Abstract
Pumpkin (Cucurbita moschata Duch.) is a versatile crop with strong stress resistance and promising growth potential. Widely cultivated in various regions of China, it ranks among the top crops globally in terms of both planting area and consumption. Known for its pleasant taste and high nutritional value, pumpkin pulp is rich in essential trace elements for the human body. Even after harvest, pumpkin fruit remains metabolically active, requiring its own nutrients to complete the postripening process. Failure to provide proper postharvest storage conditions can lead to excessive water loss and rapid nutrient depletion, resulting in rough, shriveled, and even rotten peel, ultimately diminishing the economic value of the pumpkin. This study aimed to investigate the changes in pumpkin quality and physiological indicators during storage to provide insights to determine optimal consumption and processing periods of pumpkins. The pumpkins were stored at a temperature of 16 ± 2 °C and 60% to 80% humidity during the experiment. The dynamic changes in fruit quality, hardness, respiration rate, malondialdehyde content, level of antioxidant enzymes, and other indicators of two pumpkin cultivars (BM5 and JQ) were assessed during storage, and the correlation among these indicators was evaluated. The results indicated a decrease in the vitamin C content and pulp hardness, whereas the superoxide dismutase and catalase contents initially increased and then decreased, and malondialdehyde and weight loss rates increased over the storage period. The weight loss rate exhibited significant positive and negative correlations with the malondialdehyde content (P < 0.01) of the two cultivars, whereas the vitamin C content showed a significant positive correlation with pulp hardness (P < 0.01). The findings indicate that optimal fruit quality was maintained within 40 days of postharvest storage. This study provides valuable insights into the selection of storable pumpkin cultivars.
Pumpkin (Cucurbita moschata Duch.) is a nutrient-rich vegetable crop with significant economic and medicinal values (Lin 2000). The fruit has a bright appearance, sweet yet nongreasy taste, and high vitamin C and β-carotene contents, making it highly popular among consumers. Pumpkin is enriched with essential nutrients such as proteins and polysaccharides that demonstrate anticancer properties and the ability to regulate blood sugar and lipid levels (Wang et al. 2010). The pumpkin industry plays a vital role in economic development and poverty alleviation in mountainous and impoverished regions because of the appealing taste, ease of cultivation, and medicinal benefits of pumpkin fruits (Long et al. 2021). With evolving consumer preferences, the pumpkin industry has diversified into deep processing, leading to the emergence of multiple sectors such as edible products, medicinal applications, processing, and seed utilization. This diversification has accelerated the growth of the pumpkin industry (Zhou et al. 2014).
During postharvest storage, the respiratory and metabolic activities within fruits impact their quality changes. The nutritional quality of fruits changes differently as storage time increases and is influenced by genetic factors that lead to variations in postharvest storability and quality among pumpkin cultivars. Previous studies have indicated a correlation between pumpkin perishability and pulp components during storage (Hurst et al. 1995). Liu et al. (2007) observed that as the storage time of seed pumpkin increases, nutrients degrade, outer pulp hardens, and pulp ages and decays, but at a slower rate than that of the pulp. After detachment from the plant, pumpkins undergo physiological and metabolic activities, thus depleting their nutrients. Understanding the nutritional quality changes during storage can inform production, processing, and utilization. Wang et al. (2010) found that soluble sugar, starch, and soluble solids contents in pumpkin fruits peak after 40 d of storage. Chu and Xiang (2007) noted that mature pumpkins have higher nutritional content and better storage resistance than young ones. Gonçalves et al. (2005) discovered a significant correlation between pumpkin fruit hardness and total pectin content, which decreases with the storage time. Zhang (2010) reported a decline in reducing the sugar content of pumpkin fruits over the storage period. Parichat and Phonkrit (2022) investigated the impact of postharvest storage on pumpkin and noted a significant decrease in the starch particle size and changes in texture, physiological quality, and stickiness after 30 d. The presence of reactive oxygen species (ROS) was found to accelerate fruit quality deterioration by inhibiting ROS scavenging enzymes such as superoxide dismutase (SOD) and catalase (CAT). This led to browning of the peel, reduced enzyme activity in fruit tissues, and an increased malondialdehyde (MDA) content. Both SOD and CAT, which are known as ROS scavenging enzymes, play crucial roles in reducing oxidative stress in plants by neutralizing ROS (Zhang et al. 2018).
