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Article

Tropical Fruit Wastes: Physicochemical Characterization, Fatty Acid Profile and Antioxidant Capacity

by
Mariana Ferreira dos Santos
1,2,
Beatriz Pereira de Freitas
2,
Jaqueline Souza de Freitas
2,
Luane Souza Silva Lage
2,
Alex Aguiar Novo
2,
Claudete Norie Kunigami
2,
Eliane Przytyk Jung
2 and
Leilson Oliveira Ribeiro
2,*
1
Institute of Education, Science and Technology of Rio de Janeiro, Nilópolis Campus, Nilópolis, Rio de Janeiro 26530-060, Brazil
2
Laboratory of Organic and Inorganic Chemical Analysis, National Institute of Technology, Rio de Janeiro 20081-312, Brazil
*
Author to whom correspondence should be addressed.
Resources 2025, 14(5), 83; https://doi.org/10.3390/resources14050083
Submission received: 21 March 2025 / Revised: 9 May 2025 / Accepted: 11 May 2025 / Published: 20 May 2025
(This article belongs to the Special Issue Resource Extraction from Agricultural Products/Waste: 2nd Edition)
Browse Figure
Versions Notes

Abstract

:
Wastes resulting from the depulping of tropical fruits such as siriguela (Spondias purpurea), umbu (Spondias tuberosa), and juçara (Euterpe edulis) can be used as a source of bioactive compounds and nutrients. Therefore, the aim of this work was to chemically characterize the flours of siriguela seeds and peels (FSSs and FSPs), umbu seeds and peels (FUSs and FUPs), umbu pulp refine cake (FUC), and defatted juçara pulp refine cake (FJC) based on their proximate composition and mineral content, fatty acids, total phenolic content (TPC) and antioxidant capacity (ABTS•+, DPPH•, and FRAP). The results were expressed on a dry basis. The FJC had the highest lipid and protein percentage (10% and 31%, respectively), while for carbohydrates; FUS samples had the highest value (80%). FSSs presented the highest levels of Ca (239.7 mg 100 g−1), Mg (183.3 mg 100 g−1), and FSP of K (1403.9 mg 100 g−1). Regarding the fatty acid profiles, palmitic acid (C16:0) was found as the main fatty acid in FSSs (28.87%), FSPs (69.31%), and FUC (45.68%), while oleic acid (C18:1) was found as the main fatty acid in FUSs (32.63%), FUPs (48.24%), and FJC (61.58%). The FUP sample exhibited the highest antioxidant potential (1852.81 mg GAE 100 g−1, 130 µmol Trolox g−1, 131 µmol Trolox g−1, and 590 µmol Fe2+ g−1 by TPC, ABTS•+, DPPH•, and FRAP, respectively). As the first comparative study of these specific fruits wastes, the results showed that their flours are promising sources of nutrients and bioactive compounds. In addition, their use can contribute to the circular economy and Sustainable Development Goals (SDGs) 2 and 12 of the 2030 Agenda.

