Chitosan and Ascorbic Acid Combination for Extending the Postharvest Quality of Cold-Stored Pitaya

Abstract

Pitaya is a high-value tropical fruit with a postharvest life constrained by rapid physiological deterioration. This study aimed to evaluate the efficacy of chitosan-based (CH) biopolymeric coatings, enriched with ascorbic acid (AA), on the postharvest quality and preservation of pitaya fruits stored under refrigeration (12 °C). The fruits were subjected to different treatments and evaluated for biometric and physicochemical parameters, including weight loss, total soluble solids, pH, titratable acidity, and the SS/TA ratio throughout storage. The results demonstrated that the coatings significantly reduced weight loss (e.g., 4.15% for the CH4AA treatment) and contributed to the maintenance of quality attributes, delaying senescence-associated processes. Among the treatments, the combination of chitosan with ascorbic acid was the most effective in preserving fruit quality, extending the marketable shelf life from 10 to 20 days. These findings indicate that the use of biopolymeric coatings is a promising strategy to prolong the shelf life and maintain the postharvest quality of pitaya, with potential applications in commercial supply chains.

1. Introduction

Pitaya is a perennial, climbing, and epiphytic fruit-bearing plant belonging to the Cactaceae family and the genera Hylocereus and Selenicereus [1]. Native to the tropical and subtropical regions of the Americas, the plant has adapted to diverse agroecological zones and holds significant economic importance in Brazil [2,3]. The fruits are primarily characterized by the coloration of their exocarp and mesocarp, with three main species of the genus Hylocereus being particularly notable: H. undatus (red peel and white pulp), H. polyrhizus or H. costaricensis (red peel and red/purple pulp), and H. megalanthus (yellow peel and white pulp) [1,2,3].

From a biochemical and nutritional standpoint, pitaya is recognized as a functional food due to its rich profile of micronutrients, vitamin C, B-complex vitamins, minerals, and other bioactive compounds [2,4,5]. Red-fleshed cultivars contain betalain pigments (betacyanins and betaxanthins), which are water-soluble nitrogenous compounds that exhibit potent antioxidant capacity [1,2,6]. The commercial potential of pitaya faces critical postharvest challenges. As a non-climacteric fruit, pitaya must be harvested at full physiological maturity to ensure optimum organoleptic quality [3,7]. After harvest, metabolic rates increase, which accelerates senescence and results in rapid water loss. Dehydration leads to the wilting of bracts, one of the main visual indicators of deterioration that compromises commercial acceptability [8].

Associated with metabolic changes, pitaya peels are highly susceptible to mechanical damage and the action of microorganisms during storage and transport [8]. Temperature is a crucial factor in maintaining the postharvest life of pitayas, and ambient storage temperatures (~25 °C) combined with low relative humidity are considered inappropriate for preservation, as they promote losses in appearance, organoleptic characteristics, and weight after 11 days of storage [9]. Pitaya fruits also exhibit high sensitivity to low temperatures; although refrigeration is used to extend preservation, inappropriate temperatures (generally below 5–10 °C) can induce chilling injury, manifested by pulp translucency, scale browning, and loss of flavor [3,8]. The combination of these factors limits the shelf life of fresh pitaya to a few days at room temperature, requiring a comprehensive cold chain and the application of coatings/packaging to enable its long-distance distribution [1,7,10].

The application of edible films and coatings is one of the sustainable strategies to delay postharvest senescence and add value to highly perishable fruits [1,11,12]. Chitosan is a cationic polysaccharide that acts as the structural backbone, forming a semipermeable barrier that restricts gas and water vapor exchange [13]. Furthermore, chitosan exerts antimicrobial activity against fungal and bacterial pathogens [13,14,15].

Furthermore, Nguyen et al. [16] observed that 1% chitosan applications combined with an algal polysaccharide (κ-carrageenan) and plant growth regulators can reduce fresh weight loss in pitaya fruit, while maintaining antioxidant activity, acidity, and soluble solids.