Current research of pumpkins primarily focuses on cultivar selection and disease resistance, with limited attention on changes in postharvest storage quality and the breeding of storage-stable pumpkin cultivars. Postharvest processing and storage significantly impact the nutritional quality of fruits and vegetables, ultimately affecting the quality of processed products (Liu et al. 2022). Previous findings indicated a correlation between pumpkin perishability and pulp components during storage (Hurst et al. 1995). Therefore, exploring changes in fruit quality during storage is essential to comprehensively assess the nutritional value of pumpkin and determine fruit storage durability. During this study, we assessed the physiological characteristics, nutritional quality, fruit texture, and activity of antioxidant enzymes of two pumpkin cultivars during storage to understand the dynamic changes in pumpkin fruits and provide a basis for future breeding endeavors aimed at producing storage-stable pumpkin cultivars. In addition, the findings provide insights into determining the optimal processing and consumption period for pumpkins.
Materials and Methods
Experimental materials.
Two pumpkin cultivars, Baimi No. 5 (BM5) and JQ, were sourced from the pumpkin research center at Henan Institute of Science and Technology. These cultivars were cultivated at the Pumpkin Test Base of Henan University of Science and Technology in Hongmen Town, Hongqi District, Xinxiang City, Henan Province, from Apr 2023. The plants were spaced at 0.8 m × 3.6 m, and the fruits were harvested ∼45 d postpollination. Maturity was assessed based on the color change of the melon rind and the firmness of the pumpkin fruit base connection. Pumpkins of uniform maturity and size that were free from pests and diseases were harvested. Subsequently, 100 fruits from each cultivar were harvested and promptly transported to a laboratory, where they were stored at a temperature of 16 ± 2 °C and humidity ranging from 60% to 80%.
Experimental procedures.
On the day of harvesting, six fruits of each cultivar were selected and weighed to determine the fruit weight loss rate. Sampling was conducted from day 10 of storage and continued every 10 d during the study period. Three fruits from each cultivar were randomly selected during each sampling, and three biological replicates were established. The pumpkins were peeled, and samples were taken from one-third of the melon cavity. Then, the samples were pulverized into a uniform pulp using a high-speed grinder to assess the nutritional quality and physiological indicators. The remaining samples were promptly frozen in liquid nitrogen and stored in a −80 °C ultra-low-temperature refrigerator for enzyme activity and evaluation of other indicators. In addition, six fruits were randomly selected from each cultivar and labeled to determine the respiration rate.
Soluble solids were assessed using a handheld sugar meter and reported as a percentage. The starch content was determined using the I2-KI method following the procedure outlined by Cao et al. (2007), and the results were reported in mg/g fresh weight (FW). The soluble sugar content in the fruit was measured using the anthrone colorimetric method following a protocol reported by Cao et al. (2007), and the results were reported as a percentage. The β-carotene content was evaluated by the colorimetric method described by Li (2000), and the results were reported as μg/g. Six pumpkins from each cultivar were selected to evaluate the fruit respiration rate. The fruits were weighed and placed in a 42-L container, and the respiration rate was assessed using a fruit and vegetable respiration rate meter (YT-GX10; Shandong Yuntang Intelligent Technology Co., Ltd.), and the results were presented as mg·kg−1·h−1. Malondialdehyde levels were determined using the thiobarbituric acid chromogenic method. The Solebao kit was used to extract MDA according to the manufacturer’s instructions, and the results were reported as nmol/mL. The fruit weight loss rate was evaluated using a method reported by Khaliq et al. (2015). The weight of six fruits from each cultivar was recorded on the harvest day, and these fruits were subsequently weighed every 10 d to determine the weight loss rate. Six pumpkins were selected from each cultivar to assess the peel hardness using a texture analyzer, and the results were reported in Newtons (N). The vitamin C content of the fruit was evaluated according to the 2,6-dichlorophenol-indophenol titration method described by Cao et al. (2007). The activities of SOD and CAT enzymes as well as the soluble protein content were assessed according to a method outlined by Chen (2000).
Data processing and statistical analysis.
Data were compiled using Excel 2019 (Microsoft, Redmond, WA, USA) and graphs were generated using Origin 2021 software (OriginLab, Northampton, MA, USA). A one-way analysis of variance was performed using DPS software, followed by Duncan’s new complex polarity method to compare means and determine significant differences between groups (P < 0.05).
Results
Dynamic changes in soluble solids, soluble sugar, and starch contents of pumpkin during storage.
