|JIMENEZ, LEONEL - University Of California|
|Hall Iv, Wiley|
|RODRIGUEZ, MATTHEW - University Of California|
|COOPER, WILLIAM - University Of California|
|MUHAREB, JEANETTE - Dried Fruit Association Of California|
|JONES, TOM - Dried Fruit Association Of California|
Submitted to: Journal of AOAC International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2014
Publication Date: 10/28/2015
Citation: Jimenez, L.R., Hall IV, W.A., Rodriguez, M.S., Cooper, W.J., Muhareb, J., Jones, T., Walse, S.S. 2015. Quantifying residues from postharvest fumigation of almonds and walnuts with propylene oxide. Journal of AOAC International. 98(5):1423-1427.
Interpretive Summary: Postharvest chamber fumigation provides a biological safeguard against insect and microbiological pests and, in many scenarios, is the only available tool for government and industry to guarantee pest-free security and food safety. Foodstuff residues that result from postharvest chamber fumigation must be quantified per regulatory requirement. When regulatory requirements change, new residue studies are often required and often times new analytical methodologies must be developed to support the regulatory compliance. This research involved the development of a novel methodology, involving solvent extraction with methyl tert-butyl ether (MTBE) followed by gas chromatography, to quantify residues from almonds and walnuts following a postharvest fumigation with propylene oxide. The novel method offered improved detection of several types of residues as well as enabled the first ever detection of different residues in almonds and walnuts. This work addresses a critical need to quantify residues resulting from propylene oxide fumigation of tree nuts so that treatment parameters and storage conditions can be modified to meet regulatory and consumer requirements for distribution and trade.
Technical Abstract: A novel analytical approach, involving solvent extraction with methyl tert-butyl ether (MTBE) followed by gas chromatography (GC), was developed to quantify residues that result from the postharvest fumigation of almonds and walnuts with propylene oxide (PPO). Verification and quantification of PPO, propylene chlorohydrin (PCH) (1-chloropropen-2-ol (PCH-1) and 2-chloropropen-1-ol (PCH-2)), and propylene bromohydrin (PBH) (1-bromopropen-2-ol (PBH-1) and 2-bromopropen-1-ol (PBH-2)) was with a combination of electron impact ionization mass spectrometry (EIMS), negative ion chemical ionization mass spectrometry (NCIMS), and electron capture detection (ECD). Respective GC-EIMS limits of quantification (LoQs) for PPO, PCH-1, PCH-2, PBH-1, and PBH-2 in MTBE extracts (ppm (mcg/g – nut)) were 0.85, 2.10, 2.45, 30.3, and 50 for almonds and 0.81, 2.15, 2.02, 41.62, and 45.7 for walnuts. Relative to GC-EIMS, GC-ECD analyses resulted in no detection of PPO, similar detector responses for PCH isomers, and >100-fold more sensitive detection of PBH isomers. NCIMS did not enhance detection of PBH isomers relative to EIMS and was ~10-fold less sensitive to PPO and PCH isomers. MTBE extraction efficiencies were > 90% for all analytes. The 10-fold concentration of MTBE extracts yielded recoveries of 85-105% for the PBH isomers and a concomitant decrease in limits of detection (LoDs) and LoQs across detector types. The percentage recoveries of PCH isomers and PPO in the MTBE concentrate were relatively low (ca. 50 to 75%), which confound improvements in LoDs and LoQs regardless of detector type.