Dragon fruit (Hylocereus undatus Haw.) jam: Use full, development and characterization

The aim of this study was developing formulations of H. undatus Haw. jam with pulp and peel, as well as evaluating nutritional compounds and texture properties through sensorial, instrumental, physical, biochemical and microbiological analyses of the final product. The fruit were selected, sanitized, pulped and grinded, and the formulations with different concentrations of pulp and peel (0 – 100%) were developed and evaluated. Microbiological evaluation showed that the formulations are in accordance with the current legislation. The increase in peel concentration in the jam formulations resulted in better consumer acceptance and higher concentration of phenolic compounds, antioxidants and B complex vitamins, such as B1, B5 and B6. In addition, it gave the jams acceptable and pleasant sensorial characteristics and texture. Adding peel to the formulations enabled us to make total use of the fruit, with no waste, besides making the coproduct richer in compounds that are beneficial to consumers’ health.


Introduction
Currently, food waste is an environmental problem and the increasing concern with the enviroment has been mobilizing several market segments. Food waste can be used in many ways, such as making total use of food to reduce organic matter in the environment and enhance the quantity of nutrients and health benefits. This practice has been adopted as an easy alternative for sustainable, with greater use of natural resources, which allows reducing expenses in a more considerable way, besides enabling diversified diets (Amaral, Pereira, Ferreira & Gregório, 2012).
Dragon fruit (genus Hylocereus) belongs to the Cactaceae family, and it is originally from some regions of Mexico, South and Central Americas. It is widely grown in countries such as Malaysia, Vietnam, Thailand, Taiwan (Muhammad, Mohd.Zahari, Gannasin, Mohd.Adzahan & Bakar, 2014), and it has been recently introduced in Brazil. The fruit has several varieties, which can be all differed by characteristics such as color of its epicarp and/or mesocarpthe latter contains black seeds (Ariffin et al., 2009). Studies have demonstrated that dragon fruit has compounds that are beneficial to consumers, as antioxidants (Rui, Zhang, Li & Pan, 2009;Mercado-Silva, 2018;Som, Ahmat, Hamid & Azizuddin, 2019).
In countries where the fruit is widely consumed, peel waste by juice processing and natural dying industries causes accumulation of organic matter (Muhammad et al., 2014;Phongtongpasuk, Poadang & Yongvanich, 2016). In China, dragon fruit peel is consumed as salad, due to its high antioxidant activity, beyond the functional properties (Zhuang, Zhang & Sun, 2012). Furthermore, the peel represents approximately 33% of the total weight of the fruit, which is often discarded and used as animal food (Amid & Manap, 2014).
The use of different parts of plants, such as roots, seeds and leaves, in addition to food residues from industrial processes, is currently a viable alternative for the production of coproducts and extraction of compounds of food interest and with functional properties for human health. Among these compounds, carbohydrates, antioxidants, fibers, vitamins and minerals are associated with promoting health and increasing the nutritional value of foods. Thus, total waste recovery leads to an increase in nutritional values, which makes the fruit a richer nutritional option.
Among the coproducts, jam is a popular food in many countries, and makes it possible to consume a particular fruit even outside the season. According to Touati, Tarazona-Díaz, Aguayo & Louaileche (2014), jams are a type of food with intermediate moisture content, and it is prepared by cooking fruit with the addition of sucrose, pectin, acid and other ingredients which will characterize the product. It finds its origin in the practice of food preservation for consumption throughout the year. Jams must have adequate consistency, and when they are stored at high temperatures or not stored properly, there is significant loss in terms of nutritional values and sensorial properties (Touati et al., 2014;Rababah et al., 2015;Panchal, Gaikwad, Dhemre & UD, 2018).
Another important factor for jam formulation is pectinpectic substanceswhich is responsible for gelation due to hydrophobic interactions and hydrogen bonds in acid conditions (pH < 3,5), and low water activity (Javanmard, Chin, Mirhosseni, & Endan, 2013). As a feature of a well commercially accepted product, jams must have a content of 60 ºBrix (Holzwarth, Korhummel, Siekmann, Carle & Kammerer, 2013). In front of these factors, the aim of this study is developing of dragon fruit jam using whole fruit (pulp and peel), as well as evaluating sensorial, physical, chemical, biochemical and microbiological characteristics of the final product.
Pulping was done with sterile material, and the pulp and peel were macerated and set aside for further analysis and for preparing the jam formulations.