1. Introduction

With favorable geographic and climatic characteristics for fruit production, Brazil has many native species that remain underexploited, despite their significant potential for the agroindustry and as a source of local income. It is highlighted that the country is classified as megadiverse, with approximately 50 thousand documented species of flora, of which 30 thousand are native [1].
Fruit consumption is associated with a search for healthy life, as fruits are rich in essential nutrients, micronutrients, and bioactive compounds [2].
Siriguela (Spondias purpurea), umbu (Spondias tuberosa), and juçara (Euterpe edulis) are tropical fruits found in Brazil, with umbu and juçara being natives. They are known for their richness in nutrients and for being sources of bioactive compounds. Each of these fruits has a profile of antioxidant compounds, vitamins, fibers, and minerals that promote health benefits [3,4,5]. The major distribution of these fruits in the country’s biomes is shown in Figure 1.
Umbu, a native fruit from Caatinga, is known for its contents of vitamin C and phenolic compounds, which play an important antioxidant and anti-inflammatory role [3]. Juçara, a fruit similar to açaí, but native to the Atlantic Rainforest, is rich in anthocyanins and has potent antioxidant action, which can contribute to protection against cardiovascular diseases and inflammation [4]. Siriguela, common in the Brazilian Northeast, has a profile rich in carotenoids and vitamin C, important for skin health and strengthening the immune system [5]. In addition, the fruits contain essential polyunsaturated fatty acids, linoleic acid (LA, 18:2n-6), and linolenic acid (LNA, 18:3n-3). These fatty acids are considered strictly essential because they cannot be synthesized by the human body and must be supplied through the diet [6].
Among studies on the biological properties of these fruits and their fractions, the results reported by Ribeiro et al. [3] for umbu pulp, Cardoso et al. [7] for juçara pulp, and Cangussu et al. [8] for siriguela pulp can be highlighted. Ribeiro et al. [3] showed significant values for the antioxidant capacity attributed to the phenolic compounds present, highlighting rutin and also the presence of vitamin C. Cardoso et al. [7] evaluated the photoprotective capacity and antioxidant and antimicrobial activity, highlighting juçara as a promising source of polyphenols, mainly anthocyanins. The data reported by Cangussu et al. [8] showed that the flours prepared from Siriguela pulp have rich potential in bioactive compounds, with emphasis on the tannin and fiber contents.
In this way, these tropical fruits have been consumed in natura and as frozen pulp, which is employed in the development of food formulation. However, to prepare frozen pulp, some wastes are generated through the depulping such as peels, seeds, and cakes. As reported in other studies, such as that of Ayala-Zavala et al. [9], wastes from agro-industrial processing are rich in nutrients and bioactive compounds. These authors reported that non-edible parts of exotic fruits have shown important antioxidant activities, with phenolic compounds being preferentially located in the peel and seeds.
Other authors reinforce the data on agro-industrial residues. Inada et al. [10] used jaboticaba fractions and observed high concentrations of phenolic compounds, mainly in the peel, with this fraction being rich in cyanidin-3-O-glucoside. Selani et al. [11] evaluated the by-products of mango, passion fruit, and pineapple, reporting high concentrations of phenolic compounds and dietary fibers and suggesting the use of these flours by the food industry as functional ingredients. Fruit and vegetable flours composed of the wastes of sweet orange, passion fruit, watermelon, zucchini, lettuce, carrot, spinach, mint, yam, cucumber, and arugula were evaluated as raw materials for the preparation of biodegradable films and as a source of fiber [12]. In the study carried out by Oliveira et al. [13], the umbu-cajá by-product flour was characterized as a prebiotic candidate and a new circular ingredient with added value to functionalize foods and nutraceuticals. Buriti shell flour also proved to be an important source of bioactive compounds, with phenolic compounds showing a high correlation with antioxidant activity [14].
Therefore, the peels, seeds, and cakes, which are usually discarded or used as animal feed, can be processed to produce functional flours, since they preserve part of the nutrients, minerals, and bioactive compounds and can be incorporated into various food products, adding nutritional value and helping to reduce waste [15].
The circular use of fruit wastes represents a sustainable strategy that aims to reuse by-products generated during agro-industrial processing, such as peels, seeds, and cakes. This approach is aligned with the principles of the circular economy, promoting reductions in waste and the full valorization of natural resources. By transforming waste into functional ingredients or inputs for the food, cosmetic, and pharmaceutical industries, it is possible to add value to materials that were previously discarded, reducing environmental impacts and encouraging more efficient production practices. Studies show that fruit wastes have a high potential for valorization and can also be used as substrates in bioprocesses for the production of compounds of interest, such as β-1,3-glucans and nutrient-rich biomass [16]. Different case studies illustrate strategies for valorizing these by-products. Campos et al. [17] reported the extraction of antioxidant compounds from pineapple waste, while a local biorefinery based on pomegranate waste allowed the extraction of pectin, oils, and antioxidants for sustainable industrial applications [18]. Lipiński et al. [19] demonstrated the feasibility of energy recovery from fruit waste in Europe, and recent research highlights the production of bioplastics from citrus and apple wastes, contributing to the replacement of synthetic plastics [20]. Thus, circularity in the use of fruit waste contributes not only to environmental sustainability, but also to the innovation and diversification of the production matrix.
The choice of siriguela, umbu, and juçara in this study is justified by their underutilized nature and high bioactive potential, especially present in their residual fractions. Unlike commercially exploited tropical fruits, such as orange and mango, whose wastes are already valued by different sectors of the industry, these species still lack systematic use. Orange peel, for example, has been used as a source of essential oils, pectins, and flavonoids in food, pharmaceutical, and cosmetic applications [21]. Similarly, mango processing residues, such as peels and seeds, present bioactive compounds with high antioxidant potential, including polyphenols and carotenoids, which can be explored as functional ingredients in food and cosmetics [22]. In contrast, siriguela, umbu, and juçara remain regionally exploited, with a large part of their by-products still being discarded or undervalued. The valorization of these agro-industrial residues contributes not only to the development of new functional and sustainable ingredients, but also to the promotion of Brazilian biodiversity, the inclusion of local communities in the bioeconomy, and the strengthening of the circular economy in emerging production chains.
Thus, flours made from umbu, juçara, and siriguela processing wastes emerge as sustainable alternatives for the food industry, also contributing to some of the sustainable development goals of the 2030 Agenda [23]. Therefore, this study aimed to evaluate these flours regarding their proximate composition and mineral content, fatty acids, total phenolic content (TPC) and antioxidant capacity (TPC, ABTS•+, DPPH•, and FRAP).

