Heat can induce physiological changes in plant tissues, including the inhibition of broccoli senescence. Hot water treatments at 52C for 3 or more minutes may induce off-odors in fresh broccoli. The objective of this study was to identify heat-induced volatiles that may indicate physiological injury and/or be responsible for off-odors. Heads of fresh broccoli (Brassica oleracea L. Italica group cv. `Paragon') were immersed in water at 25C for 10 min (control); 45C for 10, 15, or 20 min; or 52C for 1, 2, or 3 min. Following treatment broccoli was held at 20C in the dark. Volatiles in the headspace above treated broccoli were trapped on Tenax-GR 2, 24, and 72 h after treatment and analyzed on a GC-MS. Heat treatments increased the production of ethanol, dimethyl disulfide (DMDS), dimethyl sulfide (DMS), dimethyl trisulfide (DMTS), hexenol, methyl thiocyanate, and several other unidentified compounds. Two hours after treatment, ethanol and hexenol concentrations in the headspace of all heat-treated broccoli were greater than those of the 25C/10 min controls. In the 52C/3 min-treated broccoli, headspace concentrations of ethanol, hexenol, DMDS, and methyl thiocyanate were 600-, 42-, 4-, and 4-fold greater than those of controls. After 72 h at 20C, concentrations of DMDS, DMS, and DMTS in broccoli from all six heat treatments were 10- to 200- fold, 8- to 35-fold, and 1.5- to 23- fold greater than those of controls, respectively. Concentrations of ethanol and methyl thiocyanate did not change relative to the controls during the additional 70 h at 20C. Concentrations of hexenol decreased in heat-treated broccoli during this time. The relationship of these volatiles to physiological changes and off-odor development in treated broccoli will be discussed.
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