Jam preparation
The jam formulations were prepareted by following the composition stated by Touati et al. (2014), which contains fruit pulp, sucrose, pectin and citric acid. Pectin and citric acid were added as much as needed (quantum satis), following the rules by RDC (Technical Regulation of Good Practices for Food Services) Nº8, from March 6th, 2013. Quantification of pectin present in the pulp and peel was assessed in accordance with Pearson (1976), in order to evaluate the need of addition to the formulations.
For jam production, the ingredients were placed into a stainless steel container and exposed to cooking until the concentration of soluble solids reached 60 to 68 ºBrix. Citric acid was added until pH 3.5. After that procedure, the jam, still at a temperature higher than 85ºC, was placed into glass jars previously sterilized, closed with metal buffers, and inverted for 5 minutes. After cooling, the jars were labeled and stored at room temperature. Pectin values found in both pulp and peel, obtained on a dry weight basis, were lower than 0.10 and 14.33 g of calcium pectate 100 g -1 , respectively. Peel pectin content is 143 % greater compared to the pulp. Therefore, we did not consider the addition of commercial pectin to the jam formulations. Research, Society and Development, v. 10, n. 7, e6510716255, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i7.16255

Microbiological Evaluation
The analysis was carried out in accordance with requirements of the current legislation, RDC Nº12, from 2001 ANVISA (National Health Surveillance Agency), Brazil, (BRASIL, 2001) for preserves. Yeast and mold analysis was done in conformity with the methodology by Downes and Ito (2001), by spread plate in Dichloran 18 Glycerol agar (DG-18), for counting after 5 days of incubation at 25 ºC. Results are expressed as colony-forming units (CFU) g -1 of the sample and the acceptable tolerance limit for yeast and mold is 1,0x10 4 , according to RDC Nº12.

Sensorial analysis
Sensorial analysis was carried out by applying the 9-point hedonic scale test (9 = like extremely; 1 = dislike extremely), with 120 non-trained judges (77 women and 43 men). The parameters evaluated were global appearance, taste, texture and purchase intention (Touati et al, 2014). The latter underwent scale evaluation, from 1 to 5 (5 = I would certainly purchase; 1 = I would certainly not purchase). All samples (25 g) were placed into transparent plastic cups codified with three random numbers, at room temperature. The study was approved by the Ethics Committee for Research on Human Beings, under registration number CAAE: 43121714.1.0000.0104.

Color measurements
Dragon fruit jam measurement was determined by the digital colorimeter CR-10 model, manufactured by KONICA MINOLTA. Variables were collected as proposed by the International Commission on Illumination (ICI), using the L*, a* and b* variables, in accordance with Santos et al. (2016).

Proteins
Determination of crude protein was done according to the method by Kjeldahl (AOAC, 1998) and in triplicate. The sample was digested for 4 to 6 h with a catalytic mixture and concentrated H2SO4, neutralized with a 40% NaOH solution, and subsequent formation of borate complex, a product that results from the reaction between the nitrogen available in the sample with 4% boric acid. Ammonia titration with a 0,1 mol L -1 solution of HCI was done until the turning point, and the mean values were calculated. The results were expressed through total nitrogen percentage of the sample (% Nitrogen).

Texture properties
Texture properties of the dragon fruit jam formulations were evaluated with a TATX-Stable Microsystem texturometer. The parameters evaluated with regard to the texture profile were firmness, adhesiveness, elasticity, cohesiveness, gumminess, chewiness and resilience. The results were expressed as g.
Measures were analyzed by using a P36R probe (36mm diameter aluminum cylinder probe) at room temperature (25 ± 3 ºC). The instrument was operated at pre-test speed = 1 mm s -1 , test speed = 1 mm s -1 , post-test speed = 20 mm s -1 , distance = 15 mm, and trigger = 5 mm, automated force detection with a 5 kg load cell (force trigger = 5 g force -1 ). The analysis was carried out with 10 repetitions.

Extraction
Extracts for the unprocessed fruit and jam formulations were obtained in accordance with Gümüsay, Borazan, Ercal & Demirkol (2015), with some changes. 1 g of the sample was added to 10 mL of methanol 75 %/water 25 % (v/v) under agitation for 15 min in a magnetic agitator. The samples were centrifuged at 1500 g for 10 min, and the supernatant was recovered and stored in amber flaks to be protected from light until the analyses.

ABTS Method
Antioxidant activity by the ABTS method (2,2'-azino-bis-(-acid 3-ethylbenzothiazoline -6-sulphonic)) was carried out in accordance with Rufino et al. (2007). 30 μL of each sample extract and 3 mL of the ABTS + radical solution (5 mL of a 7 mmol L -1 ABTS solution and 88 μL of 140 mmol L -1 potassium persulfate, reaction for 16 hours protected from light) were transferred to tubes away from light, where they were kept for 6 min. Scanning was done in a spectrophotometer at 734 nm and a calibration curve was prepared with Trolox (y=-0.0003x+0.6950, R 2 =0.9931). The results were expressed as µmol trolox g -1 of the sample.

