Next Article in Journal
Seed Geometry in Species of the Nepetoideae (Lamiaceae)
Previous Article in Journal
Locating Appropriate Reference Genes in Heteroblastic Plant Ottelia cordata for Quantitative Real-Time PCR Normalization
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Horticulturae
Volume 11
Issue 3
10.3390/horticulturae11030314
horticulturae-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Effects of Glyoxylic Acid on Metabolism and Ripening of ‘Rocha’ Pears Treated with 1-MCP

by
Cindy Dias
1,
Clara Sousa
1,
Marta W. Vasconcelos
1,
António Ferrante
2 and
Manuela Pintado
1,*
1
CBQF—Centro de Biotecnologia e Química Fina—Laboratório Associado, Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Diogo Botelho 1327, 4169-005 Porto, Portugal
2
Institute of Crop Science, Sant’Anna School of Advanced Studies, Piazza Martiri della Libertà 33, 56127 Pisa, Italy
*
Author to whom correspondence should be addressed.
Horticulturae 2025, 11(3), 314; https://doi.org/10.3390/horticulturae11030314
Submission received: 3 February 2025 / Revised: 2 March 2025 / Accepted: 10 March 2025 / Published: 13 March 2025
(This article belongs to the Section Postharvest Biology, Quality, Safety, and Technology)
Browse Figures
Versions Notes

Abstract

:
The application of 1-methylcyclopropene (1-MCP) is widely used to extend the storage life of climacteric fruits, such as ‘Rocha’ pears. However, the suppression of ethylene’s action by 1-MCP often results in excessive ripening delay, compromising fruit quality and consumer acceptance. In this study, we investigated the potential of glyoxylic acid (GLA) to counteract the effects of 1-MCP and promote ripening. To evaluate this, ‘Rocha’ pears treated with 1-MCP were exposed to 3% (m/v) GLA and stored at 20 ± 2 °C for 15 days. Typical ripening indicators, such as firmness, skin color, ethylene production, respiration rate, volatile organic compounds (VOCs), sugars, and the activity of ethylene biosynthetic enzymes, were measured. Our results indicate that GLA did not induce significant effects on the ripening response, as ethylene production remained comparable to that of the control. Consequently, no significant changes in firmness, skin yellowing, or sugar content were observed in the GLA-treated pears. However, GLA significantly increased respiration rates (approximately 57%) and induced higher emissions of stress-associated VOCs, including hexanal, (E)-2-hexenal, and ethanol. This suggests that GLA may influence metabolic pathways related to energy metabolism and redox homeostasis without necessarily triggering ethylene-induced ripening. This study provides new insights into the interactions between GLA, 1-MCP, and fruit development, contributing to the development of alternative strategies to manage the effects of 1-MCP in ‘Rocha’ pear storage.

Graphical Abstract

1. Introduction

The primary challenge of the fruit sector today is not only to extend the storability of perishable fruits but also to ensure the maintenance of fruit quality during postharvest storage, including during cross-border and long-distance shipping [1,2]. To achieve this, the pear industry relies on 1-MCP and cold storage to delay senescence, thereby extending the fruit’s availability throughout the year [3,4]. However, despite its effectiveness in reducing postharvest decay, 1-MCP disrupts the normal ripening process after cold storage [5,6].
Physiologically, 1-MCP competes with ethylene, the key hormone responsible for coordinating climacteric fruit ripening, by binding to ethylene receptor proteins located in the endoplasmic reticulum membrane. This binding downregulates ethylene signaling and biosynthesis genes, thereby suppressing or delaying essential ripening responses [7,8]. Consequently, the fruits remain unripe, failing to develop desirable textural, aromatic, and flavor attributes, which reduces their commercial value and leads to economic losses.
The Portuguese ‘Rocha’ pear (Pyrus communis L. ‘Rocha’), a Protected Designation of Origin (PDO) cultivar, generates around EUR 120 to 130 million per year, having a great positive impact on the Portuguese economic balance. It is a cultivar known worldwide for its exceptional flavor. With the increase in exportation, conservation strategies have been aimed at maintaining the availability of ’Rocha’ pear throughout 10 months. At the moment, it is a cultivar particularly affected by the challenges posed by 1-MCP [5]. Currently, no alternative exists to replace this technology. However, achieving a balance between preventing postharvest disorders and ensuring proper ripening remains difficult. According to Isidoro and Almeida [9], the optimal 1-MCP concentration necessary to prevent superficial scald also prevents consistent ripening. As a result, the search for new strategies that mitigate 1-MCP’s effects while preserving fruit’s quality and marketability has become urgent.
Over recent decades, multiple approaches have been explored to restore ripening in pears treated with 1-MCP. These methods have primarily focused on physical treatments, such as exposure to exogenous ethylene [10,11], increasing the storage temperature, or a combination of both [12,13]. However, these techniques have shown limited effectiveness in overcoming the ripening blockage caused by 1-MCP [7], and they often exhibit cultivar-specific responses. According to producers, exposure to non-chilling temperatures and/or exogenous ethylene in ‘Rocha’ pears fails to restore ripening and is also energy-intensive. Therefore, the identification of effective treatments to counteract the effects of 1-MCP in ‘Rocha’ pears is a critical necessity.
Recent advancements in chemical genomics have identified specific organic compounds as regulators of fruit’s development and ripening [14,15,16,17]. Among these, GLA has emerged as a potential metabolic activator in fruit treated with 1-MCP [7,18]. GLA is an organic acid belonging to the class of alpha-keto acids, acting as a key metabolic intermediate in various biochemical pathways, including the glyoxylate cycle and amino acid metabolism. Its chemical structure contains both an aldehyde (-CHO) and a carboxyl (-COOH) group, making it a highly reactive and biologically relevant compound [19,20].
GLA is known to play various roles in plants’ metabolism, particularly as an intermediate in the glyoxylate cycle, which is crucial for gluconeogenesis and the mobilization of stored lipids. Additionally, GLA has been associated with responses to oxidative stress and metabolic adjustments under environmental stress conditions [20]. While its precise role in ethylene synthesis has not been established, it may influence hormonal crosstalk and energy metabolism, potentially affecting postharvest physiological responses in fruit.
So far, no documented attempts have been made to assess whether exogenous GLA can restore the ripening capacity of 1-MCP-treated ‘Rocha’ pears. This study aimed to investigate whether GLA treatment could significantly enhance the ripening process following 1-MCP application. Our hypothesis was that GLA could influence metabolic pathways linked to ripening, thereby mitigating the ripening delay caused by 1-MCP. To test this, we analyzed key ripening indicators, including fruit firmness, total soluble solids (TSS), volatile organic compounds (VOCs), respiration rate, and ethylene production during the ripening phase. Additionally, we examined the activity of essential enzymes related to ethylene biosynthesis, particularly assessing whether GLA treatment could induce 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) and ACC oxidase (ACO) activity in ‘Rocha’ pears.

