Natural Polyphenol Recovery from Apple-, Cereal-, and Tomato-Processing By-Products and Related Health-Promoting Properties

Abstract

Polyphenols of plant origin are a broad family of secondary metabolites that range from basic phenolic acids to more complex compounds such as stilbenes, flavonoids, and tannins, all of which have several phenol units in their structure. Considerable health benefits, such as having prebiotic potential and cardio-protective and weight control effects, have been linked to diets based on polyphenol-enriched foods and plant-based products, indicating the potential role of these substances in the prevention or treatment of numerous pathologies. The most representative phenolic compounds in apple pomace are phloridzin, chlorogenic acid, and epicatechin, with major health implications in diabetes, cancer, and cardiovascular and neurocognitive diseases. The cereal byproducts are rich in flavonoids (cyanidin 3-glucoside) and phenolic acids (ferulic acid), all with significant results in reducing the incidence of noncommunicable diseases. Quercetin, naringenin, and rutin are the predominant phenolic molecules in tomato by-products, having important antioxidant and antimicrobial activities. The present understanding of the functionality of polyphenols in health outcomes, specifically, noncommunicable illnesses, is summarized in this review, focusing on the applicability of this evidence in three extensive agrifood industries (apple, cereal, and tomato processing). Moreover, the reintegration of by-products into the food chain via functional food products and personalized nutrition (e.g., 3D food printing) is detailed, supporting a novel direction to be explored within the circular economy concept.

Keywords: agro-industrial by-products; biological activity; circular economy; health effects; phenolic compounds; re-integration; waste management.

Figure 1

Production of cereal, apples, and tomatoes (tons) in Europe. (A) Evolution of world cereal, apple, and tomato production over the last two decades; (B) production of wheat (tons) in Europe for every country in 2020; (C) production of apples (tons) in Europe for every country in 2020; (D) production of tomatoes (tons) in Europe for every country in 2020 (http://www.fao.org/faostat, accessed on 22 April 2022).

Figure 2

Distribution of phenolic compounds in apple fruit, according to Feng et al. [49]. TPC—total phenolic content; DW—dry weight.

Figure 3

The chemical structure of the predominant phenolic compounds identified in apple pomace: chlorogenic acid (A); epicatechin (B); phlorizin (C). Source: ChemDraw Software.

Figure 4

The most common cereals and their primary bioactive compounds.

Figure 5

The chemical structure of the predominant phenolic compounds identified in tomato-processing by-products: rutin (A); quercetin (B); naringenin (C). Source: ChemDraw Software.