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.
Department of Food Chemistry and Analysis, Institute of Chemical Technology, Technická 1905, 166 28 Prague, Czech Republic.
Roman
R
Kubec
Marcela
M
Hrbácová
Rabi A
RA
Musah
Jan
J
Velísek
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