A Comparison of the Biometric Characteristics, Physicochemical Composition, Mineral Elements, Nutrients, and Bioactive Compounds of Hylocereus undatus and H. polyrhizus ^†

Abstract

Pitaya (Hylocereus sp.) is an exotic and attractive fruit with promising consumption potential due to its nutritional qualities and its flavor and color. However, this fruit and its nutritional benefits for the human diet are not widely known. This paper compared the biometric and physicochemical characteristics, mineral elements, nutrients, and bioactive compounds of pitaya with white and red pulp. The nutrients and bioactive compounds were analyzed by HPLC. The total phenolic compounds and the antioxidant capacity were determined by spectrophotometry. Pitaya red pulp showed higher vitamin E (140.76 Gg µg·100 g⁻¹), antioxidant capacity (36.41 AAT%), eriodictyol (178.75 µg·100 g⁻¹), and anthocyanins. The α-carotene showed higher expression in the white pulp (110.21 µg·100 g⁻¹). The total phenolic content was similar in both fruits. Pitaya consumption should be encouraged due to the presence of nutrients and bioactive compounds relevant to our basic nutrition.

1. Introduction

Interest in pitaya from the industry, local growers, and consumers (Hylocereus sp.) has recently increased due to its flavors and exotic appearance. Pitaya is an edible, rustic, exotic fruit that belongs to Cactaceae family [1]. Originating from Latin America, it areis covered with bracts; is epiphytic, rupicolous, or terrestrial, depending on the species; and has white, nocturnal, and aromatic flowers pollinated by insects [2]. Depending on the species, it may have red or yellow flesh and white or red mucilaginous mesocarp (pulp), with small seeds distributed throughout the pulp, giving the fruit an attractive appearance to consumers and industry [3].

Studies indicate that the peel and pulp of different species of pitaya show vitamins, phenolic compounds, and antioxidant capacity [4,5,6,7], dietary fiber, and mineral elements such as N, K, Fe, Mn, and Zn [8]. Pitaya is known to have nutraceutical and therapeutic properties [1]. Its consumption is also related to decreasing cholesterol and to anti-diabetic activity [9].

However, to date, there are no studies regarding the comparison and complete characterization (physicochemical composition, mineral elements, nutritional value, and composition of bioactive compounds) of pitaya with white pulp (H. undatus) and red pulp (H. polyrhizus), which are currently the most commercialized species.

This study is important as it includes more information about pitaya varieties regarding their biometric characteristics, physiochemical composition, mineral elements, vitamins, and bioactive compounds.

2. Material and Methods

Fruit material and sampling: Red-skinned with white pulp (H. undatus) and red pulp (H. polyrhizus) pitaya at the same stage of ripeness were collected during the morning, in a consortium cultivated area, located in the rural area of Viçosa, Minas Gerais, Brazil. The fruits were selected by appearance, excluding those with no epidermal injury or mechanical damage due to transport. Then, they were washed and dried.

Determination of biometric characteristics: Fruits of each species were randomly assigned to measure length (cm) and diameter (cm) using a pachymeter (Disma, 150 mm) and weight (g) using an analytical scale (Gehaka, AG200). All pitayas were manually peeled with a sharp knife and the pulps were homogenized in a domestic multiprocessor (Phillips Wallita) and stored at −18 ± 2 °C until the time of analyses, which took place up to 36 h (carotenoids) and 72 h (vitamin E) after fruit collection.

Analyses of physicochemical composition and centesimal composition: The pH of 10 g of each sample was analyzed using a pH meter (Denver Instrument UB-10). Soluble solids were determined by refractometry (28 A, 65 Brix, model 105) using 15 g of samples, and titratable acidity was analyzed by volumetric neutralization using 1 g of samples, according to Instituto Adolfo Lutz [10].

Moisture was determined in an oven at 65 °C using 10 g of the fruit pulp; total lipids were determined by Soxhlet using 10 g of the lyophilized fruit pulp. The total ash was quantified using a muffle (Quimis, model Q320 M, Brazil) at 550 °C using 2 g of the lyophilized fruit. The protein was determined by the Kjeldahl method using 40 mg of the lyophilized fruit, and the total dietary fiber was determined by the non-enzymatic gravimetric method using 1 g of the lyophilized fruit [11].

The carbohydrates in pulp were calculated following the equation: [100 − (% moisture + % lipids + % protein + % total dietary fiber + % ash)].

Determination of mineral elements: The mineral elements (calcium, Ca; potassium, K; phosphorus, P; magnesium, Mg; sulfur, S; copper, Cu; iron, Fe; zinc, Zn; manganese, Mn; sodium, Na; chrome, Cr; and the inorganic contaminants cadmium, Cd; aluminum, Al; nickel, Ni; and lead, Pb) were determined by optical emission spectrometry with inductively coupled plasma (ICP-OES) (Varian Medical Systems, Belrose, Australia), according to the recommended instrument conditions, using 1 g of lyophilized fruit.

