Spinach (Spinacia oleracea L.) is a green herbaceous annual leafy vegetable cultivated in many parts of the world; it is characterized by its low cost and is widely used in many traditional dishes. It is considered a functional food for its nutritional composition, phytochemicals, and bioactive compounds that contribute to reduce oxidative stress, inducing the secretion of satiety hormones helping to promote protection mechanisms against hypoglycaemia, cancer, and obesity.
Plant materials were collected for the protein extraction process. Two extraction processes were conducted, in which one involved the use of CaCl2 (S2 sample), while the other one was extracted without the use of CaCl2 (S1 sample).
Then, the amino acid content was determined in both samples using the HPLC-DAD technique with the aim to investigate the phytochemical profile, together with the phenolic and flavonoid compounds. To allow the identification and quantification of amino acids using HPLC-DAD, derivatization with the fluorenylmethyloxycarbonyl (Fmoc) group was carried out following a previously described procedure.
Data reveal that sample S2 presents isoleucine (12.16 μg/mL), while sample S1 contains lysine (4412,6 μg/mL) and tyrosine (9,02 μg/mL). Both of them present a comparable total phenolic content ; however, as concerns the total flavonoid content, sample S1 shows a higher quantity (3.7 mg RE/g). Biological assays show a higher antioxidant activity in sample S1, according to ABTS (21,3 mg TE/g) and metal chelating (32,3 mg EDTAE/g) assays compared to sample S2 in antioxidant tests by CUPRAC (21,6 mg TE/g) and FRAP (13,6 mg TE/g). Finally, sample S2 exhibits a greater inhibition of tyrosinase than sample S1. In turn, sample S1 exhibits a greater inhibition of the glucosidase enzyme than sample S2. In conclusion, sample S1 presents a better amino acid content, antioxidant activity, and enzyme inhibitory activity. Further studies are required to improve the protein extraction method and to promote the development of enriched foods and beverages.
