Characterization of polyphenol oxidase from purple sweet potato (Ipomoea batatas L. Lam) and its affinity towards acylated anthocyanins and caffeoylquinic acid derivatives.

Biochemical characterization of polyphenol oxidase (PPO) present in purple sweet potato (PSP) is a key step in developing efficient methodologies to control oxidative damage caused by this enzyme to the valuable components of PSP, such as caffeoylquinic acid derivatives and acylated anthocyanins. Thus, this work focused on the assessment of the effects of pH, temperature, and chemical agents on the PPO activity as well as characterization of the PPO substrate specificity towards major phenolic compounds found in PSP. The optimum conditions of enzyme activity were pH 7 and a temperature range of 20-30 °C at which phenolic substrates were oxidized with 72.5-99.8% yield. Zn2+ ions remarkably reduced PPO activity while Cu2+ ions improved enzyme performance. The highest substrate preference was shown for 3,4,5-tri-caffeoylquinic and 3,5-di-caffeoylquinic acid, followed by 5-caffeoylquinic and caffeic acid, 3,4- and 4,5-di-caffeoylquinic acids, peonidin-3-caffeoyl-p-hydroxybenzoyl-sophoroside-5-glucoside. The highest Km values were found for 4,5-feruloyl-caffeoylquinic acid and catechol.

Quantitative Analysis of the Biologically Active Compounds Present in Leaves of Mexican Sweet Potato Accessions: Phenols, Flavonoids, Anthocyanins, 3,4,5-Tri-Caffeoylquinic Acid and 4-Feruloyl-5-Caffeoylquinic Acid.

Sweet potato is one of the oldest crops cultivated in Mexico, and Mesoamerica is considered as a region with the greatest diversity of this species. Therefore, the present study focused on the evaluation of biologically active compounds, such as caffeoylquinic acid derivatives and flavonoid compounds, in sweet potato leaves of 200 accessions of the main producing regions of Mexico. The analysis of total phenol content (TPC) showed a great variability of concentrations among the examined accessions (54.41 to 284.64 mgTPC/g DW). Likewise, total flavonoid content (TFC) was determined and ranged from 10.01 to 40.17 mgTFC /g DW. Finally, total anthocyanin content (TAC) was evaluated and concentrations obtained varied from 0.05 to 0.98 mgTAC/g DW. Additionally, HPLC analysis of all 200 accessions demonstrated the presence of caffeic acid (CA), 5-caffeoylquinic acid (5-CQA), three isomers of di-caffeoylquinic acid (di-CCA) and 4-feruloyl-5-caffeoylquinic acid (4F-5CQA) in all test samples. Only 21 accessions tested showed the quantitative amount of 3,4,5-tri-caffeoylquinic acid (3,4,5-tri-CQA) with concentrations ranging from 44.73 to 193.22 mg/100 g DW and high content of 4F-5CQA (139.46 to 419.99 mg/100 g DW). The gathered data indicate that leaves of Mexican sweet potatoes are a promising source of phenolic compounds with remarkable nutraceutical potential.