The combination of ascorbic acid with a chitosan solution (CHAA) has shown promising effects in maintaining the shelf life of fruits in general. Zou et al. [10], when analyzing papaya (Carica papaya) fruits coated with a CHAA solution, observed a robust activation of sugar metabolism driven by the energy flux of the electron transport chain and the Krebs cycle; associated with this response, the coating enhanced fruit quality. In strawberries (Fragaria × ananassa), the incorporation of CHAA had a beneficial effect against weight loss and in maintaining sensory acceptance [14]. As a result of this combination, reduced membrane damage was observed due to high enzymatic and non-enzymatic antioxidant activity, as well as the maintenance of molecules such as total phenolics and ascorbic acid itself [14]. Furthermore, the addition of ascorbic acid to this matrix not only reduces the pH of the solution—which can enhance chitosan solubility—but also acts as an exogenous reducing agent and antioxidant, preventing enzymatic browning reactions and mitigating the degradation of bioactive compounds during storage [13,17]. These studies demonstrate the preservative potential of adding ascorbic acid to chitosan, making it essential for the viable preservation of pitayas of the genus Hylocereus cultivated in Brazil.

The objective of this study was to investigate the effect of chitosan-based biopolymeric coatings, either alone or in combination with ascorbic acid, on the postharvest physiology, quality maintenance, and shelf-life extension of pitaya during cold storage at 10 °C.

2. Materials and Methods

2.1. Location of the Experimental Area and Plant Material

Experiments were conducted at the Plant Ecophysiology and Postharvest Laboratories of the Department of Plant Sciences at the Federal Rural University of the Semi-Arid (UFERSA), in Mossoró, Rio Grande do Norte, Brazil (coordinates 5°12′16″ S, 37°19′29″ W, at an altitude of 18 m). According to the Köppen classification, the region’s climate is of the BSwh’ type, characterized as dry and very hot, with a mean annual temperature of 27.4 °C, an irregular rainfall of 673 mm year⁻¹, a relative humidity of 68.9%, and an average sunshine duration of 241.7 h month⁻¹ [18].

Red pitaya fruits (Hylocereus costaricensis var. Roxa do Pará) were harvested from the experimental orchard at UFERSA, 30 days after anthesis, at the full physiological maturity stage. The fruits were sourced from plants in their second year of the annual production cycle.

We selected one hundred fruits free from physical injuries or phytosanitary defects. The fruits were selected based on their uniformity in size, shape, and color, with an average weight ranging from 300 to 400 g per fruit. The fruits were sanitized in a chlorinated solution (Sumaveg®, Diversey, São Paulo, SP, Brazil). containing 100 mg L⁻¹ of active chlorine, rinsed under running water, and subsequently air-dried in a closed room at room temperature.

2.2. Preparation and Application of the Edible Coating

The chitosan (CH) matrix (Polymar®, Fortaleza, CE, Brazil; 85% degree of deacetylation) were prepared using a mixture of distilled water and 0.5% (v/v) analytical grade acetic acid, homogenized at room temperature for 30 min. Chitosan concentrations varied, resulting in the following coating treatments: (1) 3% Chitosan; (2) 4% Chitosan; (3) 3% Chitosan + 1% Ascorbic acid; and (4) 4% Chitosan + 1% Ascorbic acid [14]. Distilled water treatment was used as the control. The fruits were immersed in their respective solutions for 1.0 min, twice each, to ensure coating homogeneity and film formation. Subsequently, the fruits were placed in plastic trays and stored in a cold chamber at 12 ± 2 °C with 80% RH for 25 days, F.

The storage temperature of 12 °C was selected based on commercial practices and physiological thresholds, as pitayas are highly susceptible to chilling injury at temperatures below 10 °C. Under these safe refrigeration conditions, uncoated pitaya fruits or those treated solely with chitosan maintain their marketable quality for a limited period. However, the application of chitosan-based coatings combined with antioxidant compounds can significantly prolong the shelf life of the fruits, potentially doubling their storage time under refrigeration [19].

Every 5 days, throughout the 25-day cold storage period, fruits from each treatment were sampled and subjected to the evaluations described below.

2.3. Physical Analyses and Visual Evaluation

The following physical variables were evaluated at 5-day intervals during storage: Weight loss was determined by weighing the fruits using a precision balance (Model M214Ai, Bel Equipamentos Analíticos, Piracicaba, Brazil). Peel and pulp firmness were measured using a digital texture analyzer TA.XT Express (Stable Micro Systems Ltd., Godalming, UK).

Peel and pulp color were determined using a digital colorimeter CR-410 (Konica Minolta Sensing, Inc., Osaka, Japan). Four fruits per treatment were evaluated, measuring the color parameters L* (lightness), C* (chroma or color intensity), and h° (hue angle). Peel readings were taken randomly at two equidistant points on the equatorial region of the fruit. For pulp color evaluation, after transversally cutting the fruit, readings were taken at the center of both sectioned halves, and the average of the obtained values was calculated.