Extraction and analyses of vitamins, carotenoids, and flavonoids: The analyses of vitamin E followed the methodology of Pinheiro-Sant’Ana [12], with modifications; carotenoid analyses followed the methodology of Rodriguez-Amaya [13], with modifications; the identification and quantification of flavonoids were conducted according to [14] and Cardoso’s modifications [15]; and anthocyanin analyses followed the methodology of [16,17].

For all analyses, the pitaya pulp was examined in four replicates in a high-performance liquid chromatography system (HPLC). During the analyses, the samples and the extracts were protected from light and heat using amber glass, aluminum foil, and blackout curtains.

Total phenolic compounds and antioxidant capacity: The total phenolic compounds were determined according to [18]. The antioxidant capacity was determined using the DPPH solution (1.1-diphenyl-2-picrylhydrazyl), and the absorbance was read using a spectrophotometer (Thermo scientific, 606 Evolution, EUA) at 517 nm [19].

Experimental design and statistical analysis: A completely randomized design was used with four replicates for vitamin E, carotenoids, flavonoids, anthocyanins, total phenolics, and antioxidant capacity. For physicochemical analyses of centesimal composition and mineral element analysis, triplicates were used. Data were submitted to ANOVA and Student’s t-test using IBM SPSS Statistics software, version 22 (IBM, 2013), adopting a significance level (α) of 5%. All numerical data are expressed as mean ± standard deviation.

3. Results and Discussion

The white and red pitaya pulp analyzed showed yellow-green bracts, indicating ripe fruits. The fruits showed a slightly elliptical shape, with no external differences.

Table 1. Biometric characteristics, physical–chemical composition, and centesimal composition in white (H. undatus) and red (H. polyrhizus) pitaya pulp.

Parameters	Pitaya
	White Pulp	Red Pulp
Biometric feature
Length (cm)	8.00 ± 0.33 a	7.24 ± 0.22 b
Diameter (cm)	6.89 ± 0.69 a	6.68 ± 0.40 a
Weight of the fruit (g)	227.02 ± 8.88 a	196.79 ± 9.02 a
Weight of the pulp (g)	131.22 ± 37.08 a	115.20 ±17.44 a
Weight of the peel (g)	95.38 ± 1.96 a	81.63 ± 1.631 a
Physical–chemical composition 1
pH	4.37 ± 0.21 a	3.78 ± 0.12 b
Soluble solids	14.86 ± 0.97 a	13.34 ± 0.55 b
Acidity (% citric acid)	0.41 ± 0.02 a	0.40 ± 0.02 a
Total dietary fiber 3 (g·100 g−1)	2.19 ± 0.15	2.31 ± 0.49
Insoluble fiber 3 (g·100 g−1)	1.81 ± 0.12	2.02 ± 0.31
Soluble fiber 3 (g·100 g−1)	0.38 ± 0.02	0.29 ± 0.18
Centesimal composition (g·100 g−1)
Moisture	85.16 ± 0.60 a	84.37 ± 0.90 a
Lipids 2	0.39 ± 0.08 a	0.44 ± 0.05 a
Total ash 2	0.30 ± 0.00 a	0.27 ± 0.10 a
Proteins 2	0.43 ± 0.05 a	0.41 ± 0.18 a
Carbohydrates 2	11.51 ± 0.08 a	12.18 ± 0.24 a
Energy value (kcal·100 g−1)	51.27	54.32

Means followed by the same letter in the columns, for each characteristic, did not differ statistically at 5% probability according to Student’s t-test; ¹ values expressed in fresh matter as mean of 3 replicates ± standard deviation (SD). ² values expressed in fresh matter as mean of triplicates ± standard deviation (SD). ³ values expressed in fresh matter as mean of duplicates ± standard deviation (SD).

shows the biometric features, physical–chemical composition, and centesimal composition, with no differences between the pitayas.

The values found for pH in the white pitaya was close to that observed by Lima et al. [20], with a pH variation between 5.70 and 4.87, and Jerônimo et al., 2015, found a pH of 5.00 in red pulp, which is close to our study. The variation found in the literature for pH values and titratable acidity may be related to the ripening aspects of fruits. In the present study, soluble solids were close to those reported in [20], with a variation of 13.90° to 14.60° Brix in white pitaya; Jerônimo et al., 2015, found 11.40 Brix in red pulp, higher than the value of our study for the same species. White and red pulp showed high moisture (around 85%), similar to that found by [12] in white (86.08%) and red pitayas (85.52%).