The contents of soluble solids in ‘JQ’ and ‘BM5’ consistently increased over the extended storage period. Notably, ‘JQ’ had a significantly higher content of soluble solids compared with that of ‘BM5’ during the storage period (Fig. 1A). The peak concentrations of soluble solids for ‘JQ’ and ‘BM5’ were observed on day 60, with increases of 12.33% and 10.62%, respectively. Significant variations in the soluble solids content were observed between ‘JQ’ and ‘BM5’ at different time points. The soluble sugar contents of JQ and BM5 cultivars initially increased and then decreased over the storage time. ‘JQ’ exhibited its highest soluble sugar content at 30 d (21.15% increase), whereas the maximum soluble sugar content for ‘BM5’ was observed at 20 d (18.67% increase). Notably, between days 50 and 60 of storage, ‘BM5’ exhibited a higher soluble sugar content than that of ‘JQ’. Significant differences in the soluble sugar content were observed between ‘JQ’ and ‘BM5’ at various time points, with ‘BM5’ exhibiting a notable decrease in the soluble sugar content between days 50 and 60 of storage (Fig. 1B). The starch contents of JQ and BM5 cultivars exhibited a similar pattern of initial increase followed by a decrease over the storage period. ‘JQ’ had the highest starch content on day 20 at 22.87 mg/g, whereas ‘BM5’ peaked on day 40, with 19.69 mg/g. ‘BM5’ showed a higher starch content than ‘JQ’ between day 40 and day 50, with significant differences observed between the two cultivars at different time points (Fig. 1C).
Dynamic changes in soluble solids, soluble sugar, and starch contents of pumpkin during storage. 10d = 10th day of storage; 20d = 20th day of storage; 30d = 30th day of storage; 40d = 40th day of storage; 50d = 50th day of storage; 60d = 60th day of storage. Data are presented as the mean ± SD of three measurements (n = 3; biological replicates). Different lowercase letters (a–f) in each column indicate significant differences at P ≤ 0.05 [least significant difference (LSD) test].
Citation: HortScience 59, 10; 10.21273/HORTSCI18000-24
β-carotene and vitamin C contents exhibit changes during pumpkin storage.
The β-carotene content of the JQ cultivar initially increased and then decreased before increasing again over the storage period, reaching its peak on day 20 (51.30 μg/g), followed by a decrease. In contrast, the β-carotene content in ‘BM5’ exhibited an initial increase followed by a decrease, with a maximum content of 47.00 μg/g on day 30. ‘JQ’ had a higher β-carotene content than ‘BM5’ on day 60 (Fig. 2A). The two pumpkin cultivars exhibited a similar decreasing trend in the vitamin C content over time, with JQ consistently maintaining higher levels than those of BM5 (Fig. 2B). On day 60, ‘JQ’ and ‘BM5’ had the lowest vitamin C content, 0.0760 mg/g and 0.0622 mg/g, respectively, representing 39.83% and 43.84% reductions relative to the levels observed on day 10. Significant differences in β-carotene and vitamin C contents were observed between ‘JQ’ and ‘BM5’ at different time points.
The β-carotene and vitamin C contents exhibit changes during pumpkin storage. Data are presented as the mean ± SD (n = 3; biological replicates). Different lowercase letters (a–d) in each column indicate significant differences at P ≤ 0.05 [least significant difference (LSD) test]. 10d = 10th day of storage; 20d = 20th day of storage; 30d = 30th day of storage; 40d = 40th day of storage; 50d = 50th day of storage; 60d = 60th day of storage.
Citation: HortScience 59, 10; 10.21273/HORTSCI18000-24
Dynamic changes in the respiration rate and malondialdehyde content of pumpkin during the storage period.
The two pumpkin cultivars exhibited a similar trend in respiration rates, with an initial increase followed by a decrease over the storage period. The respiratory rate of ‘JQ’ peaked on day 30 of storage at 55.85 mg·kg−1·h−1, whereas the respiratory rate of ‘BM5’ peaked on day 20 at 31.79 mg·kg−1·h−1 (Fig. 3A). The respiration rates of both cultivars significantly decreased after the peak periods. ‘BM5’ had a significantly lower respiration rate than that of ‘JQ’ over the storage period. Significant differences were observed in the respiratory rates of ‘JQ’ and ‘BM5’ during various time points. The malondialdehyde contents of JQ and BM5 cultivars increased with the increasing storage time. The lowest malondialdehyde contents for ‘JQ’ and ‘BM5’ were observed on day 10 of storage, with decreases of 8.50% and 9.47%, respectively. The malondialdehyde contents of ‘BM5’ and ‘JQ’ peaked on day 60 at 12.95% and 14.55%, respectively, representing increase of 71.09% and 36.66%, respectively, from the initial levels. Significant differences in the malondialdehyde content were observed between the JQ and BM5 cultivars across different time points (Fig. 3B).