The visual quality of the fruits was evaluated by a trained panel consisting of the same three assessors throughout the entire experimental period. Panel members were previously trained to consistently identify and classify visual changes in pitaya fruits during storage. A 5 to 0 rating scale was used, where scores from 4 to 3.1 indicate an optimal marketable condition (<5% of the fruit surface and bracts exhibiting defects); scores from 3 to 2.1 indicate a good condition (5–25% of the surface and bracts with defects); scores from 2 to 1.1 indicate a fair condition (26–50% of the surface and bracts with defects, showing signs of dehydration and browning); and scores from 1 to 0 indicate an unmarketable condition (>51% of the surface and bracts with defects). The marketability threshold was set at a score of 1.5. This evaluation scale was adapted from Woolf et al. [20].

For the chemical analyses, including antioxidant activity using the DPPH assay and other determinations, the fruits were previously processed. Specifically, after a transverse cut, the pulp was separated and homogenized in a food processor Ninja Auto-iQ Turbo Smooth (SharkNinja Operating LLC, Needham, MA, USA), using one individual fruit per replicate for each treatment. The resulting homogenized material was used for all subsequent analyses.

2.4. Soluble Solids, Total Acidity, SS/TA Ratio, and pH

Soluble solids (SS) of the macerated pulp were determined using a digital refractometer (refractive index 1.3330–1.4098) according to Costa et al. [21], with results expressed in °Brix. Titratable acidity (TA) was determined by titration with a 0.1 N NaOH solution, using phenolphthalein as an indicator, and the results were expressed as a percentage of malic acid (%). The pulp pH was measured using a digital benchtop pH meter, model DL-PH (Del Lab, Araraquara, SP, Brazil).

2.5. Total Metabolites and Betalain Pigments

Total soluble sugars were determined using the anthrone colorimetric method, adapted from Yemm and Willis [22]. Ethanolic extracts were reacted with the anthrone reagent, and absorbance was read at approximately 650 nm using a UV-Vis spectrophotometer Cary 60 (Agilent Technologies, Inc., Santa Clara, CA, USA). Concentrations were calculated using a standard glucose curve and expressed as g 100 g⁻¹ of fresh weight.

Reducing sugars were determined using the 3,5-dinitrosalicylic acid (DNS) colorimetric method described by Miller [23]. This assay is based on the reduction of DNS by reducing sugars in an alkaline medium. Absorbance was measured at 540 nm using a spectrophotometer, and a standard glucose curve was used to calculate the concentrations.

Vitamin C was quantified by titration with Tillmans’ solution, according to Strohecker and Henning [24]. Protein content was determined by the Bradford method [25], which is based on the binding of Coomassie Brilliant Blue dye to the proteins in the aqueous extract. Absorbance was measured at 595 nm, and a bovine serum albumin (BSA) standard curve was used to calculate the protein concentration of the samples.

Total phenolic compounds were determined using the Folin–Ciocalteu method, as described by Sánchez-Rangel et al. [26], with modifications. Pitaya samples (0.25 g) were macerated in 2 mL of analytical grade methanol and kept in the dark at 8 °C for 24 h. After this period, the methanolic extracts were centrifuged at 12,000 rpm, and the supernatant was collected for analysis. For the reaction, a 150 µL aliquot of the extract was mixed with 600 µL of distilled water and 250 µL of Folin–Ciocalteu reagent (0.25 N). After a 10-min incubation in the dark, 500 µL of a 20% (w/v) sodium carbonate solution was added. The samples were homogenized and kept at room temperature in the dark for 30 min. Absorbance was measured at 765 nm using a spectrophotometer. Quantification was performed using a gallic acid standard curve, and the results were expressed as gallic acid equivalents (GAE).

The extraction of total betalains was performed using 2 g of macerated pulp in 5 mL of distilled water, followed by centrifugation at 4 °C for 40 min. The quantification of betaxanthins, betacyanins, and total betalains was carried out using a spectrophotometer at 476 nm, 538 nm, and 600 nm, according to the methodology proposed by [27]. The results were expressed in µg 100 g⁻¹.

