Statement of Novelty

This work represents an advance in the biochemistry field, as it attempts to elucidate the intricate correlation between the chemical composition of phenolic extracts, from four different agro-industrial by-products, and their various biological properties while providing different options for the application of those extracts in different industries.

Introduction

The growing world population over the last decades led to an increase in the production and processing of food to satisfy people’s needs. However, agriculture and agro-industrial processing generate a great amount of waste. According to the UN Environment Programme, 931 million tonnes of food were wasted in 2019 [1]. Fruits and vegetables account for 22% of the global crop production and can generate numerous by-products, such as seeds, peels and shells [2]. This agro-industrial waste displays environmental, economic, and social consequences. Food waste is disposed of in landfills and contributes to greenhouse gas emissions, impairing the environment. Managing great amounts of different residues creates a challenge and the costs associated with the processing of solid waste in landfills present economic adverse impacts [3]. Finally, from a social point of view, food waste poses ethical and moral issues since it is estimated that more than 702 million people suffer from hunger [4]. A way to mitigate food waste and its associated problems is to give a new use to the by-products generated from fruits and vegetables e.g., grapes, passion fruit, chestnut and onions. These residues often present great nutritional value and biological properties since they are rich in bioactive compounds (BAC) like phenolic compounds (PC), such as phenolic acids and flavonoids, minerals and vitamins. These compounds can be applied in different industries, such as food, cosmetics and pharmaceutical, to create value-added products, contributing also to a circular economy [5, 6].

Grapes are the largest fruit crop in the world, with an annual production that surpasses 70 million tons. Approximately 80% of the produced grapes are used in the wine industry, which generates great amounts of waste [7, 8]. Grapes are rich in BAC, particularly polyphenols, and several studies reported the antioxidant, antidiabetic cardioprotective, and anticancer potential of this fruit [9,10,11,12]. Grape seeds (GS) are the fraction of the fruit with the highest total phenolic content (TPC). Flavan-3-ols (primarily proanthocyanins), flavonols and phenolic acids are the main PC found in GS. More specifically, (+)-catechin, (−)-epicatechin and type B procyanidins are the most abundant PC found in grapes [13].

Chestnuts are also a great source of BAC. In 2020, more than 2 million tons of chestnuts were produced worldwide [14]. Around 10% of this weight corresponds to both the inner skin (integument) and the outer shell (pericarp), which are removed and discarded during the peeling process, generating by-products with attractive biological properties, such as antioxidant, anticancer and anti-inflammatory activities [15,16,17,18,19,20]. The BAC composition of chestnuts, and consequently their bioactive properties, can vary according to the ecosystem where they are produced, the extraction method used and the part of the chestnut that is analysed [15, 21, 22]. Chestnut shells (CS), in particular, are rich in phenolic acids (e.g., gallic acid), flavonoids (e.g., catechin, epicatechin) and tannins (e.g., ellagic acid) [22,23,24].

Onions, whose origins go back to central Asia, are one of the oldest and most conventional vegetables in the world and their production has increased massively over the years, reaching 98 annual million tons [25, 26]. Onion peels (OP) represent about 5–10% of the global production of onions, which creates environmental issues. OP are known to possess a vast array of therapeutical properties that are beneficial to humans since they can prevent cancer, obesity, diabetes, neurodegenerative and cardiovascular disorders, as well as microbial damage [26, 27]. These biological properties arise from the presence of PC, such as phenolic acids, flavonols, anthocyanins, tannins, and flavonoids [25,26,27]; compounds from this last class, such as quercetin and kaempferol, are the most abundant ones present in OP.

Originally from South America, passion fruit is an exotic tropical fruit that is known to be a rich source of BAC and to exhibit high levels of dietary fibre. Literature reports that these BAC, occasionally, can be in higher quantities in the non-edible parts of the fruit, such as peels and seeds [28, 29]. This is an interesting opportunity as peels, for example, represent about 50% of the whole fruit and can be used as a source to obtain PC since they are considered a residue. Indeed, literature has reported that passion fruit peels (PFP) are rich in PC, mostly flavonoids and anthocyanins, mainly cyanidin-3-glucoside [30, 31].

Due to their rich composition in PC, these four by-products—CS, GS, OP, and PFP—represent an interesting, abundant, easily-obtained and cheap raw material to be used to obtain these BAC. This strategy is interesting from the point of view of sustainability and circular economy because it allows the reduction of the environmental and socioeconomic problems associated with by-products while obtaining PC that can be used in multiple industries and creating value-added products, due to their bioactive properties.

