3.1. Color and Content of β-Carotene and α-Carotene in Winter Squash
The content of β-carotene and α-carotene, in raw and cooked pulp increased with commercial fruit maturity. Statistical differences were found of both α-carotene and β-carotene, as well as the preparation form (
Table 1). Cooking resulted in a reduction of β-carotene (
p = 0.0016) and α-carotene (
p = 0.0004). The content of β-carotene significantly dropped (33.4%) after cooking only for raw immature fruits. However, significant reductions in α-carotene content were observed after cooking immature (40.2%) and mature (34.5%) fruit pulps (
Table 1). No significant interaction effect was found between the form of preparation (raw
vs. cooked) and the ripeness of the fruit for both carotenes (
Table 1).
Table 1.
Total content of β-carotene and α-carotene (mg.100 g−1 wet basis) in raw and cooked pulp from winter squash at three stages of maturity.
Table 1.
Total content of β-carotene and α-carotene (mg.100 g−1 wet basis) in raw and cooked pulp from winter squash at three stages of maturity.
| β-Carotene | α-Carotene |
---|
Raw | Cooked | Raw | Cooked |
---|
Immature | 9.54 ± 0.61 bA | 6.35 ± 0.62 bB | 9.28 ± 0.31 bA | 5.55 ± 0.54 bB |
Mature | 12.34 ± 0.47 abA | 9.37 ± 0.91 abA | 14.31 ± 0.67 abA | 9.37 ± 0.65 bB |
Very Mature | 15.77 ± 1.61 aA | 11.08 ± 0.83 aA | 16.19 ± 1.79 aA | 11.31 ± 0.89 aA |
Mains effects | p Value (β) | p Value (α) |
Stage of Maturity (SM) | 0.0016 | 0.0007 |
Preparation (P) | 0.0016 | 0.0004 |
SM x P | 0.6458 | 0.8421 |
Observed contents of α-carotene content of β-carotene in squash “type butternut”, variety CosmosF1, in all its stages of maturity were in agreement with results reported in other varieties of
Cucurbita moschata “butternut type” [
4,
7,
11,
15]. A higher concentration of carotenes (α, β) were obtained in the very mature stage (31.96 mg·100 g
−1 flesh wet basis) compared to immature raw fruits (18.32 mg·100 g
−1 flesh wet basis), and with cooked pulp (22.29 mg·100 g
−1 flesh wet basis) in very mature fruits and in immature fruits (11.90 mg·100 g
−1 flesh wet basis). These results were consistent with visual observations of the color of the pulp. Fruits with greater stage of commercial maturity had a more intense orange color in the raw pulp (
Figure 1). The hue (61.3°) and chrome (67.4) of the raw flesh of very ripe fruit (
Table 2) were statistically different from the other maturity stages and demonstrated a higher concentration of pigments in fruits with advanced ripening. Cooking changed the color of the pulp at different stages of maturity of fruit, determining a lower chroma and hue value in raw pulp (
Table 2). This effect was statistically significant in the pulp of immature and mature fruits. However, in the three stages of maturity studied, cooked pulp had lower lightness than raw pulp (
Table 2).
Table 2.
Lightness (L*), Chroma (C*ab) and Hue angle (hab) color of raw and cooked pulp from squash at three stages of maturity.
Table 2.
Lightness (L*), Chroma (C*ab) and Hue angle (hab) color of raw and cooked pulp from squash at three stages of maturity.
| Immature | Mature | Very Mature |
---|
| Lightness (L*) |
Raw | 69.4 ± 0.3 aA | 68.5 ± 0.4 aA | 65.8 ± 0.5 bA |
Cooked | 57.5 ± 1.5 aB | 62.7 ± 1.6 aB | 51.6 ± 1.5 bB |
| Hue Angle (hab) |
Raw | 67.1 ± 0.6 aA | 66.1 ± 0.3 aA | 61.3 ± 0.6 bA |
Cooked | 73.2 ± 1.0 aB | 67.8 ± 0.8 bA | 65.2 ± 1.2 bB |
| Chroma (C*ab) |
Raw | 62.3 ± 0.3 bA | 63.9 ± 1.4 bA | 67.4 ± 0.8 aA |
Cooked | 50.7 ± 1.9 bB | 59.8 ± 2.0 aA | 49.5 ± 1.8 bB |
The factors determining the final content of carotenes in fruits and vegetables are not fully understood. There are studies how the expression of specific genes played a key role in the accumulation of carotenes and ultimately determined higher or lower carotene content during fruit development [
4]. Zhang
et al. [
4] worked with
Cucurbita moschata, Max variety, raw pulp, standard production practices; at harvest mature stage index described by weeks after pollination, report lutein but not alpha carotene. In our experimental conditions,
Cucurbita moschata, Cosmos F1 variety, raw pulp, at harvest time, in three commercial mature stages described with color of the peel and stalk, lutein was not found. These results suggest, as others authors [
4,
7,
9], that the profile and amount of carotenoids is determined by several factors such as genetic material as well as handling, environmental factors and process.
