Why is my blanched broccoli turning yellowish?

We are blanching broccoli florets for 2 minutes in lightly salted water, then cooling.  Recently, the broccoli is turning to an awful shade of yellowish brown.  Any idea on why? (M.S.Y.)

The green color of freshly harvested broccoli is due to the green pigment, chlorophyll. When you heat chlorophyll it may be changed into a yellow or 'pea green' pigment. This also happens as the broccoli ages - there is generally loss of chlorophyll and development of less desirable colors. You can possibly avoid this by reducing the blanching conditions (lower temperature and/or less time) so that there is less exposure to heat. In addition, using younger broccoli will help because there will be more chlorophyll than in older broccoli.

– Diane Barrett