For soluble protein content measurement, frozen broccoli florets were ground in liquid nitrogen and 0.5 g of the resulting powder was mixed with 5 mL of a buffer solution [50 mM Tris-HCl, 0.4 mL L?1 b-mercaptoethanol and 2 mM ethylene-diaminetetraacetic acid, pH 7.5]. The mixture was centrifuged at 10,000 ? g for 10 min at 4 ?C and the soluble protein content was determined in the supernatant, according to Bradford (1976), using bovine serum albumin (Sigma, St Louis, MO, USA) as standard. For total protein content measurement, 0.3 g of frozen broccoli powder was homogenized with 10 mL of extraction buffer [0.1 mM NaOH and 10 g L?1 sodium dodecyl sulfate (SDS)] and heated at 100 ?C for 10 min. Samples were centrifuged at 10,000 ? g for 20 min at 4 ?C. In order to precipitate proteins, 5 vol ofacetonewere added to the supernatant, which was then incubated at - 20 ?C for 12 h and centrifuged at 13,000 ? g for 10 min at 4 ?C. The obtained precipitate was dissolved in 0.2 mL of 0.1 mM NaOH and 10 g L?1 SDS and the protein content was measured according to Lowry, Rosebrough, Lewis Farr, and Randall (1951) using bovine serum albumin as standard. All measurements were performed in tripli-cate and soluble as well as total protein content was expressed as gram per kg of fresh tissue.