Induction of Volatile Compounds in Broccoli by Postharvest Hot-Water Dips

Volatile emissions from heads of fresh broccoli (Brassica oleracea L. Italica group cv. Paragon) following hot-water treatments were studied to identify indicators of stress and causes of off-odors. Hot-water treatments of 45 °C for 10, 15, or 20 min and of 52 °C for 1, 2, or 3 min prevented yellowing of broccoli. However, the injurious treatment of 52 °C for 3 min enhanced off-odor development and caused visual damage to flower buds. Hot-water treatments increased the production of ethanol, 1-propanol, 1-hexanol, cis-3-hexen-1-ol, hexyl acetate, cis-3-hexenyl acetate, dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), and methyl thiocyanate (MTC) following treatment. Injury in broccoli treated at 52 °C for 3 min could be detected 2 h after treatment by 370- and 27-fold increases in headspace concentrations of ethanol and cis-3-hexen-1-ol. Ethanol headspace concentrations >100 μmol·m-3 24 h after treatment could be used to identify phytotoxic heat treatments in broccoli. Olfactory detection of gas chromatograph effluent determined that cis-3-hexen-1-ol, DMTS, and DMDS were responsible for off-odors that developed following the 52 °C/3 min treatment. Keywords: Brassica oleracea; heat stress; ethanol; off-odor