Application of Solid Phase Micro-extraction With Gas Chromatography-Mass Spectrometry for the Determination of Geosmin and 2-Methylisoborneol in Processed Navy Beans (Phaseolus vulgaris)

This investigation was conducted to address the issue of musty bean products. The main objectives of this study were to: (1) identify the source of the musty, off-flavor in processed navy beans, (2) determine and identify the associated off-flavor compounds (geosmin and 2-methylisoborneol (2-MIB)), and (3) isolate the microorganism(s) responsible for production of the compounds.

To confirm the presence of geosmin and 2-MIB in processed baked beans, an automated gas chromatographic method employing solid phase micro-extraction (SPME-GC-MS) was used. Artificially musty baked beans, known musty beans, and raw ingredients (bacon, navy beans, and water) were analyzed. Results of this investigation revealed that navy beans were the source of the musty compounds. 2-MIB and geosmin were detected in artificially musty baked beans, and 2-MIB also was detected in control beans (non-musty). Neither geosmin nor 2-MIB was detected in smoked bacon or water. Results of the analysis identified geosmin and 2-MIB as the musty-odor compounds associated with processed navy beans, with moldy navy beans being the source.

Aspergillus flavus, Penicillium commune, and Penicillium expansum were isolated from moldy navy beans. An additional experiment was performed to determine the production of geosmin and/or 2-MIB by the isolated molds. Non-moldy navy beans were inoculated with spore suspensions from A. flavus, P. commune, or P. expansum, incubated for 10 days at 25°C, and samples were analyzed for mold counts, geosmin, and 2-MIB.