Profiling of Redox-Active Lipophilic Constituents in Leaf Mustard (Brassica juncea (L.) Czern.) Cultivars Using LC-MS and GC-MS

Abstract

Leaf mustard is an important commercial and culinary vegetable. However, only limited information is available on the content and composition of the nutritionally important lipophilic constituents in these leaves. This research presents information on the contents and composition of carotenoids, tocols, phytosterols, and fatty acids in four cultivars of leaf mustard. The carotenoids and tocols were analyzed utilizing liquid chromatography (LC)-mass spectrometry (MS) with single ion monitoring (SIM), while phytosterols and fatty acids were analyzed using gas chromatography (GC)-MS and GC-flame ionization detection (FID), respectively. The LC-MS results revealed the dominance of (all-E)-lutein, within the range of 37.12 (cv. Asia Curled)-43.54% (cv. Jeok) of the total carotenoids. The highest amount of all of the individual carotenoids and total carotenoids (143.85 µg/g fresh weight; FW) were recorded in cv. Cheong. Among the studied leaf samples, 67.16 (cv. Asia Curled)-83.42 µg/g FW (cv. Cheong) of α-tocopherol was recorded. Among the phytosterols, β-sitosterol was the most dominant one among the studied mustard leaves, accounting for 80.42 (cv. Jeok)-83.14% (cv. Red frill) of the total phytosterols. The fatty acid analysis revealed the presence of a significant amount of rare hexadecatrienoic acid (C16:3n3) in the studied mustard leaves, which accounted for 27.17 (cv. Asia Curled)-32.59% (cv. Red frill) of the total fatty acids. Overall, the cv. Cheong represented the highest contents of carotenoids, tocols, and phytosterols. Moreover, cv. Red frill contains the highest amount of n-3 PUFAs and antioxidant compounds. Thus, these cultivars can be promoted in cuisines which can be eaten to obtain the highest health benefits.

Keywords: antioxidant activity; carotenoids; fatty acids; lutein; omega-3 fatty acids; phytochemicals; phytosterols; tocopherol.

Figure A1

The outline of the method used for the extraction of lipophilic compounds from the mustard leaves.

Figure A2

Methods used for the hydrolysis and the preparation of fatty acid methyl esters.

Figure A3

Method used for the hydrolysis and silylation of sterols for GC-MS analysis.

Figure A4

A representative mass fragmentation pattern of cholesterol (trimethylsiloxy (TMS) derivative) observed in the present investigation.

Figure A5

The representative gas chromatography (GC)–mass spectrometry (MS)-total ion chromatograms (TIC) of phytosterols identified in mustard leaves of various cultivars. IS: internal standard.

Figure A6

The GC-mass spectrum of 7,10,13-hexadecatrienoic acid identified in mustard leaves.

Figure 1

The phenotypic diversity among mustard cultivars used in this investigation.

Figure 2

LC-single ion monitoring (SIM)-mass spectrometry (MS) chromatograms of carotenoids and α-tocopherol identified and quantified in leaves of various mustard cultivars.

Figure 3

The representative gas chromatography (GC)-flame ionization detection (FID) chromatograms of fatty acids methyl esters (FAMEs) of leaves of various mustard cultivars. The peak numbers (from 1 to 6) are correspondent to Table 7. * Not a FAME.