2. Materials and Methods

2.1. Samples

Approximately 2 kg of siriguela was acquired in 2020 from a local market in the city of Rio de Janeiro. Before depulping, the fruits were sanitized using sodium hypochlorite (100 ppm) via immersion for 10 min. The depulping was performed manually using a domestic sieve. The peels and seeds were dried at 45 °C in an oven with forced air ventilation for 24 h. The peels were ground in a domestic mixer while the seeds were disintegrated in a knife mill to obtain the flour.
The umbu peels, seeds, and pulp refine cake used in this study were obtained via the fruit depulping process carried out in the pilot plant of Embrapa Agroindústria de Alimentos (Guaratiba, Rio de Janeiro), from fruits obtained in 2020 from a local market in the city of Rio de Janeiro. For this, the fruits were sanitized using sodium hypochlorite (100 ppm) via immersion for 10 min before depulping. Both wastes were dried at 45 °C in an oven with forced air ventilation for 24 h. After drying, the peels and cake were ground in a domestic mixer while the seeds were disintegrated in a knife mill to obtain the flour.
The defatted juçara pulp refine cake was also obtained from the pilot plant of Embrapa Agroindústria de Alimentos as a by-product of the juçara pulp’s centrifugation process, performed using a basket centrifuge with a 150 µm nylon mesh (IEC, K7165, Bellport, NY, USA), which was performed in 2020. Approximately 5 kg of the resulting material was dried at 45 °C for 24 h in a forced air oven and subsequently defatted using a continuous screw press (CA 59 O, IBG Monforts, Mönchengladbach, Nordrhein-Westfalen, Germany). The dried material was ground in a domestic mixer to obtain the flour.
In this way, flours were obtained from siriguela seeds (FSSs), siriguela peels (FSPs), umbu seeds (FUSs), umbu peels (FUPs), umbu pulp refine cake (FUC), and juçara pulp refine cake (FJC). Both samples were packaged in metallized packaging to avoid exposure to light and stored at −20 °C until analysis was performed.

2.2. Proximate Composition and Mineral Content

The proximate composition was determined according to AOAC, except for the total proteins [24]. The moisture content was determined gravimetrically at 105 °C; the lipid content via exhaustive extraction in Soxhlet using hexane as a solvent; the ash content via incineration at 550 °C in a muffle furnace; and the total protein was determined using the Dumas method, using equipment for carbon, hydrogen, and nitrogen analysis with a thermal conductivity detector for nitrogen quantification (CHN 628, Leco, St. Joseph, MI, USA), employing 6.25 as conversion factor. The carbohydrates were calculated by difference [9]. All results were expressed on a dry basis (d.b.).
The mineral content was determined from digested samples via acid digestion in a microwave digester (Ethos 1, Milestone, Sorisole, Italy) using 0.5 g of each sample and a mixture of 7 mL of 65% HNO3 and 1 mL of 30% H2O2. After digestion, Ca, Cu, K, Mg, Mn, Ni, and Na were determined using a Flame atomic absorption spectrophotometer (SpectrAA 280, Varian, Melbourne, VIC, Australia). The results were expressed as mg 100 g−1 (d.b.) [25].

2.3. Fatty Acid Profile

The fatty acid profile of the flours was determined from their methyl esters, obtained according to the methodology proposed by Jung et al. [26]. Approximately 0.1 g of the sample and 6 mL of 0.5 N NaOH solution in methanol were added to a 25 mL flask and heated for 5 min. Subsequently, 8 mL of BF3 solution in methanol was added, keeping the sample boiling for 2 min. Then, 3 mL of hexane and saturated NaCl solution were added for the separation of the organic phase, which was collected and used to determine the fatty acid profile of the sample via gas chromatography coupled to mass spectrometry (GC-MS).
The samples were analyzed using an Agilent 6890 gas chromatograph (Agilent Technologies, Palo Alto, CA, USA) with a (5–phenyl)-dimethylpolysiloxane HP-5MS capillary column (30 m × 0.25 mm, 0.25 µm film thickness; Restek, Bellefonte, PA, USA) equipped with an Agilent 5975 mass selective detector in electron impact mode (ionization energy: 70 eV), operating with an oven temperature initially maintained at 160 °C for 1 min and then increased at a rate of 4 °C/min to 250 °C, remaining at this temperature for 5 min. The injector temperature was set at 250 °C and the interface temperature at 260 °C. The quadrupole was maintained at 150 °C and the ionization source at 230 °C. Helium was used as the carrier gas at a flow rate of 1 mL min−1, and 1 µL of the sample was injected in split mode with a split ratio of 1:100, except for the FSS and FSP samples that were injected in splitless mode. Mass spectra were obtained in the range of 40 to 500 m/z. The characterization of fatty acids was obtained via comparison with the mass spectra available in the Willey7Nist05 digital mass spectral library. The quantitative composition was obtained via the area normalization method, in which the percentage indicated for each component corresponds to the contribution of each peak in area over the total area of all peaks.

