Abstract
Effect of pre-harvest methyl jasmonate (MeJA) and post-harvest 1-methylcyclopropene (1-MCP) treatments on broccoli floret glucosinolate (GS) concentrations and quinone reductase (QR, an in vitro anti-cancer biomarker) inducing activity were evaluated two days prior to harvest, at harvest and at 10, 20, and 30 days of post-harvest storage at 4 °C. MeJA treatments four days prior to harvest of broccoli heads was observed to significantly increase floret ethylene biosynthesis resulting in chlorophyll catabolism during post-harvest storage and reduced product quality. Post-harvest treatment with 1-methylcyclopropene (1-MCP), which competitively binds to protein ethylene receptors, maintained post-harvest floret chlorophyll concentrations and product visual quality in both control and MeJA-treated broccoli. Transcript abundance of BoPPH, a gene which is responsible for the synthesis of pheophytinase, the primary enzyme associated with chlorophyll catabolism in broccoli, was reduced by 1-MCP treatment and showed a significant, negative correlation with floret chlorophyll concentrations. The GS, glucobrassicin, neoglucobrassicin, and gluconasturtiin were significantly increased by MeJA treatments. The products of some of the GS from endogenous myrosinase hydrolysis [sulforaphane (SF), neoascorbigen (NeoASG), N-methoxyindole-3-carbinol (NI3C), and phenethyl isothiocyanate (PEITC)] were also quantified and found to be significantly correlated with QR. Sulforaphane, the isothiocyanate hydrolysis product of the GS glucoraphanin, was found to be the most potent QR induction agent. Increased sulforaphane formation from the hydrolysis of glucoraphanin was associated with up-regulated gene expression of myrosinase (BoMyo) and the myrosinase enzyme co-factor gene, epithiospecifier modifier1 (BoESM1). This study demonstrates the combined treatment of MeJA and 1-MCP increased QR activity without post-harvest quality loss.
Highlights
Brassica vegetables are recognized as functional foods that have putative cancer preventive effects as shown in epidemiological and animal carcinogenesis studies [1]
The glucosinolates (GS) including glucoraphanin, gluconasturtiin, and sinigrin found in the tissues of accessions of Brassica oleracea have been identified as potent cancer prevention agents because products of their hydrolysis by the endogenous enzyme myrosinase generate sulforaphane, phenethyl isothiocyanate (PEITC), and allyl isothiocyanate (AITC)
CYP79F1 and CYP79F2 genes are responsible for aldoxime metabolism leading to aliphatic GS derived from chain-elongated methionine derivatives, whereas CYP79B2 and CYP79B3 have distinct functions in indolyl GS biosynthesis, which is derived from tryptophan [10]
Summary
Brassica vegetables are recognized as functional foods that have putative cancer preventive effects as shown in epidemiological and animal carcinogenesis studies [1]. The glucosinolates (GS) including glucoraphanin, gluconasturtiin, and sinigrin found in the tissues of accessions of Brassica oleracea have been identified as potent cancer prevention agents because products of their hydrolysis by the endogenous enzyme myrosinase generate sulforaphane, phenethyl isothiocyanate (PEITC), and allyl isothiocyanate (AITC). These isothiocyanate products have been shown to induce phase II detoxification enzymes such as glutathione S-transferases (GSTs) and quinone reductase (QR) in in vitro or in vivo systems that can enhance detoxification and elimination of carcinogens from the human body [2,3,4]. The hydrolysis product of 4-methoxyglucobrassicin has been reported to be antibiotic to fungal pathogens and to the green peach aphid (Myzus persicae) [14,15]
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