Assessment of Antioxidant Properties of Plant-Based Extracts in Food Preservation

Thesis Abstract

The escalating consumer demand for natural, safe, and eco-friendly food preservatives has intensified the investigation into plant-based extracts as viable alternatives to synthetic antioxidants. This study addresses the critical need to evaluate the antioxidant efficacy of select plant extracts for their application in food preservation, aiming to provide a scientific basis for their integration into food processing industries. The specific objectives include (1) to extract bioactive compounds from selected medicinal and edible plants, (2) to quantify the total phenolic, flavonoid, and tannin contents of these extracts, (3) to assess their antioxidant activities using DPPH radical scavenging, ABTS cation decolorization, and ferric reducing antioxidant power (FRAP) assays, (4) to evaluate their effectiveness in retarding lipid oxidation in model food systems, and (5) to determine the relationship between phytochemical contents and antioxidant activity through regression analysis. The research adopts a mixed-methods approach, combining quantitative laboratory-based assays with qualitative analyses of phytochemical profiles. The study population comprises dried plant samples from five widely used medicinal and edible plants Moringa oleifera leaves, Cymbopogon citratus (lemongrass), Ocimum gratissimum (African basil), Zingiber officinale (ginger), and Allium sativum (garlic). A total of 150 samples (30 per plant) will be systematically collected from local markets and herbal stores. Extraction will be performed using solvent-based methods, primarily methanol and aqueous extracts, following standard maceration techniques. The phytochemical contents will be determined spectrophotometrically using Folin-Ciocalteu, aluminum chloride, and vanillin assays, respectively. Antioxidant activities will be quantified via spectrophotometric methods associated with DPPH, ABTS, and FRAP assays. Additionally, the most potent extracts will be incorporated into lipid-rich food models such as fried fish and mayonnaise, with oxidation monitored over 30 days via thiobarbituric acid reactive substances (TBARS) assay. Data analysis will involve analysis of variance (ANOVA) to compare antioxidant activities among different extracts, Pearson’s correlation to examine relationships between phytochemical contents and antioxidant efficacy, and regression analysis to identify the key predictors of antioxidant effectiveness. The study will also employ the theoretical framework of the Free Radical Theory of Antioxidants, which posits that plant-derived compounds can neutralize free radicals and inhibit oxidative processes, and the Gatekeeper Model of Food Preservation, emphasizing controlled release and interaction of antioxidants within food matrices. Expected findings include significant variations in phytochemical concentrations among different plant extracts, with correlational evidence indicating that higher phenolic and flavonoid contents are associated with greater antioxidant capacities. It is anticipated that extracts from Cymbopogon citratus and Zingiber officinale will exhibit superior performance in lipid oxidation inhibition, comparable to synthetic antioxidants such as butylated hydroxytoluene (BHT). The study’s contribution to knowledge lies in providing empirical data on the antioxidant potential of locally accessible plant extracts, facilitating the development of natural preservatives and promoting food safety. The study concludes that certain plant extracts possess promising antioxidant properties suitable for food preservation applications, advocating for further industrial-scale validation and sensory evaluations. It recommends standardizing extraction protocols, exploring synergistic effects among plant extracts, and conducting shelf-life studies in real food systems. The findings will inform policymakers, food technologists, and farmers on harnessing indigenous plants for sustainable, natural food preservation, aligning with consumer preferences and public health goals.