2.4. Extraction and Analysis of Bioactive Compounds

Extractions were performed by weighing 3 g of the sample in a 25 mL flask, adding 10 mL of 50% methanol, and keeping the mixture at room temperature for 60 min after agitation in vortex. The sample was then centrifuged for 15 min at 4000 rpm. The supernatant was transferred to a 25 mL volumetric flask, while 10 mL of 70% acetone was added to the residue from the first extraction. Again, after agitation, the mixture was maintained at room temperature for 60 min and then centrifuged for 15 min at 4000 rpm. The supernatant from the second extraction was combined with the methanolic extract, bringing the final volume to 25 mL with distilled water.
The total phenolic content (TPC) was determined according to the method described by Singleton and Rossi [27] using the Folin–Ciocalteu reagent. For this purpose, 250 µL of each extract was mixed with 1250 µL of 10% (v/v) Folin–Ciocalteu and 1000 µL of 7.5% (w/v) Na2CO3 solution. Subsequently, the mixtures were heated at 50 °C for 15 min and cooled in an ice bath to read the absorbance at 760 nm. The TPC of the extracts was obtained from the preparation of a gallic acid standard curve. The results were expressed as mg of gallic acid equivalent per 100 g of sample (mg GAE 100 g−1 d.b.).
The antioxidant capacity was measured using the DPPH•, ABTS•+, and FRAP methods. In the DPPH• method described by Hidalgo et al. [28], 100 μL of each diluted extract was added to 2.9 mL of the DPPH• solution (6 × 10−5 M in methanol and diluted to obtain an absorbance of 0.700 at 517 nm). The resulting solutions were left to stand for 30 min in the dark at room temperature. The absorbances were measured at 517 nm with a spectrophotometer. The results were obtained by preparing a Trolox standard curve. They were expressed as μmol Trolox g−1 d.b. In the ABTS•+ method, there was a reaction of 30 µL of the extract with 3 mL of the ABTS•+ radical solution at room temperature for 6 min. The results were obtained from the preparation of a Trolox standard curve and the absorbances were read in a spectrophotometer at 734 nm. The results were expressed as μmol Trolox g−1 d.b. [29]. The FRAP method was performed by mixing 100 µL of the extract with 3.0 mL of the FRAP solution (mixture of acetic acid buffer solution pH 3.6, 10 mmol L−1 TPTZ, and 20 mmol L−1 FeCl3). The tubes were then incubated at 37 °C for 30 min. The results were obtained by preparing a standard curve of FeSO4·7H2O. The absorbances were read in a spectrophotometer at 593 nm. The results were expressed as μmol Fe2+ g−1 d.b. [30].

2.5. Statistical Analysis

The assays were performed in triplicate, except for the determination of minerals, which was carried out in duplicate. The results were expressed as the average ± standard deviation. Analysis of variance (ANOVA), followed by Tukey’s test for homogeneous groups at a 95% confidence interval, was performed using Statistica® software v.13.0. for all determinations, except the fatty acid profile.

