Antioxidant and antimicrobial activities and UPLC-ESI-MS/MS polyphenolic profile of sweet orange peel extracts

Abstract

With growing consumer awareness, exploitation of renewable resources is cost-effective and environment friendly. This work examines the potential of citrus peels as natural antioxidants and antimicrobials for food preservation. Extraction yield, total soluble phenols and flavonoids of various citrus peels (sweet orange, lemon, tangerine and grapefruit) were optimized by varying the solvent type. While the highest extract yield (~16 ​g/100g) was obtained from the sweet orange peels in methanol, extraction with ethanol maximized the concentration of total phenols and flavonoids (~80 ​mg catechol equivalents/100 ​g dry weight). In addition, sweet orange peel extract showed the highest DPPH, ABTS and hydroxyl radical scavenging values. UPLC-ESI-MS/MS analysis of aqueous and ethanolic extracts of sweet orange peels revealed more than 40 polyphenolic compounds including phenolic acids and flavonoids, some of which have not been previously reported. The predominant polyphenols were narirutin, naringin, hesperetin-7-O-rutinoside naringenin, quinic acid, hesperetin, datiscetin-3-O-rutinoside and sakuranetin. The incorporation of sweet orange peel extract into two vegetable oils enhanced their oxidative stability. In addition, all citrus peel extracts possessed high antimicrobial activity against several food-borne pathogens, and the activity was highest for the sweet orange peel extract. Overall results suggested the great potential of sweet orange peels as natural antioxidant and antimicrobials, which can be efficiently extracted using a simple and low-cost method, for enhancing the storage stability and safety of vegetable oils.

Keywords: Antimicrobial; Antioxidant; Citrus peels; Flavonoids; Oil stability; Polyphenols; Sweet orange.

Graphical abstract

Fig. 1

Change in the peroxide value (meq/kg) of (A) soybean oil and (B) sunflower oil during storage. Blank, oil without antioxidant; Extract, oil incorporated with sweet orange peel ethanol extract; BHT, oil incorporated with synthetic antioxidants (BHT).

Fig. 2

Induction period of the Soybean and sunflower oils obtained from the Rancimat test. Blank, oil without antioxidant; Extract, oil incorporated with sweet orange peel ethanolic extract; BHT, oil incorporated with synthetic antioxidants (BHT).