Separation of Blue Pigments in Crushed Garlic Cloves: the Color-Forming Potential of Individual Amino Acids
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Unknown blue pigments responsible for the discoloration in crushed garlic cloves were synthesized, separated, and tentatively characterized by using a high-performance liquid chromatography (HPLC) and a diode array detector ranging at 200-700 nm. We developed several reaction systems for generating pure blue pigments using an isolated alliinase, isolated flavor precursors, trans-(+)-S-1-propenyl-L-cysteine sulfoxide (1-PeCSO) from onion and trans-(+)-S-2-propenyl (or allyl)-L-cysteine sulfoxide (2-PeCSO) from garlic, and all 22 amino acids. Each amino acid was reacted with flavor precursors in alliinase solutions and then incubated at 40C for several hours to generate pigments. At least 10 naturally occurring blue pigments were separated from discolored garlic extracts by using HPLC at 580 nm. This suggested that garlic discoloration was not caused by one blue pigment but instead by many pigments. Also, all amino acids (except for cysteine, proline and 4-hydroxy-proline) formed blue and purple pigments. Finally, we demonstrated the abilities of major amino acids to form blue pigments in crushed garlic.