3. Results and Discussion

3.1. Proximate Composition, Mineral Content, and Fatty Acid Profile

Data relating to the proximate composition of tropical fruit waste flours are shown in Table 1. The lipid content for FSP, FUS, FUP, and FUC was approximately 1%, while for FJC, it was 10% (p < 0.05), and negligible for FSS. These data show that FJC can be a source of lipids. Studies such as that of Borges et al. [31] describe juçara as a fruit with a high lipid content, reporting values between 18.45% to 44.08%, similar to açaí fruits. Our result was lower, due to the raw material used in the present work being a partially defatted residue. However, it still preserves a good percentage of this nutrient.
The ash content ranged from 1% to 4.2%, with the highest value observed in the FSP sample (p < 0.05). The moisture content varied between 9% (FUS) and 21% (FSP) among the samples (p < 0.05). These data indicate that the peels (siriguela and umbu) exhibited a higher ash content compared to the seeds and cakes, showing that they are richer sources of minerals.
This is consistent with the literature, which indicates that peels and seeds are often richer in minerals than the pulp. However, the specific nutritional value depends on the food in question [32]. In addition, refining cakes usually undergo processes that can concentrate or reduce the mineral fraction, depending on the steps involved. Our results for umbu peel and seed are in accordance with those of Ribeiro et al. [3], which reported data about umbu fractions.
The total protein varied from 17 to 31% among the samples. This shows that samples are statistically different (p < 0.05). The highest value for protein was obtained for the FJC sample.
According to the International Society of Sports Nutrition (ISSN), the recommended daily protein intake for sedentary adults is 0.8 g per kilogram of body weight. For physically active individuals, protein requirements can range from 1.2 to 2.0 g per kilogram of body weight, depending on the level of physical activity and specific goals, such as increasing muscle mass or recovery after exercise [33]. Based on these guidelines, 100 g of the samples provide between 31% (FSP) and 55% (FJC) of the recommended daily intake for a sedentary adult weighing 70 kg. However, it should be considered that protein quality also plays an important role, since different protein sources have distinct amino acid profiles, which can influence their biological functions and nutritional value. The carbohydrates were in a higher concentration in the samples, with the FUS sample being highlighted with 80% (p < 0.05). It is important to emphasize that the carbohydrate content is composed of sugars and fibers present in the fruit fractions. Therefore, this value includes fibers that are considered an important part of the human diet, which are related to physiological properties essential for health [34]. For peel and seed waste flours, authors such as Xavier et al. [35] reported that flour elaborated from umbu contained a total fiber content of 61.21%. For siriguela, Albuquerque et al. [5] found the value of 12.82%, and Garcia et al. [36] indicated that the total fiber content in juçara pulp waste flour is 40.1%. Thus, the flours evaluated in the current study can be used as ingredients in food formulations in order to increase their protein and fiber contents.
Minerals are essential nutrients for the proper functioning of the human body, playing an important role in enzymatic and metabolic processes [31]. Table 2 presents the mineral content in the analyzed samples, with the FSS sample showing the highest concentrations of Ca (239.7 mg 100 g−1) and Cu (27.1 mg 100 g−1) (p < 0.05). In contrast, the FSP sample exhibited the highest potassium content (1403.7 mg 100 g−1), followed by FUP (1326.7 mg 100 g−1) and FSS (1257.2 mg 100 g−1) (p < 0.05). These results emphasize their potential as rich sources of potassium, a macro-mineral essential for muscle function, nerve signaling, and others [37].
According to the Dietary Reference Intakes (DRIs) established by the U.S. National Institute of Health [38], the daily recommendation for potassium for adults is 3400 mg per day for men and 2600 mg per day for women. Therefore, 100 g of FSP flour can provide up to 41.29% of this requirement for a man, while FUP and FSS flours supply approximately 39.02% and 36.98%, respectively. Even the samples with a lower potassium content, such as FUS (288.9 mg 100 g−1), contribute to around 8.5% of the DRI. This reinforces the nutritional relevance of these fruit by-products in contributing to dietary potassium intake, particularly considering that many populations fail to meet this recommendation [39].
Other important minerals detected include calcium and magnesium. The FSP and FSS samples may, respectively, provide up to 7.63% and 23.97% of the DRI for calcium, while magnesium contributions ranged from 19.78% (FUC) to 45.83% (FSS). It is important to highlight that these recommendations vary according to sex and age group.
Regarding Mn, concentrations varied between 0.3 and 13.7 mg 100 g−1, with the FJC sample showing the highest level (p < 0.05). Ni was found at low concentrations in all samples. While this element may pose toxicity risks at high levels, its estimated daily intake remains low in several countries, and the World Health Organization (WHO) set a tolerable dietary intake of 11 µg kg−1 body weight for children in 2007 [40]. Thus, the flours in this study can be considered safe for Ni consumption, provided that the intake guidelines are respected.
Compared to the literature values for the traditionally consumed fruit pulps, the results in this study indicate a notable concentration of minerals in the waste flours. For instance, Silva et al. [41] reported 1041 mg 100 g−1 for Ca, 1091 mg 100 g−1 for K, and 974 mg 100 g−1 for Mg in juçara pulp. In comparison, the FJC sample presented values of 168.50 mg 100 g−1 for Ca, 558.06 mg 100 g−1 for K, and 129.07 mg 100 g−1 for Mg. Although lower than the pulp values, these results are still relevant, considering that they refer to the depulping residue. Similarly, Xavier et al. [35] reported contents of 231.7 mg 100 g−1, 924.2 mg 100 g−1, and 132.6 mg 100 g−1 for Ca, K, and Mg, respectively, in umbu pulp. The mineral contents in the FUC sample were close to these values, reinforcing the relevance of these residues as valuable sources of micronutrients.
In relation to the fatty acid profiles (Table 3), palmitic acid (C16:0) was found as the main fatty acid in FSS (29.34%), FSP (69.31%), and FUC (45.68%), while oleic acid (C18:1) was found as the main fatty acid in FUS (32.63%), FUP (48.24%), and FJC (61.58%).
The FJC sample (61.58%) exhibited a higher oleic acid percentage than that found in another study referring to juçara pulp (44.63% to 55.61%) [31]. In their study, Borges et al. characterized the chemical composition of juçara fruits from the Atlantic Forest, highlighting a lipid profile rich in unsaturated fatty acids, particularly oleic acid, as well as significant contents of phenolic compounds and anthocyanins that contributed to the fruit’s antioxidant capacity.
The lipid fraction of juçara is suitable for consumption due to its composition of a high content of unsaturated fatty acids, with a notable content of oleic acid, and a lower content of saturated lipids compared to other oils such as palm, babassu, and coconut [42].
FSS (24.36%), FSP (11.33%), FUS (31.85%), and FJC (15.09%) also present concentrations of linoleic acid (omega–6), essential for human nutrition, with emphasis on flours obtained from siriguela and umbu seeds. For FSS, another essential acid found was linolenic acid (omega–3), with 10.98%, in addition to the monounsaturated fatty acid, oleic acid (omega–9), with 19.42%.
In this way, the FJC sample, which presented about 77% of oleic-rich unsaturated fatty acids, can be used in the elaboration of foods with health benefits, given that the potential of these fatty acids in the cardiovascular system and other parts of the human body is well known [43,44].

