Determination of 2-Methylisoborneol and Geosmin from Corn Bins

Corn is one of the most consumed grains worldwide and is eaten fresh or processed into flour, starch, sweeteners, oil, beverages, including alcoholic drinks, etc. If contaminated water is used in irrigation, processing, and storage, or if improper storage conditions lead to the growth of mold or bacteria, off-odors can occur. Two well-known compounds responsible for these off-odors are 2-methylisoborneol (MIB) and geosmin. MIB and geosmin naturally originate from blooms and decay of cyanobacteria found in water and soil sources. These compounds will impart off-odors described as earthy, musty, and dirt and are detected by humans at concentrations of less than 10 ppt in water [1]. It is, therefore, necessary to determine if MIB and geosmin are at a detectable level in the raw material before a final product is made.

A methodology designed to rapidly detect MIB and geosmin from grain bins is desired to prevent off-odors from reaching the final product. Traditional extraction techniques, like SPME, have a limited sorbent capacity, making trace-level detection difficult, especially in complex matrices. Additionally, SPME fibers are not robust and are likely to be damaged in the field. In contrast, GERSTEL Twister stir bars and thin film solid phase microextraction (TF-SPME) membranes can easily accomplish an in-field sampling workflow. The Twister stir bars are coated in polydimethylsiloxane (PDMS), and the TF-SPME membranes are coated in PDMS/hydrophilic-lipophilic balance (HLB) particles. Using both in a combined extraction allows effective collection and concentration of MIB and geosmin. The extraction devices offer a large surface area and phase volume to the analytes of interest to ensure that low detection limits are achievable.

This work is a practical guide for farmers, processors, millers, and food and beverage manufacturers to use Twister and TF-SPME devices effectively in the field. These tools enable the precise measurement of MIB and geosmin levels in grain bins, ensuring potential issues are identified before the grain is processed into consumer goods. As highlighted in this study, sampling time, environmental factors, and precision must be considered while performing this fieldwork.