Early expression of genes encoding enzymes is a critical factor to regulate the accumulation of carotenoids [
4,
5,
6,
7,
8,
9,
10,
11,
12,
13,
14,
15,
16]. However, [
17] in watermelon indicated that there is no correlation between carotenoid biosynthesis gene expression and specific carotene accumulation. On the other hand, depending on the cooking conditions, carotenoids can be more or less affected, resulting in an increase or reduction of their concentration [
18,
19]. Furthermore, the highly unsaturated chemical structure of α and β-carotene, makes them susceptible to degradation by physical and chemical environmental factors, including oxygen, light, temperature, pH [
5,
6,
7,
8,
9]. Oxidations of carotenoids as well as the formation of new compounds have been linked to changes in the instrumental color of food and its consequent effect on nutritional and/or sensorial attributes [
8,
19,
20]. In our study of raw and cooked pulp of the CosmosF1 variety, isomers or other carotenoids detected in samples that probably help defining color were not analyzed.
A reduction in the concentration of carotenoids that has been observed could be associated with the loss of solutes in the cooking water, due time and temperature induced changes in plant tissue during cooking [
10,
11,
12,
13,
14,
15,
16,
17,
18,
19,
20,
21]. At the time of harvest, the variety CosmosF1 did not show significant difference in dry matter content after microwave cooking (
p = 0.3911) or by the stage of commercial maturity of the fruits (
p = 0.6874) (
Table 3). Other metabolic and structural modifications, like starch or fiber, may determine the retention of carotenoids during cooking [
5,
6,
7,
8].
Table 3.
Dry matter content (%) of raw and cooked winter squash pulp in three stages of maturity.
Table 3.
Dry matter content (%) of raw and cooked winter squash pulp in three stages of maturity.
| Dry matter content (%) | p Value |
---|
Immature | Mature | Very Mature |
---|
Raw | 8.75 ± 0.75 | 8.28 ± 0.29 | 8.60 ± 0.59 | 0.8403 |
Cooked | 9.26 ± 0.53 | 8.83 ± 0.17 | 8.04 ± 0.14 | 0.1426 |
p Value | 0.6779 | 0.2182 | 0.2131 | |
Main Effects | p Value | |
Maturity stage (MS) | 0.3911 | |
Preparation (P) | 0.6874 | |
MS × P | 0.6458 | |
3.2. Ratio β:α
The ratio of β-carotene to α-carotene content had values between 0.84 and 1.15 in the studied treatments, and significant interaction effect (
p = 0.0044) was found between the two factors analyzed (maturity
vs. preparation). Raw mature fruit exhibited a lower β:α ratio (0.86)
vs. all other treatments and the cooked immature pulp (1.15), other similar treatments being different to each other (
Figure 2).
Figure 2.
Relationship between β-carotene and α-carotene content, in every state of fruit maturity and preparation. Mean ± SEM (n = 3). Different letters in the column indicate that the treatments are statistically different. Main effects: state of maturity (SM) < 0.0001; Preparation (p) < 0.0001; SM × p = 0.0044.
Figure 2.
Relationship between β-carotene and α-carotene content, in every state of fruit maturity and preparation. Mean ± SEM (n = 3). Different letters in the column indicate that the treatments are statistically different. Main effects: state of maturity (SM) < 0.0001; Preparation (p) < 0.0001; SM × p = 0.0044.
As mentioned previously, the synthesis of carotenoids is a complex and continuous process where several genes express during the ripening and aging of the fruit are involved, and different variety and/or condition crop contribute for change de ratio of carotenes [
4,
5,
6,
7,
8,
9,
10,
11,
12,
13,
14,
15,
16,
17,
18]. At the same time the form of cooking can differentially reduce the carotenes present in each stage of maturity of the fruit. Immature fruit probably has a composition in the metabolic and cellular structure different from the of more mature fruits [
8], which can be determined during cooking that carotenoids are labile, removed or may have oxidations when exposed to aggressive environmental conditions [
9,
10,
11,
12,
13,
14,
15,
16,
17,
18,
19,
20,
21].
3.3. Percentage Reduction of Carotenes
The percentage reduction by the effect of cooking, both β-carotene (28.6%) and α-carotene (34.1%) had no statistical difference (
p = 0.7701,
p = 0.6507) between the states of commercial maturity. However, while the pulp of the fruits in the most advanced state of maturity (very mature) had a similar reduction of both carotenoids (27.6%), in mature and immature fruits, which lost more α-carotene than β-carotene (
Figure 3).
Similar results in the differential retention of α-carotene and β-carotene were observed by [
11] and [
16] in squash (
Cucurbita moschata), and [
22] in carrot, where α-carotene presented lower retention rate than β-carotene. The index of the amount of retention of carotene in carrot samples was similar when they were prepared with similar time and temperature, and similar relation water/pulp cooking and cutting processes before cooking.
Figure 3.
α-carotene and β-carotene reduction for cooking from winter squash pulp in three states of fruit maturity. Mean ± SEM (n = 3). For α-carotene or β-carotene, different lowercase letters indicates differences between states of maturity (Tukey, p ≤ 0.05). Different capital letters indicate differences between carotenoids to the same state of maturity (t-Student p ≤ 0.05).
Figure 3.
α-carotene and β-carotene reduction for cooking from winter squash pulp in three states of fruit maturity. Mean ± SEM (n = 3). For α-carotene or β-carotene, different lowercase letters indicates differences between states of maturity (Tukey, p ≤ 0.05). Different capital letters indicate differences between carotenoids to the same state of maturity (t-Student p ≤ 0.05).