Banana is a tropical seasonal fruit that encompasses a diverse range of species belonging to the genus Musa of the Musaceae family. It is among the world’s most popular fruits and the 4th most cultivated crop on a worldwide scale [1]. Almost all recognized cultivars are descended from two diploid species; Musa balbisiana and Musa acuminata, the most widespread of which are the Cavendish type [2]. Asia is the world’s largest banana producer, accounting for 54.4 percent of global banana production, as per the recent Food and Agriculture Organization (FAO) statistics. With an average usage of 12 kg per person per annum [3], bananas are one of the world’s primary food crops behind rice, wheat, and maize. In Australia, particularly in Queensland, banana production is one of the largest agricultural industries, with over 390,000 tonnes in 2015 [3] and around 600 merchant banana suppliers. The region of Australian banana cultivation varied between 10,000 and 16,000 ha during the period 1997–2015 [4]. Overall, 95% of banana genome groups in Australia are Cavendish, the remaining are Lady Fingers (AAB), Goldfingers (AAAB), Ducasse (ABB), Red Dacca (AAA), Sucrier (AA), and the Pacific Plantain (AAB) sub-group, and 95% of production is in North Queensland (QLD) [5].

The banana fruit is divided into two parts: the peel and the pulp. The peel, which is the fruit’s primary secondary product, accounts for around 40% of the fruit’s overall mass. Banana peels served no purpose and were discarded as waste, resulting in vast quantities of organic materials going into landfill. The central part, the pulp, the consumable portion of the fruit, is highly nutritious. Various research on banana pulp has examined various features, from its usage as a food fortification component to the extraction and recovery of numerous healthy constituents, including multiple kinds of starch, cellulose, and bioactive phytochemicals [6]. It is well established that banana flesh and skin comprise several secondary metabolites, such as catecholamines [7], phenolics [8], and carotenoids [9]. These bioactive substances promote probiotic development and help to reduce the risk of cancer and cardiovascular disease [10]. Pulp and peel parts include phenolic compounds, carotenoids, flavonoids, biogenic amines, phytosterols, and other phytochemicals [11]. Bananas have a greater antioxidant potential than various berries, herbs, and vegetables, attributed to the prevalence of these components [12]. Amongst the existing carotenoids in banana fruit, α-carotene, β-carotene, and β-cryptoxanthin have provitamin A activity, whereas others such as lycopene and lutein have a significant antioxidant capability [13]. Later, 171 various cultivars of Musa spp. were analysed for provitamin A carotenoids and 47 cultivars for two minerals, iron and zinc. It has been found that there is a great variability in provitamin A amongst the various genotypes, but a low variability in iron and zinc, regardless of the soil type and growing environmental conditions [14]. Moreover, banana pulp includes numerous antioxidants, such as phenolic compounds and vitamins, for example, catechin, epicatechin, lignin and tannin, and anthocyanin [15]. The catechins (epicatechin and gallocatechin) are most prevalent in the pulp when analysed by high-performance liquid chromatography [16]. Russel et al. have detected many phenolics in banana, such as ferulic, sinapic, salicylic, gallic, p-hydroxybenzoic, vanillic, syringic, gentisic, and p-coumaric acids as major components. Nevertheless, ferulic acid concentration was the highest among other phenolics [17]. According to Tsamo et al., hydroxycinnamic derivatives, such as ferulic acid-hexoside, were the major ones (4.4–85.1 µg/g DW) in plantain pulp. They discovered large differences in the phenolic contents among the tested varieties. In the plantain peels, rutin was the most abundant flavonol glycoside (242.2–618.7 µg/g DW). Therefore, the banana peel and pulp both are good sources of health-promoting phenolic compounds [18]. The main flavonoids detected in bananas are as follows: quercetin, myricetin, kaempferol, and cyanidin, which provide health benefits mostly due to their action as free radical scavengers [19]. Most of these phenolics, as natural antioxidants, have several biological effects, containing antiviral, antibacterial, antiallergenic, anti-inflammatory, vasodilatory and antithrombotic functions ^[20][21][20,21].

Although the concentration of phenolics in different banana cultivars has previously been investigated, a thorough profile of these compounds, especially in cultivars grown in Australia, remains inadequate due to their complicated composition and nature. Chemical analysis of these phenolics is typically performed by liquid chromatography-mass spectrometry (LC-MS) following sample extraction and filtering. Mass spectrometry is a well-established analytical technique used to infer unknown chemicals from complicated samples of various plant components, including banana [22].