2. Materials and Methods

2.1. Fruit Material and Experimental Design

‘Rocha’ pear (Pyrus communis L. ‘Rocha’) fruits were obtained from a commercial orchard in Cadaval, in the West Region of Portugal (latitude 39°25’ N; longitude 8°54’ W; elevation 120 m). Pears were harvested in August 2021 at the optimal harvest date according to local growers. After picking, the pears were held at 0 °C and 90–95% relative humidity (RH) for seven days. After this period, the pears were treated via 24 h of fumigation at the grower’s cold packinghouse with 312 ppb 1-MCP (SmartfreshTM, AgroFresh Inc., Philadelphia, PA, USA), following current industry practices, and maintained under the same cold conditions (0 °C and 90–95% relative humidity) for two months. Following this time, the pears were transferred to controlled-atmosphere storage (CA) at −0.5 °C, per the standard industry practice, until the start of the treatments.
Experiments were initiated by removing pears previously treated with 1-MCP from CA storage. The pears were split into two groups: a control group (CTRL) and a group treated with GLA. The latter pears were immersed in a 3% (m/v) GLA solution for 2 h, as described by Hewitt et al. [7]. After the treatments, all pears were kept at room temperature (20 ± 2 °C) for 15 days to simulate the ‘Rocha’ pear conditions when they reached the consumers, and they were analyzed at 0 days (T0), 7 days (T7), and 15 days (T15) after treatment.

2.2. Fruit Quality Evaluation

Color, firmness, TSS, and titratable acidity (TA) were evaluated for 9 fruits per treatment and sampling point, as described by Dias et al. [21]. Color (hue angle) and firmness (N) were measured on two opposite sides of each fruit using a portable CR-400 colorimeter (Konica Minolta, Osaka, Japan) and a texturometer (T.A. XT plus Texture Analyser, Stable Micro Systems, Cardiff, UK) equipped with an 8 mm diameter probe, respectively. The drop of the hue angle describes the surface color transition from green to yellow [22,23]. SSC was evaluated with a digital refractometer (PR1 ATAGO Co., Ltd., Tokyo, Japan), with the juice from 3 fruits per replication, in a total of 3 replicates. TA (g malic acid kg−1) was determined through titration using 0.1 M NaOH until reaching a pH of 8.1. This process consisted of homogenizing 10 g of pear (3 fruits per replication, in a total of 3 replicates for each treatment and sampling point) combined with 90 mL of distilled water.

2.3. Ethylene Production, and Related Metabolites and Biosynthetic Enzymes

At each sampling point, 3 replicates of 3 fruits each were acclimatized at 23 °C in 1.5 L glass jars. After 2 h of incubation, ethylene production (µg kg−1) was measured by injecting 1 mL of headspace into a gas chromatograph (Varian CP-3380 gas chromatograph, Walnut Creek, CA, USA) equipped with an activated alumina column (50 m length and 0.53 mm i.d.; Thermo Fisher Scientific Inc., Marietta, OH, USA) and a flame ionization detector (FID) set at 180 °C, as previously described by Saquet et al. [24]. Pear flesh samples were used to determine the enzymatic activities (ACO and ACS) and metabolites (ACC and MACC) involved in ethylene biosynthesis, as described by Bulens et al. [25].

2.4. Respiration Measurement

After ethylene measurement, the headspace of the same biological replicates was analyzed using an infrared sensor (Dansensor CheckMate 3, METEK, Chesterfield, MO, USA) in a closed-circulation circuit to determine the carbon dioxide production (mg CO2 kg−1 h−1), as described by Dias et al. [21].

2.5. Volatile Aromatic Compounds Profiling by SPME-GC-MS

VOCs were extracted by mixing 5 g of pear pulp with 1.8 g of NaCl in a 20 mL screw-cap vial, as described by Dias et al. [21]. To each sample, 20 µL of 50 mg L−1 3-octanol was added as an internal standard. Subsequently, each vial was placed at 40 °C for 2 min, followed by exposure of the SPME fiber with a 50/30 µm thickness of divinylbenzene/carboxy/polydimethylsiloxane (DVB/CAR/PDMS; Supelco Co., Bellefonte, PA, USA) to the headspace for 40 min to adsorb the volatiles. After the adsorption, the fiber was injected into a EVOQ Triple-Quadrupole mass-selective detector (Bruker, Karlsruhe, Germany), equipped with a 456-GC gas chromatograph (Bruker, Karlsruhe, Germany) for desorption, at 220 °C for 10 min. Volatiles were analyzed and quantified in this GC-MS, utilizing helium as a carrier gas at a flow rate of 1.0 mL min−1, and with the injector temperature set at 250 °C. The temperature program for volatile identification was 40 °C for 1 min, increasing by 2 °C per minute until it reached 220 °C. Then, the headspace was maintained at 220 °C for 5 min. Subsequently, spectral information was examined within the m/z range of 33–350. The identification and quantification of VOCs were accomplished with standard curves, with the results presented on a fresh weight basis (nmol kg−1). The values reported are the mean from 3 biological replicates, each comprising a pool of 3 pears.

2.6. Determination of Sugars and Organic Acids

The extraction of sugars (sucrose, glucose, fructose, and sorbitol) and organic acids (malic acid) was performed following the protocols described by Giné-Bordonaba et al. and Lindo-Garcia et al. [26,27]. Briefly, around 2 g of frozen pulp tissue was mixed with 62.5% (v/v) aqueous methanol, and the supernatants were recovered for chromatographic analysis, using a Beckman Coulter System Gold HPLC (Knauer, Berlin, Germany) coupled with RI and UV detectors. The values reported are the mean from 3 biological replicates, each comprising a pool of 3 pears.

2.7. Statistical Analysis

Data analysis was performed in Metaboanalyst 6.0. (URL: https://www.metaboanalyst.ca/MetaboAnalyst/ModuleView.xhtml; accessed on 14 September 2024). An independent Partial Least Squares Discriminant Analysis (PLS-DA) [28] and the corresponding variable importance in projection (VIP) scores were obtained. The PLSDA models were developed with measured data for firmness, hue angle, SSC, TA, ethylene, respiration, sugars, organic acids, VOCs, ACS and ACO activity, and ACC (T0 = 0 days before GLA application; T7 = 7 days after GLA treatment; T15 = 15 days after GLA treatment). A heatmap showing the concentration range of each measured parameter over time was also obtained.
The average values of each variable across shelf-life time were compared by analysis of variance (one-way ANOVA), with Tukey’s post hoc test for the identification of significant means. Additionally, the independent-samples t-test was used to detect significant differences between the two conditions for each experiment. The significance level was set at 5% in all cases.

3. Results

To address potential biological variability inherent in the data—particularly the differing physiological status of pears at the start of the experiment—data were normalized using the values recorded on day 0 of shelf-life.

