Exploring the impact of dry conditioning on the postharvest quality and longevity of torch ginger flower stems

ABSTRACT

Dry conditioning and sucrose pulsing are techniques used to improve the durability of flower stems. Dry conditioning helps to balance the osmotic potential of the flower stems and can be applied after harvest and transportation. The objective was to evaluate how different dry conditioning times followed by sucrose pulsing may affect the postharvest quality, durability, and physiological aspects of torch ginger flower stems. For this purpose, flower stems were collected and submitted to dry conditioning for different periods: 0-h, 3-h, 6-h, 12-h, and 24-h. Every 3 days, visual quality, percentage of true flowers, absorption rate, water content, fresh and dry weights, and colorimetric parameters were evaluated. The concentration of pigments, biochemistry of the antioxidant system, and macromolecules were analyzed. Dry conditioning for more than 12-h is not recommended as it leads to a loss of quality and durability in torch ginger flower stems and accelerates senescence. The absorption rate decreases and pigments break down after this period, while H₂O₂ and lipid peroxidation concentrations increase. Furthermore, sugar and protein reserves are consumed during senescence. It is recommended to hydrate harvested stems immediately to avoid the negative effects of dry conditioning on postharvest quality and durability.

Keywords:
Antioxidant system; durability; Etlingera elatior; senescence; water stress

Introduction

Postharvest practices encompass a series of procedures designed to uphold quality, enhance durability, and minimize losses of flower stems. Conditioning, when performed correctly, is a fundamental process for attaining these objectives (Carneiro et al. 2014; Malakar et al. 2023).

For the conditioning of torch ginger flower stems, it is recommended to harvest them early in the morning and promptly transport them for processing. Throughout this procedure, it is advisable to keep the stems immersed in water to maintain the hydration of the torch ginger (Nogueira et al. 2023). The most common conditioning method from harvest to commercialization involves immersion in a solution. However, unlike dry conditioning, this method presents certain drawbacks that vary according to the species, including reduced postharvest quality and occupying a considerable amount of space within the cold chamber (Almeida et al. 2011; Cunha Neto et al. 2023).

Thus, dry conditioning has been investigated as an alternative for some species that tolerate water absence, such as the genus Gladiolus. Dry conditioning prevents flower opening, thereby prolonging stem durability. Upon hydration, flower opening begins. However, dry conditioning for a prolonged period, such as exceeding 36 hours for Gladiolus, can be detrimental, inducing physiological stress and injuries (Costa et al. 2017).

Dry conditioning can be employed for calla lilies for up to 6 days; nonetheless, pretreatment involving immersing the stems in sucrose or water for 1 hour is necessary (Almeida et al. 2011). Otherwise, for many species, dry conditioning is ineffective as wilting and senescence of flower stems are closely associated with water deficit. Continuous reductions in water uptake can lead to stress and alterations in the physiology of the flower stems (Costa et al. 2021).

Water stress due to water limitation occurs when the water absorption rate is lower than the transpiration rate of the stem. Consequently, there is low hydraulic conductance, microbial growth, the formation of air bubbles, deposition of suberin and lignin in the xylem vessels, and deposition of pectin and phenols. These factors significantly impact the postharvest quality of stems, thereby restricting their overall quality and durability (Costa et al. 2017; Sales et al. 2021).

Moreover, the process of harvesting ornamental plants can be costly due to the necessity of maintaining stem hydration consistently after cutting. Therefore, the present study aimed to evaluate the effects of dry conditioning for different periods of time on the quality and physiological aspects of torch ginger after harvest. Moreover, we aimed to elucidate whether the stems of this species are tolerant to periods without immersion in water, whether dry conditioning alters the physiology and biochemistry of floral stems, and whether these changes are related to stress conditions.