To accomplish the study’s purpose, the polyphenols in six Australian grown banana cultivars, Cavendish, Ladyfinger, Red Dacca, Plantain, Monkey, and Ducasse were defined by TPC, TFC and TTC. In addition, the antioxidant capacity of all varieties was evaluated by ferric reducing antioxidant power (FRAP), 2,2′-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) assay (ABTS), ferrous ion chelating assay (FICA), reducing power assay (RPA), hydroxyl radical scavenging assay (^•OH-RSA) and total antioxidant capacity assay (TAC). Furthermore, the characterization and classification of phenolics were conducted using LC-ESI-QTOF-MS/MS, whereas the quantification of selected phenolics from various banana cultivars conducted using HPLC-PDA. As banana peel and pulp have a high antioxidant capacity, this study reinforces their usage as an origin of polyphenols in various industries, such as food, nutraceuticals, pharmaceuticals, cosmetics, and animal feed.

2. Polyphenols Assessment of Banana

The assessment of polyphenols in various banana cultivars was attained via TPC, TFC, and TTC. Diets high in fruits and vegetables have been associated with a decreased risk of heart diseases and cancer. The antioxidant components of fruit and vegetables, for example, phenolic acids, flavonoids, tannins, lignans and stilbenes with pharmacological and biological attributes, have been credited with their protecting impact ^[23][41]. Multiple factors, such as plants’ varieties, degree of ripening, growing environment, and initial treatments, can affect the composition and concentrations of these components ^[24][42].

The highest phenolic contents were found in the ripe Ducasse peel and pulp, unripe Ladyfinger peel, ripe Plantain peel, unripe Monkey peel and unripe Ladyfinger pulp, which contained 1.32, 1.28, 1.15, 0.87, 0.79 and 0.76 mg GAE/g, respectively, whereas the lowest value of TPC was found in ripe Red Dacca pulp (0.40 mg GAE/g) and ripe Plantain pulp (0.38 mg GAE/g) (Table 1).

Table 1. Polyphenol contents of six Australian grown bananas.

Banana Samples	TPC (mg GAE/g)	TFC (mg QE/g)	TTC (mg CE/g)

,47,48]. According to Von Loesecke ^[32][49], several forms of tannin and soluble tannin become insoluble throughout ripening. Barnell and Barnell ^[29][46] explained that the Latex vessels in both the pulp and peel and small dispersed cells in the peel are two kinds of tannin-containing elements. Furthermore, they suggested that the tannin structure in latex vessels varies, whereas the tannin content of the peel’s tiny dispersed cells tends to have little or no alteration. On the other hand, Kyamuhangire et al. ^[33][50] found that Mbidde bananas had a greater tannin content than Matooke bananas at both the green and mature phases. The high tannin content is due to the unusual presence of laticifer cells in the fruit of Mbidde varieties, which is similar to our findings in ripe Ducasse peel. Moreover, their results showed that the amount of extractable tannins improved with ripening in all four banana cultivars, and after ripening, the amount of water-extractable tannins increased significantly in Mbidde bananas, but a very small amount was found in Matooke bananas. The increased amount of extractable tannins appears to indicate that tannins become more accessible as the banana ripens. This contrasts with the observation that bananas lose their astringent flavour during maturation, a phenomenon explained by increasing tannin polymerisation ^[29][46] and inactivity ^[34][51].

3. Antioxidant Capacity of Banana

Polyphenols are essential antioxidants found in plants and have a variety of biological actions. They are proven to have several functions because they work in biological systems as reducing chemicals, metal chelators, hydrogen atom donors, scavengers of radical oxygen. The antioxidant capacity of banana was further studied using a variety of methods, including radical scavenging ability and reducing power of the sample. For this aim, DPPH, FRAP, ABTS, RPA, FICA, ^•OH-RSA and TAC experiments were performed, and the results presented in Table 2.

Table 2. Antioxidant activity of six Australian grown banana.