3.1. Multivariate Analysis Reveals Distinct Clustering of GLA-Treated and CTRL Samples

A PLS-DA model was developed to evaluate the impact of exogenous GLA treatment on ‘Rocha’ pear ripening under the effect of 1-MCP. Figure 1 presents the PLS-DA scores map and the corresponding VIP scores, where the first two components account for nearly 60% of the observed variability.
The PLS-DA scores map reveals two well-defined clusters separating the GLA-treated from the CTRL samples (Figure 1). Notably, the CTRL samples from day 0 and day 7 are relatively close, indicating that these fruits maintained their measured parameters with lower variability over time, remaining similar to each other. However, after 15 days, the CTRL samples, while still in the same cluster as the other CTRL samples, were noticeably distanced from the T0 and T7 samples. In contrast, the GLA-treated pears exhibited differentiation over time and from the CTRL samples, particularly between day 7 and day 15, suggesting metabolic modifications driven by the treatment.
The VIP scores evidence the most relevant variables (measured parameters) that contribute most to the differentiation between the CTRL and GLA-treated samples. From the VIP scores (those higher than 1), it can be observed that the GLA treatment impacted the volatile emission pattern of pears, the respiration rate (CO2), the ACC substrate concentration, the TA, the hue angle, and the ACO enzyme activity. These are the contributing variables that played the most significant role in distinguishing the CTRL samples from the GLA-treated samples.
Additionally, a heatmap was generated to allow for a more detailed analysis of the treatment’s impact and highlight specific trends and similarities among samples (Figure 2).
Combining the VIP scores with the heatmaps obtained from each experiment (Figure 2), it can be corroborated that the GLA treatment mainly impacted the abovementioned variables. The heatmap analysis demonstrates that the application of GLA had quite an impact on various compounds and physical characteristics, as significant color changes (from blue to red, and vice versa) in the heatmap between the CTRL and GLA conditions can be observed for some parameters, especially after 7 and 15 days. The GLA treatment significantly influenced the production of VOCs. Specifically, hexanal, 2-hexenal, butyl, and hexyl acetate showed increased levels (red intensity) in GLA-treated pears, while other VOCs, such as 2-ethyl-1-hexanol, limonene, and ethanol, exhibited varied or reduced responses to GLA treatment. Additionally, the heatmap shows that exogenous GLA increased ACO enzyme activity, while the CTRL samples exhibited a higher ACC concentration until day 7, followed by a decrease after 15 days of shelf-life. Also, based on the color intensity from the heatmap, the GLA-treated samples showed the highest ethylene and TA concentrations at all timepoints compared to the CTRL samples. Furthermore, there was a decrease in sucrose concentration (blue shades in the heatmap) and an increase in CO2 production (more intense red shades in the heatmap) in GLA-treated pears compared to the CTRL.

3.2. Multivariate Analysis Corroborates GLA-Induced Physiological Changes

Alongside the physicochemical changes indicated by the PLS-DA and heatmaps, we closely examined several key parameters, mainly those with a VIP score exceeding 1, to better understand the treatments’ impact on ripening reactivation. Figure 3 illustrates ethylene levels over time across two conditions. In both conditions, the ethylene concentrations significantly rose from day 0 to day 15, although the rates of increase differed depending on the condition.
During the first 7 days of the experiment, ethylene production in the CTRL group stayed consistently low, showing no significant increase, which reflects the suppressing effect of 1-MCP on ethylene biosynthesis. Interestingly, the 1-MCP effect was naturally overcome after 15 days. Regarding the GLA-treated group, the pears exhibited slightly higher ethylene levels than the CTRL group, but this difference was not statistically significant. This similarity aligns with the low variable importance of ethylene, as revealed by its VIP score below 1, in explaining the separation of the CTRL group from the treated one (Figure 1).
Regarding respiration rates, measured through CO2 production, both conditions experienced increasing CO2 levels throughout the 15 days. Despite no substantial difference being noted in ethylene production between the CTRL and GLA-treated groups, the GLA group demonstrated significantly elevated rates of CO2, with increases of approximately 35% and 57% recorded after 7 and 15 days, respectively (Figure 3; Table A1).
Figure 4 illustrates that the GLA treatment did not result in significant higher firmness losses compared to the CTRL. However, contrary to what would be expected in pears subjected exclusively to 1-MCP, firmness in the CTRL group significantly decreased over time, which was particularly evident after a 15-day storage period, corresponding with the increased ethylene production observed at this timepoint (Figure 3).
Similar to firmness, the CTRL pears showed no obstructive effect from 1-MCP, as Figure 4 reveals that the hue angle decreased over time. GLA showed slightly lower hue angle values, but with no significant difference from the CTRL.
Sucrose and TA are additional parameters that demonstrated their significance in differentiating CTRL from GLA-treated samples based on the VIP scores. Notably, after 7 days, the sucrose concentration decreased similarly in both conditions (Figure 5). After 15 days, the GLA group maintained its sucrose concentration, whereas the CTRL group showed higher levels, indicating a significant difference between the two groups (Figure 5). Regarding TA, the GLA group showed a minor yet noticeable increase in total acidity over time, while the TA from the CTRL group remained stable (Figure 5).
GLA application significantly impacted ACC concentrations (Figure 6). GLA-treated samples showed lower ACC levels, which continued to decrease after 15 days, while the CTRL group remained stable. Overall, 1-MCP consistently maintained ACC levels in the CTRL group, revealing GLA’s potential to reverse this particular effect of 1-MCP. In relation to ACO enzyme activity, it was observed that both conditions’ patterns were very similar, with no significant variation over time.
In order to assess the contribution of the treatment to the aroma of the fruit, the emissions of VOCs were analyzed, and those of greater importance are presented in Table 1.
Concerning the effects of GLA treatment on VOC emissions, it was observed that there was a notable spike in specific volatile compounds, such as hexanal and (E)-2-hexenal, at 7 days, followed by a drop at 15 days when compared to the CTRL group. Moreover, GLA drove a substantial increase in hexyl and butyl acetate levels by the 15th day of shelf-life, while CTRL showed only a minor rise. For limonene and ethanol, the CTRL maintained higher levels than the GLA group across time, although they were not statistically different.

