2.1. Bioactive Compounds Content
Carotenoids are an important group of bioactive compounds, which are ascribed a broad spectrum of health-promoting effects. So far research has proved high diversity in carotenoid concentration in different
Cucurbitaceae species and cultivars.
Table 1 shows the content of individual carotenoids in the pumpkin cultivars under study. We chose these carotenoids, which are most often discussed in the literature in terms of the pumpkin chemical composition. The carotenoids under analysis (zeaxanthin, lutein, and β-carotene) were found in all the cultivars. There were statistically significant differences between all the cultivars in the content of zeaxanthin and lutein. The highest content of these carotenoids was found in the ‘Melonowa Żółta’ (zeaxanthin: 192.5 µg/g, lutein: 388.79 µg/g) and ‘Green Hubbard’ cultivars (zeaxanthin: 103.87 µg/g, lutein: 239.38 µg/g). The lowest content of zeaxanthin was found in the ‘Buttercup’ cultivar (19.57 µg/g), whereas the lowest content of lutein was measured in the ‘Porcelain Doll’ cultivar (87.2 µg/g). The highest content of β-carotene was found in the ‘Melonowa Żółta’ (115.29 µg/g) and ‘Jumbo Ping Banana’ cultivars (102.45 µg/g), whereas the lowest content was measured in the ‘Porcelain Doll’ (38.67 µg/g), ‘Hokkaido’ (40.10 µg/g) ‘Marina di Chioggia’ (47.17 µg/g), and ‘Jarrahdale’ cultivars (49.38 µg/g). Lutein was the predominant carotenoid in all the cultivars. The results were used to calculate the retinol equivalent—a measure of the provitamin A content. The highest content of provitamin A was found in the ‘Melonowa Żółta’ (67.66 µg/g), ‘Green Hubbard’ (43.54 µg/g) and ‘Jumbo Pink Banana’ cultivars (41.68 µg/g), whereas the lowest content was measured in the ‘Porcelain Doll’ (15.9 µg/g) and ‘Marina di Chioggia’ cultivars (22.2 µg/g).
Seleim et al. analyzed the content of β-carotene in the ‘Faraskour’, ’El-Zarka’ and ‘Kafr El-Battikh-2’ cultivars of the
C. maxima Duchesne species and proved significant differences. The researchers noted the highest β-carotene concentration in the ‘Kafr El-Battikh-2’ cultivar (3313.46 µg/100 g). However, it was lower than the concentration measured in the cultivars analyzed in our study. Norshazila et al. [
22] studied cultivars of the
Cucurbita moschata species and observed that β-carotene was the predominant carotenoid. The cultivars also contained small amounts of lutein and α-carotene. We made different observations in our study, where lutein was the most abundant carotenoid. The different proportions of lutein: beta-carotene may be influenced mainly by two factors. The first is the type of variety. For example, in the ‘Buttercup’ variety the ratio of lutein, beta-carotene is close to 1:1. In turn for the ‘Melonowa Żółta’ variety, the ratio is over 3:1. Secondly, the proportion of lutein: beta-carotene can also be affected by the growing conditions, the maturation period, and the storage time of the pumpkin. It seems that during the growth and maturation of the plant, as well as the storage of fruit, the conversion of individual carotenoids may proceed at different rates. As Jaswir et al. showed that during pumpkin fruits storage, the concentration of lutein increases, while beta-carotene decreases. The changes in carotenoids also depend on sun exposure, temperature, water availability, and soil composition. It is believed that the highest concentration of carotenoids occurs in the first stages of fruit formation. After their maturation, the content of these compounds is significantly reduced. However, the directions of these changes are not examined in detail and may constitute an interesting and new purpose of research [
26]. Seven cultivars of three species (
C. maxima Duchesne,
C. moschata,
C. pepo L.) were characterized by high diversity in the content of β-carotene. The highest content of carotenoids was found in the ‘Kroshka’ (6.59 mg/100 g,
C. maxima Duchesne), ‘Zemcuzina’ (5.30 mg/100 g,
C. moschata) and ‘Bambino’ cultivars (4.50 mg/100 g,
C. maxima Duchesne), whereas the lowest content was measured in the ‘Zalushka’ (0.30 mg/100 g,
C. pepo L) and ‘Kustovaja’ cultivars (0.58 mg/100 g,
C. pepo L). The β-carotene concentration in the ‘Kroshka’ and ‘Zemcuzina’ cultivars was similar to the content measured in cultivars analyzed by other researchers, e.g., ‘Gomez’, ‘Blue Kuri’, ‘Jarrahdale’ [
20]. Kulaitienė et al. [
21] analyzed the ‘Justynka F1’, ‘Karowita’, ‘Amazonka’ cultivars of the
C. maxima Duchesne species and found that lutein and zeaxanthin were the most abundant carotenoids (7.96–12.31 mg/100 g).