Banana Samples	DPPH (mg AAE/g)	FRAP (mg AAE/g)	ABTS (mg AAE/g)	RPA (mg AAE/g)	FICA (mg EDTA/g)	•OH-RSA (mg AAE/g)	TAC (mg AAE/g)
Peels
Peels
					Ripe Cavendish	0.54 ± 0.03 g–i	0.01 ± 0.001 h–j	0.19 ± 0.02
Ripe Cavendish	0.67 ± 0.02 d	gh
1.28 ± 0.06	de	2.41 ± 0.19	a–c	2.22 ± 0.23 de	0.11 ± 0.01 e	104.32 ± 1.72 ab	0.12 ± 0.006
								Unripe Cavendish	DPPH	0.790 **	0.584 **	0.444
f–h
0.66 ± 0.08
c
jk	0.71 ± 0.04
Unripe Cavendish	d–f	0.49 ± 0.01 ef0.01 ± 0.0004 h–j	1.77 ± 0.04 0.5 ± 0.05 d–f
c	2.29 ± 0.22	a–d	2.26 ± 0.15	de	0.04 ± 0.003 fg	105.95 ± 0.72
1	3-Hydroxyphenylpropionic acid	C9H10O3	30.544	[M–H]–	166.0630	Ripe Ladyfinger	0.56 ± 0.05 gh	0.01 ± 0.00 g–i
165.0557	165.0556	−0.6	165, 121, 119	Ripe Ladyfinger	0.59 ± 0.01 de	1.04 ± 0.06 e–g0.12 ± 0.01 hi
RCPl	2.69 ± 0.23	a	6.15 ± 0.50	a	0.38 ± 0.03 b	103.60 ± 0.18 ab	0.17 ± 0.01 ij	FRAP	0.859 **	0.564 *	0.539 *	0.896 **
	Hydroxycinnamic acids										Unripe Ladyfinger	1.15 ± 0.04 b	0.007 ± 0.001 ij	0.12 ± 0.01 hi
Unripe Ladyfinger	0.47 ± 0.04 f	1.35 ± 0.12 d	2.49 ± 0.17 ab	4.99 ± 0.04 b	0.32 ± 0.02 c	98.02 ± 1.57 cd	ABTS0.13 ± 0.01	0.107jk	−0.040	−0.161	−0.010	0.138
2	Ferulic acid	C10H10O4	9.105	[M–H]–	194.0579	193.0506	193.0506	0.0	178, 149, 134	RCP	Ripe Red Dacca	RPA0.64 ± 0.05 e–g	0.01 ± 0.0005 d–f	0.38 ± 0.02 ef
0.706 **	0.360	0.227	0.670	0.659 **	0.338
3	Caffeic acid	C9H8O4	41.086	Ripe Plantain	0.87 ± 0.01 c	0.03 ± 0.001 a	0.53 ± 0.03 c–e
Ripe Monkey	0.56 ± 0.03 gh	0.006 ± 0.0004 j	0.56 ± 0.01 cd
Unripe Monkey
Ripe Red Dacca	0.13 ± 0.002 h	0.87 ± 0.02 g–i	1.76 ± 0.08 f–i	1.76 ± 0.09 ef	0.04 ± 0.0005 fg	96.58 ± 1.72 de	0.18 ± 0.01 h–j
[M–H]	–	180.0423	179.035	179.035	0.0	143, 133	UCP	Ripe Plantain	FICA0.66 ± 0.01 d	1.20 ± 0.03 d–f	2.17 ± 0.16 b–f	2.37 ± 0.12 d	0.1820.04 ± 0.002 fg	−0.19796.58 ± 0.36 de	0.1600.25 ± 0.01 gh
0.208	0.053
4	p-Coumaroyl glycolic acid	C	−0.216	11	0.513 *		H10O
5	62.765	[M+H]	+	222.0528	223.0601	223.0599	−0.9	163	* RCPl, ULPl, RRPl, RPPl, RMP, RDPl	Ripe Monkey	0.66 ± 0.02	•OH-RSAd	0.466 *0.93 ± 0.09 gh	0.1830.59 ± 0.07 k	0.4172.36 ± 0.08 d	0.563 *0.59 ± 0.05 a	96.04 ± 0.79 de	0.24 ± 0.01 g–i	0.736 **	0.362	0.603 **	0.069	0.79 ± 0.05 cd
Hydroxyphenylacetic acids					0.013 ± 0.001 de
Unripe Monkey	0.66 ± 0.01 d	1.02 ± 0.10 e–g	0.44 ± 0.03 d–f
1.67 ± 0.09	g–i	TAC	1.67 ± 0.17	fg	−0.016	0.1360.12 ± 0.01	0.033e	95.14 ± 0.95 de	0.12 ± 0.01 jk	0.187	0.136	−0.050	−0.171	−0.381	−0.094	Ripe Ducasse	1.32 ± 0.10 a	0.02 ± 0.0004 b	3.34 ± 0.2 a
Ripe Ducasse	1.06 ± 0.09 b	2.31 ± 0.10 b	1.49 ± 0.13 hi	4.33 ± 0.17 c	0.26 ± 0.02 d	106.67 ± 1.09 a	0.08 ± 0.01 k	Pulps

* Significant correlation at p ≤ 0.05; ** significant correlation at p ≤ 0.01.

