Avocado byproducts (remains of pulp, peel, seed, and leaves) have been considered as sources of bioactive compounds due to their polyphenol contents ^[1][17] (hydroxycinnamic acids, hydroxy-benzoic acids, flavonoids, and proanthocyanins), as well as their contents of acetogenins, phytosterols, carotenoids, and alkaloids ^[2][18]. Polyphenols are distributed in the pulp, peel, seed, and leaves, while carotenoids and tocopherols are mainly found in the avocado pulp ^[2][18]. The peel and seed are also sources of fermentable sugars and fiber ^[3][39]. Natural extracts of the seed are rich in phenols with antioxidant properties ^[4][2], with higher levels than those reported for the pulp and for common synthetic antioxidants such as Trolox ^[3][39]. Phytochemical studies on avocado seeds have identified compounds such as saponins, phytosterols, triterpenes, fatty acids, furanoic acids, flavonol dimers, and proanthocyanidins. Protocatechuic acid was the main phenolic compound found, followed by kaempferide and vanillic acid ^[5][21]. The seed extract possesses low toxicity ^[5][21]; however, some authors have reported that at concentrations of 500 mg/kg, the extracts display toxic and genotoxic activity in mice ^[1][6][7][17,40,41]. Studies with hypercholesterolemic mice have demonstrated the reduction of cholesterol and low-density lipoproteins by the seeds, an effect attributed to their phenolic content, antioxidant activity, and dietary and crude fiber content ^[5][21].

Avocado residue extracts have been reported to have numerous biological activities useful in the food and pharmaceutical industries. Therefore, they could be used as sources of fiber and phenolic compounds ^[2][18].

Mango is one of the most consumed fruits. The peel is the main byproduct of processing ^[8][9][42,43], constituting about 15–20% of the total weight of the fresh fruit ^[10][44]. There is much interest in the study of mango peel due to the large quantities generated by the concentrate industry and its potential for use as an alternative ingredient in different food matrices. It is considered a good source of bioactive components ^[11][45] such as dietary fiber; compounds with antioxidant activity; phytochemicals such as polyphenols, carotenoids, vitamin E, and vitamin C; and enzymes ^[9][10][43,44]. Mango peel is also a good source of pectin, cellulose, hemicellulose, lipids, proteins, and reducing and nonreducing sugars, which may vary according to variety ^[12][46]. Among the main phenolic compounds reported in mango peel are syringic acid, quercetin mangiferin pentoside, and ellagic acid ^[9][43]. Some studies have reported that the main phenolic compounds present in mango participate in synergistic or antagonistic interactions that modify antioxidant capacities. However, the connection between the structure of these bioactive compounds and their biological activity is still under investigation ^[13][8].

Mango peel is a good source of dietary fiber (soluble and insoluble) ^[9][14][43,47]. It can be used for the extraction of bioactive compounds. In addition, the residue obtained can be used in the preparation of foods rich in dietary fiber ^[8][12][42,46] or as a prebiotic ^[14][47].

Papaya byproducts (peels, seeds, and pulp) contain large amounts of nutrients, including dietary fiber and phenolic compounds with antioxidant activity ^[15][16][22,48]. Multiple phenolic compounds have been identified in papaya byproducts (protocatechuic acid hexoside, mangalin, quercetin 3-O-rutinoside, caffeoyl hexoside, and ferulic acid), as have lutein, zeaxanthin, β-carotene and β-cryptoxanthin, carotenoids, and ascorbic acid ^[15][22]. In total, 65% of the polyphenols associated with these dietary fiber concentrates are highly bioaccessible in the small intestine, and the nondigestible fiber portion shows antioxidant capacity ^[15][22]. Papaya peel contains vitamins like vitamin A, vitamin C, riboflavin, thiamin, and niacin. It is a source of phenols, alkaloids, flavonoids, tannins, and saponins ^[17][49]. The physicochemical properties of papaya peel vary by geographic location, variety, and season, which may affect processing and other associated activities. Therefore, extensive research is required ^[17][49].

According to Calvache et al. ^[15][22] the phenolic compounds found in dietary fiber concentrates from papaya peel were twice those found in the pulp (0.99 vs. 0.47 g/100 g). On the other hand, it was found that about 22% of the polyphenols present in fresh papaya pulp and more than 37% of the polyphenols present in the peel remained in the fiber after the concentration process.

During pineapple processing, a series of residues are generated, including peels (30%), pomace (50%), stems, crowns (13%), and fruit cores (7%). These residues or byproducts represent between 25 and 35% of the total weight of the fruit ^[18][36]. They consist of structural carbohydrates, dietary fiber, simple sugars, vitamins, and polyphenols ^[19][50]. The carbohydrates present in pineapple peel are bound to other compounds such as soluble fiber and polyphenols ^[19][20][12,50]. The main polyphenols identified in pineapple peels are gallic acid (31.76 mg/100 g of dry extracts), catechin (58.51 mg/100 g), epicatechin (50.00 mg/100 g), and ferulic acid (19.50 mg/100 g) ^[21][51]. Because of this, pineapple byproducts are considered biomass that can be exploited as a source of dietary fiber ^[19][50].

After the vinification process, more than 70% of the grape polyphenols remain in the pomace ^[22][52]. This waste from the wine industry is mainly made up of peel, residual pulp and stalks, and seeds. These polyphenols structurally have one or more aromatic rings and are usually found as esters, methyl esters, or glycosides, which can be conjugated with mono-, oligo-, or polysaccharides in plant tissues ^[23][24][6,53].

Carrot pomace is composed mainly of an insoluble, fiber-rich fraction, in which the presence of peptic polysaccharides, hemicellulose, and cellulose stands out. Studies have identified significantly enhanced functional properties, such as glucose-absorption capacity and amylase-inhibition activity, compared to those of cellulose. As carrot pomace is available in large quantities as a byproduct of juice production, it could be exploited as a good source of dietary fiber ^[25][54]. However, it has been reported that at drying temperatures above 90 °C, 20% of the β-carotene in carrots is degraded ^[26][27][35,55].