Phenolic compounds, also known as polyphenols, are secondary metabolites of plants. Their quantity in the plant relies on a variety of elements, including the cultivation method utilised, the growth environment, and the harvesting, processing, and storage procedure. Additionally, their levels in the plants may rise when they are under stress, such as from pathogen and parasite infestation, too much UV radiation, or air pollution, so that the plant can defend themselves and maintain health [26, 32]. These BAC have been gaining attention due to their biological potential, such as their capacity to inhibit tumour growth and inflammation, antimicrobial, antiviral, and antiaging properties, modulate the immune system, increase capillary resistance, and safeguard the cardiovascular and neurological systems [32]. Even though they display a variety of biological properties, PC are mainly famous due to their antioxidant capacity. Indeed, it is reported that they may offer dietary antioxidant protection for human health and illness [33, 34]. Due to their properties, PC have recently attracted a lot of attention due to active reports of their speculative role in delaying several human diseases. Table 1 summarises the different biological properties of some PC that have been reported in the literature.

Table 1 Biological properties of some phenolic compounds existent in a variety of by-products
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Phenolic compounds have been gaining attention from the food and cosmetic industries to produce value-added products due to their interesting biological activities. Therefore, as a strategy to diminish the problems associated with the incorrect disposal of by-products, phenolic-rich extracts of different agro-industrial residues, in particular CS, GS, OP and PFP, have been used in food and cosmetic products to develop value-added products. Furthermore, this approach helps to increase the sustainability of the process and contributes to a circular economy. Table 2 presents several reports where it was accessed the potential to use CS, GS, OP and PFP extracts in different products of the food and cosmetic industries.

Table 2 Examples of the incorporation of extracts from agro-industrial by-products in different products
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In most of the literature found on these studies, it is very common to find the evaluation of the physicochemical properties of the products, as well as their biological activities. However, the relationship between the physical and chemical properties and the composition of the extract, or at least of the major components, is not always studied. Hence, the main goal of this work was the identification and quantification of the main PC present in different extracts from Portuguese agro-industrial by-products. Furthermore, it was intended to relate the extracts’ composition with their biological properties.

Materials and Methods

Chemicals and Reagents

All the analytical standards caffeic acid (Ref. C0625, C9H8O4, CAS 331-39-5), catechin (Ref. 43412, C15H14O6, CAS 154-23-4), chlorogenic acid (Ref. 1115545, C16H18O9, CAS 327-97-9), epicatechin (Ref. E1753, C15H14O6, CAS 490-46-), gallic acid (Ref. 147915, C7H6O5, CAS 149-91-7), kaempferol (Ref. 60010, C15H10O6, CAS 520-18-3), quercetin (Ref. Q4951, C15H10O7, CAS 117-39-5), resveratrol (Ref. R5010, C14H12O3, CAS 501-36-0) and rosmarinic acid (Ref. R4033, C18H16O8, CAS 20283-92-5) were acquired from Sigma-Aldrich (St. Louis, MO, USA). The α-amylase from porcine pancreas (Ref. A3176) and starch from corn (Ref. S4180, C6H10O5, CAS 9005-25-8) were also acquired from Sigma-Aldrich. The solvents ethanol (Ref. 83813.360, C2H6O, CAS 64-17-5), methanol (Ref. 20834.291, C3H2O, CAS 67-56-1) and acetonitrile (Ref. 45983, C2H3N, CAS 75-05-8) were purchased from VWR (Rosny-sous-Bois, France). For ultrapure water (UPW) Merck Millipore Mill-Q water purification equipment, with 18.2 Ω of electric resistance (Billerica, MA, USA).

Standards and Samples Soluitions Preparation

To prepare standard stock solutions (1000 mg/L for gallic acid and 500 mg/L for the other standards), a precisely weighed amount of each standard was diluted in acetonitrile:ethanol:water (2:1:1 V/V/V).

The PC were extracted from 2.5 g of each sample (CS, GS, OP, PFP) using a solid–liquid extraction with a Soxhlet apparatus, for 1.5 h, using ethanol as solvent [44]. The obtained extracts were dissolved in 25 mL of acetonitrile:ethanol:water (2:1:1 V/V/V).

All solutions were stored at −20 °C until further use. Before analysis, all solutions were filtered using a 0.45 µm membrane filter.