In [21], the authors also found a moisture value of 86% in pitaya. This high moisture is related to the perishability in pitaya. Differing from our study, Abreu et al. [7] reported higher concentrations of protein in white pitaya pulp (0.87%) as well as in red fruit (1.06%). This difference between this study and our results may be related to the ripening of the fruit as well as the edaphoclimatic characteristics of each region. Among the minerals analyzed, the most abundant was potassium (average of 256.46 mg/100 g) and the least abundant was chromium (average of 0.02 mg/100 g) in the two species of pitaya pulp.

α-tocopherol is the most significant component in the two species of pitaya, followed by γ-tocopherol (

Table 2. Occurrence and concentration of vitamins, carotenoids, and bioactive compounds in white (H. undatus) and red (H. polyrhizus) pitaya pulp.

Variables	Pitaya 1
	White Pulp	Red Pulp
Total vitamin E (µg·100 g−1)	100.00 a	140.76 b
α-tocopherol	70.46 ± 4.01 a	85.71 ±1.46 b
α-tocotrienol	11.53 ± 0.55 a	16.03 ± 1.58 b
β-tocopherol	4.21 ± 0.51 a	1.12 ± 0.08 b
β-tocotrienol	Nd	Nd
γ-tocopherol	13.80 ± 0.71 a	33.07 ± 3.06 b
γ-tocotrienol	Nd	4.83 ± 0.52 a
δ-tocopherol	Nd	Nd
δ-tocotrienol	Nd	Nd
Carotenoids (µg·100 g−1)
α-carotene	110.21 ± 5.51 a	92.51 ± 8.46 b
β-carotene	19.92 ± 0.58 a	15.73 ± 0.39 b
Lutein	Nd	Nd
Flavanones (µg·100 g−1)
eriodictyol	178.75 ± 8.48 a	Nd
naringenin	Nd	Nd
Anthocyanin (µg·100 g−1)
cyanidin 3-glycoside	Nd	3604.574 ± 77.00 a
cyanidin 3-rutinoside	Nd	2350.036 ± 27.45 a
Total phenolics (mg GAE·100 g−1)	52.11 ± 4.57 a	52.83 ± 7.05 a
Antioxidant capacity (AAT%)	27.11 ± 1.94 a	36.41 ± 1.28 b

Means followed by the same letter in the rows do not differ statistically at 5% probability according to t-test. ¹ data expressed in fresh matter; nd: not detected.

). The concentrations of α-tocopherol, α-tocotrienol, and γ-tocopherol were higher (p < 0.05) in red pitaya, whereas the concentration of β-tocopherol was higher in white pitaya (p < 0.05). γ-tocotrienol was found only in red fruit. White pitaya pulp showed higher concentrations of α-carotene and β-carotene (p < 0.05) (Table 2). Among the flavonoids, only eriodictyol was identified in white pitaya pulp (Table 2). Due to a lack of studies that analyzed flavonoids in pitayas by HPLC, it is difficult to compare.

Among the flavonoids, only eriodictyol was identified in white pitaya pulp (Table 2). Due to the lack of studies that analyzed flavonoids in pitayas by HPLC, it is difficult to compare with the results obtained in the present study. One study analyzed red pitaya seeds by HPLC and found catechin, epicatechin, quercetin, myricetin, and kaempferol [22].

Although our results did not detect anthocyanins in white pulp, a recent study [23] identified five anthocyanin compounds in Hyloceurus sp., including cyanidin 3-glucoside and cyanidin 3-rutinoside in red and white pulp. According to those authors, there is a correlation between red pulp and the quantity of anthocyanin compounds present in the fruit, with red pulp showing a higher level of anthocyanins in relation to white pulp.

There was no difference in the concentration of total phenolic compounds (p > 0.05) between the two species of pitaya (Table 2). Similar values were found by Wu et al., 2006. (42.2 mg GAE/100 g) in red pitaya pulp [5], who found lower values in white and red pitayas. The antioxidant capacity of red pitaya was higher than that of white fruit (Table 2), which may be related to the higher concentration of total phenolic compounds in red fruit. The higher antioxidant capacity observed in the red pulp fruit may be related to the difference between the composition of lipophilic compounds among the studied species. Differing from our study, ref. [5] found no significant difference between white and red fruit antioxidant capacity.

4. Conclusions

The results showed that white and red pitaya pulp showed low concentrations of lipids and proteins and low caloric value. Pitayas are fruits with high perishability due to their high value of moisture, according to this study. Different mineral elements beneficial to human health were found in the two species of pitaya. Vitamin E was higher in red pitaya, while carotenoids showed higher expression in the white fruit. The total phenolic contents in the white and red pitaya were similar. The red fruit showed higher antioxidant capacity, as well as the presence of anthocyanins. These differences found in our study are probably influenced by the species. Hereby, our study is relevant to encouraging the consumption and cultivation of pitaya as a way to contribute to food diversity and to guarantee the sovereignty and food and nutritional security of agricultural families.