Allium Discoloration: The Precursor and Formation of the Red Pigment in Giant Onion (Allium giganteum Regel) and Some Other Subgenus Melanocrommyum Species

Abstract

The precursor of the orange-red pigment formed upon wounding the bulbs of Allium giganteum (Allium subg. Melanocrommyum) was isolated and shown to be S-(2-pyrrolyl)cysteine S-oxide. In addition, two other pyrrolylsulfinyl derivatives were found in an extract from the bulbs, namely, 3-(2-pyrrolylsulfinyl)lactic acid and S-(3-pyrrolyl)cysteine S-oxide. Contrary to a previous report, the latter compound was shown not to serve as the precursor of the pigment, being in fact only an artifact formed during isolation. The formation of pyrrolyl-containing compounds following disruption of A. giganteum bulbs was studied by a combination of LC-MS, LC-NMR and DART-MS. It was found that S-(2-pyrrolyl)cysteine S-oxide is cleaved by a C-S lyase (alliinase) to yield 2-pyrrolesulfenic acid. Two molecules of the latter compound give rise to highly reactive S-(2-pyrrolyl) 2-pyrrolethiosulfinate which in turn converts into red 2,2'-epidithio-3,3'-dipyrrole (dipyrrolo[2,3-d:2',3'-e]-1,2-dithiin). Several other pyrrolyl-containing compounds were detected in A. giganteum for the first time, including S-methyl 2-pyrrolethiosulfinate, S-(2-pyrrolyl) methanethiosulfinate, di(2-pyrrolyl) disulfide, and S-(2-pyrrolyl) 2-pyrrolethiosulfonate. It can be concluded that the formation of the orange-red pigment in Allium subg. Melanocrommyum species, despite sharing several analogous features, is of a different nature than the pink discoloration of onion (A. cepa).

Applications of DART‐MS for food quality and safety assurance in food supply chain

“…Certain functional ingredients in a consolidated source need to be eyed, two groups have investigated the members of different Alliums genus plants, including Allium sativum (garlic), Allium cepa (onion), Allium giganteum (giant onion), Allium porrum (leek), Allium siculum (Sicilian honey garlic), Allium stipitatum (drumstick onion), Allium tripedale, Allium tuberosum (chive), and Petiveria alliacea (Phytolaccaceae). Among these Alliums and one other plant of Citrus limon (lemon), the precursor and formation procedure of reactive secondary metabolites were shown, which mainly consisted of VOCs, such as lachrymatory thial S-oxides, pyridine N-oxides, thiosulfinates, as well as pigments (Kubec et al, 2010;Block et al, 2010;Kubec et al, 2011;Ku cerov a et al, 2011;Li, 2012). Instead of open tube, the use of a Tee-shaped PEEK flow tube could significantly enhance the probability of collision reaction between high energy metastable molecules and analytes, leading to an increased detection sensitivity by two to three orders of magnitude (Li, 2012).…”

Direct Analysis in Real Time Mass Spectrometry: a Powerful Tool for Fast Analysis

“…Recently, Kubec and coworkers used DART-MS to monitor biology process. 28 Before their work, there were several possible precursors of color change on wounded Allium subg. and Melanocrommyum detected by LC-MS method.…”

Development of formaldehyde detection method using onion juice as chromogenic agent

“…In this work, yellow onion extract was used as reagent due to the high amounts of thiosulphinates present [16]. The mechanism of the formation of pink-coloured complex from onion juice have been studied by other researchers [10,13,14,18]. The mechanisms are as follows; The first step represents the formation of thiosulphinates under the action of alliinase with onion juice.…”