4. Discussion

The suppression of ripening traits by 1-MCP negatively impacts essential fruit ripening quality attributes such as texture, sugar content, acidity, and aroma, directly affecting consumer acceptance [29,30]. Previous studies in ‘D’Anjou’ pears have shown that organic acids like GLA can modulate fruit’s metabolism, although their capacity to reverse 1-MCP-induced ripening inhibition remains largely unexplored, especially in other cultivars [7,31].
In this study, we hypothesized that GLA could influence metabolic pathways of ‘Rocha’ pears, particularly those related to ripening, under 1-MCP treatment. Multivariate data analysis revealed that GLA promoted changes in the fruit, as evident in the PLS-DA clustering patterns that distinguished GLA-treated samples from CTRL samples, thereby showing GLA’s ability to disrupt some usual effects of 1-MCP. However, GLA did not significantly promote a different pattern compared to 1-MCP-treated fruits (CTRL) in key ripening indicators such as ethylene production, fruit softening, or color changes. Instead, GLA-treated pears exhibited increased CO2 production and specific VOCs, namely, esters, aldehydes, terpenes, and alcohols (Table A1). GLA promoted higher emissions of ethyl, butyl, and hexyl acetates, which are esters strongly related to ripening, as well as limonene [32,33]. However, since these results were not accompanied by an increase in ethylene production, and combined with other ripening results, they suggest that GLA affected other metabolic pathways unrelated to ethylene-driven ripening. It is known that GLA plays a key role in amino acid metabolism, which serves as a precursor for various VOCs, including the formation of aldehydes, alcohols, and esters, contributing to fruits’ aroma [20]. Since GLA can influence amino acid metabolism, it is plausible that these VOC changes resulted from alterations in precursor availability, shifting metabolic fluxes toward stress- or defense-related pathways rather than ripening-associated volatile synthesis [7,20]. For example, studies in apples and tomatoes have shown that alterations in amino acid pathways lead to modifications in volatile production, particularly affecting aldehydes and alcohols [34,35]. In kiwifruit, shifts in amino acid metabolism have been linked to increased ester formation [36].
Additionally, as GLA is an intermediate of the glyoxylate cycle, which is connected to lipid metabolism, it may indirectly affect metabolic pathways involved in aldehyde and ester biosynthesis. In fact, higher levels of the aldehydes hexanal and (E)-2-hexenal were observed in GLA-treated pears. These compounds contribute to the green aroma present in fruits and vegetables, and they are commonly associated with plant defense mechanisms and lipid oxidation [37,38]. Notably, the alcohols ethanol, butanol, and hexanol—volatile compounds strongly associated with fermentation and oxidative stress [39]—were also present in higher amounts in the GLA-treated fruits. The higher ethanol concentration suggests that GLA may have influenced fermentation-related pathways, possibly by shifting carbon fluxes toward anaerobic metabolic routes [7].
Based on these results, GLA-treated pears exhibited increased emissions of VOCs linked to oxidative stress, suggesting that GLA may have triggered stress-related metabolic pathways rather than those directly involved in ripening. This aligns with higher respiration rates and possible ROS accumulation, leading to lipid oxidation and the release of stress-associated volatiles.
Notably, the 1-MCP-treated CTRL group exhibited a natural ripening progression, as evidenced by the distance of CTRL at T15 from T0 and T7. This suggests that these pears underwent some physiological and metabolic alterations even under the exclusive effect of 1-MCP, as evidenced mainly by a loss of firmness and increased ethylene production over time, indicating that 1-MCP’s effect was not entirely restrictive during this phase of the study. Several studies have shown that the extent of 1-MCP’s effect varies primarily based on the cultivar, the timing of postharvest treatment application, storage conditions, and the fruit’s developmental stage at analysis/treatment [6,10]. For instance, a study by Hewitt et al. [7], which used the ‘D’Anjou’ cultivar, found that GLA treatment accelerated the ripening response, leading to increased ethylene production and reduced firmness compared to 1-MCP-treated fruits. Additionally, over time, fruits synthesize new ethylene receptors that are not bound by 1-MCP [33], allowing ethylene perception to resume, and gradually restoring normal ripening processes. In our study, the 1-MCP-treated pears eventually began to ripen, suggesting that ethylene perception was restored over time due to receptor renewal. This loss of 1-MCP’s effect could explain why GLA was unable to entirely counteract its impact; by the time GLA was applied, the fruit was already regaining its ripening ability. This raises the possibility that the physiological status of the pears at the time of GLA application influenced the outcome, potentially interfering with GLA’s expected effects [34].
In this study, GLA caused no significant impact on ethylene production compared to the CTRL. This finding aligns with the lower ACC concentrations measured in GLA-treated fruits. Since ACC is the direct precursor of ethylene, its lower levels in GLA-treated fruit suggest that either ACS enzyme activity (the enzyme responsible for producing ACC) was inhibited or ACC was rapidly metabolized by the ACO enzyme into ethylene [40,41]. In fact, ACO activity showed no significant differences between the conditions, and the ethylene levels in both CTRL and GLA-treated pears were similar. So, the limiting factor was ACS enzyme activity. This suggests that the basal ACS activity caused by 1-MCP was not significantly stimulated by GLA, which explains the low ACC values and thereby limits higher ethylene biosynthesis compared to the CTRL. This demonstrates the central role of ethylene in regulating the ripening process of ‘Rocha’ pears.
Sugars play a crucial role in the ripening process and influence consumer preferences. The primary sugars that vary in pears during ripening are sucrose, glucose, and fructose [42,43]. Numerous studies have shown a positive relationship between ethylene and sucrose production, particularly through the activation of enzymes that convert starch into simpler sugars [35,44]. Hence, the significant increase in ethylene production observed in both conditions during the time of analysis supports the measured pattern of sucrose (Figure 5). The rise in sucrose levels in the CTRL samples suggests starch degradation, which aligns with the observed loss of firmness [21]. Additionally, further breakdown of sucrose into simpler sugars, such as fructose and glucose, did not occur, as indicated by the lack of increase in these sugars shown in Table A1. The slight decrease in sucrose observed in GLA-treated pears, combined with the higher respiration measured in these pears, suggests its utilization as a substrate for respiration and consequent higher CO2 production [45].
Despite the lack of ethylene stimulation, GLA-treated pears exhibited a significant increase in respiration rates, reinforcing that GLA activates alternative metabolic pathways. Elevated respiration without softening or ethylene production suggests that GLA-induced metabolic changes are more related to stress responses or energy metabolism than to ripening itself. Similar patterns were observed in citrus fruits, where exogenous organic acids altered respiration without promoting ripening-associated changes [39].

5. Conclusions

So far, no studies have investigated the effects of GLA on the postharvest ripening of ‘Rocha’ pears under 1-MCP. This study confirms that GLA influences metabolic processes in ‘Rocha’ pears under 1-MCP treatment, but its effects are not directly linked to ethylene-driven ripening. Instead, GLA primarily influenced respiration rates and the biosynthesis of stress-associated VOCs, indicating an impact on metabolic pathways related to energy metabolism and redox homeostasis rather than ethylene-mediated ripening mechanisms that need further exploration. An interesting point worth further investigation in this experiment is the unexpected ripening observed in the CTRL group, which may justify the low impact of GLA on pears. Future research should focus on analyzing the genetic expression of ethylene receptors to better understand how receptor renewal and turnover influence the recovery of ethylene sensitivity and the overall ripening process in 1-MCP-treated pears. Additionally, these findings highlight the importance of the fruit’s physiological state at the time of treatment application, suggesting that GLA’s impact on ethylene metabolism may depend largely on the residual effects of 1-MCP.
Future research should focus on the optimal timing of GLA application during storage, particularly in relation to the waning effect of 1-MCP at the time of treatment. Additionally, investigating how GLA modulates amino acid metabolism and other biochemical pathways will be crucial to optimizing its role in postharvest management strategies. Understanding these mechanisms could provide valuable insights into the modulation of fruit metabolism, particularly in climacteric species, where balancing ripening and shelf-life extension is a key postharvest challenge.

Author Contributions

Conceptualization C.D., A.F. and M.P.; methodology C.D.; validation, A.F., M.W.V. and M.P.; formal analysis, C.S., A.F., M.W.V. and M.P.V; investigation, C.D.; writing—original draft preparation, C.D.; writing—review and editing, C.S., M.W.V., A.F. and M.P.; supervision, M.W.V., A.F. and M.P. All authors have read and agreed to the published version of the manuscript.

Funding

This research was co-supported by the European Fund for Regional Development (FEDER) through the Internationalization and Competitiveness Operational Program (POCI), within the project RE-EAT ROCHA PEAR (POCI-01-0247-FEDER-040016). We would also like to thank the scientific collaboration under the FCT project UIDB/50016/2020 and FCT individual Ph.D. grant (SFRH/BD/143560/2019).

Data Availability Statement

The raw data that support the conclusions of this article will be made available upon request to the authors.

