Electroactivity of polyphenols in sweet sorghum (Sorghum bicolor (L.) Moench) cultivars

Abstract

Polyphenols and other potential health-promoting components of sorghum ( Sorghum bicolor (L.) Moench) drove its recent growth in the U.S. consumer food industry. Linear sweep (cyclic voltammetry, CV) and differential (cyclic differential pulse) voltammetry methods were developed to detect target polyphenols and amino acids in sweet sorghum juice without interference from the dominant secondary (trans-aconitic acid) and primary (sucrose) metabolites. Of 24 cultivars investigated, No.5 Gambela showed the highest electron-donating capacity, as indicated by the highest peak area, height, and peak anodic potential. Pearson’s correlation analysis indicated the contribution of polyphenols (rather than amino acids) on CV voltammograms of juice samples. The E h -pH values of 173 sweet sorghum juice samples collected in 2017 aligned with quercetin model polyphenol. Accumulation of quercetin-like polyphenols in No.5 Gambela could offer antioxidant-rich juice for conversion to edible syrup as well as an increased tolerance against a recently emerged pest, sugarcane aphid [( Melanaphis sacchari (Zehntner)].

Juice chemical properties of 24 sorghum cultivars under varying levels of sugarcane aphid (Melanaphis sacchari) infestation

“…Correlations among the various chemical traits of sorghum stem juice were previously reported for the 2015 data (Uchimiya and Knoll 2019b) and the 2017 data (Uchimiya and Knoll 2020). In general, the individual sugars, total sugars, Brix, trans-aconitic acid, and TOC were all positively correlated with one another.…”

“…Electrochemical parameters also showed correlations with aphid damage or aphid days in the 2017-1 and 2017-2 environments. A higher E pa value indicates electrochemically more recalcitrant structure of electron-donating (reductant) components in sorghum juice (Uchimiya and Knoll 2020). The negative correlation between E pa and aphid damage rating suggests multiple chemical pathways against aphids that include polyphenolic antioxidants.…”

Aconitic Acid Recovery from Renewable Feedstock and Review of Chemical and Biological Applications

“…For example, Gil Zapata [ 27 ] reported that variety L 97-128 had less than half the aconitic acid in tops/leaves when compared with cultivars LCP 85-384 and HoCP 91-555. Among the cultivars, HoCP 96-540, HoCP 04-838, HoCP 09-804, and L 01-299; HoCP 04-838 had significantly more trans -aconitic acid in the sugarcane juice (0.17%) when compared to the other cultivars [ 101 , 102 ], while HoCP 09-804 had more cis -aconitic acid than the others [ 102 ]. When a commercial process was developed for the recovery of aconitic acid from sugarcane streams, others noted that the sugarcane varieties were not grown for their high aconitic acid content but could be cultivated if so desired, at the expense of sucrose [ 99 ].…”

Proton-Coupled Electron Transfers of Defense Phytochemicals in Sorghum (Sorghum bicolor (L.) Moench)

“…(a) E h –pH diagram of sweet sorghum juice collected from 3 year (2015–2017) field experiments (symbols); values were obtained from the literature ,,, and are closest to catecholic semiquinone radical-forming quercetin . Reduction of model quinone (anthraquinon-2,6-disulfonate) to hydroquinone shifts the fluorescence peak to a higher emission wavelength (black arrow; adapted with permission from ref .…”

“…Figure presents an E h –pH diagram for one-electron half-reactions against the standard hydrogen electrode relevant to sorghum: tryptophan (to form indole radical), tyrosine (phenoxyl radical), quercetin (radical of catechol in B ring), and riboflavin (semiquinone) . Those reference structures are compared against the E h –pH values of sweet sorghum juice collected over 3 years. ,,, Filled symbols in Figure represent mean ± SD for intrinsic E h and pH values of 173 ( n ) sweet sorghum juice samples collected from the field experiment in 2017 and analogous values for 2016 ( n = 67) , and 2015 ( n = 199) …”