Sub-ambient temperature sampling of fish volatiles using vacuum-assisted headspace solid phase microextraction: Theoretical considerations and proof of concept

The extraction of volatiles from perishable food at a sub-ambient temperature using headspace solidphase microextraction (HS-SPME) has not been considered in the past due to the corresponding loss in sensitivity. We propose HS-SPME sampling under vacuum (Vac-HS-SPME) to compensate problems of sensitivity loss and achieve substantial improvement in extraction efficiencies whilst sampling at temperatures as low as 5 degrees C. The approach was applied to fish samples, representing a highly vulnerable perishable food sample. The theoretical considerations explaining the performance of Vac-HS-SPME at sub-ambient temperatures are discussed and related to the increase in gas diffusivities when sampling under vacuum. A comparative study between Vac- and regular HS-SPME for the extraction of 18 compounds from salmon was carried out at different temperatures (5, 30 and 40 degrees C) and sampling times (10 -60 min). For the majority of the compounds, Vac-HS-SPME at 5 degrees C yielded similar or superior extraction efficiencies than regular HS-SPME even when sampling at 40 degrees C. However, four compounds were better extracted at 1 atm presumably due to the intensification of competitive adsorption of analytes on the SPME fiber under vacuum or the partial losses of more volatile analytes during airevacuation in the presence of the frozen samples. Sub-ambient temperature sampling (5 degrees C) combined with Vac-HS-SPME was also applied to monitor the changes in the 18 compounds present in salmon, redfish, and cod refrigerated for up to five days. The results were compared to those obtained with regular HS-SPME at 40 degrees C. Overall, Vac-HS-SPME sampling at 5 degrees C represents a new and powerful approach for the analysis of volatiles in refrigerated foods, and has a great potential for future studies in quality control and freshness assessment. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

Vacuum headspace solid-phase microextraction (Vac-HS-SPME) sampling at sub-ambient temperatures (5 degrees C) has shown significant improvement in extraction efficiencies for volatile compounds in perishable food samples, especially fish. This new method has great potential for future applications in quality control and freshness assessment.