2.6. Antioxidant Activity by the DPPH Method

Antioxidant activity was determined using the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, utilizing the same methanolic extracts prepared for the total phenolic compounds analysis. The antioxidant capacity was determined at the ripening stage according to the method of Brand-Williams et al. [28]. For the assay, 0.84 mL of a 0.1 mM DPPH solution was mixed with 0.6 mL of the methanolic extract. The control sample was prepared by mixing 0.84 mL of the DPPH solution with 0.06 mL of analytical grade methanol. After a 30-min reaction period, absorbance was measured at 517 nm and 25 °C using a spectrophotometer. The decrease in sample absorbance corresponds to the DPPH free radical scavenging percentage (%AAO), which was calculated relative to the absorbance of the control sample.

2.7. Experimental Design and Statistical Analysis

Experiments were conducted in a completely randomized design (CRD) arranged in a 5 × 6 factorial scheme. The first factor corresponded to five coating treatments: control (uncoated), 3% chitosan (CH3), 4% chitosan (CH4), 3% chitosan combined with 1% ascorbic acid (CH3AA), and 4% chitosan combined with 1% ascorbic acid (CH4AA). The second factor consisted of six cold storage periods (0, 5, 10, 15, 20, and 25 days). Four replicates were used per treatment, with each replicate consisting of a single fruit evaluated independently at each storage time. All physicochemical and biochemical analyses were performed using these individual fruits.

Data were checked for normality using the Shapiro-Wilk test and for homoscedasticity using Levene’s test (p < 0.05). Once the assumptions of ANOVA were met, the data were subjected to analysis of variance using the F-test (p < 0.05). When significant differences were found, the means were compared using Tukey’s test (p < 0.05, n = 4). Statistical analyses were performed using RStudio^® software version 4.3.2, utilizing the Easyanova (v. 11.0) and Agricolae (v. 1.3–7) packages.

Pearson correlation analysis and Principal Component Analysis (PCA) were performed for the treatments, comparing them only at 5 and 20 days of storage, which correspond to the maximum observed time limit for maintaining the quality of cold-stored pitayas. The PCA was conducted using the correlation matrix in the OriginPro^® 2026 software (v. 10.3.0.180), which involves the prior standardization of data by z-score (mean-centered and scaled to unit variance). Four replicates per treatment were used.

3. Results

Fruit weight loss and pulp firmness exhibited no significant interaction between the coating and storage time; however, significant main effects were observed for both factors independently (p < 0.01). For peel firmness, a significant interaction was observed (p < 0.05). Weight loss increased progressively throughout the storage period. The CH4AA treatment most effectively reduced weight loss (4.15%), whereas the 3% chitosan (CH3) treatment resulted in the highest values. Between days 15 and 20, while fruits still maintained marketable quality, the control and CH3 treatments showed the highest rates of weight losses, demonstrating similar behavior to each other (Figure 1A).

Pulp firmness was influenced solely by the main effects of the factors, with the highest mean value observed under the 4% chitosan treatment (1.57 N) and the lowest in the control (1.44 N), representing a difference of less than 10% (Figure 1C). Regarding peel firmness, no significant differences were observed among treatments up to 20 days of storage. A significant interaction was evident only at 25 days, at which point the CH3 treatment exhibited the lowest firmness (6.63 N) and the treatments combined with ascorbic acid showed the highest values; however, by this period, the fruits no longer exhibited marketable quality (Figure 1D).

Uncoated fruits and those treated with 3% chitosan exhibited a decrease in their visual scores starting from day 5 of storage (Figure 1B). By day 15, the scores of these fruits had fallen below the limit for marketability (Figure 1B and Figure 2). In contrast, for fruits subjected to chitosan (3% and 4%) combined with ascorbic acid, visual evaluation scores only began to decline after 15 days (Figure 1B). At this point, visual changes were less pronounced (Figure 2). At 20 days, these fruits still retained a score equal to or greater than 3, thus remaining marketable (Figure 1B).

Soluble solids remained stable throughout the storage period, with no significant variations among treatments (Figure 3A). The progressive reduction in titratable acidity (TA) evidenced the catabolism of organic acids as respiratory substrates (Figure 3B). Consequently, the SS/TA ratio also decreased progressively, mirroring the reduction in acidity (Figure 3C). The pH exhibited a slight increase as storage progressed (Figure 3D), reflecting the gradual reduction in fruit acidity. Overall, the observed changes were more closely associated with the natural ripening dynamics rather than the specific effects of the coatings.

