Upcycling wild olive leaves with blue pea flowers and sea buckthorn berries into a functional instant tea: optimization, bioactivity, and structural insights

The growing demand for sustainable and convenient functional beverages has increased interest in valorizing underutilized plant materials and agro-industrial by-products. Wild olive leaves are commonly discarded despite their phenolic-rich composition, while blue pea flower and sea buckthorn berries provide natural pigments, organic acids, and bioactive compounds. However, the combined use of these three ingredients in an optimized instant tea tablet has not been previously reported. Therefore, this study developed a novel plant-based instant tea tablet by integrating wild olive leaf bio-waste, blue pea flower, and sea buckthorn berries using Response Surface Methodology based on a three-component mixture design. The formulation was optimized using antioxidant activity, total phenolic content, total flavonoid content, and sensory acceptability, followed by freeze-drying and compression into tablet form. The optimized tablet showed high phenolic and flavonoid contents, antioxidant activity based on DPPH, ABTS, and ferric/ferricyanide reducing power assays, and in vitro α-amylase and α-glucosidase inhibitory activity. Mineral analysis showed nutritionally relevant minerals, while simulated digestion suggested high mineral bioaccessibility. The tablet also showed rapid temperature-dependent disintegration in hot water. SEM and AFM revealed an irregular porous matrix that may have contributed to rapid reconstitution, while FTIR indicated functional groups associated with phenolics, carbohydrates, and organic acids.