Dynamic changes in the respiration rate and malondialdehyde content of pumpkin during the storage period. Data are presented as mean ± SD (n = 3; biological replicates). Different lowercase letters (a–d) in each column indicate significant differences at P ≤ 0.05 [least significant difference (LSD) test]. 10d = 10th day of storage; 20d = 20th day of storage; 30d = 30th day of storage; 40d = 40th day of storage; 50d = 50th day of storage; 60d = 60th day of storage.
Citation: HortScience 59, 10; 10.21273/HORTSCI18000-24
Dynamic changes in weight loss rate and hardness of pumpkin fruits during storage.
The weight loss rates of the two pumpkin cultivars significantly increased over the storage period. ‘JQ’ and ‘BM5’ had the highest weight loss rates on day 60 at 12.97% and 25.12%, respectively. Throughout the storage period, ‘JQ’ consistently maintained a lower weight loss rate compared with that of ‘BM5’. The weight loss rates of ‘JQ’ and ‘BM5’ exhibited significant differences at various time points (Fig. 4A). The peel hardness of ‘JQ’ initially decreased before increasing, whereas the peel hardness of ‘BM5’ increased, decreased, and finally increased again over the storage time. Notably, the peel hardness of ‘JQ’ started to increase between day 40 and day 50 of storage, reaching its peak at 29.814 N after day 50. Conversely, ‘BM5’ exhibited the highest peel hardness of 29.3167 N after day 20 of storage (Fig. 4B). The decline in peel hardness over the storage period was more pronounced in ‘BM5’ compared with that in ‘JQ’. ‘JQ’ exhibited significant differences in peel hardness compared with that of ‘BM5’ at different time points.
Dynamic changes in weight loss rate and hardness of pumpkin fruits during storage. Data are presented as mean ± SD (n = 3; biological replicates). Different lowercase letters (a–d) in each column indicate significant differences at P ≤ 0.05 [least significant difference (LSD) test]. 10d = 10th day of storage; 20d = 20th day of storage; 30d = 30th day of storage; 40d = 40th day of storage; 50d = 50th day of storage; 60d = 60th day of storage.
Citation: HortScience 59, 10; 10.21273/HORTSCI18000-24
Changes in fruit texture parameters of pumpkin during storage.
The two pumpkin cultivars exhibited a decrease in hardness and fruit crispness over the storage period (Table 1). The stickiness of ‘JQ’ fruits initially increased and then decreased, whereas that of ‘BM5’ initially decreased and then increased, followed by a decrease. The elasticity and chewiness of ‘JQ’ fruits gradually increased over time. The gumminess of both pumpkin cultivars initially decreased and then increased. The fruit texture of the two pumpkin cultivars exhibited distinct trends over the storage period that were potentially influenced by cultivar differences.
Changes in fruit texture parameters of two pumpkin cultivars during storage.
Dynamic changes in the soluble protein content of pumpkin fruits during storage.
The soluble protein content of ‘JQ’ initially increased, then decreased, and increased again over the storage time. In contrast, ‘BM5’ showed an initial increase followed by a decrease in the soluble protein content during storage (Fig. 5). The BM5 cultivar had the highest soluble protein content on day 40 of storage at 4.585 mg/g FW, whereas the soluble protein content of JQ peaked at 5.733 mg/g FW on day 50. The ‘JQ’ and ‘BM5’ pulps exhibited significant variations in soluble protein contents across different storage periods.
Dynamic changes in the soluble protein content of pumpkin fruits during storage. Data are presented as mean ± SD (n = 3; biological replicates). Different lowercase letters (a–d) in each column indicate significant differences at P ≤ 0.05 [least significant difference (LSD) test]. 10d = 10th day of storage; 20d = 20th day of storage; 30d = 30th day of storage; 40d = 40th day of storage; 50d = 50th day of storage; 60d = 60th day of storage.
Citation: HortScience 59, 10; 10.21273/HORTSCI18000-24
Dynamic changes in the antioxidant enzyme activity of pumpkin fruits during storage.
The SOD and CAT levels of both pumpkin cultivars initially increased and then decreased over the storage period. The SOD levels of ‘JQ’ and ‘BM5’ peaked on day 30 at 285.663 U/g and 352.645 U/g, respectively, before exhibiting a notable decline (Fig. 6A). The SOD levels of both cultivars were low during the first 10 d of storage. The CAT levels of ‘JQ’ peaked on day 30 of storage at 87.482 U/g, followed by a significant decrease (Fig. 6B). Conversely, ‘BM5’ exhibited the highest CAT level of 101.571 U/g on day 40 of storage, followed by a significant decrease. Notably, significant variations in the SOD and CAT contents were observed between ‘JQ’ and ‘BM5’ pulps at different time intervals.