Due to the critical antioxidant effects of polyphenols observed in vegetables and fruits, we studied TPC, TFC, and TTC in Australian bananas. TPC was shown to have a range of 0.40–1.32 mg GAE/g, with an average of 0.68 mg GAE/g (Table 1). The highest TPC value was found in Ducasse peel, while the least was reported in Red Dacca pulp. The antioxidant activity of banana extracts was determined using DPPH, FRAP, ABTS, RPA, ·OH-RSA, FICA, and TAC.

Between total phenolic content and the antioxidant activities of DPPH, FRAP, and RPA, ·OH-RSA, and TFC, a high and significant positive correlation was detected, but TFC was only correlated significantly with DPPH and FRAP. Previously, a positive correlation between antioxidant activity and total polyphenols in herbs and spices was discovered ^[47][64]. Notably, there was a negative association between TPC, TFC, and TTC and TAC, ABTS, and FICA.

TAC is also negatively correlated with ABTS, ·OH-RSA, RPA, and FICA. Total phenolics have been shown to be responsible for the antioxidant capacity of plant diets ^[48][65]. Numerous variables affect the correlation, including the number of samples analysed, the quantities measured, and the antioxidant assays used. DPPH and FRAP were highly correlated in our research. Kim, Yang, Lee and Kang discovered that TPC had a higher relationship with antioxidant activity than TFC ^[49][28].

Principal component analysis (PCA, Figure 2) demonstrated that TPC and TTC were positively correlated with ˙OH-RSA, RPA, and FICA with higher scores. Furthermore, FRAP, TFC, DPPH, and ABTS were positively correlated, while FICA showed negative correlation with TAC, TFC, ABTS, FRAP and DPPH, which revealed the divergence of bioactive components in banana cultivars.

Figure 2. Principal component analysis (PCA) of the phenolic contents (TPC, TFC, TTC, phenolic acids, and flavonoids) and their antioxidant capacities (DPPH, FRAP, ABTS, RPA, ^•OH-RSA, FICA, and TAC) of banana cultivars.

After evaluating the data, it is indicated that the antioxidant activity of banana extracts may also be related to non-phenolic elements. Even though simple phenols have relatively little contribution to antioxidant potentials, they can interact with Folin–Ciocalteu reagent [22]. The current study’s findings reveal that distinct phenolic compounds exhibit varying levels of antioxidant activity based on their structure, synergistic effect, quantity, and hostile attitude towards other components appearing in each banana extract.

5. LC-ESI-QTOF-MS/MS Identification of the Phenolic Compounds

To identify and characterize bioactive substances, such as phenolics from various fruits, vegetables, and herbal medicines, LC-MS/MS has been broadly used. A LC-ESI-QTOF-MS/MS analysis in negative and positive ionization modes was used to obtain a non-targeted qualitative analysis of phenolics from Australian banana cultivars pulp and peel samples (Table 4) utilizing Agilent LC-MS Qualitative Software and Personal Compound Database and Library, phenolics in banana samples were identified and based on their m/z value and MS spectra in both negative and positive modes of ionization ([M–H]^–/[M+H]⁺). For further MS/MS detection, (m/z) characterization, and verification, compounds with a mass error of less than ±10 ppm were used. LC-MS/MS was used to identify 24 phenolic compounds in banana samples, which include phenolic acids (6), flavonoids (13), and other polyphenols (5) mentioned in Table 4.

Table 4. Characterization of phenolic compounds from different banana cultivars by LC-ESI-QTOF-MS/MS.

