The “Kurugua” (Sicana odorifera) is a native fruit that demonstrates attractive nutritional, coloring, flavoring, and antioxidant properties. The main by-products from the processing and consumption of kurugua fruit are epicarp and seeds.
1. Introduction
Current global challenges such as food safety, climate change, poverty, and health have a direct impact on the realization of the right to adequate food.
Each challenge is negatively affected by food loss and waste, and developing sustainable global consumption and production systems is necessary
[1]. Food by-products management has been recognized by the circular economy as one of the principal keys to reducing environmental and economic problems
[2]. The recovery of bioactive molecules from the bio-residues or industrial by-products of fruits and vegetables has potential uses in the industrial sector. The processed fruits’ waste can be re-used and can lead to high-added-value products such as functional food ingredients, food coloring, novel pharmaceuticals for alternative therapies, and disease prevention
[3].
The interest of the food and cosmetic industries for products from medicinal plants has increased, and it is necessary to broaden the investigation of natural sources, including fruit waste such as seeds
[4]. The literature on value addition to fruit-derived waste is diverse. Overall, the extraction of bioactive compounds from fruit processing waste and the application of green methods for the valorization of these sources opens new avenues for food, chemical, and pharmaceutical industries, which have high potential, especially where availability of waste from fruit processing is abundant
[5]. This current trend has led researchers to explore several methods to recycle waste for manufacturing new products, emphasizing green chemistry and greener processes. Melon by-products have been used as new feedstock for proteins’ recovery, employing biological precipitation; the cucumisin was separated from these by-products with carrageenan, an environmentally friendly process for the industries, which avoids solvents
[2]. A novel bio-refinery approach would seek to produce a wider range of valuable chemicals from fruit processing waste. For instance, the residue from most of extraction processes could further be a renewable source of biofuels, and polyphenols may be useful as food products and pharmaceuticals preservatives
[5]. Quercetin and quercetin-3-glycoside are being isolated from the fruit seed waste of papaya seeds. Grape seeds are rich in polyphenols, resveratrol, quercetin, and other flavonoids, which are confirmed to impart cardiovascular protective effects
[6]. Natural flavoring agents such as limonene, pectin extraction from fruit peels, and the growing demand for natural products in the food and beverage industry show the scope of technological progress in this sector
[5].
The year 2021 has been declared as the International Year of Fruits and Vegetables, encouraging populations to increase their consumption, seeking for the reduction of waste within the framework of Sustainable Food and Food Security, and valuing the potential of by-products, such as the seeds, not used in the industrial processing of fruits
[7]. It has been reported that the processing of fruits or vegetables belonging to genera of Cucurbitaceae such as Cucumis (melon), Cucurbita (pumpkin), and Citrullus (watermelon) produce large amounts of waste and by-products, among them being discarded seeds. These by-products are an inexpensive raw material and a reliable source of bioactive phytochemicals, including antioxidant-rich polyphenols, tannins, flavonoids, and other components nutritionally important as essential fatty acids, dietary fiber, and minerals
[8]. Cucurbitaceae seeds such as pumpkin, watermelon, and melon contain many nutrients such as protein, fibers, and minerals, highlighting their potential as a dietary supplement and a source of nutraceuticals; these potential applications contribute to the valorization of processing fruits by-products
[9]. Pumpkin seed oil has been promoted as a new functional food and it is already produced and marketed as a healthy, edible cooking oil in some countries
[10].
Sicana odorifera, or “Kurugua” is from the Cucurbitaceae family, found natively in the Latin American region, where it is widely used in folk medicine for various ailments; however, it is a species that has been hardly studied
[4]. In the case of
S. odorifera fruits, although it is not a fruit for mass consumption, it is precisely the lack of a market for its bio-waste that has limited its integral use, including the parts that represent the greatest loss, such as the peels (pericarp) and seeds (endocarp). Its crop is a strategy to increase food security and a family farming source
[11]. The fruit itself has been used as a repellent, clothing perfume, or hot infusion with therapeutic uses in alternative medicine, inserted in popular wisdom at the Latin American level
[12]. However, knowledge about the validated bioactive properties of these inedible parts (peel and seeds) is still limited. The black kurugua fruit (
Sicana odorifera Naudim Vell.) is considered an exotic fruit; the large fruit contains 6% of its weight as seeds, in numbers from 900 to 1100 seeds per fruit. The epicarp of the fruit is intense purple, 30 to 60 cm in longitudinal diameter, and 9 to 15 cm in transverse diameter, and the pulp or mesocarp is approximately 2 cm thick, with oval seeds arranged in a row in the membranous endocarp. This bio-residue could have a great economic impact for the industrial processing of the pulp in the value chain, being, together with the peel, its main waste
[11]. Studies on the use of its peel as a potential source of natural colorants have been published
[13]. In
S. odorifera seeds, insect repellent activity has been reported with aromatic properties. Triterpenes and flavonoids, including karounidiol dibenzoate, Cucurbita-5,23-diene-3h,25-diol, taxifolin, and quercetin were isolated from them
[14]. The sweet aroma of the fruit, as well as the intense color of the peel, has been characterized
[15,16,17][15][16][17]. The aromatic spectrum of the pulp is characteristic and the compounds responsible for the flavor were described (94.8% free volatile; with 61.1% as aliphatic alcohols
[16], whereas studies on the composition of the seeds and the bioactivity of its components are still scarce. The phytochemical profile of the pulp is promising as a source of antioxidant compounds
[18]. Regarding the peels, flavonols and anthocyanins with antioxidant activity have been described
[17]. There are several animal models to evaluate the hepatoprotective effect of natural products; one of the effects is the model of liver damage induced by acetaminophen (APAP), a drug widely used as an antipyretic and analgesic, which in high doses can produce necrosis and insufficiency acute hepatica
[19,20,21][19][20][21].