Significant interaction effects between coating treatments and storage time were observed for all biochemical variables (Figure 4). Total soluble sugars (Figure 5A) were significantly affected by this interaction, with an initial increase up to 10 days of storage followed by a general decline. At 10 days, no significant differences were observed among treatments, as indicated by the identical lowercase letters across all groups. From 15 days onward, CH3AA and CH4AA consistently exhibited higher sugar contents compared to the control, exceeding it by approximately 30%, while CH3 and CH4 showed intermediate values. At 25 days, all treatments exhibited reduced levels, with the lowest values recorded in the control and CH3 groups, while CH4 maintained comparatively higher contents. Reducing sugars (Figure 4B) also exhibited a significant interaction effect, with the highest values recorded early in storage at day 5, particularly for CH4. At 15 days, CH4 displayed a distinctive peak that was approximately 90% higher than the control, while the remaining treatments showed statistically similar values. Thereafter, reducing sugar contents decreased progressively across all groups until the end of storage. Vitamin C content (Figure 4C) was significantly influenced by the interaction between factors, with maximum values recorded at 15 days. At this stage, CH3AA and CH4AA reached the highest concentrations, exceeding the control by more than 40%, while the other treatments remained at lower and similar levels. Although a sharp decline was recorded at 20 days, coatings enriched with ascorbic acid maintained higher retention throughout the storage period compared to the control. Finally, protein content (Figure 4D) showed a significant interaction effect, with levels increasing until day 15 and reducing at later stages. At the 15-day peak, the highest protein levels were recorded in chitosan-treated fruits (CH3, CH4, and CH4AA), showing a transient accumulation roughly 20% greater than the control. From day 20 to 25, protein levels decreased in all treatments, with no consistent statistical differences among them.

The peel and pulp colorimetric parameters (L*, C*, and h°) were influenced by storage time and coating treatments (

Table 1. Effect of chitosan and ascorbic acid coating on the color of red pitaya during storage at 12 °C and 80% RH.

	Peel			Pulpe
Coating	L Values	C Values	h° Value	L Values	C Values	h° Value
Day 0
Control	35.86 ± 2.15	21.66 ± 2.51	38.81 ± 0.38	28.27 ± 0.32	28.14 ± 0.72	16.57 ± 0.35
CH3	35.86 ± 2.15	21.66 ± 2.51	38.81 ± 0.38	28.27 ± 0.32	28.14 ± 0.72	16.57 ± 0.35
CH4	35.86 ± 2.15	21.66 ± 2.51	38.81 ± 0.38	28.27 ± 0.32	28.14 ± 0.72	16.57 ± 0.35
CH3AA	35.86 ± 2.15	21.66 ± 2.51	38.81 ± 0.38	28.27 ± 0.32	28.14 ± 0.72	16.57 ± 0.35
CH4AA	35.86 ± 2.15	21.66 ± 2.51	38.81 ± 0.38	28.27 ± 0.32	28.14 ± 0.72	16.57 ± 0.35
Day 20
Control	36.72 ± 0.25 aA	32.25 ± 1.62 aA	31.21 ± 0.90 aB	28.60 ± 0.27 aA	28.35 ± 0.71 aA	16.54 ±0.16 aA
CH3	36.20 ± 1.52 aA	26.86 ± 1.95 aABC	36.41 ± 1.87 aB	28.84 ± 0.70 aA	29.85 ± 1.59 aA	17.36 ± 0.30 aA
CH4	36.96 ± 0.49 aA	27.08 ± 1.61 aAB	38.44 ±4.32 aAB	28.02 ± 0.31 aA	27.54 ±0.88 aA	16.51 ± 0.28 aA
CH3AA	37.69 ± 0.57 aA	27.95 ± 2.06 aBC	39.58 ± 4.05 aAB	28.50 ± 0.31 aA	29.56 ± 0.78 aAB	16.48 ± 0.51 aA
CH4AA	37.14 ± 1.08 aA	27.83 ± 3.35 aAB	40.36 ± 7.04 aA	29.20 ± 0.18 aA	30.24 ± 0.78 aA	16.58 ± 0.14 aA

Control; CH3—Chitosan at 3%; CH4—Chitosan at 4%; CH3AA—Chitosan at 3% + Ascorbic acid at 1%; CH4AA—Chitosan at 4% + Ascorbic acid at 1%. Means followed by the same lowercase letters do not differ among treatments according to the Tukey test (p ≤ 0.05), and means followed by the same uppercase letters do not differ among storage days within each treatment according to the Tukey test (p ≤ 0.05).