There were similar results in our study, where lutein and zeaxanthin were the predominant carotenoids [
21]. The content of β-carotene ranged from 1.86 to 2.42 mg/100 g and it was lower than the content of this carotenoid measured in the cultivars analyzed in our study. The samples also contained lycopene (0.72–0.81 mg/100 g). Azevedo-Meleiro et al. [
19] found different carotenoids, depending on the pumpkin species and cultivar (Azevedo-Meleiro and Rodriguez-Amaya, 2007). The ‘Menina Brasileira’ and ‘Goianinha’ cultivars (
C. moschata) were characterized by high content of α-carotene (23.8–26.8 µg/g) as well as β-carotene (56.7–66.7 µg/g), like the ‘Jarrahdale’ (49.38 µg/g), ‘Gomez’ (51.28 µg/g) and ‘Blue Kuri’ (56.03 µg/g) cultivars analyzed in our study. There were smaller amounts of lutein and neoxanthin. The ‘Exposicao’ cultivar had the highest content of violaxanthin (20.6 µg/g). The ‘Tetsukabuto’ cultivar (
C. maxima Duchesne
× C. moschata hybrid) contained the most lutein (56.6 µg/g), but its content was lower than the content of this carotenoid measured in all the cultivars analyzed in our study (87.2–388 µg/g).
Table 1 shows the content of tocopherols. The pumpkin cultivars analyzed in our study contained two forms: α- and γ-tocopherol, but none of them contained δ- or β-tocopherol. The ‘Melonowa Żółta’ cultivar had the highest content of α-tocopherol (8.89 mg/100 g). The ‘Gomez’ and ‘Marina di Chioggia’ cultivars also contained high amounts of this compound (4.94 mg/100 g and 4.39 mg/100 g, respectively). The lowest concentration of α-tocopherol was measured in the following cultivars: ‘Jumbo Pink Banana’ (1.55 mg/100 g), ‘Hokkaido’ (2.82 mg/100 g) and ‘Jarrahdale’ (2.85 mg/100 g). Similarly, to the content of α-tocopherol, the ‘Melonowa Żółta’ cultivar was characterized by the highest concentration of γ-tocopherol (17.32 mg/100 g). The lowest concentration of γ-tocopherol was measured in the following cultivars: Jarrahdale” (0.97 mg/100 g), ‘Porcelain Doll’ (1.6 mg/100 g) and ‘Bambino’ (2.8 mg/100 g). The contents of individual tocopherols were used to calculate the α-tocopherol equivalent. The highest values of the α-tocopherol equivalent were measured in two cultivars, i.e., ‘Melonowa Żółta’ (10.62 mg/100 g) and ‘Hokkaido’ (5.29 mg/100 g). The lowest values of the α-tocopherol equivalent were measured in the ‘Jumbo Pink Banana’ (2.19 mg/100 g) and ‘Jarrahdale’ cultivars (2.94 mg/100 g).
