Influence of drying techniques on bioactive properties, phenolic compounds and fatty acid compositions of dried lemon and orange peel powders

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.