Polyphenols in Agricultural Grassland Crops and Their Health-Promoting Activities—A Review

Grassland crops are emerging reservoirs of undisturbed, natural antioxidants and phytochemicals, such as phenolic acids and flavonoids. The present review will focus on the most commonly cultivated crops, namely Lolium perenne L, Cichorium intybus L, Plantago lanceolata L. and Trifolium pratense L, which have been recognized for their polyphenolic composition. However, these crops are often undervalued and underutilized, yet have the means of potentially creating novel, value-added food and nutraceutical products. Previous studies relating to these crops have identified them as rich sources of caffeic acid, chlorogenic acid, daidzein, kaempferol, luteolin, and quercetin. The key to harnessing the hidden potential of these species is the recovery, identification, and characterization of the phytochemicals they contain. Considering the upsurge of research studies on alternative plant-based diets for the health of humans and the planet earth, there is a necessity to understand the phytochemical composition and the bioactivity that they possess. This review summarizes recovery methods of phytochemicals from the aforementioned grassland crops and their compositional and functional (antioxidant, anti-cancer, and anti-diabetic) characterization and discusses the potential for grassland crops as an abundant reservoir of health-promoting ingredients which can increase the nutritional composition within novel food innovations or within nutraceuticals.