Evaluation of Phenolic Antioxidant Capacity in Grains of Modern and Old Durum Wheat Genotypes by the Novel QUENCHERABTS Approach

The QUENCHERABTS (QUick, Easy, New, CHEap and Reproducible) approach for antioxidant capacity (AC) determination is based on the direct reaction of 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation with fine solid food particles. So, it may resemble the antioxidant action in foods or in human gastrointestinal trait. Here, the QUENCHER approach was used to study AC of durum wheat (Triticum durum Desf.) grains. Firstly, it was assessed which kind of antioxidants determines QUENCHER response. This has been performed by comparing AC measured by QUENCHERABTS and that measured by classical TEACABTS (Trolox equivalent antioxidant capacity) in four different extracts from whole flour of 10 durum wheat varieties containing: lipophilic, hydrophilic, insoluble-bound phenolic (IBP) and free-soluble phenolic (FSP) compounds. QUENCHERABTS data were unrelated to AC of water-extractable antioxidants and weakly correlated (r = 0.405, P < 0.05) to AC of the lipophilic ones; on the contrary, QUENCHERABTS response was mainly related to AC of IBP (r = 0.907, P < 0.001) and to a lesser extent of FSP extracts (r = 0.747, P < 0.001). Consistently, correlation was also found with the phenolic content of IBP and FSP (r = 0.760, P < 0.001 and r = 0.522, P < 0.01, respectively), thus confirming that QUENCHERABTS assay mainly assesses AC due to IBP. So, this assay was used in a first screening study to compare AC of bioactive IBP of thirty-six genotypes/landraces covering a century of cultivation in Italy. Interestingly, no relevant AC difference between modern and old genotypes was found, thus suggesting that a century of plant breeding did not decrease phenol-dependent health potential in durum wheat.