Material and methods

Evaluation of a dry conditioning period during flower stem storage

Flower stems of Etlingera elatior cv. 'Porcelain' were harvested at a semi-open stage in relation to the inflorescence aperture point, selecting those without true flowers (Mattos et al. 2018). The flower stems were obtained at the Federal University of Lavras, in the Ornamental Plants sector, responsible for cultivating tropical flowers. The average diameter of the stems was 1.2 cm +/- 2 mm, with a weight of 290 g. The flower stems were cleaned and standardized to 45 cm from the base of the stem to the beginning of the inflorescence. The treatments consisted of conditioning periods without water after harvest, which were 0 h (control), 3-h, 6-h, 12-h, and 24-h. After this period encompassing the tested treatments, the stems were placed in a 15% sucrose pulsing solution for 24-h and then transferred to fully sealed containers containing 1 L of distilled water, maintaining a temperature of 21 °C and 70% relative humidity.

Commercial quality of flower stems

The visual quality of torch ginger flower stems was assessed by three evaluators until all treatments scored a grade of 3, which represents the limit for commercialization, based on criteria described in Table 1 by Carneiro et al. (2014).

Table 1
Criteria for assigning scores to evaluate the visual quality of torch ginger inflorescences.

Score	Rating	Description
4	Excellent	Stems and inflorescences are turgid, with bracts exhibiting brilliance and characteristic coloration.
3	Good	Beginning of turgor loss (only sensitive to touch), with or without the beginning of fading and/or wilting of the edges of the bracts and stems.
2	Regular	Decline in bracts due to a visible loss of turgor and brightness of the inflorescence and stem. Borders of the bracts with a wilted appearance.
1	Bad	Loss of pronounced turgor of bracts and/or stems; edges of bracts translucent; central part of the inflorescence softened.
0	No quality	Trash: bracts that are soft and/or dry, with a soggy appearance and rotting of the central part of the inflorescence, leading to abscission of the bracts.

• Source: et al.).

In addition to visual quality, the percentage of stems with emerged true flowers after harvest; flower stems absorption rate, the fresh mass (g) and dry mass (g) of torch ginger stems, and water content (%) were evaluated using a scale for analytical precision. The absorption rate was determined by measuring the volume of water consumed in mL/stem/day, while the water content (%) was calculated using equation 1 (Sales et al. 2021):

(Eq 1) water contents (%) = [(fresh weight (g) - dry weight (g))/fresh weight (g)] × 100%

Colorimetric analyses

The changes in color were also analyzed using a colorimeter (Konica Minolta®, CM-5, Osaka, Japan) at a 10 ° angle and illuminant D65 (daylight). Three fully expanded bracts of each inflorescence, located in the second outermost row, were measured with the colorimeter positioned in the middle portion of the bract. The parameters a* (dimensionless) for the red (positive values) and green (negative values) wavelengths; b* (dimensionless) representing the yellow (positive values) and blue (negative values) wavelengths, and L* (dimensionless) indicating the luminosity of the sample (the more positive the value, the lighter the sample; the more negative the value, the darker the sample) were measured. Chroma (dimensionless) corresponds to the color purity (the stronger and brighter the color, the more distant it is from the origin of the coordinates). Additionally, the Hue angle was calculated using equation 2, defining the color hue (Lago et al. 2020).

(Eq 2) ºh = tangent-1(b*/a*)

Quantification of carotenoids and anthocyanins

The carotenoid concentration (µg g^-1 MF) was quantified by extracting 0.2 g fresh mass samples in 80% acetone. The concentration of carotenoids was determined from the extracts using a spectrophotometer at absorbance wavelengths of 470, 646.8 and 663.2 nm based on the equation 3 (Lichtenthaler & Wellburn 1983):

(Eq 3) Total carotenoids = [1000ABS470-1.82 (12.25ABS663.2-2.79ABS646.8) - 85.02 (21.50ABS646.8-5.10ABS663.2)] 198

Where ABS = absorbance

For the extraction of anthocyanins, 1 g of the sample was weighed and ground, and then 30 mL of the extraction solution (95% ethanol + 1.5 N HCl) was added at a ratio of 85:15. The samples were homogenized and filtered, and the readings were taken at 535 nm following equation 4 (Francis 1982):

(Eq 4) Anthocyanin = (ABS535 x dilution factor)/98.2

Where ABS = absorbance

Hydrogen peroxide and lipid peroxidation quantification

Samples of fully expanded bracts, located in the second outermost row of each inflorescence, weighing 0.2 g, were macerated in liquid nitrogen with 20% polyvinylpyrrolidone (PVP) (m/v), homogenized in 1.5 mL of 0.1% (w/v) trichloroacetic acid (TCA), and centrifuged at 12,000 × g for 15 minutes at 4 °C. The concentration of hydrogen peroxide (H₂O₂) was determined by measuring the absorbance at 390 nm in a reaction medium containing 100 mM potassium phosphate buffer at pH 7.0 and 1 M potassium iodide (Velikova et al. 2000).