Phenolic compounds
Determination of phenolic compounds was done in accordance with the method by Singleton & Rossi (1965), with changes. 125 μL of the sample, 125 μL of the Folin-Ciocalteu reagent / distilled water 1:1 (v/v) and 2250 μL of a 3.79 mol L -1 sodium carbonate solution was placed into tubes protected from light, where they remained for 30 min. Scanning was done in a spectrophotometer at 725 nm. The calibration curve was determined from a gallic acid solution (y=0.0009x+0.0122, R 2 =0.9914) and the results were expressed as mg of gallic acid equivalent per sample mass (GAE g -1 ).

Extraction
The QuEChERS methodology was applied as described by Lehotay, Maòtovská & Yun (2005). The pulp, peel and formulation samples (15 g) that showed better acceptance in the sensorial analysis (F2, F3 and F4) were homogenized and extracted with 15 mL of acetonitrile (CAN) with 1% of acetic acid (v:v). 6 g of anhydrous magnesium sulfate and 1.5 g of sodium acetate was added, which underwent vortex agitation for 1 min. The volume was centrifuged during 10 min at 6000 rpm and 4 ºC. Afterwards, 1 mL of the supernatant (CAN) was transferred to a microcentrifuge tube containing 50 mg of (Primary secondary amine) PSA and 150 mg of anhydrous magnesium sulfate. The tube was agitated during 20 s and, later, centrifuged for 10 min at 6,450 g and 4 ºC. The aliquot was filtered by a nylon syringe filter with 0.20 µm porosity and transferred to a flask for analysis.

Statistical analysis
The data were submitted to analysis of variance through ANOVA. For means comparison, we used the Tukey's test (p<0.05), through the statistical program Assistat 7.7 beta (Campina Grande, Paraíba, Brazil). The graphs were created with the aid of the Software SigmaPlot version 11.0.

Microbiological analysis
The microbiological analysis was carried out in accordance with what is determined by the current legislation (RDC Nº12, from January 2 nd , 2001, ANVISA (National Health Surveillance Agency), Brazil. The samples were evaluated with respect to yeast and mold, and all formulations complied with the requirements stablished, below the tolerance limit of 10 4 yeast and mold per each gram of a sample.

Sensorial analysis
The sensorial analysis was evaluated through the following parameters: overall appearance, aroma, taste, texture and purchase intention (Figure 1)  Dragon fruit peel stands out for several features, such as significant amounts of betanine, hylokenine, betacyanine, pectin, triterpenoids and steroids, which are considered anti-inflammatory and anti-tumoral, besides antioxidant properties (Phongtongpasuk et al., 2016). In addition, pectin found in the peel can be added to food and drinks with low viscosity, and it is also a functional and healthy ingredient (Muhammad et al., 2014).
In fact, research shows the importance of fruit peels that carry additive properties. For instance, we have Myrciaria jaboticaba peel, which is a source of antioxidants (Plaza et al., 2016); pomegranate peel, which contains pectin and is a source Research, Society andDevelopment, v. 10, n. 7, e6510716255, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i7.16255 8 of fibers (Abid et al., 2017); passion fruit peel flour, which is a source of pectin and fiber due to its gelling power (Coelho et al., 2017). These examples show that fruit peels are recommended for consumption, as well as used as coproducts, for they are sources of beneficial compounds. Furthermore, they are viable for food industries, since they avoid wasting that leads to organic matter accumulation.

Physicochemical determination
In regards to the color of the formulations (Table 2), lower values were identified for L* and b* parameters with peel addition. As for a*, the mean values were higher for superior peel concentrations. These mean values reflect upon consumers' preference due to more attractive colors, which is a result of peel addition, as demonstrated by the sensorial analysis. Peel addition ranging from 25 % to 75 % directly contributed to enhancing general acceptance of the jam, and there was no significant difference for L*, a* and b* parameters. Betalaine and its derivatives are bioactive compounds responsible for the intense red color of dragon fruit peel and pulp. Besides, they offer health benefits since they are sources of antioxidants, and because they are important in the food industry (Xu, Zhang & Wang, 2016;Esquivel, Stintzing & Carle, 2007).
Percentage of the protein evaluated (Table 2) did not present significant values between the fruit itself (peel and pulp) and the jam formulations. Even though the protein is unstable to thermic processing, such as pasteurization applied during jam preparation, it remained stable after the preparation of the coproduct. Zhuang et al., (2012)  When it comes to texture parameters (Table 3), the increase in peel addition to the jam formulations contributed to enhancing firmness, chewiness and gumminess (an increase of 433.65 %, 175.76 % and 287.83 % comparing F1 to F5, respectively), whereas adhesiveness and resilience decreased (32,073.75 % and 96.49 % less comparing F1 to F5, respectively). A decrease in resilience and adhesiveness because of greater firmness was expected, for the ability to spring back into shape is hindered when it comes to firmer gels. As for cohesiveness and elasticity parameters, they showed significant differences among the formulations. However, those differences had nothing to do with peel addition. The increase in firmness, chewiness and gumminess may be related to an increase in pectin and dietetic fibers found in the peel (Zhuang et al., 2012;Muhammad et al., 2014). As stated by Mercado-Silva (2018), viscous consistency of the peel is due to the concentration of pectin, which consists mainly of galacturonic acid (39.11 %), lower concentrations of mannose, rhamnose, galactose, glucose and lower quantities of xylose and arabinose. Formulations F2, F3 and F4, regarding the texture evaluated in the sensorial analysis, did not present any statistical difference, thus evidencing ideal parameters for product acceptance.