HPLC–DAD Analysis

In order to determine the chemical composition of the extracts, analysis employing high-performance liquid chromatography (HPLC) were performed. For that, HPLC (Hitachi; Tokyo, Japan) equipped with an Autosampler L-2200, a Pump L2130 and a diode array detector (DAD) L-2455 was used. Data attaining and processing were performed with the EZChrom Elite software package (Version 3.1.6). For the separation, a Purospher STAR RP-18 endcapped (4.0 mm × 250 mm ID, particle size 5 µm) reverse phase chromatography column with a LiChrosphere 100 RP-18 (particle size 5 µm) pre-column was used. The system had a constant flow rate of 0.8 mL/min, and the mobile phase was composed of UPW with 0.5% of orthophosphoric acid (phase A—aqueous phase) and methanol:acetonitrile (80:20 V/V) (phase B—organic phase). The gradient was 0–10 min, 5–15% B; 10–25 min, 15–30% B; 25–40 min, 30–50% B; 40–50 min, 50–70% B; 50–60 min, 70–5% B; 60–65 min, 5% B. The injection volume was 40 µL. The detection wavelengths were selected according to the absorption maximums of UV spectra for the analysed PC. Catechin and epicatechin were detected at 222 nm, gallic acid at 275 nm, resveratrol at 305 nm, caffeic acid and chlorogenic acid at 322 nm, rosmarinic acid at 330 nm, while kaempferol and quercetin were examined at 365 nm.

Method Validation

The linearity, sensitivity, precision, robustness and accuracy of the method were evaluated according to the Q2(R2) guideline of the International Council for Harmonization (ICH) [52]. For linearity, calibration curves were obtained for each standard: 1.25–100 mg/L for kaempferol, quercetin, and resveratrol; 2.5–250 mg/L for caffeic acid and epicatechin; 5–250 mg/L for rosmarinic acid; 5–500 mg/L for chlorogenic acid; 10–500 mg/L for catechin; and 10–1000 mg/L for gallic acid. For intra-assay precision (repeatability) and inter-assay precision (intermediate precision), six injections of each standard were evaluated and the relative standard deviation (RSD) regarding standard concentration was determined using Eq. 1:

$$\text{RSD }({\%})= \frac{\text{standard\,deviation}}{{\text{mean}}}\times 100$$
(1)

For robustness slight variations in the wavelength (λ ± 2 nm) were applied and the RSD regarding standard concentration was calculated. Finally, the recovery was used to evaluate the accuracy and was calculated according to Eq. 2:

$$\text{R}({\%})= \frac{({{\text{m}}}_{{\text{m}}}-{{\text{m}}}_{0})}{{{\text{m}}}_{{\text{s}}}}\times 100$$
(2)

where mm refers to the mass of the standard measured in the spiked extract, m0 is the mass of the standard present in the original extract (without spiking) and ms refers to the spiked mass.

Biological Characterisation of the By-Products Extracts

The TPC of the phenolic extracts weas determined using the Folin–Ciocalteu method. To do so, 20 µL of sample solution (1000 mgextract/L), 100 µL of the Folin–Ciocalteu reagent, and 1580 µL of distilled water were added to a cuvette. Subsequently, 300 µL of saturated sodium carbonate solution was added, and the cuvette was incubated for 2 hours under dark conditions. Utilising a spectrophotometer, the absorbance at 750 nm was measured. The results were expressed as gallic acid equivalents (GAE) per gram of extract.

The antioxidant properties were accessed using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,20-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays. Both the IC50 values and the percentage of inhibition of the free radicals were determined for both tests. Trolox equivalents per gram of extract (mgTE/gextract) was used to express the results [53].

The disk-diffusion assay was performed to analyse the antibacterial activity of the extracts (500 mgextract/mL) against E. coli, S. aureus and S. epidermidis. The capacity of the extracts (0.2 mgextract/mL) to absorb UV radiation and, consequently, act as UV filter, was assessed by the determination of the sun protection factor (SPF). All methods were performed according to the literature [49].

