Pressurized liquid extraction of flavonoids from spinach

Pressurized liquid extraction (PLE) using water and a 70:30 mixture of ethanol and water over the temperature range of 50 to 190 degrees C was used to extract flavonoids from dried spinach. The total phenolic content, antioxidant capacity, color, and browning indices of the extracts were also evaluated. PLE using a 70:30 mixture of ethanol and water was more effective than water in extracting flavonoids from spinach. Flavonoids were effectively extracted over the temperature band of 50 to 130 degrees C with water and 50 to 150 degrees C with ethanolic solvent. Levels of total phenolics and ORAC values increased with increasing extraction temperature, indicating that flavonoids were minor contributors to antioxidant capacity at elevated extraction temperatures. Browning of ethanolic extracts correlated highly with ORAC values over the temperature range of 50 to 190 degrees C, and the ORAC values of the large molecular weight fraction (> 1000 Da) increased linearly over the temperature range, indicating that Maillard polymers were the major contributors to antioxidant capacity. The results illustrate that PLE temperatures of < 130 degrees C for water or < 150 degrees C for ethanolic solvent may be used to extract flavonoids, followed by a high temperature (> 170 degrees C) extraction to generate antioxidant-rich moieties.