Acknowledgments

We thank the Rocha Center Institute for supplying the pears.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Appendix A

Table A1. Evolution of physicochemical parameters in ‘Rocha’ pears across shelf-life after treatments. Data are the mean ± SD. For the genetic expression results, data are the mean ± SE.
Table A1. Evolution of physicochemical parameters in ‘Rocha’ pears across shelf-life after treatments. Data are the mean ± SD. For the genetic expression results, data are the mean ± SE.
Time (d)SSC (%)TA (g kg−1)Firmness (N)Hue Angle (°)CO2 (mg (kg.h)−1)C2H4 (μg (kg.h)−1)
CTRLGLACTRLGLACTRLGLACTRLGLACTRLGLACTRLGLA
012.32 ± 0.8012.32 ± 0.8011.74 ± 0.1811.74 ± 0.1843.93 ± 3.4343.93 ± 3.4395.91 ± 2.9995.91 ± 2.991.98 ± 0.301.98 ± 0.300.74 ± 0.050.74 ± 0.05
712.93 ± 0.2012.40 ± 0.4613.80 ± 1.3013.29 ± 2.0836.88 ± 0.6135.68 ± 1.1894.81 ± 2.8391.27 ± 4.088.22 ± 0.8611.07 ± 1.420.86 ± 0.171.51 ± 0.42
1513.12 ± 0.1312.90 ± 0.2711.65 ± 0.8414.36 ± 1.1117.56 ± 1.2724.4 ± 4.1083.00 ± 2.8283.40 ± 3.2516.04 ± 4.7225.17 ± 0.4810.39 ± 2.1411.41 ± 1.18
Sucrose (mg g−1)Sorbitol (mg g−1)Glucose (mg g−1)Fructose (mg g−1)Malic acid (mg g−1)ACC (nmol g−1)
05.07 ± 1.125.07 ± 1.1222.11 ± 1.5022.11 ± 1.506.47 ± 0.806.47 ± 0.8046.48 ± 1.2846.48 ± 1.284.24 ± 0.734.24 ± 0.730.70 ± 0.070.70 ± 0.07
73.71 ± 0.204.41 ± 0.7420.61 ± 4.9817.03 ± 2.169.41 ± 0.708.77 ± 1.5240.66 ± 3.0943.44 ± 2.983.82 ± 0.323.76 ± 0.200.81 ± 0.140.56 ± 0.03
156.94 ± 1.054.46 ± 0.6115.59 ± 1.8014.78 ± 1.5714.98 ± 3.4610.39 ± 2.1349.58 ± 2.9849.23 ± 7.215.32 ± 0.505.07 ± 0.960.49 ± 0.080.33 ± 0.04
ACO (nmol (g h) −1)MACC (nmol g−1)ACS (nmol (g h) −1)Hexanal (ng g−1)Hexanol (ng g−1)Butyl acetate (ng g−1)
02.04 ± 0.202.04 ± 0.2036.84 ± 4.3436.84 ± 4.34Not detected9.99 ± 2.359.99 ± 2.3579.30 ± 11.7679.30 ± 11.7614.38 ± 4.3314.38 ± 4.33
72.14 ± 0.412.27 ± 0.3342.43 ± 4.1041.29 ± 2.45135.2 ± 36.61386.68 ± 55.255.92 ± 9.88153.36 ± 33.67.23 ± 1.9412.09 ± 1.31
152.08 ± 0.172.39 ± 0.2143.86 ± 3.8441.44 ± 4.36124.59 ± 46.1160.76 ± 31.1216.83 ± 8.01137.57 ± 3.3478.64 ± 28.96119.62 ± 15.1
Hexyl acetate (ng g−1)2-ethyl-hexanol (ng g−1)Butanol (ng g−1)Ethanol (mg g−1)Acetone (ng g−1)(E)-2-Hexenal (ng g−1)
02.07 ± 0.942.07 ± 0.945.25 ± 0.115.25 ± 0.1159.35 ± 20.2559.35 ± 20.253.90 ± 2.323.90 ± 2.3290.66 ± 25.4690.66 ± 25.463.12 ± 0.603.12 ± 0.60
71.99 ± 0.551.90 ± 0.494.44 ± 0.191.94 ± 0.3851.19 ± 8.25113.54 ± 38.55.82 ± 1.428.49 ± 3.48103.02 ± 0.6681.00 ± 25.0025.65 ± 5.59106.26 ± 17.1
154.89 ± 1.8819.64 ± 14.632.49 ± 0.672.72 ± 0.86347.24 ± 85.1281.09 ± 52.911.77 ± 1.2911.37 ± 2.33593.47 ± 88.4125.74 ± 19.638.82 ± 7.6229.36 ± 0.51
Limonene (ng g−1)Hexane (ng g−1)Linanol (ng g−1)Ethyl acetate (ng g−1)Pentyl acetate (ng g−1)
010.38 ± 0.1610.38 ± 0.16Not detected0.153 ± 0.020.153 ± 0.0267.11 ± 4.5767.11 ± 4.570.05 ± 0.0080.05 ± 0.008
710.96 ± 0.269.99 ± 1.520.11 ± 0.030.10 ± 0.0160.54 ± 5.43157.99 ± 69.11.06 ± 0.131.08 ± 0.11
1510.57 ± 0.179.67 ± 0.360.152 ± 0.020.175 ± 0.01218.08 ± 62.181.52 ± 25.531.86 ± 0.410.31 ± 0.06