3.2. TPC and Antioxidant Capacity

It is widely recognized that foods rich in antioxidants play a key role in disease prevention. The antioxidant capacity of fruits varies according to the composition and levels of bioactive compounds, highlighting the need for the chemical characterization of fruits and their fractions [45].
For the TPC, FSS, FSP, FUS, FUP, FUC, and FJC presented values of 249 ± 2, 1492 ± 6, 369 ± 2, 1850 ± 11, 1058 ± 15, and 774 ± 5 mg GAE 100 g−1, respectively, as shown in Table 4, with an emphasis on FUP, which presented the highest value (p < 0.05). Therefore, the flours used in the study may be used to develop functional foods, as phenolic compounds have been shown to be relevant for the proper functioning of the body. Toma et al. [46] claim that phenolic compounds can, due to their antioxidant activity, prevent cardiovascular diseases, reduce hypertension, and aid in the treatment of diabetes, as they promote a reduction in lipid oxidation.
However, it is important to emphasize that the Folin–Ciocalteu method used to determine the total phenolic content (TPC) lacks specificity, as the reagent also reacts with other reducing substances including phenolic compounds, ascorbic acid, reducing sugars, and other reducing agents present in the samples [47]. Therefore, the TPC values reported in this study should be interpreted as an estimate of the total reducing capacity of the samples, rather than as a direct quantification of the phenolic compounds. Despite this limitation, the method remains widely used due to its simplicity and reproducibility, and the high values indicate the antioxidant potential of these flours.
The TPC of umbu (FUP > FUC > FUS) appeared in a different order from the findings reported in the literature by Omena et al. [2] (seed > peel > pulp), who reported values of 20220 (seeds), 5250 (peel), and 4040 (pulp) mg GAE 100 g−1. That is, our values were lower than those reported by Omena et al. [2]. This could be a result of the extraction conditions and fruit maturation, for example. The authors extracted each sample three times using 95% ethanol as the solvent. Also, the extracts were dried. Thus, the results were expressed as mg 100 g−1 of dry extract and not mg 100 g−1 of dry sample, which helps to explain the differences found.
Regarding the antioxidant capacity, it was observed that all flours presented potential against the tested radicals. The antioxidant capacity from ABTS•+, DPPH•, and FRAP showed that FUP has the highest antioxidant potential (p < 0.05), showing a correlation with the TPC value (p < 0.05). This can be explained by the fact that umbu peel contains important bioactive compounds in its composition, such as polyphenols and carotenoids, which have great potential to neutralize free radicals, as well as vitamin C, known for its strong antioxidant power, as reported by Ribeiro et al. [3]. FSS presented the lowest value for TPC and antioxidant capacity among the evaluated samples (p < 0.05).
It is important to highlight that assessing antioxidant capacity using different methods is required, as they act by different mechanisms, such as neutralizing free radicals, chelating metals, and through oxidative reactions [48]. Therefore, this approach allows us to understand the antioxidant potential of the sample in a broader way.
According to Omena et al. [2], siriguela presented values for the fruit pulp regarding the TPC of 1350 mg GAE 100 g−1, and an antioxidant capacity of 30 µmol Trolox g−1 (ABTS•+). Umbu pulp showed values of 4040 mg GAE 100 g−1 regarding the TPC and 220 µmol Trolox g−1 (ABTS•+). For juçara, Inada et al. [49] found values for the TPC and antioxidant capacity of fruit pulp of 7500 mg GAE 100 g−1 and 1.004 µmol Fe2+ g−1 (FRAP), respectively. Thus, even if not as high in fruit pulp as reported above for total phenolic levels and antioxidant capacity, the tropical fruit waste flours can contribute to increasing the intake of antioxidants in the human diet.
In summary, based on the observed data, specific applications for the studied flours can be proposed. FUP, with its high total phenolic content and antioxidant capacity in all assays, shows great potential as a natural antioxidant ingredient in functional food formulations, such as cereal bars, bakery products, or beverages. FJC, despite being defatted, maintained a high lipid content and a predominance of oleic acid, suggesting its suitability as a lipid enrichment component for bakery products. FSP and FSS, distinguished by their high mineral content, especially potassium, calcium, and magnesium, can be incorporated into formulations aimed at mineral supplementation in bakery products, snack bars, or nutritional powders. These applications support the revaluation of waste from tropical fruit processing, offering nutritional, functional, and economic advantages.

4. Conclusions

The results showed that flours derived from processing residues of siriguela, umbu, and juçara possess relevant nutritional and functional characteristics that support their application in foods. Among the findings, the flours showed high potassium levels, especially FSP (1403.9 mg 100 g−1), FUP (1324.9 mg 100 g−1), and FSS (1256.2 mg 100 g−1). Furthermore, FSS was a notable source of calcium and magnesium, reaching 239.7 and 183.3 mg 100 g−1, respectively.
From a functional perspective, all samples exhibited antioxidant capacity, with FUP standing out with the highest values across all assays: TPC (1850 mg GAE 100 g−1), DPPH• (130 µmol Trolox g−1), ABTS•+ (131 µmol Trolox g−1), and FRAP (590 µmol Fe2+ g−1). Notably, FJC exhibited a high content of oleic acid (61.58%).
Thus, FUP flour can be proposed as a natural antioxidant ingredient for functional food formulations, while FJC flour may serve as a lipid-rich additive in bakery products or energy-dense foods. FSP and FSS flours, due to their high mineral content, may be incorporated into products aimed at mineral supplementation.
However, some limitations of this study should be considered. The samples were obtained from a single geographic region, which may restrict the generalization of the results. The health benefits inferred from antioxidant capacity assays require in vivo validation to confirm their bioefficacy. In addition, the bioactive compound profiles should be determined using high-resolution chromatographic methods.
In summary, the valorization of these underutilized fruit residues contributes to reducing food waste, adding value to agro-industrial chains and promoting sustainable food systems. This approach aligns with circular economy principles and advances the Sustainable Development Goals (SDGs) 2 and 12 of the 2030 Agenda.

