Phenolic Compound Profiles and Antioxidant Capacity of Persea americana Mill. Peels and Seeds of Two Varieties

Abstract

Avocado processing by the food and cosmetic industries yields a considerable amount of phenolic-rich byproduct such as peels and seeds. Utilization of these byproducts would be favorable from an economic point of view. Methanolic (80%) extracts obtained from lyophilized ground peels and seeds of avocado (Persea americana Mill.) of the Hass and Shepard varieties were characterized for their phenolic compound profiles using the HPLC-PAD technique. The structures of the identified compounds were subsequently unambiguously confirmed by ESI-MS. Compositional analysis revealed that the extracts contained four polyphenolic classes: flavanol monomers, proanthocyanidins, hydroxycinnamic acids, and flavonol glycosides. The presence of 3-O-caffeoylquinic acid, 3-O-p-coumaroylquinic acid, and procyanidin A trimers was identified in seeds of both varieties. Intervarietal differences were apparent in the phenolic compound profiles of peels. Peels of the Shepard variety were devoid of (+)-catechin and procyanidin dimers, which were present in the peels of the Hass variety. Peels of both varieties contained 5-O-caffeoylquinic acid and quercetin derivatives. The differences in the phenolic profiles between varietals were also apparent in the different antioxidant activity of the extracts. The peel extracts had a higher total phenolic compound content and antioxidant activity when compared to the seed extracts. The highest TEAC and ORAC values were apparent in peels of the Haas variety in which they amounted to 0.16 and 0.47 mmol Trolox/g DW, respectively. No significant (p > 0.05) differences were apparent between the TEAC values of seeds of the two varieties but the ORAC values differed significantly (p < 0.05). Overall these findings indicate that both the seeds and peel of avocado can be utilized as a functional food ingredient or as an antioxidant additive.

Bioactive characterization of Persea americana Mill. by-products: A rich source of inherent antioxidants

“…From the 29 different compounds found on P. americana by-products, 23 of them were found in peels (227.9 mg/g of extract) and only 8 in kernels (72.5 mg/g of extract), this represent around 3-fold higher polyphenols content in peels, these results obtained proved to be consistent with the other reports (Kosińska et al, 2012;Rodríguez-Carpena et al,2011). It is also important here to stress, the higher phenolic content in P. americana byproducts compared with the edible pulp (Wang et al, 2010).…”

“…It is also important here to stress, the higher phenolic content in P. americana byproducts compared with the edible pulp (Wang et al, 2010). This greater polyphenolic content has also displayed higher antioxidant capacity, and as expected P. americana peels proof to excel the kernels activity in around 1.5-fold higher in all the antioxidant tests performed and shown in Table 2, this result proved to be in concordance with Calderón-Oliver et al (2016), Kosińska et al (2012) and Saavedra et al (2017). Although the differences in the total phenolic content between peels and kernels is 3 times higher, the antioxidant activity observed it is only around half (1.5) greater.…”

“…Peels and kernel present a very distinct profile being the only common compounds, peaks 10 and 12. The phenolic profile of avocado has been previously described by other authors in pulp (Hurtado-Fernández et al, 2013, peels (Kosińska et al, 2012) and seeds (Kosińska et al, 2012;Ramos-Jerz et al, 2013). However, many of the identified compounds were identified for the first time in avocado by-products.…”

“…Regarding the phenolic acids, caffeoylquinic acids and p-coumaroyl quinic acid isomers were the only compounds found in both samples, being the majority of them found in kernel samples, being peaks 8 and 6 the only phenolic acids found in peels samples. Peaks 1, 2, 6 and 8 were identified as caffeoylquinic acid derivatives according to their UV spectra and pseudomolecular ions, being previously found by Kosińska et al (2012) and Ramos-Jerz et al (2013) in peels and seeds of P. americana. Peak assignments of the different caffeoylquinic acids and pcoumaroyl quinic acid isomers were made using the recommended IUPAC numbering system (IUPAC, 1976) as also the hierarchical keys previously developed by Clifford et al (2005Clifford et al ( , 2003.…”

“…There are few avocado by-product studies in literature, and the existing articles report works with non-compatible solvents allowed by the food and pharmaceutical authorities (FDA, 2017), such as methanol or hexane (Kosińska et al, 2012;López-Cobo et al, 2016;Rodríguez-Carpena et al, 2011), hindering the use of their final extracts. For this reason, we decided to performed a complete research based on an efficient food grade solvent, working on the hydrophilic and lipophilic antioxidant profile, a deep characterization of the bioactive compounds through HPLC-DAD-ESI/MS was performed, a wider antimicrobial analysis employing more pathogenic strains than those already tested by other authors and adding up the cytotoxic potential assays, to finally compile all this information in order to acquire better understanding of their intrinsic compounds and functions, which would allow to find an adequate use of these by-products as an alternative natural ingredient.…”