The enzymatic inhibitory capacity of the extracts was evaluated using α-amylase assay, with some modifications [54]. Briefly, 250 μL of extract solution (1 mgextract/mL in ethanol) were incubated at 37 °C for 10 min with 250 μL of α-amylase solution (0.5 U/mL in UPW). Afterwards, 250 μL of starch solution (1% w/v) were added and the mixture was incubated for another 10 min at 37 °C. Finally, 500 μL of 3,5-dinitrosalicylic acid (DNS) reagent were added and the samples were placed in boiling water for 10 min. The samples were allowed to cool at room temperature before adding 5 mL of UPW. The absorbance was analysed at 540 nm and the percentage of inhibition of the enzyme by the extracts was determined using Eq. 3:

$${\upalpha }-\text{amylase inhibition}\,({\%})= \frac{{{\text{Abs}}}_{{\text{control}}}-{{\text{Abs}}}_{{\text{sample}}}}{{{\text{Abs}}}_{{\text{control}}}}\times 100$$
(3)

where Abssamples refers to the absorbance of the sample and Abscontrol refers to the absorbance of the mixture without the extract (250 μL ethanol + 250 μL α-amylase + 250 μL starch + 500 μL DNS).

Results and Discussion

Validation Parameters of the HPLC–DAD Method

Following the establishment of the HPLC conditions, validation parameters were chosen following the recommendations of the Q2(R2) guideline of the ICH [52]. For that, linearity, sensitivity, precision, robustness and accuracy of the method were assessed. The chromatogram of the nine standards analysed is presented in Figure S1 (Supplementary Material). The linearity and sensitivity of the method for each standard are displayed in Table 3, while the remaining validation parameters are presented in Table S1 and Table S2 (Supplementary Material).

Table 3 Linearity and sensitive results obtained for the 9 standards analysed
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The results obtained in the precision analysis (Table S1 in Supplementary Material) showed that the method developed is, in general, more precise for phenolic acids (gallic acid, chlorogenic acid, caffeic acid, rosmarinic acid) and stilbenes (resveratrol) when compared to flavonoids (catechin, epicatechin, quercetin, kaempferol). Nonetheless, the method presented acceptable precision for all the compounds (RSD < 10%), except for epicatechin in the inter-assay precision analysis performed by the same operator on different days. Additionally, the results demonstrated that the method tested is robust (RSD < 10%). Once again, phenolic acids and stilbenes presented better results (lower RSD values) than flavonoids. The results obtained demonstrated that the developed method was suitable for the identification and quantification of the nine phenolic standards selected. The percentages of recovery for each standard were within the range of 70–120%, for all PC and extracts, which is in accordance with the Food and Agriculture Organization and the World Health Organization guidelines, as shown in Table S2 of the Supplementary Material.

Extracts Characterisation

After the validation of the method, the analytical methodology was applied to identify the main PC present in the different extracts, obtained using a Soxhlet extractor, of different Portuguese by-products: CS, GS, OP, and PFP. The obtained results are displayed in Table 4.

Table 4 Phenolic compounds identified in the extracts of different Portuguese by-products
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Through the analysis of Table 4, it is possible to observe that catechin is the only PC present in all the analysed samples. Additionally, it is noticeable that the composition of the extracts is different and that the majoritarian compounds change depending on the sample. To understand how these differences on the phenolic composition can impact the biological properties of the samples, the extracts’ TPC, antioxidant and antibacterial properties, α-amylase inhibitory capacity and SPF were analysed. The results are expressed in Table 5.

Table 5 Characterisation of the extracts from different Portuguese by-products
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The results demonstrated that the extracts presented interesting antioxidant properties, as well as antibacterial activity against S. aureus and S. epidermidis but not E. coli in the concentration tested (500 mgextract/mL). Additionally, the authors’ previous study revealed that OP and PFP extracts were also capable of inhibiting the growth and development of the same bacteria as CS and GS extracts.

