Enhancing Oxidative Stability and Shelf Life of Cooking Oils Using
Citrus Peel Extracts
Abstract
Citrus peels are nonedible by-products that are often discarded. This
work explores the bioactive compounds extracted from the peels of 4
local citrus fruits, their antioxidant and antimicrobial activities and
applicability as natural antioxidants for vegetable oils. Total soluble
phenols and total flavonoids were extracted from orange, lemon,
tangerine and grapefruit peels using various solvents. Orange peel
methanol extract produced the highest yield (~16
g/100g), however using ethanol maximized the concentration of total
phenols (~345 mg Gallic acid equivalents/100g dry
weight) as well as total flavonoids (~80 mg catechol
equivalents/100g). In general, extracts with high total phenolic
contents exhibited high antioxidant capacities. The orange peel ethanol
extract showed the highest DPPH and ABTS values while its methanol
extract exhibited the highest hydroxyl radical scavenging value. In
addition, all citrus peel extracts possessed high antimicrobial activity
against several food-borne Gram-negative and Gram-positive pathogenic
bacteria and fungi. The composition of polyphenolic compounds in orange
peel extracts analyzed by ultra-performance liquid chromatography
combined with mass spectrometry (UPLC-ESI-MS/MS) revealed the presence
of 22 and 32 compounds in the aqueous and ethanolic extracts,
respectively. The predominant compounds were narirutin, naringin,
hesperetin-7-O-rutinoside naringenin, quinic acid, hesperetin,
datiscetin-3-O-rutinoside and sakuranetin. Importantly, incorporation of
orange peel extract into vegetable oils greatly enhanced their oxidative
stability compared to a synthetic antioxidant (BHT). Overall results
support the potential of citrus peels as natural antioxidants and
antimicrobials for enhancing the shelf life, storage stability and
safety of food oils.