Identification of two novel pigment precursors and a reddish-purple pigment involved in the blue-green discoloration of onion and garlic.
By using a model reaction system representing blue-green discoloration that occurs when purees of onion (Allium cepa L.) and garlic (Allium sativum L.) are mixed, we isolated two pigment precursors (PPs) and a reddish-purple pigment (PUR-1) and determined their chemical structures. PPs were isolated from a heat-treated solution containing color developer (CD) and either l-valine or l-alanine, and their structures were determined as 2-(3,4-dimethylpyrrolyl)-3-methylbutanoic acid (PP-Val), and 2-(3,4-dimethyl-1H-pyrrolyl) propanoic acid (PP-Ala), respectively. Next, PUR-1 was isolated from a heat-treated solution containing PP-Val and allicin, and its structure was determined as (1E)-1-(1-((1S)-1-carboxy-2-methylpropyl)-3,4-dimethyl-1H-pyrrol-2-yl)-prop-1-enylene-3-(1-((1S)-1-carboxy-2-methylpropyl)-3,4-dimethyl-1H-pyrrol-2-ylidenium). The structure of PUR-1 suggested that PP molecules containing a 3,4-dimethyl pyrrole ring had been cross-linked by an allyl group of allicin to form conjugated pigments. While PUR-1 is a dipyrrole compound exhibiting a reddish-purple color, a color shift toward blue to green can be expected as the cross-linking reaction continues to form, for example, tri- or tetrapyrrole compounds.
Imai
Shinsuke
S
Somatech Center, House Foods Corporation, 1-4 Takanodai, Yotsukaido, Chiba 284-0033, Japan. s-imai@housefoods.co.jp
Akita
Kaori
K
Tomotake
Muneaki
M
Sawada
Hiroshi
H
D002087:Butyrates; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004220:Disulfides; D005737:Garlic / Q000737:chemistry*; D006358:Hot Temperature; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D019697:Onions / Q000737:chemistry*; D010860:Pigments, Biological / Q000032:analysis* / Q000737:chemistry; D011758:Pyrroles / Q000737:chemistry; D012996:Solutions; D013441:Sulfinic Acids / Q000737:chemistry
D002087:Butyrates; D004220:Disulfides; D010860:Pigments, Biological; D011758:Pyrroles; D012996:Solutions; D013441:Sulfinic Acids; C006452:allicin