). On day 0, no differences were observed among the treatments. Peel lightness (L*) remained stable throughout storage, with no signs of surface browning. The main changes occurred in chroma and hue angle. Up to 10 days—the marketable period for the control, CH3, and CH4 fruits no changes compromising the visual appearance of these treatments were observed. From day 15 onwards, hue changes became more evident in the control, indicating the advancement of the ripening process and the onset of senescence, whereas the treatments combined with ascorbic acid showed greater color stability up to 20 days.

In the pulp, colorimetric parameters remained relatively stable throughout storage. Slight variations in color intensity were observed in the treatments combined with ascorbic acid during the later stages of storage; however, these had no significant impact on visual quality up to the marketability threshold.

Overall, the coatings contributed more to maintaining color stability throughout storage than to inducing significant changes in the initial visual attributes of the fruits. The complete dataset containing the temporal dynamics of the colorimetric parameters across all evaluated sampling days is available in Supplementary Table S1.

Total betalains and betacyanins exhibited a significant interaction between coating treatments and storage time (Figure 5A,B), evidencing a behavior dependent on the combination of treatment and storage period. During the initial days, no consistent differences were observed among the treatments. Up to 10 days the period corresponding to the marketable life of the control, CH3, and CH4 fruits a downward trend in pigment content was observed, with no notable distinctions among these treatments. From day 15 onwards, the responses became more evident, with lower concentrations in fruits treated with ascorbic acid combinations and higher accumulation in those with isolated chitosan treatments, especially CH4 during the later stages of storage. At 20 and 25 days, the increase observed in CH4 and the control indicates an intensification of secondary metabolism and a possible concentration of pigments due to water loss and the advancement of ripening. For betaxanthins, there was no significant effect of the treatments throughout storage (Figure 5C), with stability observed for the control, CH3, CH4, and CH3AA, whereas CH4AA exhibited a reduction after the onset of storage. Overall, pigment variations became more pronounced after the marketable period of the control, CH3, and CH4 fruits, and were not directly associated with the maintenance of initial visual quality.

Antioxidant activity (DPPH) exhibited a significant interaction between coating treatments and storage days (p ≤ 0.05) (Figure 6A), showing an upward trend throughout storage, with the highest values observed at 20 days. Up to 10 days the period corresponding to the marketable life of the control, CH3, and CH4 fruits, no consistent differences were observed among the treatments. At day 15, an increase in antioxidant activity began, which intensified by day 20, when the control, CH3, CH4, and CH3AA treatments exhibited similar and higher responses. By day 25, differentiation among the coating treatments was observed, with CH4 standing out. Regarding phenolic compounds (Figure 6B), there was no significant effect of the coating treatments within each storage day, evidencing similar behavior among the treatments. However, a significant effect of storage time was observed, with lower contents during the initial days and an increase from day 15 onwards, remaining elevated until the end of the storage period. Overall, the increase in antioxidant activity mirrored the rise in phenolic compounds during the later stages of storage. This indicates a metabolic response associated with the advancement of ripening and senescence, especially after the marketable period of the control, CH3, and CH4 fruits had ended.

Principal Component Analysis (PCA) explained 52.65% of the total variance, with 38.47% attributed to PC1 and 13.18% to PC2, evidencing a separation between days 5 and 20 of storage (Figure 7A). PC1 was associated with fresh weight loss, total phenolic compounds, and antioxidant activity (DPPH), contributing to the distinction of fruits at 20 days. The CH3AA and CH4AA treatments showed a tendency to cluster in the positive quadrant of this component. Conversely, fruits evaluated at 5 days clustered on the negative side of PC1, associated with higher visual appearance scores, total sugars, total soluble solids, and vitamin C. PC2 contributed primarily to the separation related to betalains. These results should be interpreted as a descriptive tool for visualizing multivariate patterns and do not imply direct causal relationships.

Pearson correlation analysis corroborated the patterns observed in the PCA (Figure 7B). Fresh weight loss showed a negative correlation with the visual score, indicating the reduction of visual quality throughout storage. Antioxidant activity (DPPH) showed a positive correlation with phenolic compounds and betalains, suggesting that these metabolites are associated with the antioxidant potential of pitaya. Furthermore, a positive correlation was observed between total sugars and total soluble solids, reflecting the respiratory metabolism of the fruits. Overall, the results indicate that the CH3AA and CH4AA treatments showed a trend toward better maintenance of the physical and functional quality of pitaya for up to 20 days of storage; this interpretation should be considered in conjunction with the other analyses performed.

