Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2016
Publication Date: 11/27/2016
Publication URL: http://handle.nal.usda.gov/10113/5594375
Citation: Beck, J.J., Willett, D.S., Gee, W.S., Mahoney, N.E., Higbee, B.S. 2016. Differentiation of volatile profiles of stockpiled almonds at varying relative humidity levels using benchtop and portable GC-MS. Journal of Agricultural and Food Chemistry. 64:9286-9292. doi: 10.1021/acs.jafc.6b04220.
Interpretive Summary: Contamination of almonds and pistachios by fungi that produce toxins results in millions of dollars of lost product annually. The current method for toxin analysis, particularly aflatoxins produced by certain fungi, utilizes laboratory-based methods and is destructive, expensive, and time intensive. Because aflatoxin contamination can be limited to one or two highly contaminated nuts (hot spots), current methods do not necessarily guarantee detection of the infected nuts. An early warning detection system has been voiced as a critical need of the almond and pistachio industry. Fungal spores are known to produce certain odors when they transition from the resting stage to germination. These odors can possibly provide clues for the presence of fungal contamination. By evaluating the odors from stockpiled almonds under storage conditions and at varying humidity levels, this study sought to determine if the produced odors signaled fungal growth or development. The odors were collected and then analyzed by benchtop and portable gas chromatography-mass spectroscopy (GC-MS). The benchtop GC-MS system detected 156 odors and readily distinguished between the humidity treatments based on the almond odor profiles. The portable GC-MS system detected 42 volatiles and distinguished between treatments by identifying 18 biomarkers for the 63% and 75% relative humidity treatments. The benchtop GC-MS system efficiently detected biomarker odors, which clearly identified the almond tissues at varying relative humidity levels. The portable GC-MS system detected fewer odors, but was able to delineate among the almonds at varying humidity levels.
Technical Abstract: Contamination by aflatoxin, a toxic metabolite produced by Aspergillus fungi ubiquitous in California almond and pistachio orchards, results in millions of dollars of lost product annually. Current detection of aflatoxin relies on destructive, expensive and time-intensive laboratory-based methods. To explore an alternative detection technique, volatile emission profiles of almonds at varying humidities were sampled using both static SPME and dynamic needle-trap SPE followed by benchtop and portable GC-MS analysis. Despite the portable SPE/GC-MS system detecting fewer volatiles than the benchtop system, both systems resolved humidity treatments and identified potential fungal biomarkers at extremely low water activity levels. This ability to resolve humidity levels suggests that volatile profiles from germinating fungal spores could be used to create an early-warning, non-destructive, portable detection system.