Effects of Pre-harvest Application of Melatonin on Quality Characteristics of Cornelian cherry

Introduction: Fruit quality is an important factor in market preference, consumer acceptance and reducing fruit waste in orchard plants. Cornelian cherry (Cornus mas L.) are one of the important products in the agricultural industry and are commonly used to meet food and industrial needs. Cornelian cherry are known to be a rich source of vitamin C and polyphenols (Szczepaniak et al., 2019). With the increasing demand for these fruits, which are considered healthy foods, extensive studies have been intiated on the natural population and breeding of Cornelian cherry (Gozel, 2021). Previous studies have shown that the therapeutic effects of Cornelian cherry include: antioxidant, antimicrobial, anti-diabetic, anti-arteriosclerotic, anti-obesity, anti-glaucoma, cell- protective, neuroprotective, cardioprotective, hepatoprotective, nephroprotective, fat-reducing and blood pressure- lowering properties (Bayram and Ozturkjan, 2020). Melatonin (N-acetyl-5-methoxytryptamine) is a potent antioxidant that scavenges free radical species and stimulates antioxidant enzymes (Fracasiti et al., 2019). Melatonin is a natural hormone produced by plants and plays an important role in plant physiological processes. Studies have also shown that melatonin can act as an anti-aging agent or slow down the aging process. Application of melatonin to cherry trees increases photosynthetic pigments, carbohydrate and proline content of roots and makes the plant resistant to stresses (Saropoulou et al., 2012). Melatonin regulates cytokinin levels through auxin induction and shoot production (Arnau, 2014). In pomegranate fruit, foliar application of melatonin has been shown to increase shelf life, maintain quality, and increase yield (Garcia-Pastor et al., 2017). Researchers reported that the external application of melatonin to strawberries and lychees increased the concentration of total phenolics and anthocyanins, and also maintained the nutritional quality of the fruits (Zhang et al., 2018; Aghdam and Fard, 2017). Melatonin inhibits the activity of senescence-related enzymes through the biosynthesis of antioxidants and is known as the first line of defense to protect plants against biotic and abiotic stresses (Liang et al., 2018). Also, the use of melatonin treatment significantly delays the post-harvest senescence process during storage period and therefore increases the shelf life (Zi et al., 2021). Studies have shown that melatonin is able to significantly maintain some quality characteristics of fruits, including carotenoids, respiration rate, titratable acidity, weight loss, soluble sugars, organic acids and volatiles (Liu et al., 2019; Liu et al., 2020; Tijero et al., 2019). Recently, external melatonin treatment has been tested as an effective treatment in ripening and improving the quality of tomato fruit (Sun et al., 2015). Melatonin application helps to delay postharvest senescence and increase cold tolerance of peach fruit (Kao et al., 2016). Melatonin treatment also reduces postharvest decay and maintains the nutritional quality of ripe strawberry fruit (Aghdam and Fard, 2017) and reduces the physiological deterioration of cassava storage roots (Ma et al., 2016). It has also been reported that melatonin treatment can delay the ripening of pear fruits by reducing the expression of related genes (Zhai et al., 2018). Exogenous melatonin can significantly increase the endogenous melatonin content in a variety of fruits and regulate the expression of genes related to melatonin synthesis (Li et al., 2019; Xu et al., 2018). The use of melatonin,by affecting the Yang cycle and consequently altering the ethylene content, improved the ripening of banana fruit (Hu et al., 2017). Melatonin treatment helped maintain a higher ratio of unsaturated fatty acid and saturated fatty acid content in peach postharvest (Gao et al., 2018) and tomatoes (Jentizadeh et al., 2019) preventing membrane lipid peroxidation. These findings highlight the potential of melatonin as a beneficial treatment for improving fruit quality and shelf life, offering opportunities for optimizing post-harvest methods and preserving the freshness and nutritional value of fruit. (Arabiya et al., 2022; Llorente-Mento 2021). Research showed that the use of melatonin increases the quality of cherry fruit by enhancing the levels of total soluble solids, total phenol and ascorbic acid (Xia et al., 2020). The external use of melatonin can increase endogenous melatonin levels and enhance its effects on various physiological processes (Ball, 2021). In this regard, changes in color, firmness, total soluble solids (TSS) and titratable acidity (TA) of strawberry fruit were significantly delayed after treatment with melatonin (Liu et al., 2018). The external application of melatonin can also stimulate the ascorbic acid cycle in post-harvest peaches by re-regulating the expression and transcription of antioxidant-related enzymes, this stimulation leads to an increase in ascorbic acid levels and increase in the long-term shelf life and vegetables after harvest (Song et al., 2016; Kao et al., 2018). Pre-harvest treatment with melatonin at concentrations of 0.1 or 1 mM has shown a significant effects on yield and improvement of pomegranate fruit quality during harvest and post-harvest storage (Medina-Santamarin et al., 2021).
