Fig 1.
Structures of the phenolic acids found in mango and papaya fruit.
The number of OH groups and the chemical shifts, δ (ppm), obtained using proton NMR in DMSO-d6 for each acid.
Fig 2.
1H NMR spectra of gallic acid (top) and gallic acid + DPPH radical (bottom) in DMSO-d6.
The signals labeled by an asterisk are attributed to the DPPH radical.
Fig 3.
1H NMR spectra of chlorogenic acid (top) and chlorogenic acid + °DPPH radical (bottom) in DMSO-d6.
The signals with an apostrophe are due to the quinone formed upon the neutralization of the °DPPH radical. The signals labeled with an asterisk are attributed to the °DPPH radical.
Table 1.
Proposed mechanisms for the neutralization of the DPPH radical with the antioxidant compounds of mango and papaya.
Table 2.
Binary and ternary combinations of phenolic acids that are present in mango and their ability to neutralize the °DPPH after 3 minutes of reaction.
Table 3.
Binary and Ternary combinations of phenolic acids that are present in papaya and their ability to neutralize the DPPH after 3 minutes of reaction.
Fig 4.
1H NMR spectra representing the competitive ability of protocatechuic acid vs. chlorogenic acid to neutralize the °DPPH radical in DMSO-d6: (A) protocatechuic acid + the °DPPH radical, (B) chlorogenic acid + the °DPPH radical, (C) mixture of the two phenolic acids + the °DPPH radical and (D) mixture of the two phenolic acids.
The signals labeled with an asterisk are attributed to the °DPPH radical.
Fig 5.
1H NMR spectra representing the competitive ability of gallic acid, chlorogenic acid and vanillic acid to neutralize the °DPPH radical in DMSO-d6: (A) gallic acid + the °DPPH radical, (B) chlorogenic acid + the °DPPH radical, (C) vanillic acid + the DPPH radical and (D) mixture of the three phenolic acids + the °DPPH radical.
The signals labeled with an asterisk are attributed to the °DPPH radical.