Pitaya Fruit Research Articles

Metabolic Profiling of Sugars and Organic Acids, and Expression Analyses of Metabolism-Associated Genes in Two Yellow-Peel Pitaya Species.

Sugar and organic acids are important factors determining pitaya fruit quality. However, changes in sugars and acids, and expressions of metabolism-associated genes during fruit maturation of yellow-peel pitayas are not well-documented. In this study, metabolic and expression analyses in pulps of different fruit developmental stages of ‘Wucihuanglong’ (‘WCHL’, Hylocereus undatus) and ‘Youcihuanglong’ pitaya (‘YCHL’, Hylocereus megalanthus) were used to explore the sugar and organic acid metabolic process. Total phenols and flavonoids were mainly accumulated at S1 in pitaya pulps. Ascorbic acid contents of ‘WCHL’ pitaya were higher than that of ‘YCHL’ pitaya during fruit maturation. Starch was mainly accumulated at early fruit development stages while soluble sugars were rich in late stages. Sucrose, fructose, and glucose were the main sugar components of ‘YCHL’ pitaya while glucose was dominant in ‘WCHL’ pitaya. Malic and citric acids were the main organic acids in ‘WCHL’ and ‘YCHL’ pitayas, respectively. Based on the transcriptome analyses, 118 genes involved in pitaya sugar and organic acid metabolism were obtained. Results from the correlation analyses between the expression profiling of candidate genes and the contents of sugar and organic acid showed that 51 genes had a significant correlation relationship and probably perform key role in pitaya sugar and organic acid metabolism processes. The finding of the present study provides new information for quality regulation of pitayas.

Metabolic Profiling of Organic Acids Reveals the Involvement of HuIPMS2 in Citramalic Acid Synthesis in Pitaya

Pitayas are rich in organic acids, especially citramalic acid, which is significantly higher than the plants. However, the mechanism of citramalic acid biosynthesis remains to be fully elucidated. In this study, organic acid compositions and contents, as well as expression patterns of key genes related to organic acid metabolism were analyzed during fruit maturation of four different pitaya cultivars i.e., ‘Guanhuabai’ (GHB), ‘Guanhuahong’ (GHH), ‘Wucihuanglong’ (WCHL), and ‘Youcihuanglong’ (YCHL). The total organic acid contents increased first and then declined during fruit maturation. The main organic acids were citramalic acid during the early stages of GHB, GHH, and WCHL pitayas, and dominated by malic acid as fruit maturation. In comparison, citric acid and malic acid were main organic acid for ‘YCHL’ pitaya. Citramalate synthase (IPMS) was involved in the synthesis of citramalic acid, and three types of HuIPMS i.e., HuIPMS1, HuIPMS2, and HuIPMS3, were obtained in our study. Highest expression levels of HuIPMS1 were detected in sepals, while HuIPMS2 and HuIPMS3 exhibited preferential expression in tender stems and ovaries. The expression levels of HuIPMS2 and HuIPMS3 were positively correlated with the content of citramalic acid in the four pitaya cultivars. HuIPMS2 was a chloroplast-localized protein, while HuIPMS3 presented a cytoplasmic-like and nuclear subcellular localization. These findings provide an important basis for further understanding of the molecular mechanism that leads to citramalic acid metabolism during pitaya fruit maturation.

Application of biowaste generated by the production chain of pitaya fruit (Hylocereus undatus) as an efficient adsorbent for removal of naproxen in water.

Pharmaceutical compounds are a serious problem in the environment. They cause damage to the aquatic, animal, and human organisms and soon became considered emerging pollutants where their removal is extremely urgent. Among the techniques used, adsorption has been used with success, where several adsorbent materials, including those from residual biomass, have been used to remove these pollutants. In this study, the skins of the pitaya fruit (Hylocereus undatus) productive chain were carbonized with ZnCl2 to obtain activated carbon and later used in the adsorption of the drug naproxen (NPX) in a batch system. The Freundlich model demonstrated a better adjustment for the equilibrium isotherms. A high adsorption capacity for NPX (158.81mgg-1) was obtained at 328K, which can be attributed to the remarkable textural properties of the adsorbent, besides certain functional groups present on its surface. Thermodynamic studies confirmed the endothermic nature of the adsorption process (∆H0 = 0.2898kJmol-1). The linear driving force model (LDF) presented a good statistical adjustment to the experimental kinetic data. The application of the material in the treatment of simulated wastewater composed of various pharmaceutical drugs and salts was very promising, reaching 75.7% removal. Therefore, it can be inferred that the application of activated carbon derived from pitaya bark is highly promising in removing the NPX drug and treating synthetic mixtures containing other pharmaceutical substances.