References

  1. Gwanpua, S.G.; Verlinden, B.E.; Hertog, M.L.; Nicolai, B.M.; Geeraerd, A.H. A Conceptual Model of the Inhibitory Effect of 1-methylcyclopropene on Ripening of Apples. Acta Hortic. 2017, 1154, 41–46. [Google Scholar] [CrossRef]
  2. Hu, B.; Sun, D.-W.; Pu, H.; Wei, Q. Recent Advances in Detecting and Regulating Ethylene Concentrations for Shelf-Life Extension and Maturity Control of Fruit: A Review. Trends Food Sci. Technol. 2019, 91, 66–82. [Google Scholar] [CrossRef]
  3. Vanoli, M.; Grassi, M.; Buccheri, M.; Cortellino, G.; Lovati, F.; Caramanico, R.; Levoni, P.; Dalla Mora, A.; Spinelli, L.; Torricelli, A. Quality Characteristics, Sensory Profiles and Ethylene Production of Stored ‘Abate Fetel’ Pears Sorted at Harvest by Time-Resolved Reflectance Spectroscopy. Plants 2023, 12, 4013. [Google Scholar] [CrossRef] [PubMed]
  4. Watkins, C.B. The Use of 1-Methylcyclopropene (1-MCP) on Fruits and Vegetables. Biotechnol. Adv. 2006, 24, 389–409. [Google Scholar] [CrossRef]
  5. Gago, C.M.; Miguel, M.G.; Cavaco, A.M.; Almeida, D.P.; Antunes, M.D. Combined Effect of Temperature and Controlled Atmosphere on Storage and Shelf-Life of ‘Rocha’ Pear Treated with 1-Methylcyclopropene. Food Sci. Technol. Int. 2015, 21, 94–103. [Google Scholar] [CrossRef]
  6. Zhi, H.; Dong, Y. Effect of 1-Methylcyclopropene on Superficial Scald Associated with Ethylene Production, α-Farnesene Catabolism, and Antioxidant System of Over-Mature ‘d’Anjou’ Pears After Long-Term Storage. Food Bioprocess Tech. 2018, 11, 1775–1786. [Google Scholar] [CrossRef]
  7. Hewitt, S.L.; Ghogare, R.; Dhingra, A. Glyoxylic Acid Overcomes 1-MCP-Induced Blockage of Fruit Ripening in Pyrus communis L. Var. ‘D’Anjou’. Sci. Rep. 2020, 10, 7084. [Google Scholar] [CrossRef]
  8. Dias, C.; Ribeiro, T.; Rodrigues, A.C.; Ferrante, A.; Vasconcelos, M.W.; Pintado, M. Improving the Ripening Process after 1-MCP Application: Implications and Strategies. Trends Food Sci. Technol. 2021, 113, 382–396. [Google Scholar] [CrossRef]
  9. Isidoro, N.; Almeida, D.P.F. α-Farnesene, Conjugated Trienols, and Superficial Scald in ‘Rocha’ Pear as Affected by 1-Methylcyclopropene and Diphenylamine. Postharvest Biol. Technol. 2006, 42, 49–56. [Google Scholar] [CrossRef]
  10. Minas, I.S.; Tanou, G.; Krokida, A.; Karagiannis, E.; Belghazi, M.; Vasilakakis, M.; Papadopoulou, K.K.; Molassiotis, A. Ozone-Induced Inhibition of Kiwifruit Ripening Is Amplified by 1-Methylcyclopropene and Reversed by Exogenous Ethylene. BMC Plant Biol. 2018, 18, 358. [Google Scholar] [CrossRef]
  11. Pongprasert, N.; Srilaong, V.; Sugaya, S. An Alternative Technique Using Ethylene Micro-Bubble Technology to Accelerate the Ripening of Banana Fruit. Sci. Hortic. 2020, 272, 109566. [Google Scholar] [CrossRef]
  12. Rizzolo, A.; Grassi, M.; Vanoli, M. Storage Protocol Modulates Ripening Behavior and Physiological Disorders of 1-MCP Treated ‘Abate Fetel’ Pears. Acta Hortic. 2018, 1194, 701–708. [Google Scholar] [CrossRef]
  13. Zhou, X.; Dong, L.; Zhou, Q.; Wang, J.; Chang, N.; Liu, Z.; Ji, S. Effects of Intermittent Warming on Aroma-Related Esters of 1-Methylcyclopropene-Treated ‘Nanguo’ Pears during Ripening at Room Temperature. Sci. Hortic. 2015, 185, 82–89. [Google Scholar] [CrossRef]
  14. Brumos, J. Gene Regulation in Climacteric Fruit Ripening. Curr. Opin. Plant Biol. 2021, 63, 102042. [Google Scholar] [CrossRef]
  15. Dias, C.; Rodrigues, A.C.; Vasconcelos, M.W.; Ferrante, A.; Pintado, M. Preliminary Results on the Effect of 1-Naphthaleneacetic Acid on Restoring ‘Rocha’ Pear Ripening Treated with 1-MCP. Acta Hortic. 2024, 1396, 61–66. [Google Scholar] [CrossRef]
  16. Kondo, S.; Seto, H. Changes of Jasmonic Acid During Ripening in Pear Fruit and Interactions Between Jasmonic Acid and Abscisic Acid. Acta Hortic. 2004, 636, 537–543. [Google Scholar] [CrossRef]
  17. Siebeneichler, T.J.; Crizel, R.L.; Camozatto, G.H.; Paim, B.T.; da Silva Messias, R.; Rombaldi, C.V.; Galli, V. The Postharvest Ripening of Strawberry Fruits Induced by Abscisic Acid and Sucrose Differs from Their In Vivo Ripening. Food Chem. 2020, 317, 126407. [Google Scholar] [CrossRef]
  18. Dhingra, A.; Hendrickson, C. Control of Ripening and Senescence in Pre-Harvest and Post-Harvest Plants and Plant Materials by Manipulating Alternative Oxidase Activity. U.S. Patent 9,123,456, 17 July 2017. [Google Scholar]
  19. Nikiforova, V.J.; Giesbertz, P.; Wiemer, J.; Bethan, B.; Looser, R.; Liebenberg, V.; Ruiz Noppinger, P.; Daniel, H.; Rein, D. Glyoxylate, a New Marker Metabolite of Type 2 Diabetes. J. Diabetes Res. 2014, 2014, 685204. [Google Scholar] [CrossRef]
  20. Norikura, T.; Sasaki, Y.; Kojima-Yuasa, A.; Kon, A. Glyoxylic Acid, an α-Keto Acid Metabolite Derived from Glycine, Promotes Myogenesis in C2C12 Cells. Nutrients 2023, 15, 1763. [Google Scholar] [CrossRef]
  21. Dias, C.; Ribeiro, T.; Rodrigues, A.C.; Ferrante, A.; Vasconcelos, M.W.; Pintado, M. Cold Storage Demand for “Rocha” Pear Ripening: A Comparison between a Shorter and Longer Cold Period. Sci. Hortic. 2022, 299, 111033. [Google Scholar] [CrossRef]
  22. Fernández-Cancelo, P.; Muñoz, P.; Echeverría, G.; Larrigaudière, C.; Teixidó, N.; Munné-Bosch, S.; Giné-Bordonaba, J. Ethylene and Abscisic Acid Play a Key Role in Modulating Apple Ripening after Harvest and after Cold-Storage. Postharvest Biol. Technol. 2022, 188, 111902. [Google Scholar] [CrossRef]
  23. De Martin, M.S.; Steffens, C.A.; Do Amarante, C.V.T.; Brackmann, A.; Rodrigues, M.F.; Soethe, C. Pears Stored Under Controlled Atmosphere with Ultra-Low and Low O2 Associated with Different CO2 Levels. Rev. Bras. Frutic. 2017, 39, e143. [Google Scholar] [CrossRef]
  24. Saquet, A.; Almeida, D. Internal Disorders of ‘Rocha’ Pear Affected by Oxygen Partial Pressure and Inhibition of Ethylene Action. Postharvest Biol. Technol. 2017, 128, 54–62. [Google Scholar] [CrossRef]
  25. Bulens, I.; Van de Poel, B.; Hertog, M.L.; De Proft, M.P.; Geeraerd, A.H.; Nicolaï, B.M. Protocol: An Updated Integrated Methodology for Analysis of Metabolites and Enzyme Activities of Ethylene Biosynthesis. Plant Methods 2011, 7, 17. [Google Scholar] [CrossRef]
