My wife and I recently put up a dozen cases of ripe mangos in Mason jars, in two batches. The first batch was hand-peeled, cut up, and then brought to 180F, and put in the jars. The second batch was cut from the pit, without peeling, and the pieces were fed through a screw-fed food mill, then brought to 180, etc.
The first batch is a nice yellow-orange mango color; the second batch is grey-green. Both taste fine. I am thinking that the metal screw and screen of the machine (not stainless) caused the discoloration. I am assuming that it’s OK to eat the greyish stuff, but do you have any ideas about why this happened? (B.S.)
There are naturally-occurring color changes from green (chlorophyll) to orange (beta-carotene) as mangoes mature. The green color stays there in the background ‘behind’ the orange to some degree. There is an enzyme called lipoxygenase which catalyzes ‘bleaching’ of carotenoids such as beta-carotene. This enzyme would be more active as you cut up the fruit. Heating to 180F will inactivate this enzyme, so perhaps in the case of your first batch this happened and you did not bleach the beta-carotene. In the case of the second batch there may have been longer time at room temperature which allowed the enzyme to act. Metals such as copper can also accelerate these reactions, so you may be correct that using stainless steel would alleviate this to some degree. Bottom line is to try heating the mango product quickly! I hope this helps.
October 2009: In response to the September 2009 question about a batch of canned mango turning grey-green, Dr. Linda Harris from the UC Davis Dept. of Food Science and Technology added her comments to those of Dr. Diane Barrett whose response was included in the September issue:
When preparing home preserved fruits and vegetables at home it is critical to follow published guidelines.
The National Center for Home Preservation: http://www.uga.edu/nchfp/ has a brochure on preserving mangos: http://www.uga.edu/nchfp/publications/nchfp/factsheets/the_mango.html. A recipe for canning green mangos is also provided http://www.uga.edu/nchfp/how/can_02/green_mangoes.html.
The pH of mango can vary considerably from about 3.9 to 4.7. The pH increases at the fruit ripens. At the high end of that range there are concerns with safety which is why the canning recipe is for green mangoes only.