Author Contributions

Conceptualization, L.O.R. and C.N.K.; methodology, L.O.R. and E.P.J.; formal analysis, M.F.d.S., B.P.d.F., J.S.d.F., and L.S.S.L.; investigation, A.A.N. and L.O.R.; resources, L.O.R. and E.P.J.; data curation, C.N.K., A.A.N., J.S.d.F., and L.S.S.L.; writing—original draft preparation, M.F.d.S. and B.P.d.F.; writing—review and editing, C.N.K. and E.P.J.; supervision, L.O.R. and E.P.J. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data used to support the findings of this study can be made available by the corresponding author upon request.

Acknowledgments

The authors acknowledge the support from the National Institute of Technology (INT) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and Embrapa Agroindústria de Alimentos for the samples provided.

Conflicts of Interest

The authors declare no conflicts of interest.

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Resources 14 00083 g001
Figure 1. Overall distribution of siriguela (Caatinga), umbu (Caatinga), and juçara (Atlantic Rainforest) fruits in Brazilian biomes. Source: From authors (adapted from IBGE).
Figure 1. Overall distribution of siriguela (Caatinga), umbu (Caatinga), and juçara (Atlantic Rainforest) fruits in Brazilian biomes. Source: From authors (adapted from IBGE).
Resources 14 00083 g001
Table 1. Proximate composition of tropical fruit waste flours.
Table 1. Proximate composition of tropical fruit waste flours.
Samples
FSSFSPFUSFUPFUCFJC
Lipids (%)0.35 ± 0.02 b0.88 ± 0.04 b1.13 ± 0.07 b1.08 ± 0.04 b0.67 ± 0.04 b10.63 ± 1.14 a
Moisture (%)15.70 ± 0.49 c21.05 ± 0.50 a9.43 ± 0.18 e14.31 ± 0.33 d17.69 ± 0.34 b9.74 ± 0.20 e
Ashes (%)2.11 ± 0.05 b,c4.17 ± 0.05 a1.09 ± 0.01 c3.35 ± 0.02 a,b2.58 ± 0.02 c2.07 ± 0.01 b,c
Proteins (%)24.01 ± 0.42 a,b17.17 ± 0.42 b17.68 ± 0.27 b25.50 ± 0.59 a,b25.04 ± 0.18 a,b30.89 ± 0.05 a
Carbohydrates (%)73.54 ± 2.63 a,b77.83 ± 2.77 a,b80.23 ± 1.74 a70.09 ± 3.78 b71.72 ± 1.07 a,b57.06 ± 0.56 c
Siriguela seed (FSS), siriguela peel (FSP), umbu seed (FUS), umbu peel (FUP), umbu pulp refine cake (FUC), and juçara pulp refine cake (FJC). Different lowercase letters in the same line indicate that the results are statistically different (p < 0.05). Results are expressed on a dry basis.
Table 2. Mineral contents of tropical fruit waste flours.
Table 2. Mineral contents of tropical fruit waste flours.
Minerals
(mg 100 g−1)		Samples
FSSFSPFUSFUPFUCFJC
Ca239.83 ± 1.87 a76.23 ± 1.33 e170.37 ± 1.52 d216.35 ± 1.12 b179.01 ± 0.01 c168.50 ± 0.82 d
Cu27.10 ± 12.25 a5.10 ± 0.02 b6.61 ± 0.23 a,b8.87 ± 0.14 a,b1.11 ± 0.04 b3.72 ± 0.16 b
K1257.18 ± 27.29 b1403.72 ± 31.56 a288.91 ± 3.25 e1326.72 ± 24.86 a,b924.48 ± 22.47 c558.06 ± 34.17 d
Mg183.49 ± 2.19 a147.25 ± 5.19 a,b177.73 ± 19.53 a145.53 ± 3.14 a,b79.13 ± 4.18 c129.07 ± 11.81 b
Mn0.26 ± 0.02 f0.97 ± 0.01 d0.75 ± 0.04 e3.62 ± 0.01 b1.55 ± 0.01 c13.68 ± 0.05 a
Ni0.81 ± 0.21 a,b0.76 ± 0.00 b1.15 ± 0.08 a0.91 ± 0.15 a,b1.05 ± 0.01 a,b0.98 ± 0.01 a,b
Na6.44 ± 0.37 a7.57 ± 0.11 a2.78 ± 0.14 b1.49 ± 0.72 b,c0.88 ± 0.47 c2.80 ± 0.47 b
Siriguela seed (FSS), siriguela peel (FSP), umbu seed (FUS), umbu peel (FUP), umbu pulp refine cake (FUC), and juçara pulp refine cake (FJC). Different lowercase letters in the same line indicate that the results are statistically different (p < 0.05). Results are expressed on a dry basis.
