Designing Stable Mayonnaise: Rheological and Structural Performance Fortified with Antioxidant Star Fruit (<i>Averrhoa carambola</i>) Extract from Ultrasound-Assisted Extraction

The preparation and characterization of phenolic extracts from <i>Averrhoa carambola</i> were performed to develop enriched mayonnaise-type emulsions, evaluating the effect on their physicochemical, rheological, and microstructural properties. Extracts were obtained by Ultrasound-Assisted Extraction (UAE) employing different ethanol:water ratios, followed by the analysis of their Total Phenolic Content (TPC) and Antioxidant Activity (AA). The 50:50 extract (AEt50) exhibiting the highest bioactivity was selected for the development of enriched mayonnaise, which was then subjected to stability, physicochemical, rheological, and microstructural analyses. Extraction yields ranged from 13% to 28%, with TPC values spanning 3251 to 4661 mg GAE/g of extract, and AA values between 49.25 and 81.67 µMol Trolox/g of extract. Subsequently, the strategic incorporation of the extract, coupled with pH adjustment, successfully maintained the pH of the final products at approximately 4.63 and preserved emulsion stability. This process resulted in a significant, dose-dependent increase in TPC and AA in the mayonnaise, with the highest concentration achieving nearly 9.0 mg GAE/g and the antioxidant activity de 60.0 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi mathvariant="sans-serif">μ</mi></mrow></semantics></math></inline-formula>Mol Trolox/g. The microstructural integrity was maintained, with all droplet sizes remaining under 4 µm, though a visible change in color (ΔE) was observed. All samples exhibited shear-thinning, non-Newtonian behavior, accurately fitted to the Ostwald–de Waele model (R² > 0.982), and demonstrated a dominant elastic structure (G′ > G″) characteristic of high-quality solid-like gels. Thus, the incorporation of <i>Averrhoa carambola</i> extracts is a technically viable and effective alternative to develop stable food products enriched with functional bioactive compounds.