Breeding an underutilized fruit crop: a long-term program for Hylocereus.

This review describes three decades of introduction, agro-technology development, breeding and selection of Hylocereus species, known as pitaya or dragon fruit, as an example of a holistic program aimed to develop the horticultural potential of a perennial underutilized fruit crop. Interspecific homoploid and interploid crosses and embryo rescue procedures produced improved hybrids, some of which have been released to farmers. Molecular tools and morphological and phenological comparisons between the parental species and the resulting hybrids provided valuable information on dominant/recessive traits and on genetic relationships that could be exploited for further hybridizations. In addition, Hylocereus were crossed with species of the closely related genus Selenicereus, producing valuable intergeneric hybrids. In situ chromosome doubling resulted in the production of autopolyploid lines, from which an understanding of the effect of increased ploidy on fruit traits and metabolomic profiles was obtained. Gamete-derived lines were produced, adding to our biobank homozygote lines that were subsequently used for further hybridization. Spontaneous chromosome doubling occurred in haploid gamete-derived Hylocereus monacanthus lines and in interspecific interploid Hylocereus megalanthus × H. undatus hybrids obtained from an embryo rescue procedure, resulting in plants with double the expected ploidy. Challenging technical problems were addressed by the development of protocols for DNA isolation, flow cytometry, in situ chromosome doubling, androgenesis, gynogenesis and embryo rescue following interspecific and interploidy crosses. Current research leading to the development of genomics and molecular tools, including a draft genome of H. undatus, is also presented. Perspectives for further development of Hylocereus species and hybrids are discussed.

Pitaya fruit extract ameliorates the healthspan on copper-induced toxicity of Caenorhabditis elegans.

Copper (Cu) is an essential metal and it is important for metabolism. However, in high concentrations, it becomes toxic. Metal-induced toxicity is the cause of many neurodegenerative diseases. So it is necessary to search mechanisms to find ways of healthy aging. Natural compounds and diets based on fruits are increasingly common and could lead to a healthy life. Pitaya (Hylocereus undatus) is a tropical and Latin American, fruit that is gaining more popularity due to its antioxidant properties. Here, we evaluate the preventive and curative effect of different doses of microencapsulated pulp H. undatus extract on copper-induced toxicity. For this we use the nematode Caenorhabditis elegans, to investigate the effects of pitaya extract on behavior, lipid peroxidation, antioxidant chaperon, and cholinergic nervous system (ColNS). Results showed behavioral changes, decreased cell death biomarkers, and lipid peroxidation caused by copper, and these toxic effects were prevented and reverted by Pitaya's extract. After all, the extract can be used in diet as a supplement and studied to treat or prevent specific diseases, some of them linked to contamination and senility-related conditions. PRACTICAL APPLICATIONS: This research has been aimed to provide the uses of Hylocereus undatus microencapsulated pulp extract for the prevention and treatment of copper-induced toxicity. We have been shown that Pitaya is a good source of antioxidant compounds that can ameliorate the antioxidant system as well as the cholinergic nervous system avoiding behavior changes before and after the metal toxicity of copper. Therefore, the potential applications and common use of this extract can serve as food supplementation to prevent metal oxidative damage as well as to repair clinical cases of copper poisoning.

Exogenous melatonin treatment in the postharvest storage of pitaya fruits delays senescence and regulates reactive oxygen species metabolism

Pitaya fruits have high senescence rates throughout their postharvest storage period. Additionally, studies have confirmed that melatonin plays a regulatory role in plant senescence. However, the involvement of melatonin in the postharvest senescence of fruits remains unclear. In this study, two cultivars of pitaya fruit, ‘Zihonglong’ and ‘Jinghonglong’, were treated with melatonin and then evaluated for characteristics of senescence while in storage for 10 days. The results showed that melatonin treatment delayed fruit senescence in both pitaya cultivars, as indicated by the inhibition of weight loss, decay incidence, relative membrane permeability, and malondialdehyde (MDA) content, as well as the maintenance of the total soluble solids and ascorbic acid contents and the reduced respiration intensity. In addition, melatonin treatment reduced the O2·- production rates, H2O2 contents, and lipoxygenase activities but enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) in both pitaya cultivars. These results indicate that melatonin may contribute to delaying senescence in pitaya fruits. This study shows the potential of the use of melatonin in the postharvest storage of pitaya fruits, as well as other horticultural fruits.