  26. Giné-Bordonaba, J.; Echeverria, G.; Ubach, D.; Aguiló-Aguayo, I.; López, M.L.; Larrigaudière, C. Biochemical and Physiological Changes during Fruit Development and Ripening of Two Sweet Cherry Varieties with Different Levels of Cracking Tolerance. Plant Physiol. Biochem. 2017, 111, 216–225. [Google Scholar] [CrossRef]
  27. Lindo-García, V.; Larrigaudière, C.; Echeverría, G.; Murayama, H.; Soria, Y.; Giné-Bordonaba, J. New Insights on the Ripening Pattern of ‘Blanquilla’ Pears: A Comparison between on- and off-Tree Ripened Fruit. Postharvest Biol. Technol. 2019, 150, 112–121. [Google Scholar] [CrossRef]
  28. Alsberg, B.K.; Kell, D.B.; Goodacre, R. Variable Selection in Discriminant Partial Least-Squares Analysis. Anal. Chem. 1998, 70, 4126–4133. [Google Scholar] [CrossRef]
  29. Gao, Q.; Tian, Y.; Zhang, J.; Zhang, P.; Zhang, M.; Bi, J.; Li, J.; Xue, Y. Discriminant Analysis of ‘Fuji’ and ‘Hanfu’ Apples under 1-Methylcyclopropene (1-MCP) and Cold Storage Conditions Based on Their Postharvest Quality and Aroma Properties. J. Food Meas. Charact. 2024, 18, 9492–9507. [Google Scholar] [CrossRef]
  30. Lee, H.Y.; Yoon, G.M. Kinase Assay for CONSTITUTIVE TRIPLE RESPONSE 1 (CTR1) in Arabidopsis Thaliana. In Ethylene Signaling; Methods in Molecular Biology; Humana Press: Totowa, NJ, USA, 2017; Volume 1573, pp. 133–140. ISBN 9781493968541. [Google Scholar]
  31. Wu, Q.; Tao, X.; Ai, X.; Luo, Z.; Mao, L.; Ying, T.; Li, L. Contribution of Abscisic Acid to Aromatic Volatiles in Cherry Tomato (Solanum lycopersicum L.) Fruit during Postharvest Ripening. Plant Physiol. Biochem. 2018, 130, 205–214. [Google Scholar] [CrossRef]
  32. Xu, Y.; Gao, G.; Tian, L.; Cao, Y.; Dong, X.; Huo, H.; Qi, D.; Zhang, Y.; Xu, J.; Liu, C. Changes of Volatile Organic Compounds of Different Flesh Texture Pears during Shelf Life Based on Headspace Solid-Phase Microextraction with Gas Chromatography–Mass Spectrometry. Foods 2023, 12, 4224. [Google Scholar] [CrossRef]
  33. Barbosa, R. Avaliação dos Compostos Orgânicos Voláteis Associados à Maturação da Pera Rocha; Instituto Técnico de Lisboa: Lisbon, Portugal, 2020. [Google Scholar]
  34. Kou, X.; He, Y.; Li, Y.; Chen, X.; Feng, Y.; Xue, Z. Effect of Abscisic Acid (ABA) and Chitosan/Nano-Silica/Sodium Alginate Composite Film on the Color Development and Quality of Postharvest Chinese Winter Jujube (Zizyphus jujuba Mill. cv. Dongzao). Food Chem. 2019, 270, 385–394. [Google Scholar] [CrossRef] [PubMed]
  35. Farcuh, M.; Rivero, R.M.; Sadka, A.; Blumwald, E. Ethylene Regulation of Sugar Metabolism in Climacteric and Non-Climacteric Plums. Postharvest Biol. Technol. 2018, 139, 20–30. [Google Scholar] [CrossRef]
  36. Tipu, M.M.H.; Sherif, S.M. Ethylene and Its Crosstalk with Hormonal Pathways in Fruit Ripening: Mechanisms, Modulation, and Commercial Exploitation. Front. Plant Sci. 2024, 15, 1475496. [Google Scholar] [CrossRef] [PubMed]
  37. Ashitha, G.N.; Sunny, A.C.; Nisha, R. Effect of Pre-Harvest and Post-Harvest Hexanal Treatments on Fruits and Vegetables: A Review. Agric. Rev. 2020, 41, 124–131. [Google Scholar] [CrossRef]
  38. Lu, H.; Zhao, H.; Zhong, T.; Chen, D.; Wu, Y.; Xie, Z. Molecular Regulatory Mechanisms Affecting Fruit Aroma. Foods 2024, 13, 1870. [Google Scholar] [CrossRef]
  39. Torregrosa, L.; Echeverria, G.; Illa, J.; Giné-Bordonaba, J. Emission of VOCs and Quality Evolution in Response to Repeated Oxygen Pull Downs on ‘Conference’ Pears during Long-Term Cold Storage. Postharvest Biol. Technol. 2020, 170, 111322. [Google Scholar] [CrossRef]
  40. Khan, S.; Alvi, A.F.; Saify, S.; Iqbal, N.; Khan, N.A. The Ethylene Biosynthetic Enzymes, 1-Aminocyclopropane-1-Carboxylate (ACC) Synthase (ACS) and ACC Oxidase (ACO): The Less Explored Players in Abiotic Stress Tolerance. Biomolecules 2024, 14, 90. [Google Scholar] [CrossRef]
  41. Polko, J.K.; Kieber, J.J. 1-Aminocyclopropane 1-Carboxylic Acid and Its Emerging Role as an Ethylene-Independent Growth Regulator. Front. Plant Sci. 2019, 10, 1602. [Google Scholar] [CrossRef]
  42. Tucker, G.; Yin, X.; Zhang, A.; Wang, M.; Zhu, Q.; Liu, X.; Xie, X.; Chen, K.; Grierson, D. Ethylene and Fruit Softening. Food Qual. Saf. 2017, 1, 253–267. [Google Scholar] [CrossRef]
  43. Zhu, X.; Song, Z.; Li, Q.; Li, J.; Chen, W.; Li, X. Physiological and Transcriptomic Analysis Reveals the Roles of 1-MCP in the Ripening and Fruit Aroma Quality of Banana Fruit (Fenjiao). Food Res. Int. 2020, 130, 108968. [Google Scholar] [CrossRef]
  44. Roy Choudhury, S.; Roy, S.; Das, R.; Sengupta, D.N. Differential Transcriptional Regulation of Banana Sucrose Phosphate Synthase Gene in Response to Ethylene, Auxin, Wounding, Low Temperature and Different Photoperiods during Fruit Ripening and Functional Analysis of Banana SPS Gene Promoter. Planta 2008, 229, 207–223. [Google Scholar] [CrossRef] [PubMed]
  45. Zhou, H.; Wang, L.; Su, M.; Zhang, X.; Du, J.; Li, X.; Zhang, M.; Hu, Y.; Zheng, X.; Ye, Z.; et al. Comparative Network Analysis Reveals the Regulatory Mechanism of 1-Methylcyclopropene on Sugar and Acid Metabolisms in Yellow Peach Stored at Non-Chilling Temperatures. Plant Physiol. Biochem. 2024, 216, 109100. [Google Scholar] [CrossRef] [PubMed]
Horticulturae 11 00314 g001
Figure 1. PLSDA scores map and VIP scores of ’Rocha’ pear characteristics after treatment with GLA (T7_GLA and T15_GLA) and their respective controls (T0_CT; T7_CT and T15_CT) across 15 days of shelf-life (T0; T7 and T15).
Figure 1. PLSDA scores map and VIP scores of ’Rocha’ pear characteristics after treatment with GLA (T7_GLA and T15_GLA) and their respective controls (T0_CT; T7_CT and T15_CT) across 15 days of shelf-life (T0; T7 and T15).
Horticulturae 11 00314 g001
Horticulturae 11 00314 g002
Figure 2. Heatmap obtained from the measured pear parameters during the experience time for CTRL samples (T0_CT; T7_CT and T15_CT) and GLA-treated samples (T7_GLA and T15_GLA). Blue and red squares indicates lower or higher intensity of the variables measured, respectively.
