Silo-stored pistachios at varying humidity levels produce distinct volatile biomarkers

Authors: Beck, John; Willett, Denis; Mahoney, Noreen; Gee, Wai

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2016
Publication Date: 12/26/2016
Citation: Beck, J.J., Willett, D.S., Mahoney, N.E., Gee, W.S. 2016. Silo-stored pistachios at varying humidity levels produce distinct volatile biomarkers. Journal of Agricultural and Food Chemistry. 65:551-556.

Interpretive Summary: Contamination of tree nuts (almonds, pistachios and walnuts) by fungi that produce toxins results in millions of dollars of lost product annually. The current method for toxin analysis, particularly aflatoxins which are produced by certain fungi, utilizes a laboratory-based method that 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 tree nut 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. We evaluated the odors from pistachios obtained from a commercial storage silo, and then evaluated at varying humidity levels. The study sought to determine if the produced odors signaled fungal growth or development. The odors were collected and then analyzed by benchtop gas chromatography-mass spectroscopy (GC-MS). Data from the GC-MS system readily distinguished between the humidity treatments based on the pistachio odor profiles. The benchtop GC-MS system efficiently detected biomarker odors, which clearly identified the tissue tissues at varying relative humidity levels. The application of these results using a portable GC-MS system may allow for the early detection of fungal growth and prior to the production of fungal toxins.

Technical Abstract: Aflatoxin contamination in California tree nuts results in millions of dollars of lost product annually. The current method for detection of aflatoxin is destructive, expensive and time-intensive. Previous studies have demonstrated that volatile profiles of fungal-contaminated tissues are different than the profiles from tissues that are not contaminated. Additionally, fungi require certain humidity levels before growth can occur. To this end, the volatile headspace of pistachios stored in a commercial silo were analyzed at humidity levels of 63%, 75%, 84% relative humidity, and at ambient relative humidity (no humidity added to the headspace). The headspace volatiles were collected onto SPME fibers and analyzed by GC-MS. Multivariate analysis of the volatile data demonstrated significant differences among the volatile profiles of the tested relative humidity levels. Moreover, five volatiles were identified as biomarkers of increased humidity and fungal development. This ability to resolve humidity levels suggests that volatile profiles from developing fungal spores could be used in an early-warning, non-destructive, portable detection system.