Rapid Determination of Polyphenols and Vitamin C in Plant-Derived Products

TLDR

Polyphenols, widely present in plant foods, are commonly quantified with the Folin‑Ciocalteu reagent, which reacts with other reducing non‑phenolic substances and can overestimate polyphenol content. This paper reports an optimized Folin‑Ciocalteu method for the specific determination of total polyphenols and vitamin C. The method employs solid‑phase extraction with Oasis HLB to eliminate water‑soluble reducing interferences, subtracts the interfering substances from the raw extract, uses heating to destroy vitamin C in the washing extract, and was validated on synthetic solutions and fruit product extracts. Keywords: Polyphenols, vitamin C, Folin‑Ciocalteu, colorimetry, solid‑phase purification, fruit, puree, juice.

Abstract

Polyphenols, widely spread in our diet by the consumption of plant food products, are commonly determined using Folin−Ciocalteu reagent that interacts with other different reducing nonphenolic substances and leads to an overestimation of polyphenol content. In this paper we report an optimized Folin−Ciocalteu method to specifically determine the contents of total polyphenols and vitamin C. After the optimal conditions for the colorimetric assay were set, solid-phase extraction (Oasis HLB (hydrophilic−lipophilic balance)) was carried out to eliminate the water-soluble reducing interferences including vitamin C. Colorimetric correction was thus performed by subtracting interfering substances contained in the water washing extract from the raw extract. Moreover, vitamin C present in the water washing extract can be destroyed by heating and thus colorimetrically deduced. This procedure was set up with synthetic solutions and validated on different extracts from fruit products. Keywords: Polyphenols; vitamin C; Folin−Ciocalteu; colorimetry; solid-phase purification; fruit; puree; juice