Solid-state fermentation – assisted extraction of bioactive compounds from hass avocado seeds
Graphical abstract
Introduction
Bioactive compounds have been gaining importance due to their ability to promote benefits for human health, such as the reduction in incidence of some degenerative diseases such as cancer and diabetes (Conforti et al., 2009; Kim et al., 2009) and minimizing risk factors for cardiovascular disease (Kris-Etherton et al., 2002, Pérez-Jiménez et al., 2008). Much of the bioactive compounds are phytochemicals such as antibiotics, alkaloids, pigments, and phenolic compounds (Hölker et al., 2004). Due to the myriad beneficial characteristics of these substances, research has been intensified with the aim of finding fruits, vegetables, plants, agricultural and agro-industrial wastes/byproducts as a source of these compounds (Torres-León et al., 2018). Agro-industrial wastes and food byproducts are generated in large quantities. Currently, these byproducts are undervalued and discarded without any use (Torres-León et al., 2018). In this sense, greater attention has been paid to these residues that are abundantly available for the production of bioactive compounds.
In avocado processing pulp is used in the avocado industry, while peels and seeds (byproducts) are disposed of as residues or wastes. These byproducts are rich in polyphenols with antioxidant and antimicrobial power, including catechin, epicatechin, and protocatechuic acid which have been found especially in the seed (Soong and Barlow, 2004). Exploring the bioactive compound content of these wastes can lead to new products and add value to the industry (Torres-León et al., 2018).
Bioactive compounds are usually extracted from natural sources by solid-liquid extraction using organic solvents (Martins et al., 2011). However, other techniques have recently been proposed to obtain these compounds (Dulf et al., 2018, Wang and Weller, 2006). SSF is a bioprocess that can be used in the extraction of bioactive compounds from agro-industrial by-products (Torres-León et al., 2019; Vattem et al., 2004). The enzymes released by them act as biocatalysts and allow better release and extraction of bioagents (Soares et al., 2014). This biotechnological process is economical and easy to implement as it requires small equipment, lower capital and reduced operating costs (Torres-León et al., 2019). There are several important aspects that should be considered in an SSF bioprocess to produce any bioactive compound. These aspects include the selection of the appropriate microorganism, the substrate, the optimization of fermentation parameters and the selection of methods for the recovery and purification of the desired products. There is preliminary evidence of the physicochemical characteristics and functional phytochemical content of avocado seed as well as some possible applications, however, there is no background on the production and extraction of compounds antioxidants by SSF. This study reports the influence of SSF with A. niger GH1 on the release of phenolic antioxidants from avocado seed. The conditions of fermentation were optimized taking as a variable response the antioxidant capacity of the extracts obtained.
Section snippets
Chemicals and reagents
DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS+ (2,2′-azino-bis (3- ethylbenzothiazoline-6-sulphonic acid)), Trolox, Folin-Ciocalteu reagent and Gallic Acid (GA) were purchased from Sigma Chemical Co.
Microorganism and inoculum
A. niger GH1 strain from DIA-UAdeC (Food Research Department of the Autonomous University of Coahuila) was used. The strain was preserved in dextrose potato agar (PDA) at 4 °C. The inoculum was brought to a concentration of 2 × 107 spores/g of dried seed.
Plant material
Avocado seeds (Persea americana Mill cv. Hass)
Tests of support in solid-state fermentation
The WAI represents the amount of water that can absorb the SSF support material (Buenrostro et al., 2017; Buenrostro-Figueroa et al., 2014; Mussatto et al., 2009; Torres-León et al., 2019). CHP constitutes the amount of water linked to the material, it cannot be used by microorganisms for their metabolic functions during SSF (Buenrostro et al., 2017; Torres-León et al., 2019).
The avocado seed had WAI and CHP values of 3.00 g/g of dried seed ± 0.01 and 14.33 % ± 0.09 for the size of 1.5 mm and
Conclusion
The results of the present study revealed the ability of the fungus A. niger GH1 to degrade compounds present in the avocado seed and improve its antioxidant capacity. The particle size ≤ 2.5 mm, 60% humidity and 120 h were the best conditions for the increase in antioxidant capacity. The addition of culture medium to the SSF did not significantly improve the degradability of compounds by the fungal strain, compared to the SSF with sterile water. The profiles of gallic acid, (+) - catechin, (-)
Conflict of interest
The authors declare no conflict of interest.
Declaration of Competing Interest
The authors report no declarations of interest.
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