Phenolic acids and flavonoids of peanut by-products: Antioxidant capacity and antimicrobial effects
Introduction
Nuts and oilseeds, including peanuts, their products and by-products are well recognized sources of phenolic compounds (Alasalvar & Bolling, 2015). Phenolics and/or polyphenolics may render a wide range of health benefits through prevention of cardiovascular diseases, diabetes, and obesity. Furthermore, their anticancer, anti-inflammatory, and antimicrobial effects have also been documented (Lin et al., 2016, Shahidi and Ambigaipalan, 2015). The antioxidant activity of phenolic compounds, which stems from their ability in scavenging radicals by single electron transfer (SET) and hydrogen atom transfer (HAT), is widely studied (Leopoldini, Marino, Russo, & Toscano, 2004). Although phenolic compounds from different resources have been reported to act as scavengers of radicals and other reactive oxygen species (ROS), the deactivation of metal ions due to reduction and/or chelation has also been contemplated (Zhang & Tsao, 2016).
The literature provides extensive data on the antioxidant activity of different phenolic compounds such as phenolic acids, and flavonoids, including anthocyanins (Zhang & Tsao, 2016). Among flavonoid-related compounds, proanthocyanidins (PAC) have received special attention due to their complex structure, which makes their characterization and quantification challenging (Ma et al., 2014b, Oldoni et al., 2016). Based on their linkages, PAC are classified as PAC type A and PAC type B. Grapes are rich sources of B-type PAC whereas peanuts are sources of A type PAC (Ma et al., 2014b, Melo et al., 2016). The antioxidant activity of PAC from grapes and their products and/or by-products have been well documented whereas PAC from peanuts have received less attention. Peanuts have been used for oil extraction for many years; however, a quick search of the literature reveals little data on the contents of phenolic compounds in peanut meal. Peanut skins (PS) have been used for the development of new food products (de Camargo et al., 2014, Ma et al., 2014b) with enhanced content of bioactive compounds. Nevertheless, the use of phenolics from peanut by-products as antioxidants in food model systems and as antimicrobial compounds should also be considered.
Gamma irradiation is an effective treatment to reduce and/or eliminate microorganisms in different food products such as spices, oilseeds, meat, and fish, therefore improving their safety and shelf-life (Badr, 2012, Ben Fadhel et al., 2016, Di Stefano et al., 2014, Kirkin et al., 2014). However, gamma irradiation induced oxidation and consequent sensory quality changes have been an issue of concern. Thus, antioxidants may serve as an alternative to prevent oxidation, thus improving the process by decreasing oxidative reactions and formation of undesirable chemical products. However, there is a concern about the safety of synthetic antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and tert-butylhydroquinone (TBHQ) (Shahidi & Ambigaipalan, 2015). Therefore, phenolics from natural resources have been receiving increasing attention as clean label alternatives.
Phenolic compounds have also been reported to act as antimicrobials against pathogenic gram-positive and gram-negative bacteria such as Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Salmonella Typhimurium (Caillet, Cote, Sylvain, & Lacroix, 2012). Several research groups have examined the contamination of foods with these bacteria (Giombelli et al., 2015, Maffei et al., 2016). Additionally, a recent study (Polewski, Krueger, Reed, & Leyer, 2016) demonstrated the synergism among probiotic bacteria and an A type PAC rich extract in diminishing the invasiveness of extra-intestinal pathogenic E. coli which may decrease the onset of urinary tract infections in women, thereby demonstrating that the antimicrobial effect of phenolics may also be extended to the field of functional foods.
The antioxidant activity of phenolics from PS has been evaluated in lipid model systems using the Rancimat test (de Camargo, Vieira, Regitano-D'Arce, Calori-Domingues, & Canniatti-Brazaca, 2012). However, to the best of our knowledge, neither PS nor the meal from dry-blanched peanuts (MDBP) has been tested as potential sources of phenolic compounds in a gamma-irradiated fish model system. In addition, the complexity of the mechanism of action of phenolics towards microorganisms has demonstrated that different classes of phenolic compounds and bacteria may influence the effectiveness of these natural compounds in inhibiting their growth. Therefore, in the present study, phenolic extracts from PS and the MDBP were screened for their total phenolic content, antioxidant activity and reducing power. In addition, HPLC-DAD-ESI-MSn was used for the evaluation of the profile of phenolics present. The application of phenolic extracts as antioxidants was tested in a gamma-irradiated fish model system and their antimicrobial effect was investigated using gram-positive and gram-negative bacteria.
Section snippets
Materials
Dry-blanched peanuts and PS obtained as by-product from the process (cv. Runner 886) were kindly donated by a local company (CAP—Agroindustrial, Dumont, São Paulo state, Brazil). According to the suppliers, the dry-blanching process was carried out at 80 ± 10 °C for 2 h.
Folin Ciocalteau’s phenol reagent, DPPH, ABTS, mono- and dibasic potassium phosphates, hydrogen peroxide, DMPO (5,5-dimethyl-1-pyrroline-N-oxide), ferrous sulphate, potassium ferricyanide, ferric chloride, butylated hydroxyanisole
Total phenolic content, scavenging activity and reducing power
PS showed the highest TPC content, which was 42 times higher than that found for MDBP (Table 1). The antioxidant capacity of phenolic and/or polyphenolic compounds has been demonstrated in biological and food model systems (Shahidi & Ambigaipalan, 2015). The trend observed in TPC assay was also noted on the capacity of different phenolic extracts in scavenging ABTS radical cation, DPPH radical, and hydroxyl radical, which was confirmed with the results obtained with the reducing power assay. A
Conclusions
PS and MDBP were investigated for their TPC, phenolic profile, antiradical activity and reducing power. The TPC of PS was 42 times higher than that of MDBP, which reflects a higher phenolic content, as evaluated by HPLC-DAD-ESI-MSn, as well as a greater antiradical activity and reducing power; therefore, phenolics from PS were tested for their antioxidant capacity in gamma-irradiated salmon model system, showing antioxidant protection of up to 37%. The oxidative status of gamma-irradiated
Acknowledgments
The first author acknowledges FAPESP (São Paulo Research Foundation) for granting an international PhD internship (Process 2015/00336-4). This research was also supported by the doctoral scholarship granted by FAPESP to the first author in Brazil (Process 2012/17683-0). One of us (F. Shahidi) thanks the Natural Science and Engineering Research Council (NSERC) of Canada for partial financial support. A.S. Sant'Ana acknowledges the financial support of “Conselho Nacional de Desenvolvimento
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