Dynamic changes in the antioxidant enzyme activity of pumpkin fruits during storage. Data are presented as mean ± SD (n = 3; biological replicates). Different lowercase letters (a–d) in each column indicate significant differences at P ≤ 0.05 [least significant difference (LSD) test]. 10d = 10th day of storage; 20d = 20th day of storage; 30d = 30th day of storage; 40d = 40th day of storage; 50d = 50th day of storage; 60d = 60th day of storage.
Citation: HortScience 59, 10; 10.21273/HORTSCI18000-24
Correlation analysis of individual indicators of pumpkin fruits during the storage period.
The relationships between quality indicators, malondialdehyde content, and antioxidant enzymes of the two pumpkin cultivars were evaluated during storage. The results revealed significant correlations among the different indicators. Notably, the pulp hardness of the JQ and BM5 cultivars exhibited a significant positive correlation with the vitamin C content (P < 0.01). Conversely, the weight loss rate of the two cultivars showed a significant positive and negative correlation with malondialdehyde, respectively (P < 0.01). The vitamin C content in the JQ cultivar showed a significantly negative correlation with the weight loss rate (P < 0.01) (Fig. 7A). In contrast, the starch content exhibited a significant positive correlation with the β-carotene content (P < 0.05). In addition, a significant negative correlation was observed between pulp hardness and soluble solids in the JQ cultivar (P < 0.01). The vitamin C content in the BM5 cultivar was significantly negatively correlated with the malondialdehyde level (P < 0.01) and weight loss rate (P < 0.01), whereas the starch content displayed a significant positive correlation with CAT activity (P < 0.01) (Fig. 7B). A significant positive correlation was observed between the soluble solids content and weight loss rate (P < 0.01), whereas pulp hardness was significantly negatively correlated with the respiration rate (P < 0.01).
Correlation analysis of individual indicators of pumpkin fruits during the storage period. (A) ‘JQ’. (B) ‘BM5’.
Citation: HortScience 59, 10; 10.21273/HORTSCI18000-24
Synchronicity of pumpkin quality changes during storage.
The values of the soluble sugar, soluble solids, respiration rate, weight loss rate, hardness, and starch content were normalized and plotted together (Fig. 8). The trends of the six indicators, except for soluble solids, during storage were similar for both JQ and BM5 cultivars. However, the key change points varied, possibly because of cultivar differences. Over the initial 40 d of storage, the weight loss rate increased gradually, whereas the respiration rate and hardness gradually declined. The other quality indicators remained relatively stable. This finding indicates that the 40-d threshold is critical for postharvest storage of pumpkins.
Synchronicity of pumpkin quality changes during storage. (A) ‘JQ’. (B) ‘BM5’.
Citation: HortScience 59, 10; 10.21273/HORTSCI18000-24
Principal component analysis of pumpkin indicators during storage.
The principal component analysis results of the relevant indicators for two pumpkin cultivars are presented in Table 2. Three principal components were derived from the analysis, with all eigenvalues exceeding 1.0. Table 3 displays the load coefficients for 11 indicators. The first principal component (PC1) had an eigenvalue of 4.040, contributing to 36.727% of the variance. The weight loss rate, soluble protein, and soluble solids significantly influenced PC1. The second principal component (PC2) had an eigenvalue of 3.334, explaining 30.308% of the variance, with notable loads from soluble protein, soluble sugar, β-carotene, respiratory rate, and starch. The third principal component (PC3) had an eigenvalue of 1.656, contributing to 15.052% of the variance, with CAT showing strong loading. The cumulative contribution rate of the first three principal components was 82.081%, indicating the accuracy of these components for assessing the storability of pumpkin fruits.
Principal component characteristic values and contribution rates.
Principal component load matrix.
Discussion and Conclusion
Pumpkins are suitable for long-term storage before consumption and processing (Chang 2004). After harvesting, pumpkins undergo a period of postripening characterized by a gradual decrease in the water content, softening of the surface peel, and reduced hardness. Moreover, the nutritional composition of the pumpkin fruit underwent significant changes over time. Despite these changes, pumpkins maintained a relatively high level of stability, exhibiting high nutritional value and good flavor, which are key factors in assessing their storability.
