Identification of specific odour compounds from garlic cloves infected with the potato tuber nematode, Ditylenchus destructor, using gas chromatography-olfactometry

Summary The potato tuber or potato rot nematode, Ditylenchus destructor, causes severe damage to garlic (Allium sativum) produced in Japan. Although consumption of a nematode-infected garlic bulb is not harmful to human health, it causes consumer dissatisfaction because the infected bulb deteriorates quickly. In addition, nematode-contaminated garlic cloves are inadvertently used as seed garlic for next season, which then leads to nematode-infested fields and increases yield loss. However, infected garlic bulbs look the same as healthy ones, and hence have been unknowingly distributed and sold. A method is needed to discriminate infected garlic bulbs from non-infected garlic bulbs before distribution in the market, but to date no suitable technique has been developed. The objective of this study was to identify specific odour-active compounds associated with nematode-infected garlic through the use of analytical chemistry. Garlic cloves were infected with cultured nematodes under controlled conditions, and the volatile odour-active compounds were analysed by an ‘odour identification system’ which included gas chromatography-olfactometry (GC-O), GC-fractionation (GC-F), GC-mass spectrometry (GC-MS), and odour/aroma-specific database. Two specific odour-active compounds associated with nematode-infected garlic cloves were identified as allyl methyl disulfide and eugenol, and two others were tentatively identified as (E)-1-allyl-2-(prop-1-en-1-yl)disulfane and allyl methyl trisulfide. These specific odour-active compounds may be useful as indicators to detect nematode-infected garlic bulbs in a non-destructive manner.