FOOD PRESERVATIVE ACTIVITY OF PHENOLIC COMPOUNDS IN ORANGE PEEL EXTRACTS (CITRUS SINENSIS L.)
A. Abd El-Aal Hussein, Fathi T. Halaweish
The objective of this study was to evaluate the preservative/antioxidant activity of orange peel extract in soybean oil after accelerated oxidation at 65°C. Ethanol extracts of two varieties of Egyptian oranges (Baladi and Novel) were prepared, and their total phenolic and flavonoid contents and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity were determined via standard colorimetric assays. Oil containing extract and butylated hydroxytoluene (BHT) or butylated hydroxylanisole (BHA) was stored at 65°C for 7 days. Free fatty acid (FFA) content, Peroxide (POV), 2-Thiobarbituric acid (TBA), and P-anisidine (P-AV) values were assessed every 24 hr. Total phenolic and flavonoid contents ranged from 559.3 to 591.8 mg tannic acid/100g peel and from 80.94 to 87.71 mg rutin/100g peel, respectively. DPPH scavenging activity was 72.33% and 65.05% for Baladi and Novel respectively. After accelerated oxidation, oil-containing extract showed significantly (P= 0.05) lower FFA (0.122, 0.120, 0.119, 0.117%), POV (35.18, 29.96, 20.77, 12.72 meq/kg), TBA (0.063, 0.061, 0.060, 0.055) and P-AV contents (6.31, 6.20, 5.97, 5.61) than the control (FFA 0.177%, POV 48.70 meq/kg, TBA 0.078, P-AV 10.65). BHT and BHA showed FFA contents of 0.129% and 0.134%, POV 34.36 and 35.46 meq/kg, TBA 0.066 and 0.650 and P-AV 7.24 and 7.39, respectively after 7 days. The inhibition of oil oxidation values (IO) were 32.01, 29.75, 30.32, 41.06, 59.92 and 76.45% for BHT, BHA, 400, 800, 1200, 1600 ppm extract, respectively. These results illustrate that orange peel extracts exhibit strong antioxidant activity. Therefore the use of these extracts in food is recommended to suppress lipid oxidation.
Key words: orange peel, extract, phenolic compounds, lipid oxidation, protection