High dietary fibre powders from orange and lime peels: associated polyphenols and antioxidant capacity

High dietary fibre powders from Valencia orange and Persa lime peels were prepared and their dietary fibre composition and antioxidant capacity studied. Fibres from both peels had a high total dietary fibre content (61–69%) with an appreciable amount of soluble fibre (19–22%). The concentration of antioxidant AA₅₀] required to achieve a 50% inhibition of oxidation of linoleic acid at 40°C was measured using the ferric-thiocyanate method. The higher the AA₅₀], the lower the antioxidant capacity. Lime peel fibre AA₅₀] was half the value of DL--tocopherol and 23 times lower than orange peel fibre; the AA₅₀] of commercial butylated hydroxyanisole (BHA) was half the value of lime fibre. HPLC analyses of the polyphenols extracted from orange and lime peels fibres showed the presence of caffeic and ferulic acids, as well as naringin, hesperidin and myricetin in both fruit fibres. The different antioxidant power of these fibres could be in part explained by the presence in lime peel fibre of ellagic acid, quercetin and kaempferol which are strong antioxidant polyphenols.