Liver disease is one of the leading causes of death in the world, and there is still an urgent demand for effective and safe hepatoprotective agents, despite advances in modern pharmacology
[22]. The hepatoxicity of APAP is primarily caused by metabolism by cytochrome P450 to produce N-acetyl-p-benzoquinone imine (NAPQI), which can react with glutathione (GSH) to cause oxidative stress that can trigger the mitochondrial signal pathway and cause cell damage
[23]. On the other hand, the solid evidence that demonstrates the multiple healthy effects of-3 PUFA for humans has stimulated the consumption of ω-3 PUFA. Its supply is limited, and is focused mainly on the consumption of fatty fish or bluefish and nutritional supplements based on fish oils or microalgae, thus hindering the increase in the consumption of these fatty acids in the western population. The incipient industrial production of vegetable oils rich in ALA in some Latin American countries is a novel and innovative alternative to increase the consumption and production of ω-3 fatty acids, specifically from its metabolic precursor, ALA
[24,25][24][25]. Currently, plant residues in the form of
S. odorifera seeds represent an opportunity to explore their properties and to give an integral use to industrialized fruits, following the current trend of generating more sustainable alternative processes, and the interest in the sustainable production of bioactive molecules
[3]. The aim of this work was to describe the proximate composition, minerals and antioxidant activity of
S. odorifera seeds and their fatty acids profile as well as the profile of polyphenol compounds, acute toxicity, behavior and hepatoprotective effect in mice of the methanolic extract, to explore their nutritional and nutraceutical potential in order to promote the use of this bio-residue.
2. Seeds Composition
2.1. Proximate and Minerals Composition
The results of the physical properties, proximate composition, minerals, and caloric value of the pulp and seeds of
S. odorifera fruits are shown in
Table 1. The mature fruits show an oblong shape, dark purple color in the epicarp (peel), and orange color in the mesocarp (pulp). The mesocarp had a more intense lightness color than that of the seeds. The seeds were bicolor, both brown and beige. The main components of the seeds were lipids and dietary fiber, whereas the mesocarp showed more water and total carbohydrate. Thus, their caloric value was higher than that of the pulp. On the mineral composition of the seeds, potassium, was predominant, followed by magnesium and calcium, while zinc and calcium were major in the pulp (
Table 1).
Table 1. Sicana odorifera seeds and mesocarp physical characterization, proximate and minerals composition.
Parameter |
Mesocarp (Fresh Weight) |
Seeds (Dry Base) |
Weight (g) |
1970 ± 51 |
0.11 ± 0.01 |
Color |
L* = 66.00 ± 2.45 a* = 11.71 ± 3.28 b* = 69.43 ± 2.32 |
L* = 34.80 ± 10.44 a* = 4.50 ± 5.52 b* = 8.70 ± 3.07 |
Longitudinal diameter (cm) |
26.90 ± 1.4 |
1.58 ± 0.12 |
Transverse diameter (cm) |
10.42 ± 0.7 |
0.80 ± 0.04 |
Water (g/100 g) |
86.70 ± 0.4 |
10.06 ± 0.30 |
Total lipids (g/100 g) |
1.31 ± 0.02 |
35.51 ± 0.40 |
Ash (g/100 g) |
0.13 ± 0.01 |
2.55 ± 0.10 |
Total protein (g/100 g) |
1.07 ± 0.08 |
18.05 ± 0.56 |
Total carbohydrate (g/100 g) |
7.35 ± 0.31 |
2.80 ± 0.06 |
Dietary fiber (g/100 g) |
3.11 ± 0.00 |
34.67 ± 0.31 |
Caloric value (Kcal/100 g) |
45.5 ± 5 |
403 ± 5 |
Fe (mg/100 g) |
0.35 ± 0.06 |
6.35 ± 0.69 |
Mn (mg/100 g) |
0.55 ± 0.02 |
1.82 ± 0.10 |
Cu (mg/100 g) |
0.25 ± 0.02 |
0.69 ± 0.09 |
Zn (mg/100 g) |
42.31 ± 0.05 |
2.31 ± 0.09 |
Mg (mg/100 g) |
5.16 ± 0.07 |
177.00 ± 4.66 |
Ca (mg/100 g) |
29.61 ± 2.35 |
124.98 ± 9.17 |
Na (mg/100 g) |
4.27 ± 0.54 |
29.51 ± 1.27 |
K (mg/100 g) |
Nd |
784.05 ± 52.40 |