Solid-Liquid Extraction by Manothermosonication: Recapturing the Value of Pomegranate Peels and Nanocomplexation of Extracts with Pea Protein

Manothermosonication (MTS) is a treatment that combines ultrasonication with mild temperature and pressure. MTS extraction was evaluated for recapturing bioactive compounds of pomegranate peel waste. The influence of extraction time (0.5-3 min), temperature (25-50 °C), and pressure (100-500 kPa) on the yield of total phenolic content (TPC) and antioxidant activity (AOA) was assessed. Pea protein isolates (PPIs) and PPI-modified starch (PPI-S) were used to form nanocomplexes with the phenolic extract (PE). Lyophilized peels were extracted with an ethanol/water (30%, v/v) mixture, at a peel:solvent ratio of 1:50. MTS extraction reduced the extraction time by 40 times compared with conventional extraction (35 °C and 60 min) for achieving the same amount of 2,2-diphenyl-1-picrylhydrazyl (DPPH). The samples treated under 500 kPa for 3 min had the highest TPC (1007 μmol GA/g DW) and AOA (1.57 mmol TE/g DW). Nanocomplexes produced from PPI-PE and PPI-S-PE had similar encapsulation efficiency (∼73%). The mean diameters of freeze-dried PPI-PE complexes were 54.5 ± 19.7 nm, as determined by ImageJ, while that of PPI-PE in emulsion was 111.3 ± 6.4 nm measured by dynamic light scattering (DLS). MTS is shown to be a green and efficient alternative to improve the extraction of bioactive compounds from pomegranate peel waste.