Comparison of Characteristic Flavor and Aroma Volatiles In Melons and Standards Using Solid Phase Microextraction (SPME) and Stir Bar Sorptive Extraction (SBSE) with GC-MS

Stir bar sorptive extraction (SBSE) is a technique for extraction and analysis of organic compounds in aqueous matrices, similar in theory to solid phase microextraction (SPME).  SBSE has been successfully used to analyze several organic compounds, including food matrices.  When compared with SPME, considerably higher recoveries have been reported yet, we find no SBSE for melon and fresh-cut melons.  Several articles indicate that roughly 1 h exposure for SBSE delivers an optimized analyte recovery.  We previously used 12.5 min adsorption time in fruit juices held at 40 °C in order to attain reliable volatile headspace recovery via SPME-GC-MS, whilst not inducing substantial flavor compound changes due to sampling.
Here, we evaluated differences in 30 compounds in Proteo cantaloupe and honeydew melons [propyl acetate, ethyl 2-methyl propanoate, isobutyl acetate, methyl 2-methyl butanoate, (Z) 3-hexenal, ethyl butanoate, ethyl 2-methyl butanoate, (E) 2-hexenal, 3-methyl 1-butyl acetate, 2-methyl butyl acetate, methylthiobutyrate, ethyl (methylthio) acetate, ethyl hexanoate, (Z) 3-hexenyl acetate, hexyl acetate, eucalyptol, (Z) 3-octenol, ethyl 3-(methylthio) propanoate, (Z) 6-nonenal, (E,Z) 2,6-nonadienal, (Z) 3-nonenol, (E,Z) 3,6-nonadienol, (E) 2-nonenal, benzyl acetate, (E,Z) 2,6-nonadienol, (Z) 6-nonenol, octyl acetate, 3,6-nonadienyl acetate, and (E,Z)-2,6-nonadienyl acetate] via mixed external standards (0.05, 0.1, 1, 10, 50, 100, 500, and 1000 ppb) by SBSE.  Occasional comparisons were drawn between SBSE and SPME in subsample groups.  An internal standard (amyl isovalerate) was used.  Thirty, 60 and 90 min SBSE exposure at 37.5 °C did not appear to deliver consistent trends across all 30 volatiles analyzed.  While comparing SBSE to SPME with 12.5 or 25 min exposures at 37.5 °C, a standard gradient yielded similar results for several compounds (e.g. 2-methylbuty acetate, hexyl acetate and eucalyptol), whereas occasionally the SPME recovery exceeded SBSE linearly (e.g. amyl isovalerate).  Due to the impressive amount of polydimethylsiloxane (PDMS) loaded onto a SBSE as compared with SPME, an occasional compound of interest (e.g. butyl acetate) was not resolved due to siloaxane impurities.  Data analysis continues since certain volatile standards were recently acquired and verified, resulting in changes to our MS quantification ions and calculation methods.  Data for various melons, based on authentic standards, per SBSE and/or SPME will be presented.