“…The most common key compounds from F&V by-products are polyphenols ( Figure 1 : phenolic acids and their polymeric derivatives, such as lignans, stilbenes, tannins, and flavonoids) in skins, pulp, seeds, or pomace [ 24 ]. Phenolic acids are common in F&V by-products such as apple pomace (chlorogenic acid, and cryptochlorogenic acid) [ 25 ], artichoke (bracts, leaves and stems) (chlorogenic acid) [ 26 ], mango kernel and leaves (gallic acid, and ellagic acid) [ 27 ], pomegranate peel (caffeic acid, chlorogenic acid, ellagic acid, and gallic acid) [ 28 ], potato peel (chlorogenic acid, ferulic, gallic, protocatechuic and caffeic acid) [ 29 ], tomato peel (3-caffeoylquinic acid, 5-caffeoylquinic acid, 3,4-di-O-caffeoylquinic acid, and 3,4,5-tri-caffeoylquinic acid) [ 30 ] and blueberry pomace (cinnamic acid derivatives) [ 22 , 31 , 32 , 33 ]. Among flavonoids, flavones, flavanones, anthocyanidins, and flavonols can be found in grape pomace (catechins, anthocyanins, stilbenes, and flavonol glycosides), onion skin (quercetin 3,40-O-diglucoside and quercetin 4-o-monoglucoside and isorhamnetin-3-glucoside) [ 34 ], tomato peel (lycopene, naringenin chalcone and naringenin) [ 30 ], apple pomace (hydroxycinnamates, phloretin glycosides, quercetin glycosides, catechins, procyanidins, and epicatechin) [ 25 ], figs peel (cyanidin-3-rutinoside, cyanidin-3,5-diglucoside, cyanidin-3-O-diglucoside, epitecatechin, catechin and quercetin-rutinoside) [ 32 ], blueberry pomace (anthocyanins and flavonol-glycosides) [ 33 ], and citrus peel (eriocitrin, hesperidin, and naringin) [ 22 , 31 , 32 , 35 ].…”