Allium discoloration: precursors involved in onion pinking and garlic greening.
Precursors involved in the formation of pink and green-blue pigments generated during onion and garlic processing, respectively, have been studied. It has been confirmed that the formations of both pigments are of very similar natures, with (E)-S-(1-propenyl)cysteine sulfoxide (isoalliin) serving as the primary precursor. Upon disruption of the tissue, isoalliin and other S-alk(en)ylcysteine sulfoxides are enzymatically cleaved, yielding 1-propenyl-containing thiosulfinates [CH3CH=CHS(O)SR; R = methyl, allyl, propyl, 1-propenyl] among others. The latter compounds have been shown to subsequently react with amino acids to produce the pigments. Whereas the propyl, 1-propenyl, and methyl derivatives form pink, pink-red, and magenta compounds, those containing the allyl group give rise to blue products after reacting with glycine at pH 5.0. The role of other thiosulfinates [RS(O)SR'] (R, R' = methyl, allyl, propyl) and (Z)-thiopropanal S-oxide (the onion lachrymatory principle) in the formation of the pigments is also discussed.
Kubec
Roman
R
Department of Food Chemistry and Analysis, Institute of Chemical Technology, Technická 1905, 166 28 Prague, Czech Republic.
Hrbácová
Marcela
M
Musah
Rabi A
RA
Velísek
Jan
J
D000490:Allium / Q000737:chemistry* / Q000378:metabolism; D005511:Food Handling; D006863:Hydrogen-Ion Concentration; D010860:Pigments, Biological / Q000096:biosynthesis* / Q000737:chemistry; D013441:Sulfinic Acids / Q000378:metabolism; D013454:Sulfoxides / Q000378:metabolism
D010860:Pigments, Biological; D013441:Sulfinic Acids; D013454:Sulfoxides; C100040:thiosulfinic acids