Lipid peroxidation was determined by quantifying the reactivity of species to thiobarbituric acid (TBA), as described by Buege and Aust (1978). Samples weighing 0.2 g were macerated in liquid nitrogen supplemented with 20% PVP (w/v) and homogenized in 1.5 mL of 0.1% TCA (w/v). The homogenate was centrifuged at 12,000 × g for 15 minutes at 4 °C. Aliquots of the supernatant (250 µL) were added to the reaction medium, which included 0.5% TBA (w/v) and 10% TCA (w/v), and then incubated at 95 °C for 30 minutes. Rapid cooling on ice halted the reaction, and the absorbance readings were taken at 535 nm and 600 nm using a spectrophotometer.

Analysis of superoxide dismutase and catalase

Using electrophoresis, the expression of the enzymatic activities of superoxide dismutase (SOD) and catalase (CAT) was determined by extracting 1 g of fresh matter (FM) in 0.2 M Tris-HCl buffer at pH 8.0 with 0.1% beta-mercaptoethanol for SOD and CAT. The material was vortexed and refrigerator for 12 hours, followed by centrifugation at 14,000 rpm for 30 minutes at 4 °C. The electrophoretic run was conducted using a polyacrylamide gel system with a discontinuous setup, consisting of a 7.5% separating gel and a 4.5% stacking gel. Tris-glycine running buffer with a pH of 8.9 was used. A volume of 60 μL of the sample supernatant was applied to the gel, and the electrophoretic run was performed at 150 V for 5 hours. After the run, the gels were used to detect the activities of SOD and CAT enzymes, following the methods described by Silva Neta et al. (2020).

Concentration of total soluble sugars, reducing sugars, and proteins

To assess the macromolecules associated with primary metabolism, 0.2 g of dry mass was extracted using 0.1 M potassium phosphate buffer (pH 7.0) and incubated in a water bath at 40 °C for 30 minutes. Then, the extract was centrifuged at 10,000 G for 20 minutes, and the supernatant was collected. Additional buffer was added, and the centrifugation process was repeated. The collected supernatant was promptly stored at -80 °C. Total soluble sugars, reducing sugars, and proteins were quantified using the Anthrone, Dinitrosalicylic acid (DNS), and Bradford spectrophotometric methods, respectively, following the protocols by Yemm and Willis (1954) and Miller (1959) and Bradford (1976), with some modifications.

Statistical analyses

The experiment was replicated twice using a completely randomized design with three repetitions, with 3 stems per plot, in a double factorial scheme (5 treatments x 5 evaluations). As treatment, we considered five dry conditioning periods, with five evaluations performed on different days. The results were obtained from the means of the two replicates, and the data were tested for normality using ANOVA and subjected to regression analysis. For the parameters of visual quality and absorption rate, the Skott-Knott test was performed using Sisvar software, version 5.6 (Ferreira 2019).

Results and discussion

According to the senescence scale, inflorescences with a score below 3 do not possess the optimal qualitative characteristics for commercialization and should be discarded. Therefore, all the selected flower stems had scores higher than "4". Among the various dry conditioning periods, the flower stems that remained dry for 24 hours exhibited a decrease in visual quality compared to those that maintained a maximum score (Fig. 1, Fig. 2).

Figure 1
Visual assessment of the quality (grades) of torch ginger flower stems exposed to various postharvest dry conditioning periods.

Figure 2
Visual assessment of the quality (grades) of torch ginger flower stems exposed to various postharvest dry conditioning periods. Means sharing the same uppercase letter (Treatment comparison within the same time) and lowercase letters (Comparison between times within the same treatment) indicate no significant difference based on the Scott-Knott test, with a 5% error probability. The bars represent the standard errors.

