Phytochemical Quality and Antioxidant Effects of Solanum retroflexum Dun. Leaf Extracts on Oxidation Markers in a Sunflower Oil–Based Salad Dressing Emulsion

Synthetic compounds that are commonly employed to hinder lipid oxidation in high-fat foods have been linked to numerous detrimental health effects. The use of plant extracts that exhibit antioxidant activity is preferred and deemed natural. The current study is aimed to evaluate the phytochemical quality (total flavonoid content (TFC) and total phenolic content (TPC)) and antioxidant activity (FRAP and ABTS) of aqueous reconstituted Solanum retroflexum methanolic leaf extracts. Thereafter, the phenolic profile was analyzed with high-performance liquid chromatography (HPLC), followed by the determination of the antioxidative effects of the S. retroflexum leaf extracts in salad dressing. The TFC and TPC of the S. retroflexum leaf extracts were 575.35 mg quercetin equivalents/g (dw) and 130.00 mg gallic acid equivalents/g (dw), respectively. The antioxidant activity was 1054.39 μM Trolox equivalents/g (dw) (ABTS) and 176.77 μM Fe equivalents/g (dw) (FRAP). Phenolic compounds identified with HPLC included protocatechuate, ellagic acid, and 4-hydroxycinnamic acid. All the extracts of S. retroflexum retarded hydrolysis of fat in salad dressing under accelerated Schaal oven test conditions, that is, as effective as butylated hydroxy anisole. In addition, S. retroflexum leaf extracts, when present at 300 mg/mL, slightly delayed peroxide formation in salad dressing perhaps owing to their high polar plant phenolic concentration. The outcomes of this research point out that S. retroflexum leaf extracts show potential as natural sources of antioxidants in high-fat foods like salad dressing emulsions. Further studies must determine how incorporation of the leaf extracts influences the sensory quality of the salad dressing.