.
• Electronic noses are subject to significant drift, susceptible to contamination and false positive readings (e.g. from ethanol residues), and cannot identify individual flavour components.
• Traditional direct mass spectrometric (DMS) methods are too harsh or not selective enough to give unique spectral fingerprints.
Selected ion flow tube mass spectrometry Figure 1. Schematic diagram of SIFT-MS – a direct chemical-ionisation analytical technique.
(SIFT-MS), on the other hand, is a direct mass spectrometry (DMS) technique that eliminates chromatography and applies very soft chemical ionisation. In doing so, SIFT-MS can selectively fingerprint samples of proprietory composition – without identification of flavour compounds – in less than one minute.
Recently, rapid geographical classification of Mediterranean olive oils [1] and Moroccan Argan oils [2] has been achieved using untargeted SIFT-MS analysis combined with multivariate statistical analysis. In this paper, a similar approach is applied to classify various commercial strawberry flavour mixes for intra-mix (i.e. batch) and inter-mix variations.
Method 1. The SIFT-MS technique
SIFT-MS [3,4,5] uses soft chemical ionisation (CI) to rapidly quantify VOCs to low parts- per-trillion concentrations (by volume, pptV). The SIFT-MS technique is represented schematically in Figure 1. Eight individually selectable reagent ions (H3 -, NO2
O+ OH- , O2 - and NO3 , NO+ , O2 +, O- , -) are generated in a
microwave discharge through moist or dry air. These eight reagent ions react with VOCs and other trace analytes in well-controlled ion-molecule reactions, but they do not react with the major components of air (N2 O2
,
and Ar). This enables real-time analysis of air samples at trace and ultra-trace levels
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