Emission of volatile organic compounds from healthy and diseased onions

In this study, onions were selected from a sorting machine and divided into three groups, i.e., heathy onions, soft-rot onions, and Penicillium-infected onions, by visual and tactical judgement. For each of the groups, consumption of O ₂ and emission of CO ₂ were tested in closed jars. Besides, volatile organic compounds (VOCs) from healthy and diseased onions were sampled by solid-phase microextraction (SPME) and analyzed on GC-MS. The results showed that healthy and soft-rot onions had lower respiration rate than Penicillium-infected onions. Also the concentration of total VOCs was higher from soft-rot onions than from healthy onions and Penicillium-infected onions. Ten compounds were selected to describe differences in the VOC profiles between samples. These were ethanol, 1-propanol, 1-propanethiol, acetic acid, (E)-l-(methylthio)-l-propene, l-(methylthio)-propane, dimethyl disulphide, 3-methyl-lbutanol, styrene, and methyl propyl disulphide. The levels of all ten compounds from the soft-rot onions and six from the Penicillium-infected onions were significantly different (P≥s0.05) from the levels of the healthy onions. The soft-rot onions had high levels of ethanol, 1-propanol, 1-propanethiol, acetic acid and methyl propyl disulphide as compared to the healthy and Penicillium-infected onions. 3-methyl-lbutanol was specific to the soft-rot sample, while styrene was specific to soft-rot and Penicillium-infected onions.