Antioxidant Dietary Fiber Sources
Fruit and vegetable wastes from industrial food processing are usually discarded or used as animal feed and fertilizers. The studies indicated that these so-called wastes of nutritive plant originated processed foods are rich in ADF. However, since the antioxidant capacity and dietary fibre content of the studied material are high, they can be referred to as “good sources of ADF”, therefore, they were included in this review.
Apple: Apple contains antioxidant activity mainly due to phenolics acids and flavonols. The peel of apple has a higher antioxidant capacity than the pulp of apple. A study on proximate composition analysis of three apple varieties showed that 83.28–89.92% of apple consists of water while the amount of dietary fibre is only 0.86–1.81% (Lim and rabeta., 2007). However, the apple pomace which was separated during processing is reported to have 51.10 g/100 g Dm of total dietary fibre, of which 14.60 g/100 g Dm is soluble and 36.50 g/100 g Dm is insoluble dietary fibre besides the total phenol content of 10.16 mg/g (Sudha et al., 2007) . However, these contents depend on pressing, use of enzymes and additional extraction with water etc.
Cabbage: Species of cabbage (Brassica oleracea) are widely used in traditional medicine due to their antibacterial properties and anti-inflammatory. There are studies on the production of ADF powder from cabbage (B. oleracea L. var. capitata) from outer leaves, which are usually separated as processing waste and are used only as fertilisers. In one of the study it has been reported that (Nilnakara et al., 2009)  the crude fibre content of cabbage leaves was found to be 19.92– 47.47 g/100 g Dm, which was similar to the study results (total dietary fibre 40.89 g/100 g Dm) obtained by Tanongkankit et al. (2010) . In addition, the total antioxidant capacity was reported to be 89.57–96.00% with the total phenolic content up to 571.50 mg GAE/100 g Dm. The authors also investigated that the effects of heat treatments and slicing steps during powder production on dietary fibre content and antioxidant capacity of cabbage outer leaves at different steps, which indicated that these byproducts are good sources of ADF.
Carrot: Carrot is known for its high beta-carotene content. However, its antioxidant properties are not only limited to carotenoids. Carrot is extensively used in the food industry, but its peels or pomace of carrot are discarded or used as an animal feed. The byproducts have 45.45 g/100 g Dm of dietary fibre with a high antioxidant capacity (94.67%), which is appropriate for the production of ADF powder. Their conclusion indicated that blanching improves the total dietary fibre (TDF) yield and the insoluble dietary fibre (IDF) to soluble dietary fibre (SDF) ratio while having no significant consequence on total phenolics content.
Guava: Guava (Psidium guajava L.) is a tropical fruit, commonly consumed fresh and also in processed forms like beverages, syrup, ice cream, and jam (Jimenez-Escrig et al., 2001) . Helpful health effects of guava fruit and its byproducts are reported due to their high antioxidant capacity. The guava concentrate and by-products exhibited high dietary fibre content (up to 69.1 g/100 g Dm), antioxidant activity (up to 462 µmol Trolox eq./g Dm) and associated polyphenols (26.2–77.9 g GAE/kg Dm), which indicated that guava is rich in ADF (Martínez et al., 2012).
Grapes: Grapes are cultivated mainly as Vitis vinifera for wine production. It is estimated that around 13% of the total weight of grapes used for wine making results in grape pomace, which is a by-product in this process. Grape pomace consists of seeds, skins and stems, and in some cases this byproduct is used to extract grape seed oil (Torres et al., 2002) . Grape pomace has 64.6% Dm of dietary fibre with 400 mg dl-a-tocopherol/g lipid oxidation inhibition and 100 mg dl-a-tocopherol/g free radical scavenging capacity. A similar findings reported that white grape pomace and stem with total dietary fibre content of 715.6–790.5 g/kg Dm and total extractable polyphenols content of 34.9–87.3 g GAE/kg Dm could also be considered as ADF (Llobera and Canellas., 2008)
Mango: mango (Mangifera indica L.) is a popular fruit that can be cultivated in various regions, mainly in the tropics (Sultana et al.,2012). Mango is generally rich in ß-carotene, L-ascorbic acid, total phenols and individual phenolic compounds (Liu et al.,2013) . Its peels, leaves, stem bark and kernels were also found promising as functional food ingredients due to their high levels of antioxidants (Pitchaon 2011) . Mango fibre concentrate (Martinez et al.,2012) and powder from mango peels (Ajila et al., 2010) also possessed high dietary fibre content (total dietary fibre 28.05–70.0 g/100 g Dm) and polyphenols (16.14–283 mg GAE/100 g), which makes mango a good source of ADF.
Melon: Watermelon rinds and Sharlyn melon peels, which are usually discarded as wastes, are good sources of ADF with a crude fibre content of 17.28–29.59% (Al-Sayed and Ahmed., 2013) . The authors worked on fortification of cakes with powder produced from these by-products and found out that it is possible to evaluate water melon rinds and Sharlyn melon peels for enriching foods with functional components while providing better freshness to the product.
Orange: Orange is well known for its high vitamin C and phenolic content. Orange juice is also rich in these bioactive compounds contributing effectively to its antioxidant activity (Stella et al., 2011). Some studies confirmed their results of high phenolics (40.67 mg GAE/g Dm) and they also indicated that the orange peel has high dietary fibre content (71.62 g/100 g Dm).
Pineaplle: Pineapple (Ananas cosmosus), a member of the family Bromeliaceae, is a widely consumed tropical fruit which can be consumed as fresh fruit, juice, jam, jelly and dried product. The pineapple stem, which is separated as waste, has moderate antioxidant and antimicrobial effects, while antifungal effect was considerable probably due to high benzoic acid content (Upadhyay et al., 2012) . Pineapple fibre concentrate, obtained as waste from industrial productions and showed that pineapple fibre concentrate is rich in total dietary fibre (75.8 g/100 g Dm) and shows high antioxidant activity (1.7–7.7 µmol Trolox eq /g).
Tomato: Tomato (Solanum lycopersicum) is a good source of the carotenoids lycopene and ß-carotene, phenols, flavonoids, and ascorbic acid which is widely used in the food industry as well as its domestic use is important (Kavitha et al., 2014) . Processes that tomato goes through during preparation have an effect on antioxidant capacity. Peeling was shown to cause serious losses in lycopene, ß-carotene, ascorbic acid, and phenolics contents. While seed removal resulted in a loss of carotenoids and phenolics which consequently cause a decrease in antioxidant capacity (Vinha et al., 2014) . The tomato peel is rich in phenolics (158.10 GAE/100 g) with high dietary fibre content as high as 86.15% (NavarroGonzalez et al., 2011).