Like in our study, Seleim et al. [
23] observed that the pulp of pumpkins of the
C. maxima Duchesne species contained α-tocopherol. The authors of the study found that the ‘El Zarka’ cultivar had the highest content of this component (1547.35 µg/100 g). However, it was smaller than the content of α-tocopherol measured in all the cultivars analyzed in our study and it was very similar to the content measured in the ‘Jumbo Pink Banana’ cultivar (1.55 mg/100 g). The lowest content of α-tocopherol was found in the ‘Kafr El-Battikh-2’ cultivar (774.52 µg/100 g). The statistical analysis also confirmed that the content of this component in pumpkin pulp was significantly greater than in pumpkin skin. There are no data on the content of individual tocopherols in pumpkin pulp. Stevenson et al. [
27] characterized the profile of these compounds in oil extracted from pumpkin seeds. They observed the highest content of α-tocopherol in the following cultivars: ‘Warren Scarlet’ (75.1 µg/g), ‘Big Max’ (61.3 µg/g) and ‘Zapallo Macre’ (57.6 µg/g). Our study showed that the pulp of the ‘Melonowa Żółta’ cultivar was the most abundant in α-tocopherol (8.89 mg/100 g). The other cultivars contained smaller amounts of this compound (1.55–4.94 mg/100 g) [
27]. There was low content of α-tocopherol in pumpkin seed oil extracted from the following cultivars: ‘Delica’ (27.1 µg/g), ‘Yogorou’ (29.6 µg/g) and ‘Cha Cha’ (29.9 µg/g). As far as γ-tocopherol is concerned, the ‘Big Max’ (492.8 µg/g), ‘Rouge Vif d’Etampes’ (285.7 µg/g) and ‘Yogorou’ cultivars (227.0 µg/g) were the most abundant in this compound. There was considerable diversity between the cultivars in their content of δ-tocopherol, which ranged from 35.3 to 1109.7 µg/g. The highest content of this compound was found in the ‘Kurijiman’ cultivar. We did not find δ-tocopherol in the pumpkin pulp in our study. Ryan et al. compared the content of tocopherols in different seeds, cereals, and leguminous plants [
28]. They proved that pumpkin seeds contained more α-tocopherol (0.9 mg/100 g) than butter beans (0.7 mg/100 g), spelt (0.6 mg/100 g), buckwheat (0.1 mg/100 g), maize (0.2 mg/100 g), millet (0.2 mg/100 g), linseed (0.1 mg/100 g), mustard (0.6 mg/100 g), and poppy (0.2 mg/100 g). Apart from that, the research proved that pumpkin seeds contained the largest amounts of β + γ-tocopherol (14.8 mg/100 g).
The analysis of the content of phenolic acids confirmed high diversity between the pumpkin cultivars (
Table 2). This work focuses on the determination of the selected phenolic compounds content. For the study, phenolic acids and flavonols, which are most often analyzed in plant-derived products and discussed in literature were selected. The ‘Melonowa Żółta’ cultivar had the highest content of gallic acid (18.90 mg/100 g) and protocatechuic acid (47.89 mg/100 g). The highest content of
p-coumaric acid was found in the ‘Hokkaido’ cultivar (3.47 mg/100 g), and the highest content of ferulic acid was found in the ‘Melonowa Żółta’ cultivar (33.50 mg/100 g). The lowest content of 4-hydroxybenzoic acid (4.95 mg/100 g) and ferulic acid (6.87 mg/100 g) was found in the ‘Green Hubbard’ cultivar. The ‘Bambino’ cultivar was characterized by the lowest concentration of gallic acid (2.58 mg/100 g) and protocatechuic acid (5.09 mg/100 g). Apart from that, it did not contain phenolic acids or
p-coumaric acid, which was also the case with the ‘Gomez’ cultivar. The ‘Jarrahdale’, ‘Buttercup’, ‘Porcelain Doll’, and ‘Gomez’ cultivars did not contain any sinapic acid.
The analysis of the samples showed diversified content of flavonols (
Table 2). All the cultivars contained rutin. The highest content of this compound was found in the ‘Bambino’ cultivar (51.92 mg/100 g), whereas the lowest content was measured in the ‘Marina di Chioggia’ cultivar (5.09 mg/100 g). The ‘Bambino’ cultivar was also characterized by the highest concentration of astragalin (28.03 mg/100 g) and myricetin (9.04 mg/100 g). Some pumpkin cultivars did not contain kaempferol (‘Bambino’, ‘Porcelain Doll’, ‘Buttercup’, ‘Jarrahdale’), astragalin (‘Hokkaido’, ‘Gomez’, ‘Buttercup’, ‘Jumbo Pink Banana’, ‘Green Hubbard’), myricetin (‘Gomez’, ‘Melonowa Żółta’, ‘Jarrahdale’, ‘Marina di Chioggia’), or isoquercetin (‘Buttercup’, ‘Green Hubbard’). The ‘Jumbo Pink Banana’ cultivar did not contain quercetin. There are few publications on the profile of phenolic compounds in pumpkin fruit.