On the 5th day of evaluation, all the stems remained suitable for commercialization with a score higher than 3. The control treatment exhibited the highest score, followed by the flower stems subjected to dry conditioned for 3-h, 6-h , and 12-h. The flower stems that underwent 24-h of dry conditioning received a score of 3, indicating the lowest score on the evaluation day.

On the 8th day, the flower stems in the control treatment obtained the highest score, followed by those in the treatments where the stems underwent dry conditioning for 3-h, 6-h, and 12-h. These stems received scores of 3, indicating their continued suitability for commercialization. The stems that were subjected to 24-h of dry conditioning received a score of 2, rendering them unsuitable for sale.

On the 11th day, all the stems had a score of less than 3, and the stems in the control treatment and those that underwent dry conditioning for 3-h, 6-h, and 12-h had similar scores, ranging from 2 to 2.5. The stems that received 24-h of dry conditioning obtained a score of 1 due to the high degree of senescence.

Observing the stages of senescence in flower stems and quantifying them using grades enables us to standardize the characteristics of commercial quality, thereby enhancing cultivation, harvesting, and distribution processes, while considering transportation time (Mattos et al. 2020). The results indicated that torch ginger stems could tolerate up to 12-h of dry conditioning. Nevertheless, the highest quality was achieved by keeping the stems continuously immersed in water.

The torch ginger stems were collected at the recommended opening stage, as described by Mattos et al. (2020), with no presence of fully bloomed flowers. Prior to the sucrose pulsing treatment, conducted two days after harvest, there were no flowering true flowers observed. However, following this period, the stems underwent 24-h of dry conditioning were the first to exhibit true flowers, appearing on 20% of the stems. By the 5th day, true flowers began to bloom on the stems subjected to all other treatments, with 20% of the stems displaying true flowers. Among the stems that received the 24-hour dry treatment, this percentage increased to 60% (Fig. 3).

Figure 3
Presence of true flowers (%) on torch ginger stems subjected to various postharvest dry conditioning durations. (A) Representative stem harvested without the presence of a true flower. (B) Floral stem illustrating the occurrence of a true flower in the treatments.

The patterns observed on the 8^th and 11^th days of evaluation were similar, with 100% of the stems included in the 12-h and 24-h dry treatments exhibiting true flowers. In contrast, the maximum percentage of stems with true flowers observed in the remaining treatments was 60%.

With an extended dry conditioning period followed by rehydration during post-harvest, the stems absorbed a greater amount of water, consequently facilitating the opening of the true flowers and maintaining fresh mass through cell turgidity. Water supply is one of the factors influencing anthochron, which is the time interval between successive flower openings in inflorescences, as it can impact water stress and the translocation of stem sugars during flowering (Schwab et al. 2014).

Anthochron is a factor that influences commercial quality as it measures the rate of flower opening. A faster anthochron leads to quicker mobilization of reserves to sustain floral stem metabolism, consequently accelerating senescence. In both gladiolus and torch ginger flower stems, the sequential opening of flowers was faster among stems receiving lower water supply and slower among those receiving higher water supply (Santos et al. 2021).

These findings indicate that the postharvest opening of flower stems is closely linked to water availability and significantly influenced by the rehydration process following dry conditioning (Santos et al. 2021). This correlation is observed in torch ginger stems, where rehydration after extended dry conditioning periods (12-h and 24-h) promotes the accelerated opening of true flowers, resulting in more rapid quality deterioration.

Regarding water absorption (Fig. 4A), the dry conditioning treatments of 6-h, 12-h, and 24-h exhibited the lowest rates. By the 8^th day, the absorption rates decreased for all the treatments compared to the previous evaluation. Stems subjected to 3-h and 6-h dry conditioning displayed similar values, while lower absorption rates were observed for the 12-h and 24-h treatments. The same patterns observed on the 8^th persisted during the 8^th day evaluation.

Dry conditioning can induce stress due to water deficit, which accelerates the senescence process, depletes reserves, and triggers stomatal closure, resulting in reduced transpiration and increased CO₂ accumulation. Consequently, these factors lead to a decrease in water absorption rate (Piroli et al. 2020), as observed in torch ginger stems. Stems subjected to longer dry conditioning periods, specifically 12-h and 24-h, experienced greater reductions in absorption rates and water content and, ultimately affecting their quality, even after rehydration through sucrose pulsing.