The association of HpDof1.7 and HpDof5.4 with soluble sugar accumulation in pitaya fruit by transcriptionally activating sugar metabolic genes

Abstract Soluble sugar is one of the most important factors affecting fruit flavor and quality. Here, we report the identification of two Dof (DNA-binding with one finger) transcription factors termed HpDof1.7 and HpDof5.4 and their roles in influencing sugar accumulation in pitayas. HpDof1.7 and HpDof5.4 share a similar expression pattern with sugar metabolism-related genes HpSuSy1 and HpINV2, and sugar transporter genes HpTMT2 and HpSWEET14 during pitayas maturation, and their expression pattern was also consistent with the accumulation of glucose and fructose, which were the predominant sugars in pitayas. HpDof1.7 and HpDof5.4 were both typical nucleus-localized proteins with trans-activation ability. Gel mobility shift assay revealed that HpDof1.7 and HpDof5.4 were bound to promoters of HpSuSy1, HpINV2, HpTMT2 and HpSWEET14. Finally, transient expression assays in tobacco leaves showed that HpDof1.7 and HpDof5.4 increased the activities of HpSuSy1, HpINV2, HpTMT2 and HpSWEET14 promoters, thus facilitating sugar accumulation by transcriptionally enhancing sugar metabolic pathway genes. Our findings provide a new perspective on the regulatory mechanisms of Dof transcription factors in sugar accumulation and pitaya fruit quality formation.

Extraction and stability of pigments obtained from pitaya bark flour (Hylocereus costaricensis)

Red pitaya fruits have become a source of natural dye, because they are rich in betacyanin, a pigment that imparts a red-violet colour. However, natural dyes can be highly unstable and prone to rapid degradation. In this study, an experiment was initially carried out to determine the best extraction solution with an extraction time of 20 min for each solution at room temperature (50% methanol, water, 95% ethanol and 80% acetone), in different pH ranges (4.0 to 9.0) and wavelength (485, 535 and 700 nm), for the red pitaya bark. The stability of the pigments extracted from pitaya peel meal was analysed taking into account the best extraction solutions by spectrophotometric measurements at 15-day intervals, during a 60-day storage period, in the absence and presence of light and under different storage conditions. Pigments stored in the absence of light at freezing temperatures for less than 15 days showed least degradation. The FTIR spectrum in shows two distinct peaks at 3263.870 and 1636.807, these absorption bands are characteristic of betalain functional groups. The spectrum indicates the presence of hydroxy and amine groups as strong, broad, stretching-mode bands, appearing between 3200 cm-1 and 3600 cm-1.

Use of fruit epicarps to formulate pectin-based bioactive films / Utilização de epicarpos de frutos para formulação de filmes bioativos à base de pectinas

The functional properties of biofilms can vary according to the biopolymer used as the raw material; thus, in the search for alternative sources for preparation of biodegradable films, fruits and vegetables have been used to extract compounds of interest with applications in the food industry. The objective of this work was to obtain and characterize bioactive films based on pectin extracted from the epicarps (skin) of the fruit. The genipap (Genipa americana), red pitaya (Hylocereus polyrhizus) and star fruit (Averrhoa carambola) were collected, washed, pulped and dried at 50 °C for 24 h, and their epicarps were ground and subjected to pectin extraction using the casting method. The films were characterized as to their visual appearance, moisture, pH, water solubility and antioxidant activity. The pectin-based films of G. americana and H. polyrhizus showed a yellowish color, while A. carambola was dark brown. The highest pectin yield (29%) and moisture content (13.9%) were obtained from the H. polyrhizus film, while A. carambola showed the highest solubility in water (98.6%) and had the highest pH (3.9). Additionally, the film based on A. carambola showed greater antioxidant potential against ABTS (30.5%) and DPPH (34%), as well as greater reducing power (0.262 absorbance at 750 nm) and content of total phenolic compounds (553 mg GAE/100 g), whereas H. polyrhizus had a higher percentage of chelating ability (27%). The physicochemical characteristics and bioactive properties exhibited make the film formulation a viable alternative for the food industry.

