Biological Evaluation of Avocado Residues as a Potential Source of Bioactive Compounds

Abstract

Avocado seed and peel are the main by-products from avocado industrialisation, and account for nearly 30% of fruit weight. Although they are usually discarded, their high phenolic content has been deeply associated with several nutritional and functional benefits. Thus, for a comprehensive analytical evaluation of both semi-industrial extracts, various steps have been developed: tentative characterisation and quantification of the phenolic composition using HPLC-ESI-qTOF-MS, determination of TPC and antioxidant activity by Folin–Ciocalteu, FRAP, TEAC and ORAC methods, evaluation of scavenging capacity against different ROS and measurement of the enzymatic inhibitory potential against potentially harmful enzymes. Finally, their bioactive potential was tested in a human platelet model where antiaggregatory activity was measured. Hence, 48 different compounds were identified, where flavonoids and procyanidins were the most representative groups. The higher TPC was found in avocado peel extract (190 ± 3 mg/g), which showed more antioxidant power and more capacity to decrease ROS generation than seed extract (60 ± 2 mg/g). In addition, both extracts showed enzymatic inhibition, especially against hyaluronidase, xanthine oxidase and acetylcholinesterase. Lastly, avocado peel was proven to inhibit platelet aggregation with significant results at 1, 0.75 and 0.5 mg/mL, where the extract showed reducing effects on agonists’ expression such as p-selectin or GPIIb/IIIa complex. These results demonstrate that both semi-industrial extracts—above all, avocado peel—have an interesting potential to be exploited as a natural by-product with antioxidant properties with multiple applications for the prevention of different pathologies.

Determination of the Bioactive Effect of Custard Apple By-Products by In Vitro Assays

“…Custard apple seed and peel extracts at 5000 mg/L were analysed by using high performance liquid chromatography (ACQUITY UPLC H-Class System; Waters, Milford, MA, USA) coupled to electrospray (ESI) quadrupole time-of-flight mass spectrometry (Synapt G2, Waters Corp., Milford, MA, USA). The separation was performed in a ACQUITY UPLC BEH Shield RP18 Column, 130 Å, 1.7 µm, 2.1 mm × 150 mm at a flow rate of 0.7 mL/min using volume injection of 10 μL [ 47 ].…”

“…Most reference compounds were not available in the sample, so the quantification was majorly performed using structurally related substances, considering the phenolic compound standard has a similar aglycon moiety. Quantification values are expressed as mean ± standard deviation in mg of analyte per gramme of dry extract (DE) [ 47 ]. Table 5 summarises analytical parameters:…”

“…All undermentioned assays performed were adapted to a 96-well polystyrene microplate and the absorbance measurement was carried out on a Synergy H1 Monochromator-Based Multi-Mode microplate reader (Bio-Tek Instruments Inc., Winooski, VT, USA). Moreover, the methodologies used were performed following previous papers [ 47 ].…”

“…As previously reported, while only superoxide was evaluated by the colorimetric method, a fluorometric-based assay was used for nitric oxide and HOCl [ 47 ]. The results were expressed as the custard apple by-products extract concentration needed to inhibit the ROS/RNS formation by half (IC 50 ).…”

“…The extracts were lyophilized and dissolved in phosphate buffered saline (PBS) for platelet aggregation studies. Steps were followed as previous papers [ 47 ].…”