Figure 4
(A) Absorption rate (mL/stem/day) and (B) water content (%) of the torch ginger flower stems subjected to various postharvest dry conditioning durations. Means sharing the same uppercase letter (Treatment comparison within the same time) and lowercase letters (Comparison between times within the same treatment) indicate no significant difference based on the Scott-Knott test, with a 5% error probability. The bars represent the standard errors.

The torch ginger stems exhibited a water content of 93% immediately after harvest (Fig. 4B). Following dry conditions, a similar pattern of reduction in water content was observed across all stems, indicating water loss and a decrease in the percentage of their moisture content. When comparing the different treatments groups, the control stems maintained the highest water content, reaching 90% on the 11^th day of evaluation. This was followed by the 3-h and 6-h treatment stems, which had a water content of 86%. In contrast, the stems that underwent 12-h and 24-h of dry conditioning exhibited lower water content, measuring below 84%.

The turgor of a flower stem is contingent upon the equilibrium between absorption and transpiration rates, as well as various physiological processes governing water transport, loss, and tissue water retention - all factors affecting water content. Mass loss can be attributed to transpiration, which diminishes water absorption. This reduction may arise from xylem obstruction caused by microorganisms and air bubbles, or it may be influenced by genetically determined factors (Santos et al. 2021).

When evaluating the fresh and dry weights of the stems (Fig. 5A), similar patterns were observed between these two parameters. The control treatment and the 3 hours dry conditioning treatment exhibited the highest mass, while the stems subjected to 24-h of dry conditioning had the lowest fresh weights. It is worth noting that the greatest mass loss in all treatments occurred between the conclusion of sucrose pulsing and the 5th day of evaluation, particularly in the stems that underwent dry conditioning for durations exceeding 6 hours.

Figure 5
(A) Fresh weight (g) and (B) dry weight (g) of torch ginger flower stems subjected to various postharvest dry conditioning durations.

In contrast to fresh weight, dry weight (Fig. 5B) exhibited the most significant reduction for all treatments between harvest and the conclusion of sucrose pulsing. Regarding the different treatments, the stems in the control and 3-h dry conditioning groups displayed higher dry weights. The stems submitted to the 24-h dry condition had the lowest dry weights in all evaluations.

Studies indicate that, similar to torch ginger stems, there is a decline in fresh and dry masses of flower stems within the initial days following harvest. This decline is attributed to natural transpiration and reductions in absorption rates due to hydraulic conductance limitations in the xylem. This process is intensified in stems that undergo dry conditioning, which is one of the primary causes of turgor loss contributing to product deterioration, as observed through visual quality analysis (Santos et al. 2021).

Regarding the colors of the bracts, among the parameters evaluated by the colorimeter, the hue angle (hº) determines the color quadrant in which a sample is located. Values between 0° to 90° fall within the red spectrum. The torch ginger stems obtained an average hue angle of 40.50°, which justifies the analysis of parameter a*. The analysis of parameter b* did not identify any differences between treatments over time (value of 20.90). This analysis corresponds to the blue range for negative values and yellow range for positive values. The parameter C* had an average value of 27.05, indicating that there were no significant differences between treatments.

Positive values of the parameter a* were observed for the torch ginger stems (Fig. 6A), which indicate the intensity of the red color. These values increased as the conditioning time progressed, indicating the occurrence of senescence. The stems kept in the control and the 3 hours treatment exhibited similar behavior, with slight changes in the red color. The stems subjected to the 12-h and 24-h dry conditioning treatments showed the most pronounced change in the red color, especially between the 5^th and 8^th days of evaluation, indicating the progress of the senescence process.

Figure 6
The parameters (A) a* (dimensionless) and (B) L* (dimensionless) were assessed for the torch ginger flower stems that underwent various postharvest dry conditioning durations.

The parameter L* (Fig. 6B) quantifies the quality of light and brightness in numerical values. Consequently, the torch ginger stems, regardless of the treatment, exhibited similar behavior until the 8^th evaluation, maintaining consistent values since the harvest period. Distinctions began to emerge on the 11^th day of evaluation when the values decreased significantly, and greater reductions were observed in the conditioned stems.

