Role of Natural Antioxidants on the Oxidation Stability of Fats and Oils

Abstract

Background: The enhancement of oxidation stability in fats and oils through natural antioxidants has garnered significant research interest. Given the susceptibility of fats and oils to oxidation, the incorporation of antioxidants is essential to preserving their quality, nutritional integrity, and safety. This study aims to identify reliable antioxidant sources through a comprehensive analysis of their antioxidant activity, total phenolic and flavonoid content, and polyphenolic composition. Additionally, it assesses the impact of natural extracts on the oxidative stability of fats and oils using induction time monitoring technology and evaluates their effects on unsaturated fatty acids to demonstrate their efficacy in inhibiting oxidation. Methods: A total of 33 plants, sourced from local and ethnic origins, were collected, and their ethanolic extracts were prepared to evaluate their potential as rich sources of natural antioxidants and to analyze their polyphenolic composition. This study utilized a UV spectrophotometer to evaluate total flavonoid, tannin, and phenolic content, as well as antioxidant activity and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity (IC50 value) in 33 ethanol extracts from local and ethnic plant sources. High-performance liquid chromatography with diode array detector (HPLC-DAD) was employed to identify bioactive polyphenolic compounds. Fourteen extracts were selected for further investigation based on their IC50 value, economic significance, and availability. The oxidative stability index (OSI) of soybean oil and hydrogenated fat (dalda) was measured using the Rancimat 743 instrument under varying temperatures (120ºC, 140ºC, and 180ºC) and airflow conditions (15L/h and 20L/h). Additionally, plant ethanolic extracts from betel leaves, tea leaves, spirulina, shime alu leaves, baruna leaves, radish leaves, and shati were viii tested for their OSI performance (induction time >7.0 hours at 120ºC and 20L/h airflow). To assess oxidation stability in baked products, biscuits were prepared using dalda enriched with these extracts, followed by peroxide value, acid value, and thiobarbituric acid reactive substances (TBARS) analysis, along with sensory evaluation. The effect of three extracts on fatty acid stability in soybean oil was further examined using gas chromatography-flame ionization detection (GC-FID) after heating at 180ºC for six hours over seven days. Results: The IC50 values of all tested spices ranged from 60 to 105 µg/mL, while spirulina, betel, tea, and amila leaves exhibited values between 80 and 150 µg/mL. Other extracts, including zinger, turmeric flower, radish, sabarang, uzon, shime alu, boruna, dinge, moringa leaves, and shati, showed IC50 values of 150–200 µg/mL. The ethanolic extracts demonstrated significant flavonoid, tannin, and phenolic content, along with bioactive polyphenolic compounds such as hydroxybenzoic acid, flavonoids, and hydroxycinnamic acids, highlighting their potential as nutraceuticals. Oxidation stability index values for spirulina (8.29 hours), betel leaves (11.39 hours), tea leaves (10.7 hours), and other extracts were comparable to or exceeded that of 0.02% BHT (7.2 hours). Spirulina extract exhibited the highest stability in unsaturated fatty acids, followed by betel and tea leaves. Biscuits prepared with extract-enriched dalda exhibited superior oxidation stability, with betel leaves demonstrating the most favorable effects, followed by spirulina and tea leaves. Sensory evaluation indicated that biscuits with betel and tea leaf extracts were preferred. Conclusion: Among the selected plant extracts, ethanolic extracts of betel leaves, spirulina, and tea leaves exhibited strong natural antioxidant properties, enhancing ix oxidative stability in processed foods by reducing rancidity and extending shelf life. Their rich bioactive polyphenolic composition further suggests potential nutraceutical applications, offering both health benefits and preservative advantages. These findings support the incorporation of natural antioxidants in food processing and underscore the need for further research to explore their broader applications and potential benefits.