Fruit hardness is a crucial parameter for evaluating the storability of fruits and assessing the impact of storage on fruit quality. Fruit hardness directly affects storage characteristics and shelf life, and it ultimately influences consumer preference. Moisture status also plays a significant role during fruit storage because it influences fruit texture by affecting the cell turgor pressure. Water loss from fruits during storage leads to reduced fruit weight and hardness. In this study, we observed significant changes in the peel and pulp hardness of the two pumpkin cultivars with the increasing storage time. ‘BM5’ exhibited a significant decrease in peel hardness compared with that of ‘JQ’ during the storage period. Additionally, ‘JQ’ had significantly lower pulp hardness than ‘BM5’ throughout the storage period. The alterations in fruit firmness may be attributed to changes in internal structure and chemical composition over time, leading to breakdown and loss of original structure and elasticity.
The respiration rate is a crucial indicator for assessing the vigor of respiration in postharvest fruits. A higher respiration rate leads to accelerated physiological metabolism, increased nutrient consumption, and reduced storage life. The respiration rate varies significantly among fruit cultivars, with fruits with good storage properties exhibiting lower respiration rates compared with those of cultivars with poor storage capabilities. The two pumpkin cultivars in this study exhibited similar trends of respiration rate changes over the storage time, with an initial increase followed by a decrease. The BM5 cultivar had a lower respiration rate than that of JQ throughout the storage period.
Fruit water loss is an inevitable process during storage that is influenced by postharvest respiration and transpiration. Reduced tissue moisture and cell turgor pressure cause fruit tissue wilting and weight loss. The rate of weight loss is an indirect indicator of fruit water loss that provides insights regarding the storage quality of fruit. In addition, the weight loss rate is a crucial metric for assessing fruit aging, shrinkage, and wilting, with higher weight loss rates indicating more severe wilting and reduced commercial value (Geng et al. 2021). In this study, the two pumpkin cultivars exhibited an increasing weight loss rate over time, consistent with previous findings of kiwifruit (Zhang et al. 2022). ‘BM5’ exhibited a higher weight loss rate, consistent with the fruit’s later-stage mottled and shrunken peel. Fruit water loss results in weight reduction, disrupts normal respiration, affects physiological metabolism, enhances hydrolysis, increases enzyme activity, and accelerates water loss and nutrient decomposition, thereby ultimately affecting fruit storability and disease resistance. The weight loss rate of the two pumpkin cultivars demonstrated a strong positive correlation with the malondialdehyde content, indicating that increased water loss was associated with increased weight loss rates, enhanced peel shrinkage, accelerating aging, and increased malondialdehyde content. During this study, the vitamin C content in the fruits of both pumpkin cultivars decreased over the storage time, which aligned with the research findings of kiwifruits (Dong et al. 2022). Similarly, Gong et al. (2010) observed a gradual decrease in the vitamin C content in crown pear fruits over time during low-temperature storage, consistent with the present results.
Components of pulp tissue, such as soluble solids and sugars, can significantly impact fruit storability. The soluble solid content is a crucial indicator for assessing fruit maturity, with soluble sugar as its primary component. Soluble sugar serves as the main flavor constituent of the fruit and plays a key role in antioxidant metabolism during fruit ripening and aging. The quality of pumpkin fruit is determined by its taste and texture, with the soluble sugar and starch contents directly influencing the sweetness and floralness of the fruit (Gao et al. 2023). Consequently, the soluble sugar and starch contents are essential quality indicators for pumpkins and are both quantitative traits influenced by multiple genes and environmental factors (Zeeman et al. 2010). Starch, which is composed of amylose and amylopectin, significantly influences the eating quality of pumpkin by serving as a crucial storage carbohydrate and sugar conversion component. Dry matter and starch content contribute to the taste of pumpkin pulp, with higher starch contents associated with a stronger flowery texture. Research has indicated that the composition and content of pumpkin starch are related to the powdery and waxy texture of the fruit (Wang 2017). The proportion of amylopectin is positively correlated with the degree of waxiness, and smaller starch granules are associated with a more delicate taste. Sucrose plays a critical role in determining the sweetness of pumpkin fruit and contributes the most to the sweetness compared with other soluble sugars. Pumpkin fruit starch is a crucial storage form of sugar substances in plants and can be converted to soluble sugars in the fruit. Starch is broken down into maltose, and further into sucrose, by hydrolases. Pumpkin starch is correlated with the levels of sugar anabolic enzymes. During storage, fruit amylase activity increases, facilitating starch degradation, whereas sucrose phosphate synthase activity increases, leading to an accumulation of soluble sugars (Stefano et al. 2015). Liu et al. (2011) observed a decrease in the starch content of Indian pumpkins during storage. Conversely, Wang et al. (2010) reported an increase in the starch content of five pumpkin cultivars during a 40-d postharvest period. Sharma and Ramana (2013) observed a decrease in the pumpkin starch content over time, accompanied by a gradual accumulation of sugars. In the current study, the two pumpkin cultivars exhibited a significant increase in the starch content that peaked between day 20 and day 40 of storage, followed by a gradual decline. Concurrently, the soluble sugar content and soluble solids increased during this period, indicating enhanced fruit metabolism. However, the soluble sugar content of the two pumpkin cultivars decreased over time, indicating persistent respiratory metabolism during storage.