4. Discussion

The film-forming properties of chitosan (CH) polymers are well-documented for their ability to generate a homogeneous coating, which effectively delays postharvest senescence across various horticultural crops [29]. Furthermore, the successful application of CH on fruits depends on the optimal concentration required to form a uniform barrier that controls water vapor loss [30]. In the present study, uncoated pitaya fruits and those coated with chitosan alone maintained commercial quality for a maximum of 10 days (Figure 1B and Figure 2), whereas the synergistic application of CH combined with ascorbic acid (CH3AA and CH4AA) extended the shelf life to 20 days.

The decline in the visual and physical quality of the control, CH3, and CH4 fruits after 10 days was attributed to excessive dehydration (Figure 1B and Figure 2). Water loss compromises cell turgor, promotes peel shriveling, and reduces firmness, ultimately impacting commercial acceptance [31,32]. The enhanced preservation observed in this study was directly related with the reduced dehydration of fruits treated with CH3AA and CH4AA treatments (Figure 1 and Figure 2).

This extended shelf life is likely due to the maintenance of tissue structural integrity during storage. Previous studies have highlighted the effectiveness of the CH + AA combination on membrane stability in strawberry fruits [14], and a similar protective effect on cell wall integrity has been reported in papaya (Carica papaya) [33]. The efficacy of these coatings is largely derived from the formation of a semipermeable biopolymeric barrier by chitosan, which restricts the transpiration and respiration rates of the fruits. This physical barrier operates synergistically with the antioxidant properties of ascorbic acid, which neutralizes reactive oxygen species (ROS) and delays postharvest physiological senescence, a phenomenon similarly observed in various cold-stored fruits treated with chitosan and antioxidant compounds [29,34].

Chemical changes accompanied the progression of senescence and exhibited a strong interdependence among the evaluated constituents. Overall, soluble solids (SS) remained stable during the early storage fase, with more pronounced increments observed in the control fruits at 20 days. This was associated with greater water loss and the subsequent concentration of sugars. Soluble sugars followed a similar trend to SS, showing a more significant increase in the control during the advanced stages of storage, which reinforces the concentration effect induced by water loss and the degradation of structural reserves.

This behavior was accompanied by a progressive reduction in titratable acidity (TA) and an increase in pH (Figure 3A,D), evidencing the consumption of organic acids as metabolic substrates during respiration. In coated fruits, particularly those treated with ascorbic acid, enhanced TA stability and a smaller rise in pH were observed at 10 and 20 days, indicating downregulated respiratory metabolism. Concurrently, vitamin C levels declined progressively throughout storage, most notably in control at 20 days, whereas the antioxidant treatments contributed to a higher retention of this compound. The attenuation of these respiratory processes by the coatings resulted in a more balanced SS/TA ratio and, consequently, preserving of sensory quality [34].

Chitosan-based coatings, especially when combined with ascorbic acid (CH3AA and CH4AA), contributed to maintaining the postharvest quality of pitaya during the periods when the fruits remained marketable, with the most evident effects observed during the intermediate days of storage. Given that pitaya is a non-climacteric fruit, the observed metabolic behavior, an initial preservation followed by a gradual decline in reducing sugars and vitamin C contents, is physiologically expected. This occurs because these fruits lack a pronounced respiratory peak, exhibiting instead a progressive metabolic evolution [9].

Fruit metabolism appeared to be dependent on both storage time and coating formulation. The initial peak, followed by a reduction during the more advanced stages, suggests a possible interplay among reserve hydrolysis, respiratory consumption, and the antioxidant response. For treatments containing chitosan combined with ascorbic acid, the higher metabolite levels observed while the fruits still retained marketable quality may indicate a better metabolic balance. Conversely, the later decline could be associated with the advancement of senescence and an increased respiratory demand. It is important to note that these interpretations are based on indirect indicators, as no direct measurements of respiration or energy metabolism were performed [35]. Taken together, the evaluated phytochemicals exhibited a behavior consistent with the physiology of non-climacteric fruits, wherein the modulation promoted by the coatings acts primarily by attenuating oxidative processes and regulating respiration, without altering the species’ characteristic physiological pattern [12,36].