No.	Proposed Compounds	Molecular Formula	RT (min)	Ionization (ESI+/ESI−)	Molecular Weight	Theoretical (m/z)	Observed (m/z)	Error (ppm)	MS2 Product ions	Sample Code
	Phenolic acid
	Hydroxyphenylpropanoic acids
5	3,4-Dihydroxyphenylacetic acid	C8H8O4	20.831	[M–H]–	168.0423	167.035	167.0341	−5.4	149, 123	* RRPl, UCPl
	Hydroxybenzoic acids
Ripe Cavendish
Pulps								0.43 ± 0.01 h–j	0.01 ± 0.0003 e–g	0.02 ± 0.01 i
Ripe Cavendish	0.13 ± 0.002 h	0.69 ± 0.06 hi	1.82 ± 0.16 e–h	0.20 ± 0.05 i	0.06 ± 0.002 f	94.78 ± 0.48 de	0.39 ± 0.03 e	Unripe Cavendish	0.55 ± 0.03 g–i
Unripe Cavendish	0.16 ± 0.01 h	1.004 ± 0.02 fg	2.20 ± 0.09 b–e	1.71 ± 0.21 f	0.05 ± 0.003 f	103.06 ± 0.48 a–c
6	3,4-O-Dimethylgallic acid	C9H10O5	5.557	[M+H]+	198.0528	199.0601	199.0595	−3.0	153, 139, 125, 111	RLPl
	Flavonoids										0.58 ± 0.03 c	Ripe Ladyfinger	0.42 ± 0.01 ij	0.001 ± 0.0001 k	0.42 ± 0.012
Ripe Ladyfinger	0.26 ± 0.01 g	d–f
0.86 ± 0.06
	Anthocyanins			g–i	1.77 ± 0.19 f–h	-	-	99.46 ± 6.04 b–d	0.27 ± 0.003 fg	Unripe Ladyfinger	0.76 ± 0.02 c–e	0.01 ± 0.001 g–i	1.52 ± 0.09 b
Unripe Ladyfinger	0.79 ± 0.05 c	1.42 ± 0.05 d	1.98 ± 0.14 c–g	1.33 ± 0.06 f–h	0.03 ± 0.002 fg	97.48 ± 0.36 de	1.03 ± 0.08 a	Ripe Red Dacca	0.40 ± 0.01 j	0.01 ± 0.0001 f–i	-
a	0.01 ± 0.001	Ripe Plantain	0.38 ± 0.01 j	0.01 ± 0.001 d	-
Ripe Monkey	0.43 ± 0.03 h–j	0.02 ± 0.001 c	0.001 ± 0.0 i
Unripe Monkey	0.58 ± 0.03 fg	0.02 ± 0.001 c	0.02 ± 0.01 i
Ripe Ducasse	1.28 ± 0.03 a	0.03 ± 0.001 a	0.34 ± 0.04 fg

Values are mean ± standard deviation per gram fresh weight; n = 3 samples per sample. Values within the same column with different superscript letters (^a–k) are significantly different from each other (p < 0.05). TPC (total phenolic contents); TFC (total flavonoid contents); TTC (total tannin contents); GAE (gallic acid equivalents); QE (quercetin equivalents); and CE (catechin equivalents).

TPC values ranging from 0.15 to 55.5 mg GAE/g had already been reported in twenty-seven different banana cultivars in which the Brazilian Cavendish has the second highest value (29.2 mg GAE/g) ^[24][42]. However, TPC differences can be ascribed to extraction circumstances (solvent kind, concentration, solvent/sample ratio, and time/temperature combination for extracting), cultivar variations, and the geographical location of where the bananas were grown ^[25][43]. Flavonoids are the most abundant class of phenolic compounds present in practically all plants, as shown in this study using the aluminium chloride colorimetric method.

Aluminium chloride interacts with the flavonoids’ carbonyl group, generating a stable compound ^[26][44]. The TFC values in the banana samples had a similar pattern of TPC results, in which the most prevalent flavonoid compounds were identified in the ripe Ducasse pulp (0.03 mg QE/g), and peel (0.02 mg QE/g), whereas the lowest values were found in ripe Monkey peel (0.006 mg QE/g). TFC values ranged from 8.56 ± 0.22 to 16.15 ± 0.28 mg QE/g in Egyptian banana cultivars, according to Aboul-Enein, et al. ^[27][45], which was higher than our Australian samples. This may be due to varieties divergence or type of solvent used for the extraction of phenolic compounds. Comparing to other tropical fruits, it has been found that the mango peel showed the maximum concentration of flavonoid (1.75 ± 0.08 mg QE/g), then pineapple and banana peels (1.47 ± 0.07 and 1.32 ± 0.12 mg QE/g), respectively ^[28][38].

