Emergent Technologies for the Extraction of Antioxidants from Prickly Pear Peel and Their Antimicrobial Activity.

Elisabete M. C. Alexandre,Marta C. Coelho,Kardelen Ozcan,Jorge A. Saraiva,José A. Teixeira,Carlos A. Pinto,Manuela Pintado

doi:10.3390/foods10030570

Abstract

Phenolic compounds are important bioactive compounds identified in prickly pear peel that have important antioxidant and antimicrobial properties. However, conventional thermal extraction methods may reduce their bioactivity, and technologies such as high pressure (HP) and ohmic heating (OH) may help preserve them. In this study, both technologies were analyzed, individually and combined (250/500 MPa; 40/70 °C; ethanol concentration 30/70%), and compared with Soxhlet with regard to total phenolics, flavonoids, and carotenoids as well as antioxidant (ABTS, DPPH, ORAC), DNA pro-oxidant, and antimicrobial (inhibition halos, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), growth curves, and viable cells) activities of prickly pear peel extracts. Total phenolics extracted by each technology increased 103% (OH) and 98% (HP) with regard to Soxhlet, but the contents of total flavonoids and carotenoids were similar. Antioxidant activity increased with HP and OH (between 35% and 63%), and OH (70 °C) did not induce DNA degradation. The phenolic compound present in higher amounts was piscidic acid, followed by eucomic acid and citrate. In general, their extraction was significantly favored by HP and OH. Antimicrobial activity against 7 types of bacteria showed effective results only against S. aureus, S. enteritidis, and B. cereus. No synergetic or additive effect was observed for HP/OH.

Highlights

The edible portion of the prickly pear (Opuntia ficus-indica L.) is the pulp, which is usually eaten raw but can be processed to produce dehydrated derived products and juices, alcoholic beverages, jams, and jellies
Total phenolics were extracted in higher amounts under any Ohmic heating (OH) and/or High pressure (HP) conditions when compared with Soxhlet extraction (8.14 ± 0.21 mg/g DW; Table 1)
A possible explanation for this is that HP and OH promote the release of phenolic compounds from their intracellular compartments since the entrance of higher quantities of solvent through their membranes can facilitate the extraction of compounds, making them more extractable

Summary

Introduction

The edible portion of the prickly pear (Opuntia ficus-indica L.) is the pulp, which is usually eaten raw but can be processed to produce dehydrated derived products and juices, alcoholic beverages, jams, and jellies. High pressure (HP) extraction is usually applied between 100 and 600 MPa at low-tomoderate temperatures In these conditions, HP is able to protect the structure of the compounds since it acts differently on covalent and noncovalent bonds [4]. Ohmic heating (OH) is another emerging technology, where alternating electric current is passed directly through a liquid or solid food product, resulting in an instantaneous generation of heat within the product due to the electrical resistance of the food [6] This extraction technology can be used to increase the efficiency of solute diffusion throughout the membrane, known as the electro-osmosis effect, improving extractions and resulting in the extraction of high-quality compounds

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