Dragovic-Uzelac et al. observed chlorogenic acid (15.59–23.05 mg/kg) in all pumpkin cultivars under study [
29]. This content was similar to the one measured in the cultivars analyzed in our study: ‘Gomez’ (1.39 mg/100 g), ‘Jarrahdale’ (1.94 mg/100 g) and ‘Marina di Chioggia’ (2.45 mg/100 g). All the cultivars contained syringic acid (19.56–27.13 mg/kg) (Dragovic-Uzelac et al., 2005). Two cultivars, i.e., ‘Turkinja’ (
C. maxima Duchesne) and ‘Argenta’ (
C. moschata) contained small amounts of caffeic acid (1.05 and 2.33 mg/kg, respectively), which were smaller than the content of caffeic acid measured in all the cultivars analyzed in our experiment. Only the ‘Argenta’ cultivar contained
p-coumaric acid (1.27 mg/kg). This acid was identified in nearly all the cultivars in our study, except ‘Bambino’ and ‘Gomez’. Zdunic et al. identified eight polyphenolic compounds in pumpkin fruit (
C. maxima Duchesne): protocatechuic acid, chlorogenic acid, salicylic acid, p-hydroxybenzoic acid,
p-coumaric acid, hesperidin, vanillin, and eriodictyol-7-neohesperidoside [
30]. The researchers found that the total content of polyphenols amounted to 905.9 µg/g. Biesiada et al. [
31] measured the highest content of phenolic compounds in the following pumpkin cultivars: ‘Amazonka’ (
C. maxima Duchesne, 29.82 mg/100 g), ‘Jet F1’ (
C. pepo L., 24.90 mg/100 g), and ‘Junona’ (
C. pepo L, 23.10 mg/100 g). The smallest content of these compounds was identified in the ‘Melonowa Żółta’ (
C. maxima Duchesne, 14.75 mg/100 g), ‘Ambar’ (
C. maxima Duchesne, 18.05 mg/100 g) and ‘Pyza’ cultivars (
C. pepo L, 18.18 mg/100 g) [
31]. Telesiński et al. observed that there were statistically significant differences (
p < 0.05) in the total content of polyphenols and flavonoids between pumpkin cultivars (‘Kurinishiki F1’, ‘Butternut Rugosa’, ‘Muscade de Provence’, ‘Muskatna’) of the
C. moschata species [
32]. The authors proved that the ‘Kurinishiki F1’ cultivar had the highest content of total polyphenols (998.63 mg/kg), whereas the ‘Muscade de Provence’ cultivar contained the smallest amount of these compounds (737.02 mg/kg). The ‘Kurinishiki F1’ cultivar also had the highest content of total flavonoids (725.29 mg/kg). The lowest content of total flavonoids was measured in the ‘Butternut Rugosa’ cultivar (548.36 mg/kg). Altemimi et al. found that pumpkin fruit contained ellagic acid (2.96 µg/g) and myricetin (2.95 µg/g) [
33].
The research results show that there was considerable diversity between the cultivars in their content of minerals (
Table 3). The highest content of potassium was found in the ‘Bambino’ cultivar (9965.7 mg/100 g). The concentration of this mineral was slightly different in the ‘Jumbo Pink Banana’ (8306.43 mg/100 g) and ‘Marina di Chioggia’ cultivars (7441.2 mg/100 g). The following cultivars were the most abundant in calcium: ‘Melonowa Żółta’ (264.89 mg/100 g), ‘Marina di Chioggia’ (241.91 mg/100 g), ‘Jumbo Pink Banana’ (228.6 mg/100 g) and ‘Porcelain Doll’ (217.01 mg/100 g). The smallest amount of calcium was found in the ‘Hokkaido’ cultivar (92.12 mg/100 g). There was a high content of magnesium measured in the ‘Bambino’ (135.35 mg/100 g) and ‘Marina di Chioggia’ cultivars (127.91 mg/100 g). The largest amounts of copper and manganese were measured in the Bambino’ cultivar (0.59 mg/100 g and 0.86 mg/100 g, respectively). The highest concentrations of iron and zinc were measured in the ‘Melonowa Żółta’ cultivar (2.67 mg/100 g and 1.33 mg/100 g, respectively). The content of sodium in the pumpkin cultivars ranged from 226.16 to 370.40 mg/100 g. The highest content was found in the ‘Porcelain Doll’ cultivar, whereas the lowest content was measured in the ‘Buttercup’ cultivar. The data provided by the United States Department of Agriculture Food Composition Databases (USDA, 2015) indicate that potassium is the most abundant mineral in pumpkin. This statement is in agreement with the results of our study. The content of potassium varied between the cultivars as follows: ‘Butternut’ (352 mg/100 g), ‘Hubbard’ (320 mg/100 g), ‘Spaghetti’ (108 mg/100 g) [
34]. Blessing et al. also noted low amounts of iron, calcium, and phosphorus in their study [
35]. The contents of these elements ranged from 0.0069 to 0.136 mg/100 g (iron), from 0.461 to 0.610 mg/100 g (calcium), and from 0.145 to 1.093 mg/100 g (phosphorus) [
35]. Elinge et al. analyzed the content of minerals in pumpkin seeds and found that like in pumpkin pulp, potassium was the most abundant element (237.24 mg/100 g) [
36]. Apart from that, pumpkin seeds contained relatively large amounts of sodium (170.35 mg/100 g), magnesium (67.41 mg/100 g) and zinc (14.14 mg/100 g). They also contained small amounts of iron (3.75 mg/100 g), calcium (9.78 mg/100 g) and manganese (0.06 mg/100 g).
