**3. Methods used in extraction of polyphenols**

comprise simple phenols, hydroxybenzoic acids and cinnamic acid derivatives, flavonoids,

The results from the last decade's research have shown that polyphenols have important beneficial properties for human health, including antioxidative, antiaging, antibacterial and antimutagenic [7–11]. Moreover, the recent evidence of their interaction with proteins, DNA and other biological molecules has enhanced their exploitation for the production of new natural product-derived therapeutic agents. Despite these advantages, several limitations still persist, particularly those related with their extraction efficiency, which affects the large-scale use of some of these substances. The difficulties in screening, extracting, separation and purifying these compounds have increased the development of new and modern methods to address these limitations. In this context, the aim of this chapter is to present an updated review about sources, technologies and methods that have been developed until now to improve the extraction, detection, separation and full characterization of such beneficial compounds, with special emphasis to their possible application in the design of nutraceuticals and functional

Polyphenols have been exhaustively studied in their different natural matrices such as fruits, vegetables, teas, algae and microalgae and more recently agro-food wastes (peels, seeds, pulps, stems and roots) [12–15]. In the three last decades, there has been a prolific publication of scientific studies showing that plant-derived foods and agro-food wastes from industrial transformation have huge quantities of polyphenols. In **Table 1** are summarized some recent studies, and as result from these and other studies, there is a diverse source of polyphenols in plant materials, but both type and amount seem to be highly influenced by their chemical nature, extraction methods, sample particle size, storage time and conditions, as well as by the presence other of interfering substances [25]. Also, their chemical structure and nature vary from simple to highly polymerized substances that include varying proportions of phenolic acids, phenylpropanoids, anthocyanins and tannins, among others [26–28]. Moreover, they might also exist in complex mixtures with carbohydrates, proteins and some quite insoluble high-molecular-weight phenolics [28]. Therefore, the phenolic extraction from plant materials is always a mixture of different steps, and many modifications of a particular method are often needed for the removal of unwanted non-phenolic substances such as waxes, fats, terpenes, pigments (chlorophylls and carotenoids). Solid-phase extraction (SPE) techniques, purification and fractionation based on acidity, are commonly used to remove unwanted

Although the recent advances in the technology had providing innovative approaches to obtain enriched polyphenol natural extracts, we must ware that their extraction efficiency will always be dependent of several factors in which the nature of samples and solvent, pH, temperature, light, length of extraction period, particle size, solvent/sample ratio and liquid-liquid or solid-liquid

coumarines, stilbenes and tannins, among others [4–6].

62 Phenolic Compounds - Natural Sources, Importance and Applications

**2. Foods as natural resources of phenolics**

non-phenolic substances or even other unwanted phenolics [29].

extraction process [25], among others, are the most critical.

food products.

It is widely accepted that the extraction step is one of the most important stage in isolation of polyphenols, but based in literature, there is no consensus about one single and effective standard extraction method. On contrary, there are several reported methods with very accurate results, and according to the literature in some cases, the solid-liquid extraction with different types of solvents is more adequate [30], and in others, the ultrasound-assisted extraction method (UAE) increases the extraction efficiency [31], while in others, this increment is higher when a microwave-assisted extraction (MAE) is used [32], and advanced methods such as pressurized fluid extraction (PFE), supercritical CO<sup>2</sup> extraction (SC-CO<sup>2</sup> ) and enzyme-assisted extraction (EAE) are even better to enhance the content of polyphenols in the extracts [33–39]. Despite this diversity, all have the common fact that the extraction must be conducted carefully but exhaustively with simple, rapid and feasible procedures, and if possible open to automation [40]. In the next paragraphs, we present a summarized information of the most commonly used methods for the extraction of polyphenols in several pant and food matrices.