Figure 2. Heatmap obtained from the measured pear parameters during the experience time for CTRL samples (T0_CT; T7_CT and T15_CT) and GLA-treated samples (T7_GLA and T15_GLA). Blue and red squares indicates lower or higher intensity of the variables measured, respectively.
Horticulturae 11 00314 g002
Horticulturae 11 00314 g003
Figure 3. Ethylene and CO2 variations in ‘Rocha’ pears during shelf-life at 20 °C, after treatment. Values are means ± standard deviations of normalized data. Different capital letters indicate significant differences (p < 0.05) across time for each condition. Different small letters indicate significant differences (p < 0.05) between conditions at each timepoint (0, 7, and 15 days).
Figure 3. Ethylene and CO2 variations in ‘Rocha’ pears during shelf-life at 20 °C, after treatment. Values are means ± standard deviations of normalized data. Different capital letters indicate significant differences (p < 0.05) across time for each condition. Different small letters indicate significant differences (p < 0.05) between conditions at each timepoint (0, 7, and 15 days).
Horticulturae 11 00314 g003
Horticulturae 11 00314 g004
Figure 4. Firmness and hue angle variation of ‘Rocha’ pears during shelf-life at 20 °C after treatment. Values are means ± standard deviations of normalized data. Different capital letters indicate significant differences (p < 0.05) across time for each condition. Different small letters indicate significant differences (p < 0.05) between conditions at each timepoint (0, 7, and 15 days).
Figure 4. Firmness and hue angle variation of ‘Rocha’ pears during shelf-life at 20 °C after treatment. Values are means ± standard deviations of normalized data. Different capital letters indicate significant differences (p < 0.05) across time for each condition. Different small letters indicate significant differences (p < 0.05) between conditions at each timepoint (0, 7, and 15 days).
Horticulturae 11 00314 g004
Horticulturae 11 00314 g005
Figure 5. Sucrose and TA content variation in ’Rocha’ pears after treatment with GLA during shelf-life at 20 °C. Values are means ± standard deviations of normalized data. Different capital letters indicate significant differences (p < 0.05) across time for each condition. Different small letters indicate significant differences (p < 0.05) between conditions at each timepoint (0, 7, and 15 days).
Figure 5. Sucrose and TA content variation in ’Rocha’ pears after treatment with GLA during shelf-life at 20 °C. Values are means ± standard deviations of normalized data. Different capital letters indicate significant differences (p < 0.05) across time for each condition. Different small letters indicate significant differences (p < 0.05) between conditions at each timepoint (0, 7, and 15 days).
Horticulturae 11 00314 g005
Horticulturae 11 00314 g006
Figure 6. ACC content and ACO activity variation in ’Rocha’ pears after treatment with GLA during shelf-life at 20 °C. Values are means ± standard deviations of normalized data. Different capital letters indicate significant differences (p < 0.05) across time for each condition. Different small letters indicate significant differences (p < 0.05) between conditions at each timepoint (0, 7, and 15 days).
Figure 6. ACC content and ACO activity variation in ’Rocha’ pears after treatment with GLA during shelf-life at 20 °C. Values are means ± standard deviations of normalized data. Different capital letters indicate significant differences (p < 0.05) across time for each condition. Different small letters indicate significant differences (p < 0.05) between conditions at each timepoint (0, 7, and 15 days).
Horticulturae 11 00314 g006
Table 1. Major VOC emissions in ‘Rocha’ pears after treatment during shelf-life at 20 °C. Values are means ± standard deviations of normalized data.
Table 1. Major VOC emissions in ‘Rocha’ pears after treatment during shelf-life at 20 °C. Values are means ± standard deviations of normalized data.
Aroma Volatile0 D7 D15 D
HexanalCTRL1 ± 0.22 B12.94 ± 3.50 Ab11.92 ± 4.41 Aa
GLA1 ± 0.22 C37.00 ± 5.28 Aa15.38 ± 2.98 Ba
Hexyl acetateCTRL1 ± 0.45 A0.96 ± 0.26 Aa2.36 ± 0.91 Aa
GLA1 ± 0.45 B0.92 ± 0.24 Ba12.70 ± 4.34 Ab
Butyl acetateCTRL1 ± 0.28 B0.46 ± 0.13 Bb5.04 ± 1.86 Aa
GLA1 ± 0.28 B0.77 ± 0.08 Ba7.66 ± 0.96 Aa
(E)-2-HexenalCTRL1 ± 0.19 B8.24 ± 1.79 Ab12.46 ± 2.45 Aa
GLA1 ± 0.19 C34.11 ± 5.48 Aa9.43 ± 0.16 Ba
LimoneneCTRL1 ± 0.02 B2.08 ± 0.05 Aa1.02 ± 0.02 Ba
GLA1 ± 0.02 A0.96 ± 0.15 Ab0.93 ± 0.03 Aa
2-Ethyl-hexanolCTRL1 ± 0.02 B0.85 ± 0.04 Aa0.48 ± 0.13 Aa
GLA1 ± 0.02 A0.37 ± 0.07 Bb0.52 ± 0.17 Ba
EthanolCTRL1 ± 0.06 B1.49 ± 0.36 Ba3.02 ± 0.33 Aa
GLA1 ± 0.06 B2.18 ± 0.9 ABa2.92 ± 0.60 Aa
Different capital letters indicate significant differences (p < 0.05) across time for each condition. Different small letters indicate significant differences (p < 0.05) between conditions at each timepoint (0, 7, and 15 days).
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Dias, C.; Sousa, C.; Vasconcelos, M.W.; Ferrante, A.; Pintado, M. Effects of Glyoxylic Acid on Metabolism and Ripening of ‘Rocha’ Pears Treated with 1-MCP. Horticulturae 2025, 11, 314. https://doi.org/10.3390/horticulturae11030314

AMA Style

Dias C, Sousa C, Vasconcelos MW, Ferrante A, Pintado M. Effects of Glyoxylic Acid on Metabolism and Ripening of ‘Rocha’ Pears Treated with 1-MCP. Horticulturae. 2025; 11(3):314. https://doi.org/10.3390/horticulturae11030314

Chicago/Turabian Style

Dias, Cindy, Clara Sousa, Marta W. Vasconcelos, António Ferrante, and Manuela Pintado. 2025. "Effects of Glyoxylic Acid on Metabolism and Ripening of ‘Rocha’ Pears Treated with 1-MCP" Horticulturae 11, no. 3: 314. https://doi.org/10.3390/horticulturae11030314

APA Style

Dias, C., Sousa, C., Vasconcelos, M. W., Ferrante, A., & Pintado, M. (2025). Effects of Glyoxylic Acid on Metabolism and Ripening of ‘Rocha’ Pears Treated with 1-MCP. Horticulturae, 11(3), 314. https://doi.org/10.3390/horticulturae11030314

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop