Steam vs. Hot Water Blanching Modulates Warmed-Over Flavor in Broccoli by Preserving Cellular Structure

Blanching is a critical postharvest step that influences broccoli color, texture, flavor, and nutritional quality, and may affect the formation of warmed-over flavor (WOF) related volatile compounds under thermal processing. This study compares hot water blanching (HWB, 98 ± 1 °C, 30 to 150 s) and steam blanching (SB, 100 °C, 30 to 150 s) by analyzing color, texture, peroxidase activity, electronic nose, volatile compounds, sulforaphane content, and scanning electron microscopy (SEM) to determine how blanching conditions influence physicochemical attributes, cellular organization, and WOF-related volatile profiles in broccoli. Overall quality retention was superior with SB, particularly at 60 s, as evidenced by lower residual enzyme activity, improved firmness retention, better maintained cellular structure as observed microscopically, and higher sulforaphane retention relative to HWB. Multivariate analysis identified nine key volatile markers (variable importance in projection (VIP) > 1 and relative odor activity value (ROAV) > 1), including the WOF-associated aldehyde pentanal. Broccoli treated by SB for 60 s exhibited markedly lower levels of these aldehydes than samples subjected to HWB. Correlation analysis revealed a positive correlation between sulforaphane and sulfur-containing volatile compounds, including dimethyl disulfide and dimethyl trisulfide. This correlation mainly derived from the superimposed degradation of different precursor pools under thermal action: at high temperatures, dimethyl disulfide is one of the main volatile products generated from the thermal degradation of sulforaphane; meanwhile, during heating, intermediates derived from S-methyl-l-cysteine sulfoxide undergo thermal reactions to form dimethyl disulfide and dimethyl trisulfide. Collectively, these results support SB as an effective strategy to mitigate WOF while maintaining the nutritional quality of broccoli and potentially other cruciferous vegetables.