A Combination of Melatonin and Ethanol Treatment Improves Postharvest Quality in Bitter Melon Fruit

Revealing the specific regulations of nitric oxide on the postharvest ripening and senescence of bitter melon fruit

Bitter melon fruit is susceptible to yellowing, softening, and rotting under room-temperature storage conditions, resulting in reduced commercial value. Nitric oxide (NO) is an important signaling molecule and plays a crucial role in regulating the fruit postharvest quality. In this study, we investigated the effects of NO treatment on changes in sensory and firmness of bitter melon fruit during postharvest storage. Moreover, transcriptomic, metabolomic, and proteomic analyses were performed to elucidate the regulatory mechanisms through which NO treatment delays the ripening and senescence of bitter melon fruit. Our results show that differentially expressed genes (DEGs) were involved in fruit texture (CSLE, β-Gal, and PME), plant hormone signal transduction (ACS, JAR4, and AUX28), and fruit flavor and aroma (SUS2, LOX, and GDH2). In addition, proteins differentially abundant were associated with fruit texture (PLY, PME, and PGA) and plant hormone signal transduction (PBL15, JAR1, and PYL9). Moreover, NO significantly increased the abundance of key enzymes involved in the phenylpropanoid biosynthetic pathway, thus enhancing the disease resistance and alleviating softening of bitter melon fruit. Finally, differential metabolites mainly included phenolic acids, terpenoids, and flavonoids. These results provide a theoretical basis for further studies on the physiological changes associated with postharvest ripening and senescence of bitter melon fruit.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-023-00110-y.

Using ethanol as postharvest treatment to increase polyphenols and anthocyanins in wine grape

Red wine grapes are qualitatively evaluated for their content in polyphenols and anthocyanins. Due to certain conditions (weather, latitude, temperature), the concentration of these compounds may be not at the right level for reaching a high-quality wine, thus postharvest technologies can be operated as a remediation strategy. Ethanol is a secondary volatile metabolite and its application has been demonstrated to delay fruit ripening, to reduce decay, and to increase secondary metabolites. The present study investigates the effects of ethanol post-harvest application on wine grapes' metabolism and composition. Red wine grapes (Vitis Vinifera L. cv Aglianico) were exposed to different ethanol doses (0.25, 0.5, or 1 mL L-1) for 12, 24, or 36 h. Ethanol increased sugar concentration, malic acid, free amino nitrogen, polyphenols, and anthocyanins. Particularly, anthocyanins reached an average value of 1820 mg/L in treated samples versus the 1200 mg/L of control grapes already after 12 h whatever the concentration was. Moreover, the highest concentration of ethanol modified berry metabolism shifting from aerobic to anaerobic one. Obtained results suggest that 12 h of ethanol postharvest treatment could be an interesting solution to improve anthocyanins in wine grapes, especially when the quality is not as good as expected.

MaC2H2-like regulates chilling stress response of ‘Fenjiao’ banana by modulating flavonoid synthesis and fatty acid desaturation

Chilling injury (CI) is a major problem that affects fruit quality and ripening. Herein, chilling stress severely inhibited the expression of transcription factor MaC2H2-like. MaC2H2-like activates the expression of genes associated with flavonoid synthesis (MaC4H-like1, Ma4CL-like1, MaFLS, and MaFLS3) and fatty acid desaturation (MaFAD6-2 and MaFAD6-3), the leading indicators of chilling tolerance. MaC2H2-like interacts with MaEBF1 and boosts the transcriptional activity of MaFAD6-2, MaFAD6-3, Ma4CL-like1, and MaFLS. The overexpression of MaC2H2-like reduced fruit CI, induced the expression of these genes and increased the content of flavonoid and unsaturated fatty acid. Meanwhile, the silencing of MaC2H2-like increased fruit CI and downregulated the expression of those genes and reduced the content of flavonoid and unsaturated fatty acid. These results indicate that MaC2H2-like function as new player in modulating fruit CI by regulating flavonoid synthesis and fatty acid desaturation. MaC2H2-like could be a useful candidate gene for improving cold tolerance in 'Fenjiao' banana.

Comparative Physiological and Transcriptomic Analyses of Improved Heat Stress Tolerance in Celery (Apium Graveolens L.) Caused by Exogenous Melatonin

Melatonin (MT) is crucial in plant growth, development, and response to stress. Celery is a vegetable that grows in a cool climate, and a hot climate can deteriorate its growth, yield, and quality. This study investigates the effect of exogenous melatonin on celery physiology. Transcriptional levels were analyzed by spraying celery with exogenous MT before exposing it to high temperatures. The regulatory mechanism of exogenous MT-mediated heat tolerance was examined. The results show that the exogenous MT reduced the thermal damage state of celery seedlings, as well as the malondialdehyde (MDA) content and relative conductivity (REC), increasing the oxidase activity, the osmotic regulatory substances, and chlorophyll, enhancing the leaf transpiration and the light energy utilization efficiency. We examined the mechanism of exogenous MT in mitigating high-temperature damage using the transcriptome sequencing method. A total of 134 genes were expressed differently at high temperature in the celery treated with MT compared with the untreated celery. Functional annotation analysis revealed that the differentially expressed genes were abundant in the “pyruvate metabolism” pathway and the “peroxidase activity” pathway. According to the pathway-based gene expression analysis, exogenous MT can inhibit the upregulation of pyruvate synthesis genes and the downregulation of pyruvate consumption genes, preventing the accumulated pyruvate from rapidly upregulating the expression of peroxidase genes, and thereby enhancing peroxidase activity. RT-qPCR verification showed a rising encoding peroxidase gene expression under MT treatment. The gene expression pattern involved in pyruvate anabolism and metabolism agreed with the abundant transcriptome expression, validating the physiological index results. These results indicate that the application of exogenous MT to celery significantly enhances the ability of plant to remove reactive oxygen species (ROS) in response to heat stress, thereby improving the ability of plant to resist heat stress. The results of this study provide a theoretical basis for the use of MT to alleviate the damage caused by heat stress in plant growth and development.

Hydrogen Sulfide Treatment Alleviates Chilling Injury in Cucumber Fruit by Regulating Antioxidant Capacity, Energy Metabolism and Proline Metabolism

Although low-temperature storage could maintain the quality of fruits and vegetables, it may also result in chilling injury (CI) in cold-sensitive produce, such as cucumbers. This can seriously affect their quality.” The antioxidant capacity, energy metabolism and proline metabolism of cucumbers treated with hydrogen sulfide (H2S) were studied in this assay. The outcomes displayed that H2S treatment effectively reduced CI and delayed the increase in electrolyte leakage (EL) and malondialdehyde (MDA) content. In addition, the H2S-treated cucumber fruit exhibited higher L* and hue angle values, as well as nutrients such as ascorbic acid (AsA). The H2S-treated fruit showed lower levels of reactive oxygen species (ROS) and higher antioxidant enzyme activities. Meanwhile, H2S treatment also increased the activities of the essential enzymes involved in energy metabolism, including cytochrome C oxidase (CCO), succinate dehydrogenase (SDH), H+-ATPase and Ca2+-ATPase, which improved the energy supply. H2S induced higher ornithine δ-aminotransferase (OAT) and Δ-1-pyrroline-5-carboxylate synthetase (P5CS) activities, and reduced proline dehydrogenase (PDH) activity, promoting the accumulation of proline. These results indicated that H2S could alleviate CI in the cucumber fruit by modulating antioxidant capacity, energy metabolism and proline metabolism, thereby extending the shelf life of postharvest cucumbers.

Effects of Ethanol Treatment on Storage Quality and Antioxidant System of Postharvest Papaya

Papaya is the fourth most favored tropical fruit in the global market; it has rich nutrition and can be used for medicine and food processing. However, it will soften and mature in a short time after harvest, resulting in a lot of economic losses. In this study, papaya fruits were soaked in 0, 12.5, 25, 50, and 100 ml/L ethanol solutions for 2 h and stored at 25°C for 14 days, by which we explored the effects of ethanol treatment in papaya after harvest. At an optimal concentration of ethanol treatment, color changing of the papaya fruits was delayed for 6 days, and decay incidence and average firmness of the fruits were shown as 20% and 27.7 N, respectively. Moreover, the effect of ethanol treatment on antioxidant systems in the papaya fruits was explored. It was observed that ethanol treatment contributed to diminish the development of malondialdehyde (MDA), ethylene, and superoxide anions. Furthermore, the activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) were promoted than those of control group, while the activities of peroxidase (POD), phenylalanine ammonia-lyase (PAL), and polyphenol oxidase (PPO) were brought down. In addition, the principal component analysis (PCA) showed that PAL, ethylene, and superoxide anions were the main contributors for the maturity and senescence of postharvest papaya. In this experiment, ethanol treatment had the potential of delaying the ripening and maintaining the storage quality of papaya fruits.