An indicator of the response to abiotic stress in fruits and vegetables is ROS (Wang et al. 2021). Typically, these tissues have mechanisms that inhibit the early formation of ROS and an enzymatic defense system to eliminate ROS, maintaining a redox balance. However, under adverse conditions, the decrease in the ROS scavenging capacity leads to the accumulation of ROS, accelerating fruit softening and browning (Wang et al. 2020; Zhang et al. 2018). Enzymes such as SOD and CAT aid in mitigating oxidative stress by scavenging ROS (Nie et al. 2019). Research has indicated that ROS can reduce fruit quality by affecting the activity of ROS-scavenging enzymes. This effect accelerates browning, reduces enzyme activity, and increases the MDA content in postharvest fruits. Initially, ROS accumulation triggers the fruit’s antistress mechanism and enhances antioxidant enzyme activity. However, as the storage time progresses, the balance of ROS in tissue cells is disrupted, leading to increased ROS generation and accumulation, ultimately promoting mildew and rot in pumpkins.
With the extension of storage time, both cultivars exhibited a decrease in the vitamin C content and pulp hardness. The levels of SOD and CAT initially increased before decreasing, whereas malondialdehyde and weight loss rates showed an upward trend. A significant correlation was found between the weight loss rate and malondialdehyde (P < 0.01) for both cultivars, as well as a significant positive correlation between the vitamin C content and pulp hardness (P < 0.01). Overall, it can be concluded that the fruit quality remains favorable within 40 d of postharvest storage.
References Cited
Cao JK, Jiang WB, Zhao YM. 2007. Guidance on postharvest physiological and biochemical experiments of fruits and vegetables. China Light Industry Press, Beijing, China.
Chang W. 2004. The study on the component analysis and machining technology of pumpkin. Northwest Sci-Tech University of Agriculture and Forestry, Shaanxi, China.
Chen JX. 2000. Plant physiology guided experiment. China Agricultural Press, Beijing, China.
Chu PP, Xiang CP. 2007. Change patterns and correlations of nutritional quality of Chinese pumpkins. Chin Veg. 12:15–19.
Dong HF, Chen Y, Xu YB0, Zhang XD, Liu YB, Yang J. 2022. Effects of different storage methods on the quality of three varieties of kiwifruit. Northern Hortic. 8:82–88.
Gao T, Zhu CH, Sha YC, Lu L, Wang JL, Long RH. 2023. Research status and prospects of several main pumpkin breeding objectives. Northern Hortic. 20:125–129.
Geng XL, Zheng HY, Zhang CH, Yao J, Zhang YH, Liao XF. 2021. Research on the effect of ozone on the storage performance of melon. Preservation and Processing. 6:8–11.
Gonçalves EM, Brazão R, Pinheiro J, Abreu M, Silva CLM, Moldão-Martins M. 2005. Influence of maturity stage on texture, pectincomposition and microstructure of pumpkin. Conference Paper, 2005.
Gong XM, Guan JF, Zhang JS. 2010. Effects of postharvest 1-MCP and Calcium treatments on the quality and occurrence of brown spots on the peel of Huangguan pear. Acta Hortic Sin. 3:375–382.
Hurst PL, Corrigan VK, Hannan PJ, Lill RE. 1995. Storage rots, compositional analysis, and sensory quality of three cultivars of buttercup squash. N Z J Crop Hortic Sci. 23(1):89–95. https://doi.org/10.1080/01140671.1995.9513872.
Khaliq G, Mohamed MTM, Ali A, Ding P, Ghazali HM. 2015. Effect of gum arabic coating combined with calcium chloride on physico-chemical and qualitative properties of mango (Mangifera indica L.) fruit during low temperature storage. Sci Hortic. 190:187–194. https://doi.org/10.1016/j.scienta.2015.04.020.
Li HS. 2000. Principles and techniques of plant physiological and biochemical experiments. Higher Education Press, Beijing, China.
Lin DP. 2000. Origin and classification of pumpkin plants. Chin Watermelon Melon. 1:36–38. https://doi.org/10.16861/j.cnki.zggc.2000.01.017.