Tannins are also a substantial family of phenolic substances that could be partitioned into hydrolysable and non-hydrolysable tannins. In our banana samples, the ripe Ducasse peel had the highest amount (3.34 ± 0.2 mg CE/g), followed by the unripe Ladyfinger pulp (1.52 ± 0.09 mg CE/g) and unripe Cavendish pulp (0.66 ± 0.08 mg CE/g). Most fruits show a reduction in tannins content when they ripen, which is believed to be due to tannin polymerisation ^[29][30][31][46

0.17 ± 0.005

ij
Ripe Red Dacca
0.09 ± 0.01	h	0.36 ± 0.02 j	1.34 ± 0.07 ij	0.89 ± 0.07 h	0.02 ± 0.001 fg	96.58 ± 1.18 de	0.34 ± 0.004 ef
Ripe Plantain	0.069 ± 0.004 h	0.62 ± 0.01 ij	2.35 ± 0.05 a–c	1.12 ± 0.03 h	0.06 ± 0.005 f	97.12 ± 1.003 de	0.29 ± 0.003 fg
Ripe Monkey	0.26 ± 0.01 g	0.80 ± 0.02 g–i	0.98 ± 0.05 jk	0.84 ± 0.07 h	0.05 ± 0.003 f	94.96 ± 0.65 de	0.40 ± 0.017 de
Unripe Monkey	0.32 ± 0.01 g	0.87 ± 0.05 g–i	1.91 ± 0.06 d–h	1.18 ± 0.10 gh	0.06 ± 0.002 f	92.25 ± 0.65 e	0.47 ± 0.03 d
Ripe Ducasse	1.68 ± 0.06 a	2.85 ± 0.28 a	1.86 ± 0.14 d–h	5.67 ± 0.04 a	0.04 ± 0.003 fg	106.85 ± 1.77 a	0.69 ± 0.04 b

Values are mean ± standard deviation per gram fresh weight; n = 3 samples per sample. Values within the same column with different superscript letters (^a–k) are significantly different from each other (p < 0.05). DPPH (2,2′-diphenyl-1-picrylhydrazyl assay); FRAP (ferric reducing antioxidant power assay); ABTS (2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid assay); TAC (total antioxidant capacity); AAE (ascorbic acid equivalents); RPA (reducing power assay); FICA (ferrous ion chelating activity); ^•OH-RSA (hydroxyl-radical scavenging activity); and EDTA (ethylenediaminetetraacetic acid).

The DPPH, FICA, ABTS, and ^•OH-RSA tests have been primarily utilized to assess the scavenging activity of bioactive metabolites, primarily polyphenols ^[35][52]. In contrast, the FRAP assay assesses samples’ ability of electrons donation to convert a ferric-TPTZ complex to a blue ferrous-TPTZ complex. DPPH can supply hydrogen ions to the biological system or act as a scavenger of free radicals. When DPPH is combined with banana samples, it accepts hydrogen atoms, and diminishing violet colour occurs. The DPPH, ABTS, and FRAP values of ripe Ducasse pulp and ripe Ladyfinger peel (1.68 mg AAE/g, 2.69 mg AAE/g, and 2.85 mg AAE/g, respectively) were considerably greater than those of other listed cultivars. In contrast, ripe Plantain pulp, ripe Red Dacca pulp, and ripe Monkey peel had the lowest DPPH, FRAP, and ABTS values (0.069 mg AAE/g, 0.36 mg AAE/g and 0.59 mg AAE/g), respectively.

The DPPH values of 23 variant banana cultivars grown in different countries, ranging from 0.68 to 66.9 mg AAE/g, were recorded in a previous review, and our findings were close to some of those varieties ^[24][42]. The ability of banana peels to scavenge free radicals (DPPH) decreases as the fruit progresses from green to ripe to overripe ^[36][37][53,54]. Nevertheless, the electron transfer/hydrogen donating capacity of phenolics’ nature is also recognized to be connected to their DPPH^• radical scavenging activity. Numerous substances of botanical origin have an antioxidant activity proportional to their phenolic content, indicating a causative correlation between total phenolic concentration and antioxidant activity ^[38][55]. Furthermore, our banana FRAP values were within the range of other banana cultivars studied (0.32–17.64 mg AAE/g) by Vu, Scarlett and Vuong ^[24][42]. The FRAP value of the Brazilian Cavendish peel, which is yellow with a green edge, was higher (14 mg AAE/g) ^[39][56]. Guo ^[33][50] mentioned that most fruit peels demonstrated 2- to 27-fold greater antioxidant activity than the fruit flesh, and variations between varieties can occur because the antioxidant activity of fruits can be influenced by geographical location, variety, and harvesting or storing period. Furthermore, it is well established that phenolics’ antioxidant capacity depends on their molecular weight, the amount of aromatic rings, and the number and position of hydroxyl groups attached to aromatic ring ^[40][57]. Additionally, it has been claimed that parameters such as the stereoselectivity of the radicals or the solubility of phenolics in various testing conditions influence the capacity of extracts to react with and eliminate various radicals ^[41][58]. According to Hagerman, et al. ^[42][59], tannins, as high molecular weight phenolics, have a greater capacity to scavenge free radicals (ABTS^•+).