Melatonin-mediated postharvest quality and antioxidant properties of fresh fruits: A comprehensive meta-analysis

At postharvest, fruits have a short shelf life. Recently, there has been much literature on the effects of melatonin on the postharvest quality of horticultural crops. However, reports of various findings comprise mixed claims and product-specific conclusions. Therefore, a meta-analysis systematically dissects the comprehensive effect on several fruits. In this meta-analysis, standard mean difference (SMD) was adopted using a random-effect model. The study used 36 articles and isolated 24 indicator parameters of postharvest quality and antioxidant properties based on the inclusion criteria. As exhibited in the forest plot, melatonin reduced chilling injury, weight loss, respiration rate, and ethylene content (SMD -0.90, 95% CI [-1.14, -0.65]; I²  = 81%; p < .00001). Similarly, the application of melatonin significantly suppressed electrolyte leakage, malondialdehyde (MDA), hydrogen peroxide, superoxide anion, lipoxygenase, and polyphenol oxidase (SMD -0.89, 95% CI [-1.09, -0.69]; I²  = 70%; p < .00001). In addition, exogenous melatonin application induced endogenous melatonin content, phenolic content, and flavonoid and anthocyanin contents (SMD 1.15, 95% CI [0.91, 1.39]; I²  = 71%; p = .01). Moreover, melatonin treatment enhanced antioxidant activities (catalase, superoxide dismutase, peroxidase, ascorbate peroxidase, and phenylalanine ammonia-lyse) (SMD 1.37, 95% CI [1.03, 1.71]; I²  = 86%; p < .00001). Thus, in the whole study, the overall effect was significantly high in treated fruit (p < .0001), and the overall heterogeneity was above (I² ) > 70%. In addition, the funnel plot showed symmetry in the most selected studies. To sum up, the result gives a further understanding of melatonin's capabilities in reducing postharvest losses and maintaining the quality of fresh fruits.

Genetic and Pre- and Postharvest Factors Influencing the Content of Antioxidants in Cucurbit Crops

Cucurbitaceae is one of the most economically important plant families, and includes some worldwide cultivated species like cucumber, melons, and squashes, and some regionally cultivated and feral species that contribute to the human diet. For centuries, cucurbits have been appreciated because of their nutritional value and, in traditional medicine, because of their ability to alleviate certain ailments. Several studies have demonstrated the remarkable contents of valuable compounds in cucurbits, including antioxidants such as polyphenols, flavonoids, and carotenoids, but also tannins and terpenoids, which are abundant. This antioxidant power is beneficial for human health, but also in facing plant diseases and abiotic stresses. This review brings together data on the antioxidant properties of cucurbit species, addressing the genetic and pre- and postharvest factors that regulate the antioxidant content in different plant organs. Environmental conditions, management, storage, and pre- and postharvest treatments influencing the biosynthesis and activity of antioxidants, together with the biodiversity of this family, are determinant in improving the antioxidant potential of this group of species. Plant breeding, as well as the development of innovative biotechnological approaches, is also leading to new possibilities for exploiting cucurbits as functional products.

Extending the Shelf-Life of Fresh-Cut Green Bean Pods by Ethanol, Ascorbic Acid, and Essential Oils

Green beans are a perishable crop, which deteriorate rapidly after harvest, particularly when minimally processed into ready-to-eat fresh-cut green beans. This study investigated the effectiveness of ethanol, ascorbic acid (AsA), tea tree essential oil (TTO), and peppermint essential oil (PMO) on the quality and storability of fresh-cut green bean pods samples stored at 5 °C for 15 days. Our results indicated that samples treated with ethanol, AsA, TTO, and PMO preserved appearance, firmness (except ethanol), chlorophyll content, and moisture compared with the samples without any treatment (control). Additionally, higher vitamin C, total soluble solids (TSS), total sugars, and total phenolic compounds (TPC) were observed in samples treated with ethanol, AsA, TTO, and PMO compared with the control. The most effective treatments for controlling microbial growth were ethanol followed by either TTO or PMO. All the treatments had positive effects on shelf life, maintained quality, and reducing microbial growth during 15 days of cold storage. A particular treatment can be selected based on the economic feasibility and critical control point in the value chain.