Residual peel of pitaya fruit (Hylocereus undatus) as a precursor to obtaining an efficient carbon-based adsorbent for the removal of metanil yellow dye from water

The pitaya peel (Hylocereus undatus) was carbonized in the presence of ZnCl2 to obtain a carbon-based adsorbent to remove the Metanil Yellow dye (MY) from colored waters. The characterization techniques confirmed that the material had morphological changes with the appearance of new irregularities and cavities. Besides, the alternative adsorbent was formed mainly by carbon and functional groups characteristic of lignin and cellulose. Isothermal and kinetic studies were carried out at the natural pH of the solution at a dosage of 0.4 g L−1. The Langmuir model demonstrated the best adjustment of the equilibrium isotherms of the system, reaching the maximum adsorption capacity of 144.07 mg g−1 at 298 K. The thermodynamic behavior indicated that it is a spontaneous and favorable process of an exothermic nature (ΔH0=−34.02 kJ mol−1), consistent with a mechanism involving electrostatic interactions. The MY concentration influenced the kinetic. The homogeneous surface diffusion model (HSDM) showed good statistical adjustment to the kinetic values, showing a slight increase in the diffusivity coefficient from 2.4 × 10−9 to 4.5 × 10−9 cm2 s−1 with the increased MY concentration. The material application in a mixture containing several dyes and salts in the circumstances close to the real ones showed removal of 82.5%. The adsorbent could be regenerated and used 12 times. Therefore, it can be concluded that the pitaya fruit residual biomass can be used as a precursor for preparing carbon-based adsorbents. The adsorbent, in turn, is a promising alternative in the treatment of MY dye and mixtures of organic molecules.

Maturation Process, Nutritional Profile, Bioactivities and Utilisation in Food Products of Red Pitaya Fruits: A Review

Red pitaya (Hylocereus polyrhizus, red pulp with pink peel), also known as dragon fruit, is a well-known species of pitaya fruit. Pitaya seeds and peels have been reported to exhibit higher concentrations of total polyphenols, beta-cyanins and amino acid than pulp, while anthocyanins (i.e., cyanidin 3-glucoside, delphinidin 3-glucoside and pelargonidin 3-glucoside) were only detected in the pulp extracts. Beta-cyanins, phenolics and flavonoids were found to increase gradually during fruit maturation and pigmentation appeared earlier in the pulp than peel. The phytochemicals were extracted and purified by various techniques and broadly used as natural, low-cost, and beneficial healthy compounds in foods, including bakery, wine, dairy, meat and confectionery products. These bioactive components also exhibit regulative influences on the human gut microbiota, glycaemic response, lipid accumulation, inflammation, growth of microbials and mutagenicity, but the mechanisms are yet to be understood. The objective of this study was to systematically summarise the effect of red pitaya’s maturation process on the nutritional profile and techno-functionality in a variety of food products. The findings of this review provide valuable suggestions for the red pitaya fruit processing industry, leading to novel formulations supported by molecular research.

Suitability of pitaya fruit fermented by sourdough LAB strains for bread making: its impact on dough physicochemical, rheo-fermentation properties and antioxidant, antifungal and quality performance of bread

The objective of this study was to investigate the suitability of incorporating pitaya fruit fermented by antifungal LAB strains Lactiplantibacillus plantarum and Pediococcus pentosaceus at 1: 30 °C for 24h or 2: 31 °C for 19.5h as an ingredient with respect to bread making performance and bio-preservation effect. Underlying mechanisms related to gluten protein hydrolysis, starch hydrolysis, and yeast activity in dough were explored. The antioxidant activity, antifungal activity and bread making performance of the resulted breads were analyzed. Also, the antifungal phenolic acids in the breads were identified and quantified. Incorporation of fermented substrates in dough increased yeast activity and gas production capacity, but decreased gas retention capacity. This was attributed to increased dough acidity after incorporating fruit substrates. As a result, reducing sugar and free sulfhydryl (SH) groups increased in these doughs which indicated higher starch and gluten protein hydrolysis, respectively. However, SH groups increased at lower rate in presence of substrates fermented by L. plantarum and P. pentosaceus at condition 2 than 1. This could be due to improvement of gluten network as revealed by decreased α-helix (%) and increased β-turn (%) in secondary gluten structures in these doughs which subsequently resulted in more homogeneous microstructural properties than in presence of unfermented substrate compared to wheat dough. Subsequently, bread specific volume increased (6.6–20.0%) in presence of fermented substrates, especially fermented by L. plantarum at (2). Moreover, bread incorporated with fermented substrates (P. pentosaceus than L. plantarum at 1 than 2) had enhanced antioxidant activities, lower fungal growth rates based on challenge tests and mold free shelf life. Antifungal phenolic acids such as gallic acids, caffeic acid, protocatechuic acid were only detected in bread incorporated with fruit substrates, and their total content higher in fermented substrates.