Antioxidant activity, assessed via the DPPH assay, increased progressively during storage, reaching its maximum on the 20th day. The increase observed throughout storage is likely related to metabolic changes associated with ripening and senescence. Although the coatings may have influenced this response, the results indicate a predominant effect of storage time, and the variations should not be attributed exclusively to the treatments [37]. Additionally, it should be noted that the DPPH assay reflects strictly an in vitro radical scavenging capacity. Therefore, these results do not necessarily fully represent the complex in vivo antioxidant processes occurring within the fruit tissue. Indeed, on days 10 and 15, the effect of storage time predominated, with no significant differences observed among the treatments.

In non-climacteric fruits, the antioxidant activity is associated with a gradual increase in postharvest oxidative stress, which triggers defense mechanisms and upregulates the synthesis or release of phenolic compounds [8,38]. Although total phenolics did not differ among the coating treatments, they increased significantly from day 15 onwards and remained elevated until the end of the storage period, explaining the higher antioxidant potential observed. Thus, the elevation in antioxidant activity reflects an adaptive response to the physiological progression of the fruit, whereas the coatings contributed primarily to attenuating oxidative degradation and maintaining metabolic stability [39,40].

The multivariate separation observed in the PCA demonstrates that storage time was a determining factor in modulating pitaya characteristics, with PC1 primarily responsible for discriminating between the 5-day and 20-day stages. The positive association of PC1 with fresh weight loss, total phenolic compounds, and antioxidant activity (DPPH) especially at 20 days [36] indicates that as storage progressed, there was an intensification of stress-related responses and antioxidant mechanisms. The clustering of the CH3AA and CH4AA treatments in the positive quadrant suggests that chitosan combined with ascorbic acid maintained functional quality, possibly by modulating oxidative processes. Conversely, fruits evaluated at 5 days, which were associated with higher visual appearance scores, total sugars, SS, and vitamin C, reflect conditions typical of the early stages of storage, during which no significant physical impairment has yet occurred [33].

However, the joint interpretation of the PCA and Pearson correlation indicates that physical changes were decisive in defining marketable quality. The negative correlation between fresh weight loss and visual score underscores that water loss directly impacts appearance, which serves as the primary determinant for commercial acceptance. Although phenolic compounds, betalains, and antioxidant activity showed a positive association among themselves indicating that these metabolites sustain the fruit’s antioxidant potential these variables played a complementary role in quality assessment. Similarly, the positive correlation between total sugars and SS reflects the respiratory metabolism characteristic of a non-climacteric fruit, without indicating abrupt changes in sensory quality. Thus, while the CH3AA and CH4AA treatments preserved functional attributes for up to 20 days, it was the physical variables, especially appearance and weight loss, governed the maintenance or loss of the marketable quality of pitaya.

It is important to highlight that the rationale for the experimental treatments adopted in this study is grounded in well-established evidence regarding the use of chitosan-based edible coatings combined with antioxidant compounds, which are recognized for their ability to modulate physiological processes and extend the postharvest life of fruits. In this context, data reliability is corroborated by the consistency of our results with the existing literature, as well as by the rigorous experimental design employed and the statistical analyses applied—including ANOVA and Tukey’s test—which ensure robust inferences. Furthermore, the reproducibility of the results is supported by the strict standardization of experimental conditions and the use of widely described methodologies, facilitating the replication of these findings in future studies [19,41].

However, it is important to acknowledge that using a single fruit per replicate introduces inherent biological variability, particularly in the biochemical analyses. While our statistical design accounted for this variance, future studies employing pooled samples could further refine and validate these findings.

5. Conclusions

Pitaya fruits stored under refrigeration (12 °C and 80% RH), whether uncoated or treated with chitosan alone, maintained their marketable quality for a maximum of 10 days. However, the application of chitosan-based coatings combined with ascorbic acid (CH3AA and CH4AA) successfully doubled the shelf life to 20 days. This technology shows potential for application in refrigerated supply chains, contributing to the reduction of postharvest losses.

While these findings demonstrate a strong proof-of-concept under controlled experimental conditions, direct extrapolation to large-scale commercial scenarios requires caution. Future studies must validate these applications in commercial packinghouse environments, including the assessment of different cultivars and economic feasibility. However, as the results were obtained under controlled conditions, their direct extrapolation is limited. Future studies should validate these applications under commercial conditions, including the assessment of different cultivars and economic feasibility.