Total Soluble Phenolic Compounds Quantification Is Not As Simple As It Seems

Despite the important role of total soluble phenolic compounds (TSPC) in plant and human health, a large number of studies that have evaluated the TSPC in food matrices did not consider possible interfering compounds such as soluble sugars, ascorbic acid (AA), and other reducing compounds in the Folin-Ciocalteu (F-C) quantification method. Thus, the present study describes steps for the optimization of a methodology to extract the TSPC using banana leaves as an example. In addition, the method was tested using ascorbate oxidase (AOX) as a tool to determine and emphasize the importance of the evaluation of AA interference in food products using orange juice as an example. The results showed that two extraction cycles with 80 % acetone and a posterior hexane extraction cycle to remove the excess of chlorophylls were able to obtain a good TSPC extraction yield from banana leaves without extracting compounds that may interfere with the F-C method. The methodology has proven to be accurate, precise, simple, rapid, and inexpensive. Additionally, an overestimation of the TSPC levels in AA-rich matrices was proven using orange juice as an example. Finally, it was demonstrated that the use of AOX could be a useful and simple tool to verify and reduce the AA interference. This work proves and emphasizes the importance of evaluating the yield of the extraction and interferences in the quantification of the TSPC in vegetal-derived foods, which are complex matrices that should be cautiously evaluated.