Abstract
Lemon peel powder (LPP) obtained after drying (microwave, infrared, and oven) showed the lowest (58.72%) DPPH-radical scavenging activity in oven-dried and the highest (67.84%) in infrared-dried LPP while that of fresh lemon peel remained 63.22%. Orange peel powder (OPP) showed the lowest DSA (61.65) after microwave and the lowest (63.54%) after infrared-drying while that of fresh orange peel was 63.48%. Total phenolics were between 114.58 (fresh) and 179.69 mgGAE/100 g (oven) in LPP and between 158.54 (fresh) and 177.92 mgGAE/100 g (infrared) in OPP. The total flavonoid contents were 380.44 (fresh)–1043.04 mg/100 g (oven) in case of LPP and 296.38 (fresh)–850.54 mg/100 g (oven) in case of OPP. The gallic acid contents were 2.39 (fresh)–14.02 mg/100 g (oven) in LPP. The (+)-catechin contents were 1.10 (fresh)–49.57 mg/100 g (oven) for LPP and 0.82 (fresh)–7.63 mg/100 g (infrared) in case of OPP. The oleic acid content was 22.99 (infrared)–58.85% (fresh) in LPP-oil and 28.59 (microwave)–61.65% (fresh) in OPP-oil. The linoleic acid contents were 13.76 (fresh)–36.90% (oven) in LPP-oil and 14.14 (fresh)–37.08% (infrared) in case of OPP-oil. The drying techniques showed profound but variable effects on radical scavenging activity, total phenolics, flavonoid, carotenoids, phenolic compounds and fatty acid composition of both LPP and OPP and oven-drying (60 °C) was the most effective in improving these bioactive constituents.