Extraction and quantification of polyphenols from kinnow (Citrus reticulate L.) peel using ultrasound and maceration techniques

Abstract

An investigation was carried out to extract polyphenols from the peel of kinnow (Citrus reticulate L.) by maceration and ultrasound-assisted extraction (UAE) techniques. The antioxidant potential of these polyphenols was evaluated using ferric reducing antioxidant power (FRAP), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and superoxide radical scavenging assays; and their antimicrobial activity was assessed against bacterial strains Staphyloccoccus aureus, Bacillus cereus, and Salmonella typhimurium. The highest extraction yield was obtained through the solvent ethanol at 80% concentration level, whereas UAE was a more efficient technique and yielded comparatively higher polyphenol contents than maceration. Maximum polyphenols were extracted with 80% methanol [32.48 mg gallic acid equivalent (GAE)/g extract] using UAE, whereas minimum phenolics (8.64 mg GAE/g extract) were obtained with 80% ethyl acetate through the maceration technique. Elevated antioxidant activity of kinnow peel extracts was exhibited in three antioxidant assays, where 80% methanolic extracts showed the highest antioxidant activity (27.67±1.11mM/100 g for FRAP) and the highest scavenging activity, 72.83±0.65% and 64.80±0.91% for DPPH and superoxide anion radical assays, respectively. Strong correlations between total polyphenols and antioxidant activity were recorded. Eleven phenolic compounds-including five phenolic acids and six flavonoids-were identified and quantified by high performance liquid chromatography. Ferulic acid and hesperidin were the most abundant compounds whereas caffeic acid was the least abundant phenolic compound in kinnow peel extracts. Maximum inhibition zone was recorded against S. aureus (16.00±0.58 mm) whereas minimum inhibition zone was noted against S. typhimurium (9.00±1.16 mm). It was concluded that kinnow mandarin peels, being a potential source of phenolic compounds with antioxidant and antimicrobial properties, may be used as an ingredient for the preparation of functional foods.

Keywords: antimicrobial activity; antioxidant capacity; kinnow peel; maceration; phenolic compounds; ultrasound.

Figure 1

Yield (%) of kinnow mandarin peel extracts by maceration and ultrasound-assisted extraction. Values are presented as mean ± standard error of triplicate analyses. Same alphabetical letters denote nonsignificant difference at p < 0.05.

Figure 2

Total polyphenol content (mg GAE/g extract) of kinnow peel extracts by maceration technique. Values are presented as mean ± standard error of triplicate analyses. Data with different letters denote significant difference at p < 0.05. GAE =gallic acid equivalent.

Figure 3

Total polyphenol content (mg GAE/g extract) of kinnow peel extracts by ultrasound assisted extraction. Values are presented as mean ± standard error of triplicate analyses. Different alphabetical letters denote significant difference at p < 0.05. GAE = gallic acid equivalent.

Figure 4

(A) Typical chromatogram of polyphenols standards (200 μg/mL) at 280 nm. 1 = gallic acid, 2 = chlorogenic acid, 3 = catechin; 4 = epicatechin; 5 = caffeic acid; 6 = hesperidin; 7 = transferulic acid; 8 = coumaric acid; 9 = naringenin. (B) Typical chromatogram of polyphenol standards (200 μg/mL) at 370 nm. 1 = magniferin; 2 = myricetin; 3 = rutin; 4 = quercetin; 5 = kaempferol.

Figure 5

(A) Typical chromatogram of polyphenols of kinnow mandarin peel 50% methanolic extract at 280 nm. 1 = gallic acid, 2 = chlorogenic acid, 3 = catechin, 4 = epicatechin, 5 = hesperidin, 6 = ferulic acid, 7 = coumaric acid. (B) Typical chromatogram of polyphenols of kinnowmandarin peel 50% methanolic extract at 370 nm, 1 = quercetin, 2 = kaempferol. (C) Typical chromatogram of polyphenols of kinnow mandarin peel 100% methanolic extract at 280 nm, 1 = gallic acid, 2 = chlorogenic acid, 3 = catechin, 4 = hesperidin, 5 = ferulic acid, 6 = coumaric acid. (D) Typical chromatogram of polyphenols of kinnow mandarin peel 100% methanolic extract at 370 nm, 1 = quercetin, 2 = kaempferol. (E) Typical chromatogram of polyphenols of kinnow mandarin peel 80% ethanolic extract at 280 nm, 1 = gallic acid, 2 = chlorogenic acid, 3 = catechin, 4 = epicatechin, 5 = hesperidin, 6 = ferulic acid, 7 = coumaric acid. (F) Typical chromatogram of polyphenols of kinnow mandarin peel 80% ethanolic extract at 370 nm, 1 = quercetin, 2 = kaempferol.