Considering the TPC, the results obtained in the present work are superior to the ones found in the literature (as seen in Table 6), demonstrating the great potential of using solid–liquid extraction methods coupled with Soxhlet apparatus to extract PC. The extracts also displayed higher antioxidant capacity in comparison to the values described in the literature (Table 6). The antioxidant potential can be explained by the presence of different PC on the extracts (Table 4), as they are know for their antioxidant effect. Gallic acid, the major PC found in CS (as seen in Table 4), is a phenolic acid that has the capacity to act as an antioxidant agent due to its scavenging ability [55]. Studies have shown that the relative apolar nature (hydrophobic character) of gallic acid and its derivatives is related to their antioxidant action. An essential element controlling the antioxidant activity against numerous types of oxidative stress was shown to be hydrophobicity [56]. Gallic acid, however, has less antioxidant action than its esters because it is more hydrophilic. In methylated gallic acid derivatives, hydroxyl groups, particularly those in the para position to the carboxylic group, preserve the radical scavenging activity in addition to being hydrophobic [55]. Furthermore, catechin, epicatechin and kaempferol, present in GS, OP and PFP extracts, are flavonoids associated with high antioxidant capacity. This fact is related to the distinct substitution patterns in their chemical structure; moreover, they can act as hydrogen-donating molecules displaying radical scavenging properties [57]. The basic structure of flavonoids is displayed in Fig. 1A. As previously shown in Table 1, the identified compounds possess the 3′,4′-dihydroxy catechol configuration on the B ring, which is a potential radical target, allowing these molecules to have radical scavenging abilities by delocalising unpaired electrons in the B ring; however, from the flavonoids identified in GS, only kaempferol structure allows from the unpaired electrons to leave the B ring and be stabilised across the hole molecule. Additionally, the 3-hydroxyl group also in the C ring in combination with the 2,3 double bond increases the radical-scavenging capacity of kaempferol [58, 59]. Quercetin and resveratrol, the main PC in the OP extract, are also known to exhibit great antioxidant capacity [42, 43]. In the case of quercetin (Fig. 1B), since this compound belongs to the flavonoid category, the antioxidant capacity is associated with the previously explained mechanism. In the case of resveratrol, this molecule has an extremely high antioxidant potential towards reactive oxygen species, which is a result of its chemical structure. Indeed, the presence of the meta-hydroxyl groups, the para-hydroxyl group as well as the double bond (as seen in Fig. 1C), are the functional groups responsible for this biological property [60]. As demonstrated by these results, the antioxidant properties of the extracts are in accordance with their phenolic composition. Thereby, there is potential for the phenolic-rich extracts from these four by-products to be incorporated into different industries as antioxidant agents. This biological property is of utmost importance since it can help to delay oxidative stress and allows to scavenge free radicals, protecting cells, proteins, and DNA, while preventing various health issues and accelerated ageing. With their wide range of antioxidant protective effects, phenolic extracts, from natural by-products, serve as vital allies in promoting overall health and well-being. Moreover, extracts that display this type of biological properties are able to be incorporated into food and cosmetic products, delaying their oxidation.

Table 6 Literature results for the total phenolic content, antioxidant and antibacterial capacities and phenolic composition of the extracts of different Portuguese by-products
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Fig. 1
figure 1

Basic chemical structure of flavonoids (A) and chemical structure of quercetin (B) and resveratrol (C). In the quercetin structure, the rectangle highlights the double bond between carbons 2 and 3 on the C ring that allow conjugation. In the resveratrol structure, the rectangles highlight, from left to right, the meta-hydroxyl groups, the double bond and the para-hydroxyl group

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Regarding the antibacterial properties, OP extract was the one that displayed higher antibacterial capacity against both S. aureus and S. epidermidis when compared to E. coli. This tendency was also demonstrated in the literature for all extracts (as seen in Table 6). This result seems to highlight that the OP extract is a suitable candidate to be used as an antibacterial agent in different products in many industries and can be explained by the presence of resveratrol in the OP matrix (as seen in Table 4). Resveratrol has shown antibacterial capacity towards some microorganisms, such as E. coli and S. aureus. Research indicates that resveratrol might be able to cleavage the DNA and, consequently, inhibit these bacteria. Furthermore, it has been revealed that resveratrol is capable of reducing cellular activity in terms of the metabolism of membrane damage and can act as a deterrent to cell reproduction [43]. Furthermore, the antibacterial activity of the remaining extracts (CS, GS, and PFP) could be related to the existence of catechin and epicatechin, both belonging to the catechins family which present antibacterial activity against Gram-negative and Gram-positive bacteria, probably to their capacity to disrupt bacterial membranes. These molecules are able to penetrate the lipid bilayer, causing the lateral expansion of the phospholipids and ultimately the disruption of the cell [61].