Regarding RPA, ^•OH-RSA and FICA assays, Ladyfinger, Monkey, and Ducasse peels had higher antioxidant capacity than other varieties. In RPA, ripe Ladyfinger peel had the highest antioxidant potential, followed by ripe Ducasse pulp and unripe Ladyfinger peel. In FICA assay, Ripe Monkey peel had high antioxidant activity compared to other cultivars. On the other hand, ripe Ducasse peel had higher ^•OH-RSA value (106.67 mg AAE/g), followed by unripe Cavendish peel (105.95 mg AAE/g). To our best knowledge, this is the first time that banana’s antioxidant potential has been analysed through the RPA, ^•OH-RSA and FICA assays. Previously, a thorough phenolic analysis of custard apples cultivated in Australia has been performed by Du et al. ^[43][60]. They found that African Pride peel possessed the greatest antioxidant capacity for RPA (5.32 ± 0.14 mg AAE/g), ^•OH-RSA (1.23 ± 0.25 mg AAE/g) and FICA (3.17 ± 0.18 mg EDTA/g). Based on the current iron chelating findings, the extracts may be able to protect against oxidative stress by isolating Fe(II) ions that would otherwise accelerate Fenton-type reactions or engage in metal catalysed hydroperoxide breakdown reactions. The samples’ Fe(II) chelating properties may be a result of their endogenous chelating compounds, primarily phenolics ^[44][61]. Grinberg et al. ^[45][62] claimed that tea polyphenols’ protective action against OH-dependent salicylate hydroxylation was due to iron chelation. The research on polyphenols’ deleterious effects on iron bioavailability has emphasized that iron binding to flavonoid antioxidants can diminish iron’s accessibility to oxygen molecules. In contrast, non-flavonoid polyphenols can reduce Fe³⁺ ions and then create inert Fe²⁺ polyphenol complexes ^[46][63].

In the TAC assay, which was conducted by reducing molybdenum (VI) to molybdenum (V) in the presence of phenolics, the pulps of the banana varieties had generally higher values than peels. The highest value was observed in unripe Ladyfinger pulp (1.03 ± 0.08 mg AAE/g), followed by ripe Ducasse pulp (10.43 ± 0.20 mg AAE/g) and unripe Cavendish pulp (0.58 ± 0.03 mg AAE/g).

Remarkably, the antioxidant activity of fruits varies depending on the extraction method that was utilized. Fruit extracts contain a diverse array of bioactive chemicals. The amount of phenolic acids and flavonoids in each type is highly variable and is influenced by cultivar, geographic location, and climates. There are several procedures for determining the antioxidant capacity, and each methodology has several advantages and disadvantages. To summarize, our findings indicate that each banana cultivar’s antioxidant activity varies according to its phenolic profile or the method utilized to quantify it. Numerous in vitro experiments may be used to determine the antioxidant capacity of banana, while modern analytical techniques like as LC-ESI-QTOF-MS/MS can be used to identify and confirm these antioxidant components.

Phenolics are a broad collection of molecules that are garnering attention in research due to their possible health benefits. Due to the antioxidant properties of polyphenols, they may be used to prolong the shelf life of lipid-rich products. Additionally, bananas have diverse antibacterial phenolic compounds that act as preservatives for food during storage. Furthermore, because phytochemicals have a complex structure, no one approach accurately evaluates polyphenols’ antioxidant capacity due to the various pathways and reactions occurring in the biological system. Thus, LC-MS characterization is one of the sophisticated research approaches used to profile polyphenols and better understand the banana’s total antioxidant capacity. The polyphenol contents of banana and their antioxidant capacity indicate that additional research should be undertaken to determine the true contribution of phenolics to the antioxidant potential while excluding or limiting non-phenolic substances’ involvement.

4. Correlation between Polyphenols and Antioxidant Potentials

A regression analysis was used to determine the association between the findings of the experiments undertaken (Table 3).

Table 3. Pearson’s linear correlation between banana phenolic content and their antioxidant capacity.