Fruit extract of red pitaya (Hylocereus undatus) prevents and reverses stress-induced impairments in the cholinergic and antioxidant systems of Caenorhabditis elegans.

The addition of fruit to the diet is very important, and we can use nutraceutical and functional foods for this supplement. A little-known fruit is a red pitaya (Hylocereus undatus) that has been widely reported to have a high antioxidant potential. In this study, we analyzed the in vitro and in vivo antioxidant capacity of microencapsulated pitaya extract on the behavior, antioxidant, and nervous system of the nematode Caenorhabditis elegans. The worms were treated with fruit extract before and after juglone-induced stress, to determine the protective or curative effects of pitaya. We have been evaluated cholinergic, antioxidant, and behavioral biomarkers. We have evidenced that the pulp of pitaya contains antioxidant compounds and can serve as a potential nutraceutical product. In addition, the fruit extract was effective in preventing and/or reverse the stress-induced damages, even at high levels of chemical stress at all evaluated parameters. PRACTICAL APPLICATIONS: The potential applications and uses aimed by this research are related to the supplementation of foods given the antioxidant effect. Our data suggested that the effect of the pitaya fruit microencapsulated pulp extract was effective to prevent and repair the damage caused by oxidative stress. Besides the use of this microencapsulated extract can be an auxiliary in the treatment of diseases related to oxidative damage as well as promoting senescent aging. Another important use is the application of this extract as a dietary supplement to fortify the antioxidant system.

Maintenance of Postharvest Quality and Reactive Oxygen Species Homeostasis of Pitaya Fruit by Essential Oil p-Anisaldehyde Treatment.

The performance of p-Anisaldehyde (PAA) for preserving pitaya fruit quality and the underpinning regulatory mechanism were investigated in this study. Results showed that PAA treatment significantly reduced fruit decay, weight loss and loss of firmness, and maintained higher content of total soluble solids, betacyanins, betaxanthins, total phenolics and flavonoids in postharvest pitaya fruits. Compared with control, the increase in hydrogen peroxide (H2O2) content and superoxide anion (O2•−) production was inhibited in fruit treated with PAA. Meanwhile, PAA significantly improved the activity of antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT). Moreover, PAA-treated pitaya fruit maintained higher ascorbic acid (AsA) and reduced-glutathione (GSH) content but lower dehydroascorbate (DHA) and oxidized glutathione (GSSG) content, thus sustaining higher ratio of AsA/DHA and GSH/GSSG. In addition, activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydrogenation ascorbic acid reductase (DHAR), as well as the expression of HpSOD, HpPOD, HpCAT, HpAPX, HpGR, HpDHAR and HpMDHAR, were enhanced after PAA treatment. The findings suggest that postharvest application of PAA may be a reliable method to control postharvest decay and preserve quality of harvested pitaya fruit by enhancing the antioxidant potential of the AsA-GSH cycle and activating an antioxidant defense system to alleviate reactive oxygen species (ROS) accumulation.

The effect of ultrasound‐vacuum‐assisted extraction on bioactive properties of pitaya (Hylocereus undatus)

SummaryThis study aimed to investigate the effect of ultrasound‐assisted extraction under vacuum on bioactive properties of peel and flesh of pitaya fruit, and also compare with sonication under atmosphere condition using the principal component analysis (PCA). Vacuum sonication exhibited better results for total phenolic (56.78–71.54 mg GAE per 100 g for peel; 11.03–17.92 mg GAE per 100 g for flesh) and total flavonoid (95.33–115.71 mg QE per 100 g for peel; 13.26–19.36 mg QE per 100 g for flesh) amounts. DPPH free radical scavenging activity values of peel and flesh increased from 1.97 to 2.53 mmol TE kg‐1; from 0.33 to 0.50 mmol TE kg‐1 after sonication process, respectively. The main phenolic compounds of pitaya were identified as catechin (1.15–20.31 mg per 100 g) and rutin (0.88–14.55 mg per 100 g) in peel; catechin (1.11–9.35 mg per 100 g) and 3,4‐dihydroxybenzoic acid (1.29–3.60 mg per 100 g) in flesh. The combination of vacuum and ultrasound process can be used as a green extraction technology in order to enhance the amounts of bioactive compounds of pitaya fruit.

Selection and validation of reference genes for qRT-PCR analysis during fruit ripening of red pitaya (Hylocereus polyrhizus).

Red pitaya (Hylocereus polyrhizus) is widely cultivated in southern and southwestern China. To provide a basis for studying the molecular mechanisms of the ripening of this fruit, we carried out RNA sequencing (RNA-seq) analysis to identify differentially and stably expressed unigenes. The latter may serve as a resource of potential reference genes for normalization of target gene expression determined using quantitative real-time PCR (qRT-PCR). We selected 11 candidate reference genes from our RNA-seq analysis of red pitaya fruit ripening (ACT7, EF-1α, IF-4α, PTBP, PP2A, EF2, Hsp70, GAPDH, DNAJ, TUB and CYP), as well as β-ACT, which has been used as a reference gene for pitayas in previous studies. We then comprehensively evaluated their expression stability during fruit ripening using four statistical methods (GeNorm, NormFinder, BestKeeper and DeltaCt) and merged the four outputs using the online tool RefFinder for the final ranking. We report that PTBP and DNAJ showed the most stable expression patterns, whereas CYP and ACT7 showed the least stable expression patterns. The relative gene expression of red pitaya sucrose synthase and 4, 5-dihydroxyphenylalanine-extradiol-dioxygenase as determined by quantitative real-time PCR and normalized to PTBP and DNAJ was consistent with the RNA-seq results, suggesting that PTBP and DNAJ are suitable reference genes for studies of red pitaya fruit ripening.

Potential of Postharvest Coatings to Maintain Freshness of Red-Fleshed Pitaya (Hylocereus costaricensis)

Pitaya is a non-climacteric fruit that has white or red flesh with numerous small, black seeds. It has a high moisture content; however, water loss during handling and storage negatively affects the fresh weight, firmness and appearance of the fruit, decreasing market value. Application of compatible postharvest coatings has been shown to benefit postharvest quality of many crops. The objective of this study was to evaluate the effect of two commercial coatings on weight loss and quality of pitaya during storage. Pitaya fruit were commercially harvested and sorted for uniformity of size and freedom from defects. Fruit were briefly immersed in either a vegetable oil-based coating (VOC; Sta-Fresh® 2981) or a carnauba-based coating (CC; Endura-Fresh™ 6100) according to manufacturer’s recommendations. Fruit immersed in tap water served as a control. Fruit were fan-dried at room temperature for 20 min, then stored at 7 °C with 85% relative humidity (RH) and evaluated for selected physical quality parameters each 5 days during 20 days. After each evaluation, fruit were peeled and frozen for later analysis of soluble solids content (SSC), total titratable acidity (TTA); on day 15 fresh samples were evaluated by an untrained consumer sensory panel. CC prevented exocarp shriveling for 15 days of storage, compared to uncoated pitaya (16.3% area affected); shriveling in VOC was intermediate and not significantly different from the other treatments. Mesocarp firmness remained constant throughout 15 days of storage regardless of treatment. Fruit exocarp h* angle increased slightly by day 20, becoming slightly less red, and there were no negative treatment effects for the other quality factors measured: SSC (11.33%), TTA (0.25%), weight loss (5.5%) or sensory evaluations (appearance, flavor, texture, firmness, and juiciness). After 20 days storage, appearance for fruit from all treatments was rated unacceptable due to development of anthracnose lesions. It was concluded that both CC and VOC maintained quality of pitaya for 15 days at 7 °C and 85% RH by delaying exocarp shriveling.

Transcriptomics‐based identification and characterization of genes related to sugar metabolism in ‘Hongshuijing’ pitaya

Sugar composition not only affects fruit flavor but is also an important determinant of fruit taste and consumer preference. In this study, changes in the sugar content and sugar-metabolizing enzymes were investigated from different sections of various fruit development phases of ‘Hongshuijing’ pitaya (Hylocereus monacanthus). Genes related to sugar metabolism were also screened by transcriptome analyses. The results indicated that glucose was the major sugar in mature pitaya fruit, and was mainly regulated by vacuolar acid invertase (VAI) and sucrose synthase (SS) (degradative direction). Sugar accumulation varied in pulp between different sections of the pitaya fruit. VAI, neutral invertase (NI) and SS (degradative direction) are crucial enzymes for sugar accumulation in pitaya. The expression of 17 genes related to sucrose metabolism obtained from seven databases [NCBI non-redundant protein database (Nr), NCBI non-redundant nucleotide sequence database (Nt), EuKaryotic Orthologous Groups (KOG), The Protein Families (Pfam), Kyoto Encyclopedia of Genes and Genomes (KEGG), Swiss-prot, and Gene Ontology (GO)] were analyzed in different pitaya pulp sections. HpVAI1 had the highest relative expression level on the 29th day after pollination (DAP). Positive correlations were found between HpVAI1 expression and VAI activity; HpNI4 and NI activity; HpSS2, HpSS5, and SS activity (synthetic direction), indicating that HpVAI1, HpNI4, and HpSS2 and HpSS5 were involved in the regulation of VAI, NI, and SS (synthetic direction), respectively. HpVAI1 and HpNI4 regulated sucrose degradation and the accumulation of glucose and fructose, while HpSS2 and HpSS5 regulated sucrose synthesis. These results suggest that HpVAI1 plays a key role in sugar metabolism during fruit development of ‘Hongshuijing’ pitaya. The results of this study provide new information about sugar metabolism in pitaya fruit that could help improve fruit quality and the breeding of new cultivars.

Effect of Preharvest Application of CPPU and Perforated Packaging on the Postharvest Quality of Red-Fleshed Pitaya (Hylocereus polyrhizus sp.) Fruit

The objective of this study was to investigate the effect of the preharvest application of forchlorfenuron (CPPU) and perforated polyethylene bag packaging (PPE) on maintaining the postharvest quality of red-fleshed cv. ‘Da-Hong’ pitaya (Hylocereus polyrhizus sp.) fruit. On the flowering day, 100 mg·L−1 CPPU was sprayed on the bracts and water was used as the control. After harvest, all fruits were divided into three package treatments, which were packed without bags, packed with and without PPE bags, and stored at 5 ± 0.5 °C and 90 ± 5% relative humidity for 21 days, followed by 7 days at 20 °C and 75 ± 5% relative humidity without bags for quality evaluation. Significantly higher bract thickness (2.26 vs. 1.44 mm), longer fruit length (120.5 vs. 109.04 mm), and greater firmness (1.56 vs. 1.04 kg·cm−2) were recorded for the CPPU treated fruit at harvest. Preharvest application of CPPU with perforated packaging resulted in significantly greener bracts, a lower yellow index, fewer chilling incidences, and a lower decay ratio, but there was a slight decrease in respiration rate during cold storage at 5 °C for 21 days. However, all criteria reached the threshold when fruits were transferred to 20 °C for 7 days. In conclusion, preharvest CPPU application plus perforated packaging is the best combination for the long-term storage of red-fleshed pitaya fruit at 5 °C.

Transcriptomic analysis reveals key genes associated with the biosynthesis regulation of phenolics in fresh-cut pitaya fruit (Hylocereus undatus)

Wounding stress induces phenolic accumulation in pitaya fruit (Hylocereus undatus). This study aimed to elucidate the possible molecular mechanism underlying the wound-induced phenolic biosynthesis in fresh-cut pitaya fruit based on transcriptomic and bioinformatic analysis. Wounding stress induced the activation of metabolic pathways associated with phenolic biosynthesis, including secondary metabolism such as phenylpropanoid pathway and flavonoid pathway, signaling molecules metabolism such as ethylene, reactive oxygen species and jasmonic acid, and primary metabolism such as glycolysis, pentose phosphate pathway and shikimate pathway. Moreover, weighted gene coexpression network analysis and evolutionary relationship analysis revealed that 1 HuMYB, 3 HubHLHs, 7 HuAP2-EREBPs could be identified as putative transcription factors participating in the regulation of wound-induced phenolic biosynthesis in pitaya fruit. These findings validated previous study that wounding stress induces the conversion of hexose pool to supply essential carbon skeletons for the phenolic accumulation in fresh-cut pitaya fruit in transcriptional level and provide important and useful genetic information for further studies on the functions of transcription factors in wounding response in pitaya fruit.