Regarding the capacity to act as an α-amylase inhibitor, it is observable, from Table 5, that all the extracts, especially CS extract, display a considerably high inhibitory effect towards this enzyme, for a concentration of 1 mgextract/mL. This result is particularly important since the inhibition of α-amylase, an enzyme that is associated with carbohydrates digestion, is a strategy applied to prevent type II diabetes. People with this disease have a deficient production of insulin, a molecule responsible for the absorption of glucose from the blood into the cells. Therefore, an accumulation of glucose in the blood can occur in these individuals when carbohydrate-rich food are ingested since α-amylase breaks carbohydrates in smaller molecules. Thus, the inhibition of the enzyme can prevent the accumulation of glucose in the blood of people with type II diabetes. The present results proved that these phenolic-rich extracts are capable of being employed as inhibitory agents of this enzyme as an approach to overcome problematic diseases such as diabetes. This ability stems from the presence of flavonoids and phenolic acids in the composition of the extracts under analysis (as seen in Table 4). The structure of gallic acid (as well as other phenolic acids, such as caffeic and chlorogenic) is characteristic, displaying a double carbon bond conjugated with a carbonyl group. This structure allows the stabilisation of the binding forces between the molecule and the enzyme’s active site [69]. On the other side, flavonoids (such as catechin, epicatechin, kaempferol, and quercetin) are also capable to act as α-amylase inhibitors. This property is the result of the presence of the hydroxyl groups. These functional groups are capable of establishing hydrogen bonds with amino acid residues present in the active site, stabilising the interaction with the active site and, consequently, inhibiting the enzyme [70].

Finally, from Table 5, it is observable that all the extracts exhibited the ability to absorb UV radiation, with OP extract exhibiting the highest SPF value among the four. Indeed, it was anticipated that the OP extract would display this biological property, due to the presence of quercetin in high concentrations (as shown in Table 4) since this PC exhibits exceptional characteristics as a UV-absorbing agent. As seen in Fig. 1B, quercetin has a double bond between carbons 2 and 3 on the C ring, linked with the 4-carbonyl group also on the C ring. Because of its structure, quercetin has an unsaturated heterocyclic C ring that aids in the coupling of the A and B rings [71]. Because of the complete molecular structure of quercetin being conjugated, it is able to absorb UV rays very effectively [72, 73]. Other compounds, such as catechin (present in all the extracts studied), can also protect from UV radiation [74]. However, even though the other extracts also display this biological property, the SPF value of the OP extract was significantly different, proving that this extract is the most adequate for applications as UV filter. The potential to absorb UV radiation makes these extracts extremely interesting for both the cosmetic and food industries. In the first one, these extracts can be incorporated in sunscreens or formulations with SPF, to diminish or even replace the use of synthetic ones. On the case of the food industry, there is potential for them to be incorporated in the packaging protecting, not only the packaging itself, but also the food from the light, moderating the possible damages.

Therefore, the present study intended to highlight the importance of the identification of the main compounds present in extracts from by-products. Additionally, it was evidenced that, even though being rich in PC, the composition of the extracts is dissimilar, which can influence their final application. Hereupon, it is important to characterise extracts, through the identification of their main compounds, to infer their potential biological capacities and, consequently, to define which applications are more appropriate for them.

Conclusions

This work intended to comprehend the correlation between the chemical composition and the biochemical properties of the phenolic-rich extracts from different Portuguese by-products. To determine the phenolic composition of the extracts, an HPLC–DAD analytical method was applied to identify and quantify their main PC. The selected compounds for this study were caffeic acid, catechin, chlorogenic acid, epicatechin, gallic acid, kaempferol, quercetin, resveratrol and rosmarinic acid. The validated analytical method was used to analyse the phenolic composition of the extracts of different by-products: CS, GS, OP and PFP. Catechin was the only phenolic present in all extracts. Gallic acid and catechin were the major compounds found in CS, while catechin, epicatechin and kaempferol were the main phenolics found in GS. Due to their composition, it is expected that these extracts present antioxidant capacity. Regarding OP, quercetin and resveratrol were the PC found in higher quantities. The presence of resveratrol and quercetin in OP extract indicates that this extract may confer antibacterial properties and may have the capacity to act as a UV filter. Finally, since the passion fruit extract is rich in compounds from the catechins family (e.g., catechin and epicatechin), which according to literature may present antibacterial and antioxidant properties, it is expected that this extract has these biological properties. Moreover, although the results revealed that the composition of the extracts is different, it was observed that, for the same concentration, the four extracts were able to inhibit the activity of α-amylase with high percentages of inhibition. Therefore, the present work intended to display the importance of identifying the main components of different phenolic extracts to understand their main biological properties, and, consequently, to conclude about their promising applications in different food, cosmetic and/or pharmaceutical products.