There were statistically significant differences in the content of vitamins between the pumpkin cultivars (
Table 3). The highest content of vitamin C was found in the ‘Melonowa Żółta’ cultivar (84.23 mg/100 g). There were slightly smaller amounts of this vitamin in the ‘Jarrahdale’ (80.94 mg/100 g) and ‘Porcelain Doll’ cultivars (71.84 mg/100 g). The lowest concentration of vitamin C was measured in the ‘Hokkaido’ (49.16 mg/100 g) and ‘Buttercup’ cultivars (49.06 mg/100 g). The highest amounts of thiamine were found in the ‘Hokkaido’ (0.6 mg/100 g), ‘Jumbo Pink Banana’ (0.54 mg/100 g) and ‘Jarrahdale’ cultivars (0.52 mg/100 g). The smallest amount of vitamin B1 was measured in the ‘Blue Kuri’ cultivar (0.15 mg/100 g). There was only one form of folates in the samples, i.e., 5-methyltetrahydrofolate (5CH3FH4). There was no tetrahydrofolate (FH4) or 5-formyltetrahydrofolic acid (5-HCO-FH4). The highest concentration of folates was measured in the ‘Marina di Chioggia’ (65.04 ± 0.88 µg/100 g), ‘Bambino’ (52.10 µg/100 g) and ‘Melonowa Żółta’ cultivars (50.99 µg/100 g). The lowest content of these compounds was found in the ‘Jarrahdale’ (20.44 µg/100 g) and ‘Hokkaido’ cultivars (22.46 µg/100 g). The content of vitamin C in different pumpkin cultivars was analyzed in a few studies. Assous et al. [
37] found that the pumpkin of the
C. moschata species contained L-ascorbic acid (33.81 mg/100 g of fresh weight). The content was smaller than in our study (49.16–80.94 mg/100 g of dry mass). Offor et al. noted a low concentration of this compound (4.93 mg/100 g), which was similar to that of cabbage (4.40 mg/100 g) [
38]. Nawirska-Olszańska et al. observed that the content of vitamin C in the ‘Karowita’ pumpkin cultivar (
C. maxima Duchesne) amounted to 14.12 mg/100 g [
39]. Biesiada et al. [
31] observed considerable diversity between the cultivars in their content of ascorbic acid. The highest concentration of this compound was measured in the following cultivars: ‘Ambar’ (42.48 mg/100 g), ‘Amazonka’ (34.97 mg/100 g), ‘Karowita’ (29.18 mg/100 g), and ‘Bambino’ (26.05 mg/100 g). The ‘Jet F1’, ‘Junona’ and ‘Miranda’ cultivars contained small amounts of ascorbic acid, i.e., 10.80, 9.22, and 5.54 mg/100 g, respectively. The study also proved that the content of this compound decreased as the storage time increased. After 90 days of storage, the concentration of vitamin C dropped by about 40–50%. Sharma and Rao [
40] proved that the content of vitamin C differed according to the phase of maturity.
The longer the maturity period was, the more ascorbic acid was found. The content of ascorbic acid in young fruits was 4.30 mg/100 g, whereas fully mature fruits contained 15.00 mg/100 g. The data provided by the USDA [
34] also indicated differences between cultivars in the content of vitamin C. The content of vitamin C in the ‘Butternut’ cultivar amounted to 21.0 mg/100 g. The concentration of ascorbic acid in other cultivars was lower, i.e., 11.0 mg/100 g (‘Acorn’, ‘Hubbard’) and 2.1 mg/100 g (‘Spaghetti’). The highest content of thiamine was measured in the ‘Acorn’ (0.140 mg/100 g) and ‘Butternut’ cultivars (0.100 mg/100 g). There were smaller amounts of vitamin B1 in the ‘Hubbard’ (0.070 mg/100 g) and ‘Spaghetti’ cultivars (0.037 mg/100 g). The largest number of folates was found in the ‘Butternut’ cultivar (27 µg/100 g), whereas the smallest amount was noted in the ‘Spaghetti’ cultivar (12 µg/100 g) [
34].