Variables	TPC	TFC	TTC	DPPH	FRAP	ABTS	RPA	FICA	•OH-RSA
TFC	0.599 **
TTC	0.575 **	0.286
7
Delphinidin 3-
O
-(6’’-acetyl-galactoside)
C
23
H
23
O	13	82.037	[M–H]	–	507.1139	506.1066	506.1066	0.0	303, 507	* RPPl, UCPl, UCP, RLP, ULP, UMPl, UMP, RMPl, RMP
8	Pelargonidin 3-O-(6’’-succinyl-glucoside)	C25H25O13	40.051	[M–H]–	533.1295	532.1222	532.1181	−7.7	533, 473, 443, 383, 353	UCP
9	Cyanidin 3,5-O-diglucoside	C27H31O16	89.507	[M+H]+	611.1612	612.1685	612.1674	−1.8	449, 287	* RCP, RRPl
10	Malvidin 3-O-(6’’-acetyl-glucoside)	C25H27O13	6.241	[M+H]+	535.1452	536.1525	536.1525	0.0	535, 481, 463, 445	RRPl
	Isoflavonoids
11	2’-Hydroxyformononetin	C16H12O5	24.296	[M+H]+	284.0685	285.0758	285.0755	−1.1	270, 229	RMP
	Flavonols
12	Isorhamnetin 3-O-glucoside 7-O-rhamnoside	C28H32O16	29.971	[M–H]–	624.169	623.1617	623.1622	0.8	433, 315, 300, 271	UCPl
13	Myricetin 3-O-rutinoside	C27H30O17	24.472	[M–H]–	626.1483	625.141	625.1397	−2.1	301	UCPl
14	Patuletin 3-O-glucosyl-(1->6)-[apiosyl(1->2)]-glucoside	C33H40O22	37.955	[M–H]–	788.2011	787.1938	787.1918	−2.5	625, 463, 301, 271	RRPl
15	Quercetin 3-O-xylosyl-glucuronide	C26H26O17	38.624	[M+H]+	610.117	611.1243	611.1238	−0.8	479, 303, 285, 239	UCPl
	Flavanols
16	(+)-Gallocatechin 3-O-gallate	C22H18O11	3.075	[M–H]–	458.0849	457.0776	457.0773	−0.7	305, 169	RRPl
	Flavones
17	Apigenin 7-O-apiosyl-glucoside	C26H28O14	88.42	[M–H]–	564.1479	563.1406	563.1402	−0.7	503, 443, 383, 353, 325, 297	UCP
18	Chrysoeriol 7-O-glucoside	C22H22O11	89.788	[M+H]+	462.1162	463.1235	463.1224	−2.4	445, 427, 409, 381	RCPl
	Flavanones
19	Neoeriocitrin	C27H32O15	27.305	[M–H]–	596.1741	595.1668	595.1696	4.7	431, 287	RRPl
	Other polyphenols
	Hydroxycoumarins
20	Scopoletin	C10H8O4	7.392	[M–H]–	192.0423	191.035	191.0349	−0.5	176	* RPPl, RCP, UCP
21	Urolithin A	C13H8O4	4.563	[M–H]–	228.0423	227.035	227.035	0.0	198, 182	UCPl
22	Umbelliferone	C9H6O3	35.668	** [M+H]+	162.0317	163.039	163.0387	−1.8	145, 135, 119	* RMPl, UCP
	Hydroxyphenylpropenes
23	2’-Hydroxyformononetin	C16H12O5	24.296	[M+H]+	284.0685	285.0758	285.0755	−1.1	270, 229	RMP
	Furanocoumarins
24	Isopimpinellin	C13H10O5	5.61	[M+H]+	246.0528	247.0601	247.0583	−7.3	232, 217, 205, 203	ULP

* = compound detected in more than one sample, with data presented only asterisk, ** = compound found in both positive [M+H]⁺ and negative modes [M–H]^–. RT stands for “retention time”. Bananas were presented with abbreviations. Ripe Cavendish peel (RCPl), Ripe Cavendish pulp (RCP), Unripe Cavendish peel (UCPl), Unripe Cavendish pulp (UCP), Unripe Ladyfinger peel (ULPl), Ripe red dacca peel (RRPl), Ripe Plantain peel (RPPl), Ripe Monkey pulp (RMP), Ripe Ducasse peel (RDPl), Ripe Ladyfinger peel (RLPl), Ripe Ladyfinger pulp (RLP), Unripe Ladyfinger pulp (ULP), Unripe Monkey peel (UMPl), Unripe Monkey pulp (UMP), and Ripe Monkey peel (RMPl).