Liu C, Li YZ, Yin JM, Deng Y, Sun J, Wang JL. 2022. Analysis of changes and correlations in texture characteristics, physical and chemical indicators, sensory quality of Dengkou Wallace honeydew melon at different storage temperatures. Chin Melon Veg. 1:47–45. https://doi.org/10.16861/j.cnki.zggc.2022.0019.
Liu WX, Li M, Sun LQ. 2011. Effect of storage temperature on the respiration rate and quality indicators of winter squash (Indian pumpkin) fruits. Chin Veg. 16:61–66. 10.19928/j.cnki.1000-6346.2011.16.011.
Liu YX, Tang GQ, Liu XH. 2007. Study on postharvest physiological characteristics of pumpkin seeds. Zhejiang Agric Sci. 6:635–638,640.
Long RH, Wang Y, Liu JL, He PB, Luo J, Gao T. 2021. Research on the development of pumpkin industry in the Nanpanjiang River Basin of Yunnan. Northern Hortic. 24:149–115.
Nie ZP, Wan CP, Chen CY, Chen JY. 2019. Comprehensive evaluation of the postharvest antioxidant capacity of Majiayou pomelo harvested at different maturities based on PCA. Antioxidants. 8(5):136–136. https://doi.org/10.3390/antiox8050136.
Parichat T, Phonkrit M. 2022. Physico-chemical and cooking qualities of fresh and stored pumpkins. Hortic Environ Biotechnol. 63(1):101–113. https://doi.org/10.1007/s13580-021-00385-4.
Sharma S, Ramana RTV. 2013. Nutritional quality characteristics of pumpkin fruit as revealed by its biochemical analysis. Int Food Res J. 20:2309–2231.
Stefano C, Gerardo V, Enrico A, Gianluca C. 2015. Effects of production system and transplanting time on yield, quality and antioxidant content of organic winter squash (Cucurbita moschata Duch.). Sci Hortic. 183:136–143. https://doi.org/10.1016/j.scienta.2014.12.003.
Wang AJ. 2017. The metabolic and molecular regulating mechanism of pumpkin fruit quality development using RNA-Seq. National Chi Nan University, Nantou County, Taiwan.
Wang D, Li WX, Li D, Li L, Luo ZS. 2021. Effect of high carbon dioxide treatment on reactive oxygen species accumulation and antioxidant capacity in fresh-cut pear fruit during storage. Sci Hortic. 281:109925. https://doi.org/10.1016/j.scienta.2021.109925.
Wang H, Chen YH, Lin HT, Lin MS, Chen YH, Lin YF. 2020. 1-Methylcyclopropene containing-papers suppress the disassembly of cell wall polysaccharides in Anxi persimmon fruit during storage. Int J Biol Macromol. 151:723–729. https://doi.org/10.1016/j.ijbiomac.2020.02.146.
Wang J, Yang LJ, Zhao M, Ding JZ, Cong WH, Hu QR. 2010. Change patterns of several nutritional quality indicators of pumpkin fruits after harvest. Food Sci Technol. 1:52–55. 10.13684/j.cnki.spkj.2010.01.023.
Wang Y, Li HY, Zhang SZ. 2010. Research and development of functional ingredients of pumpkin. Tianjin Agric Sci. 5:133–113.
Zeeman CS, Kossmann J, Smith MA. 2010. Starch: Its metabolism, evolution, and biotechnological modification in plants. Annu Rev Plant Biol. 61(1):209–234. https://doi.org/10.1146/annurev-arplant-042809-112301.
Zhang GX. 2010. Dynamic changes in reducing sugars during the growth and development of pumpkin fruits. Anhui Agric Sci. 38(32):18017–18018. https://doi.org/10.13989/j.cnki.0517-6611.2010.32.156.
Zhang HL, Lei H, Xiang L, Qi S, Huang CM. 2022. Storage tolerance characteristics of kiwifruit varieties mainly grown in Yichang. Hubei For Sci Technol. 2:18–22.
Zhang YY, Huber DJ, Hu MJ, Jiang GX, Gao ZY, Xu XB, Jiang YM, Zhang ZK. 2018. Delay of postharvest browning in litchi fruit by melatonin via the enhancing of antioxidative processes and oxidation repair. J Agric Food Chem. 66(28):7475–7484. https://doi.org/10.1021/acs.jafc.8b01922.
Zhou CL, Liu W, Zhao J, Yuan C, Zhang M, Li QH. 2014. Research progress on pumpkin postharvest processing. Food Ind. 10:222–222.