It is possible to establish a correlation between the parameters analyzed by the colorimeter and the scores related to visual quality. Noticeable changes in the parameters a* and L* took place on the 5^th and 8th evaluation days, respectively, corresponding to periods when the visual quality declined, receiving the lowest scores.

Changes in color can indicate the stage of senescence. The intensification of red color is linked to the oxidation process of the bracts, as it is associated with the breakdown of molecules, such as sugars, through reactions with oxygen (Endo et al. 2007). The utilization of a colorimeter reinforces and improves the accuracy of visual quality evaluations (Mattos et al. 2020).

The reduction in the L* parameter of the torch ginger stems initiated on the 8^th day after harvest, signifying a decrease in brightness and an increase in bract browning caused by stress-induced injuries and senescence. Darkening and loss of brightness can occur due to water loss, as evidenced by parameters such as absorption rate, water content, and fresh mass. These factors lead to cellular disruption and the presence of anthocyanin, the pigment responsible for the red color, which undergoes color changes due to oxidative enzymes (Mattos et al. 2020).

The concentration of carotenoids (Fig. 7B) and anthocyanins (Fig. 7C) did not undergo any changes during the period between harvest and the completion of sucrose pulsing. However, a notable shift in both pigments occurred between the end of sucrose pulsing and the 5^th day post-harvest, with an increase in carotenoid concentration and a decrease in anthocyanin concentration. In addition, no significant difference was observed in the concentration of anthocyanin, whereas higher concentrations of carotenoids were found in the stems subjected to 24-h of dry conditioning.

Figure 7
(A) Detailed view of color alterations occurring at the edges of the stems following 24 hours of dry conditioning. (B) Concentration of carotenoids and (C) anthocyanins in the torch ginger flower stems treated with different postharvest dry conditioning times.

The increase in carotenoid concentration in the torch ginger stems was found to be correlated with the rise in red color quantified by the colorimeter. This pigment is responsible for mitigating damage caused by stress to the photosynthetic apparatus. Increasing the concentration of this pigment can be a strategy to dissipate excess light energy under water deficit conditions, in which carotenoids play a photoprotective role (Silva et al. 2016).

The degradation of anthocyanins observed in the torch ginger stems is linked to the increase in H₂O₂ levels (Fig. 8). This flavonoid act as a non-enzymatic antioxidant that is essential for the homeostasis of flower stems, and its production helps mitigate intracellular oxidative stress (Moustaka et al. 2020).

The torch ginger stems that underwent 12-h and 24-h of dry conditioning demonstrated a higher concentration of H₂O₂ production (Fig. 8A) compared to the stems in the other treatments. The concentration of H₂O₂ increased gradually over time, showing a correlation with the senescence of the stems.

Figure 8
(A) Hydrogen peroxide and (B) lipid peroxidation in the torch ginger flower stems exposed to various postharvest dry conditioning durations.

A similar pattern was observed for lipid peroxidation (Figure 8B). The torch ginger stems that underwent 12-h and 24-h of dry conditioning displayed a higher concentration of peroxidation compared to the other stems, and this phenomenon intensified upon rehydration. In terms of the duration of dry condition, the stems in the control, 3-h and 6-h treatments exhibited an increase in lipid peroxidation, indicating the onset of senescence in the stems on the 8^th day.

The rise in hydrogen peroxide levels in the torch ginger stems treated with 12-h and 24-h of dry conditioning is linked to water stress and senescence. This oxidative process occurs because hydrogen peroxide is one of the reactive oxygen species that causes oxidative damage to the cell’s lipid membrane (Bhattacharjee 2005).

The senescence of flower stems and the occurrence of stress may be linked to the concentration of malondialdehyde (MDA), which serves as an indicator of lipid peroxidation. The increase in MDA begins upon the cutting of the floral stem and continues throughout the vase life (Pourzarnegar et al. 2020).

Analyzing the activity of the enzymes superoxide dismutase (SOD) and catalase (CAT), no expression was detected, even in the stems that underwent the dry conditioning process. The absence of these enzyme activities, coupled with lipid peroxidation and the rise in H₂O₂ levels, contributes to understanding the effects of dry conditioning on the quality and durability of torch ginger stems. Dry conditioning induces an increase in reactive oxygen species (ROS), and the enzymes are degraded by anthocyanins, thereby accounting for the reduction in this pigment.

