From waste to wealth: High recovery of nutraceuticals from pomegranate seed waste using a green extraction process

Waste pomegranate seed (WPS) from the pomegranate juice industry is an interesting substrate for the food processing industry as it contains high quality oil which is rich in conjugated fatty acids, high quality proteins and dietary fibres. However, the majority of the work reported extraction of only oil and employed organic solvents which decrease the nutritional quality of pomegranate seed protein and fibres. Therefore, in this study, a one pot enzymatic green process was investigated for recovery of high quality oil, food-grade proteins and fibres from WPS. The WPS were treated with protease followed by centrifugation to recover the oil, protein and insoluble fibres in different phases. The mechanism of extraction was confirmed by FTIR-imaging and scanning electron microscopy analysis of WPS. The highest oil recovery of 22.9% (out of which 97.4% in free form) and protein recovery of 13.2% (out of which 90.2% in free form) were obtained, when WPS was incubated with protease at a concentration of 50 U/g for 14 h, at 45 °C and pH 7.2. The remaining WPS residue was rich in insoluble fibres (97.6 g per 100 g WPS residue). The protease-derived oil had 2.3% higher content of conjugated fatty acids and 1.4 times higher total phenolic content than the hexane-extracted oil. Moreover, the protease-derived oil displayed 4% higher antioxidant activity than the hexane-extracted oil. The extracted free proteins were in protein hydrolysate form and had high values of the essential amino acid index (91.6%), protein efficiency ratio (5) and biological value (88.5) confirming their high quality. The insoluble fibre rich WPS residue possessed improved water and oil holding capacity, glucose absorption capacity and glucose dialysis retardation index compared to raw WPS.