Emission of Blanched Broccoli Volatiles in Headspace During Cooking

Abstract

Glucosinolates and myrosinase are characteristics components of all wild and cultivated Brassica species (Mithen et al., 1987). A major part of the brocolli crop (Brassica oleracea L. var. Italica) is stored fresh for a short time only, though industrial production of frozen florets has increased repidly. Optimized blanching is always necessary to keep a high quality frozen product. Special use of NH₂HCO₃ in stream‐blanching gave frozen broccoli better color and acceptability than that blanched in steam or water only (Odland and Eheart, 1975).

Broccoli florets (Brassica oleracea L.) were cut, blanched at 85°C for two minutes and frozen for the experiments. The emission of 14 volatile compounds was followed by headspace gas chromatography - mass spectrometry while cooking the material in water for 13 min at 95°C. After cooking in closed or open vessels the volatiles were swept with 120 mL He into a trapping column. Five traps were tested and a liquid phase with 100% recovery was found (0V-1/0V-25, 1/1). The percent coefficient of variance CV % of the major compounds typically varied between 3 and 30%, including an internal variation of different broccoli samples from the same lot. The major volatiles in the headspace, measured with a flame ionization detector, were n-pentanal, 3-methyl-2-pentanone, n-hexanal, n-heptanal, cyclopentanecarboxaldehyde, ethyl acetate, 3-methylbutanal, 3-butenenitrile, 2-methylbutanal, dimethyl trisulfide and di-methyl disulfide indicating an effective inactivation of enzymes, including myrosinase. The method has been applied to optimizing the processing of broccoli.