High pressure assisted extraction of bioactive compounds from yellow prickly pear peels

The main objective of this research was to study the effect of pressure (0.1, 300 and 600 MPa), extraction time (5, 17.5 and 30 min) and ethanol concentration (0, 40 and 80%) on total phenolics, flavonoids, anthocyanins and betalains from yellow prickly pear peels, a sub product of vinegar production. Antioxidant activity (ABTS, DPPH and FRAP methods) and total extraction yields were also determined for all extracts. A Box–Behnken design and Response Surface Methodology (RSM) were used to evaluate the effects and to estimate the optimum extraction conditions. Antimicrobial activity was evaluated against Escherichia coli and Listeria innocua in extracts performed under optimized conditions. Ethanol concentration was the variable that showed the greatest effect on extraction yields, followed by pressure and then the extraction time. In general, high pressure increased extraction yields between 6 and 17%, when compared with extractions performed under same conditions but at 0.1 MPa. The models showed satisfactory fitting and adequacy to the experimental data and the high correlation of mathematical models indicated that the quadratic polynomial models could be employed to predict the results and optimize the extraction conditions. The optimum extraction conditions were dependent on the class of compounds analyzed. Experimental and predicted results differ less than 10%. The selected extracts inhibited Escherichia coli and Listeria innocua growth. High pressure assisted extraction showed advantages in relation to Soxhlet increasing the antioxidant activity in average 27% and presenting similar total extraction yields. Total phenolic compounds and betaxanthins increased 19% and 117%, respectively. Moreover, the extraction times were between 8 to 48 times smaller when high pressure extraction was used. The prickly pear residues are rich in bioactive compounds that, when conveniently recovered, can have numerous applications in different sectors and at same time valorising the fruit residue. The optimizations obtained in this work make the high pressure technology applied to extraction process a promising process for scale up.