Abstract
Recently polyphenols attracted great interest in the field of food and nutrition as well as in the pharmaceutical and cosmetics industries due to their health benefits through antioxidative behavior in the human body. However, because of the high number of compounds characterized as phenols and their structural diversity, quantification of polyphenols turns out to be a highly complex task. Although, a wide variety of analytical methods are used for the determination of total polyphenolic content, they are all found to be lacking in a variety of different tasks, such as their limits of detection and quantification, repeatability, accuracy and specificity. For this reason, a novel approach combining the advantages of solid phase purification, near infrared analysis and multivariate data analysis was investigated for the prediction of total polyphenolic content, suitable for a wide range of sample matrices. Dispersive solid phase extraction was performed and optimized using polyvinylpyrrolidone as sorbent, known to selectively bind polyphenols. Near-infrared detection of adsorbed polyphenols was carried out subsequently. Furthermore, the method was in-house validated, examining selectivity, repeatability and accuracy, working range, as well as multivariate limit of detection and limit of quantification, comparing it with two routinely used methods—namely, Folin–Ciocalteu photometric assay and Löwenthal titration. The novel established method was applied for the prediction of total polyphenolic content in tea and wine samples.
Highlights
Considering a daily intake of about 1 g per day, polyphenols represent the most abundant antioxidant in human diet, as well as the largest group of phytochemicals, being present in fruit juices, tea, wine, coffee, vegetables, cereals and much more [1,2]
There exist a high number of methods for predicting total polyphenolic content, most of them are found to be lacking in different tasks when it comes to considering their precision and selectivity of analysis, required amount of time or instrumentation for analysis and usage of harmful chemicals
high performance liquid chromatography (HPLC) measurements for quantification of remaining gallic acid in sample solution was performed in order to ensure optimal binding conditions for the extraction process
Summary
Considering a daily intake of about 1 g per day, polyphenols represent the most abundant antioxidant in human diet, as well as the largest group of phytochemicals, being present in fruit juices, tea, wine, coffee, vegetables, cereals and much more [1,2]. There exist a high number of methods for predicting total polyphenolic content, most of them are found to be lacking in different tasks when it comes to considering their precision and selectivity of analysis, required amount of time or instrumentation for analysis and usage of harmful chemicals Most of these methods are based on photometric assays or oxidation of phenolic constituents. Folin–Ciocalteu represents a commonly used spectrophotometric method for the estimation of total polyphenolic content and is based on the reduction of phosphomolybdicphosphotungstic acid reagent, forming a colored complex in alkaline solutions and in the presence of phenolic compounds, detected at a wavelength of 785 nm Even though it is routinely used, the method is not very specific and shows wrongly increased results for samples containing reducing agents, including but not exclusively ascorbic acid [2,7]. Polyphenolic constituents are expressed as a sum parameter such as gallic acid equivalent (GAE) or tannic acid equivalent (TAE) in mg L−1
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