Table 3. Fatty acids of tropical fruit waste flours.
Table 3. Fatty acids of tropical fruit waste flours.
Fatty Acids (%)Samples
FSSFSPFUSFUPFUCFJC
(C12:0) Lauric acid1.02 ± 0.24-----
(C14:0) Myristic acid3.11 ± 0.0810.41 ± 0.220.39 ± 0.012.27 ± 0.042.88 ± 0.00-
(C16:0) Palmitic acid29.34 ± 1.0469.31 ± 1.0123.35 ± 0.0942.30 ± 0.0945.68 ± 0.3520.19 ± 0.01
(C16:1) Palmitoleic acid-----0.62 ± 0.01
(C17:0) Margaric acid1.49 ± 0.06-----
(C18:0) Stearic acid7.27 ± 0.118.95 ± 0.2311.79 ± 0.087.19 ± 0.026.14 ± 0.092.51 ± 0.02
(C18:1) Oleic acid19.42 ± 0.27-32.63 ± 0.0348.24 ± 0.0345.30 ± 0.2661.58 ± 0.02
(C18:2) Linoleic acid24.36 ± 0.2411.33 ± 1.0031.85 ± 0.03--15.09 ± 0.02
(C18:3) Linolenic acid10.98 ± 0.70-----
(C20:1) Gadolinic acid1.77 ± 0.18-----
(C22:0) Behenic Acid1.19 ± 0.33-----
Siriguela seed (FSS), siriguela peel (FSP), umbu seed (FUS), umbu peel (FUP), umbu pulp refine cake (FUC), and juçara pulp refine cake (FJC). Results are expressed on a dry basis.
Table 4. Total phenolic content and antioxidant capacity of tropical fruit waste flours.
Table 4. Total phenolic content and antioxidant capacity of tropical fruit waste flours.
AssaysSamples
FSSFSPFUSFUPFUCFJC
TPC
(mg GAE 100 g−1)		249.11 ± 1.86 f1491.84 ± 6.11 b369.04 ± 2.48 e1852.81 ± 10.99 a1058.81 ± 14.68 c774.66 ± 5.44 d
DPPH•
(µmol Trolox g−1)		9.79 ± 0.08 f106.70 ± 1.80 b19.92 ± 0.21 e129.80 ± 1.02 a61.52 ± 0.49 c26.90 ± 0.42 d
ABTS•+
(µmol Trolox g−1)		12.69 ± 0.20 e12.24 ± 0.74 e18.76 ± 0.36 d130.99 ± 2.78 a63.14 ± 1.01 b33.81 ± 1.49 c
FRAP
(µmol Fe2+ g−1)		39.40 ± 1.18 f311.51 ± 1.54 c82.38 ± 0.40 e591.10 ± 2.73 a391.10 ± 2.73 b119.78 ± 1.20 d
Siriguela seed (FSS), siriguela peel (FSP), umbu seed (FUS), umbu peel (FUP), umbu pulp refine cake (FUC), and juçara pulp refine cake (FJC). Different lowercase letters in the same line indicate that the results are statistically different (p < 0.05). Results are expressed on a dry basis.
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dos Santos, M.F.; de Freitas, B.P.; de Freitas, J.S.; Lage, L.S.S.; Novo, A.A.; Kunigami, C.N.; Jung, E.P.; Ribeiro, L.O. Tropical Fruit Wastes: Physicochemical Characterization, Fatty Acid Profile and Antioxidant Capacity. Resources 2025, 14, 83. https://doi.org/10.3390/resources14050083

AMA Style

dos Santos MF, de Freitas BP, de Freitas JS, Lage LSS, Novo AA, Kunigami CN, Jung EP, Ribeiro LO. Tropical Fruit Wastes: Physicochemical Characterization, Fatty Acid Profile and Antioxidant Capacity. Resources. 2025; 14(5):83. https://doi.org/10.3390/resources14050083

Chicago/Turabian Style

dos Santos, Mariana Ferreira, Beatriz Pereira de Freitas, Jaqueline Souza de Freitas, Luane Souza Silva Lage, Alex Aguiar Novo, Claudete Norie Kunigami, Eliane Przytyk Jung, and Leilson Oliveira Ribeiro. 2025. "Tropical Fruit Wastes: Physicochemical Characterization, Fatty Acid Profile and Antioxidant Capacity" Resources 14, no. 5: 83. https://doi.org/10.3390/resources14050083

APA Style

dos Santos, M. F., de Freitas, B. P., de Freitas, J. S., Lage, L. S. S., Novo, A. A., Kunigami, C. N., Jung, E. P., & Ribeiro, L. O. (2025). Tropical Fruit Wastes: Physicochemical Characterization, Fatty Acid Profile and Antioxidant Capacity. Resources, 14(5), 83. https://doi.org/10.3390/resources14050083

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