The enzymes of the antioxidant system, such as SOD and CAT, play a crucial role in protecting plant tissues against stress-induced damage during growth, development, and senescence. Studies have shown that a high concentration of activity of these antioxidant enzymes is associated with greater post-harvest longevity in floral stems (Ren et al. 2017). In contrast, Nogueira et al. (2023) investigated the antioxidant system of floral stems from the torch ginger species cv "Red Torch" and observed the absence of expression of the SOD and CAT enzymes, which may justify the low post-harvest longevity of this species. However, the authors found that the peroxidase enzyme remained active during the senescence of post-harvest stems.

The protein, total soluble sugars, and reducing sugars reserves in the torch ginger stems were reduced when exposed to dry conditioning. Initially, the stems conditioned for 0 and 3 hours did not exhibit reduced protein concentrations (Fig. 9A). The depletion of these reserves commenced on the 5th day, coinciding with the onset of senescence. In the stems subjected to the other treatments, the consumption of reserves began on the first day of evaluation, with the most substantial reduction occurring between the completion of sucrose pulsing and the 5th day of evaluation.

Figure 9
(A) Proteins, (B) reducing sugars and (C) total soluble sugars in torch ginger flower stems exposed to various postharvest dry conditioning durations.

The concentrations of reducing sugars (Fig. 9B) and total soluble sugars (Fig. 8C) in the reserves decreased prior to the pulsing process and immediately after harvest when the stems were subjected to dry conditioning. The sugar concentration was maintained until the end of pulsing in the stems of the control treatment. The duration of dry conditioning is related to the depletion of sugars, as longer conditioning times are associated with a higher utilization of these reserves. In addition, among the available reserves for the torch ginger stems, the initial consumption of sugars was greater than that of proteins.

There is a correlation between protein concentration and senescence since, during the senescence process, there is an increase in proteolytic activity in the bracts and petals of flower stems. The breakdown of proteins depends on the species analyzed and the organ where the reserve is located (Rabiza-Świder et al. 2019), and in the case of torch ginger flower stems, protein breakdown begins after the 8^th day from harvest, following the breakdown of sugars.

After harvest, the sugar reserves in the stems are no longer utilized for cell expansion and are translocated as an energy source to be used in cellular respiration. Due to the water stress caused by dry conditioning, the presence of sugar reserves leads to an influx of water, reducing the absorption rate, and consequently decreasing the fresh weight of the stems. In addition, it also induces floral opening, accelerating senescence and consequently reducing the quality (Sales et al. 2018).

Given the results, dry conditioning for more than 12-h is not recommended because it results in a loss of quality and durability and accelerates the senescence process in torch ginger stems. After this period, reductions become apparent in the absorption rate and pigment breakdown. In addition, it is evident that the stems experienced water stress due to dry conditioning, as indicated by increases in the concentration of H₂O₂ and lipid peroxidation. Another finding related to senescence and the stress induced by dry conditioning is the depletion of sugar and protein reserves, necessary for metabolic and respiratory processes.

Conclusions

Dry conditioning can cause several physiological alterations in torch ginger stems, including a reduction in absorption rates, water content, fresh and dry weights, as well as protein and sugar concentrations. Additionally, dry conditioning for 12-h and 24-h resulted in an increase in hydrogen peroxide concentration and lipid peroxidation in the stems, indicating water stress. Although the stems can tolerate up to 12-h of dry conditioning, their shelf life under these conditions was only eight days. Therefore, it is recommended to hydrated the stems immediately after harvest to preserve their post-harvest quality and durability.

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• Funding

  The authors thank the govenmental agencies Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES - Brazil)and "CAPES/BRASIL PDPG-POSDOC No. 2930/2022", Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG - Brazil), and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq - Brazil) for finantial support and scholarships

• Data Availability

  The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.

Publication Dates

• Publication in this collection
  11 Dec 2023
• Date of issue
  2023

History

• Received
  29 Apr 2023
• Accepted
  19 Sept 2023