Recovery of proteins and bioactive compounds from turmeric (Curcuma longa) and ginger (Zingibber officinale) wastes using sustainable extraction techniques. Tentative identification of main extracted compounds by UHPLC-Q-TOF-MS/MS

Ginger and turmeric are spices increasingly employed in juice production due to their outstanding composition and health benefits. This practice results in wastes that, like whole spices, likely constitute a cheap and sustainable source of proteins, as well as antioxidant and antimicrobial compounds, whose recovery has not yet been proposed. This work aims to evaluate low environmental impact techniques to make the most of these wastes: high-intensity focused ultrasounds (HIFU), subcritical water extraction (SWE), and enzyme-assisted extraction (EAE). In all cases, water was used as extracting solvent and experimental design chemometric tools (Box-Behnken and factorial 3² design) were employed to maximize the recovery of proteins, antioxidants, and antimicrobial compounds, while minimizing the formation of potentially harmful Maillard products during extraction. HIFU demonstrated a greater capability for extracting proteins, which increased significantly when combined with EAE using a polysaccharidase enzyme. The largest protein extraction was achieved from the ginger extract using HIFU for 18 min, at 60 ºC and 80 % amplitude, combined with EAE using Celluclast enzyme. The extracts obtained using SWE showed significant antioxidant activity, with a slight improvement observed when using 2 cycles instead of one. The highest antioxidant activity was observed in the extract obtained from the turmeric waste using SWE at 175 ºC for 15 min. The extracts also exhibited antimicrobial activity, especially against Staphylococcus aureus, highlighting the minimum inhibitory concentration obtained from the turmeric waste extract using SWE at 155 ºC for 9 min (0.15 mg/mL). The extracts showing the highest antioxidant or antimicrobial activity were analyzed by ultrahigh-performance liquid chromatography coupled to high-resolution tandem mass spectrometry for the tentative identification of main compounds responsible for the observed activities. Phenolic compounds, such as 6-gingerol and its derivatives in ginger waste extracts, and curcuminoids in turmeric waste extracts, were tentatively identified as the predominant constituents.