Antioxidant Properties
Antioxidant activity showed higher mean values regarding the fruit peel in both methods evaluated, DPPH ( Figure   2.A) and ABTS (Figure 2. (Chen et al., 2014) for the ABTS method. As for the DPPH method, values such as 10.39 μmol VC g -1 were found for the fruit pulp (Li et al., 2017). Those values are lower than the ones shown by our study.
With regard to phenolic content, only the jam a 100 % made of peel was close to the content found in unprocessed peel, a phenomenon on account of pulp and peel dilution with sugar during jam preparation (Naeem et al., 2017). Previous studies present lower values of phenolic compounds compared to the ones found in this study: 77.50 and 39.70 mg AGE 100 g-both the pulp and the peel of Hylocereus sp. are considered rich in phenolic compounds and antioxidants (Dembitsky et al., 2011).

Determination of vitamins B1, B5 and B6
In order to evaluate complex B vitamins (B1, B5 and B6), the formulations which showed greater acceptance in the sensorial analysis (F2, F3 and F4) was considered, fresh peel and pulp. The results are shown by Figure 3.
According to Figure 3, the fruit pulp showed higher mean values in comparison with the peel, except for vitamin B5.
The jam formulations (F2, F3 and F4) achieved higher contents of vitamins B1 and B5 in comparison with the unprocessed fruit; on the other hand, they had lower contents of vitamin B6. Fruit are high in vitamins, such as fat-soluble (A, D, K and E) and hydro-soluble ones (C and B complex), besides minerals (Rababah et al., 2015). Fruit of the species Hylocereus sp., such as red dragon fruit (Hylocereus polyrhizus) have in their composition some vitamins as B1, B2, B3 and C (Yenrina, Azima & Khumairoh, 2016). *Capital letters between columns for the same vitamin stand for significant difference (p˃0.05) among the samples evaluated. Source: Authors.
As pointed out by Mercado-Silva (2018), H. undatus fruit has in its composition 0.2 mg of niacin (vitamin B2) and 25 mg of ascorbic acid for every 100 g of fresh pulp. As for Thiamine (B1) and Riboflavin (B2), they were not detected in this species. That differs from our study, for it presented B1 content in the samples analyzed. A study evaluating the composition of dragon fruit (H. undatus) jam with the fruit extract during storage for 3 months evidenced a decrease in ascorbic acid in the aforementioned period at room temperature (30 ºC) and refrigerated (5 ºC). The mean values were 2.45 to 2.96 mg 100 g -1 of jam, and 2.47 to 2.96 mg 100 g -1 of jam, respectively (Panchal et al., 2018).
Vitamins, among other compounds of bioactive character, can be affected or lost during processing, cooking and storage (Rababah et al., 2015). However, these results suggest stability and, consequently, the concentration of vitamins B1 and B5 when they are exposed to thermal treatment, such as cooking. Vitamins B1, B2, B3 and C also were analyzed, but, were not determined due to absence or degradation during the processes we carried out.

Conclusion
The addition of peel to dragon fruit jam showed feasibility of a coproduct that was entirely developed with total waste recovery, with emphasis being placed on the F3 formulation, which had good acceptance, besides bioactive compounds. Apart from reducing the amount of waste from personal consumption and industries, it enhances the beneficial properties of dragon fruit peel, leading to a better taste according to consumers, who strongly approved peel addition. Furthermore, it results in a considerable source of antioxidant compounds, vitamins such as B1, B5 and B6, besides sensorial features that were considered pleasant by consumers, within food safety and quality standards. It is important to mention that future studies should be carried out to evaluate the shelflife of this product, as well as the stability of bioactive compounds and sensory attributes during storage.