Phenolic Compounds Profiling and Their Antioxidant Capacity in the Peel, Pulp, and Seed of Australian Grown Avocado

Abstract

Avocados (Persea americana M.) are highly valued fruits consumed worldwide, and there are numerous commercially available varieties on the market. However, the high demand for fruit also results in increased food waste. Thus, this study was conducted for comprehensive profiling of polyphenols of Hass, Reed, and Wurtz avocados obtained from the Australian local market. Ripe Hass peel recorded the highest TPC (77.85 mg GAE/g), TTC (148.98 mg CE/g), DPPH (71.03 mg AAE/g), FRAP (3.05 mg AAE/g), RPA (24.45 mg AAE/g), and ABTS (75.77 mg AAE/g) values; unripe Hass peel recorded the highest TFC (3.44 mg QE/g); and Wurtz peel recorded the highest TAC (35.02 mg AAE/g). Correlation analysis revealed that TPC and TTC were significantly correlated with the antioxidant capacity of the extracts. A total of 348 polyphenols were screened in the peel. A total of 134 compounds including 36 phenolic acids, 70 flavonoids, 11 lignans, 2 stilbenes, and another 15 polyphenols, were characterised through LC-ESI-QTOF-MS/MS, where the majority were from peels and seeds of samples extract. Overall, the hierarchical heat map revealed that there were a significant amount of polyphenols in peels and seeds. Epicatechin, kaempferol, and protocatechuic acid showed higher concentrations in Reed pulp. Wurtz peel contains a higher concentration of hydroxybenzoic acid. Our results showed that avocado wastes have a considerable amount of polyphenols, exhibiting antioxidant activities. Each sample has its unique value proposition based on its phenolic profile. This study may increase confidence in utilising by-products and encourage further investigation into avocado by-products as nutraceuticals.

Unravelling the Influence of Chlorogenic Acid on the Antioxidant Phytochemistry of Avocado (Persea americana Mill.) Fruit Peel

“…The detailed protocol for this assay has recently been reported in our publication [23]. In summary, linoleic acid (50 mM) peroxidation was induced using FeSO 4 •7H 2 O (FS) (2 mM in assay volume) after pre-treatment with the different concentrations (5,10,20,40, and 80 µg/mL in assay volume) of the samples and ascorbic acid (positive control). The thiobarbituric acid (TBA) method was used to measure the level of lipid peroxidation.…”

“…The detailed protocol for this assay has recently been reported in our publication [23]. In summary, oxidative stress was induced in cultured cells using FS (1 mM in assay volume) after pre-treatment with the different concentrations (10,20,40, and 80 µg/mL in assay volume) of the fraction 8, chlorogenic acid and ascorbic acid. The thiobarbituric acid (TBA) method was used to measure the level of lipid peroxidation in the cell lysate, which was extrapolated from an MDA standard plot as thiobarbituric acid reactive substances (TBARS).…”

“…The cosmetic applications and documented anticancer, antibacterial, anti-inflammatory, and anti-hypertensive potentials of the peel have been strongly linked to its antioxidant properties [16,17]. Phenolic acids, including hydroxybenzoic and hydroxycinnamic acids and flavonoids, including anthocyanins, flavanols, flavanones, and flavonols, are some of the classes of polyphenols reported in the avocado peel, which could contribute to its antioxidant effects [18][19][20]. The radical scavenging activity of the peel extract has been documented [18][19][20][21].…”

“…Phenolic acids, including hydroxybenzoic and hydroxycinnamic acids and flavonoids, including anthocyanins, flavanols, flavanones, and flavonols, are some of the classes of polyphenols reported in the avocado peel, which could contribute to its antioxidant effects [18][19][20]. The radical scavenging activity of the peel extract has been documented [18][19][20][21]. Also, the peel has been shown to exert anti-inflammatory effects in lipopolysaccharide (LPS)-treated murine macrophage cells by suppressing TNF-α expression and NO production [18].…”

Possible Side Effects of Polyphenols and Their Interactions with Medicines

“…Among the richest food sources of polyphenols are seasonings and dried herbs (e.g., cloves, peppermint, anise, oregano, and rosemary), green tea, cocoa, dark-coloured berries, some seeds and nuts (e.g., flaxseed, soybean, chestnut, and hazelnut), and some vegetables (e.g., black olives, globe artichoke heads, and red chicory) [ 7 , 8 ]. However, various fresh, frozen, and dried fruits should also be taken into account (e.g., pomegranate and tropical fruits) [ 9 , 10 , 11 ]. In addition, many people take polyphenols in the form of dietary supplements that contain either purified polyphenols (e.g., quercetin [ 12 ] and resveratrol [ 13 ]) or extracts from raw materials which are rich in these ingredients (such as extracts from tea, red wine, grapes, blueberries, pomegranate, etc.)…”