Materials and methods: This experiment was conducted in a randomized complete block design with four melatonin concentrations (0, 150, 200, 250 μM) and four replications (north, south, east, west directions of the trees).Folior spraying was performed 10 days before harvest and after harvest, the fruits were uniformly transferredto the laboratory and quality parameters were evaluated. pH values were measured using a pH meter (Tabatabai, 2018). Soluble solids were measured using a digital refractometer based on Brix. The titration method with 0.1 normal sodium was used to measure total acidity (Mustafi and Najafi, 2014). As explained, the titration method with indophenol was used to measure ascorbic acid (AOAC, 2000). Total phenolic content was calculated using the Folin-Ciocaltean method (Lin and Tang, 2007). Total flavonoid content was measured using the aluminum chloride colorimetric method (Chang et al., 2002). And to determine the antioxidant capacity of fruit extracts, the DPPH method was used (Kolova et al., 2002). In the end, SAS software and Duncan's multiple range test were used to compare the means.
Results and discussion: Our results showed that the increase in pH following melatonin treatment with (250 µM) was significantly greater than the control. The use of melatonin at a concentration of (250 μM) led to an increase in TSS and TA, similar results were obtained regarding the increase in soluble solids and glucose caused by melatonin treatment in tomato fruit (Sun et al., 2015). In another study, it was reported that in pear fruit, external melatonin treatment increased the amount of soluble sugars, especially sucrose and sorbitol in the fruit, which was due to lower expression of the invertase gene and increased sucrose phosphate synthase activity under the influence of external melatonin treatment (Liu et al., 2019). Specifically, in tomato fruit, it was reported that 0.1 mM melatonin treatment had a significant difference from the control and increased amount of soluble solids (Liu et al., 2016). The use of external melatonin may lead to quality maintenance through the mechanism of respiratory inhibition. As a result, fruit quality is mintained by slowing down the rate of degradation of nutrients such as TA, which has been reported for broccoli (Zhou et al., 2018) and peach (Gao et al., 2016). The antioxidant capacity of cornelian cherry treated with melatonin at a concentration (250 μM) remained higher than the control. Many studies show that melatonin treatment helps to improve antioxidant activity in oranges by increasing the amounts of phenolic compounds and the content of flavonoid compounds (Saro et al., 2015). In addition, immersion of pears with melatonin enhances the enzymatic antioxidant system and inhibits free radical activity (Zhai et al., 2018). Foliar application of melatonin induced antioxidant activity and increased proline levels to counteract stress with in grape fruit (Wang et al., 2013). As shown in this study, the amount of total flavonoids, total phenols and ascorbic acid increased at a concentration of 250 μM. (Zhang et al., 2018) noted that compared to the control fruit, the total flavonoid levels in melatonin-treated litchi fruit were significantly higher during storage, and the levels of phenolic compounds was also significantly increased by melatonin treament. Similar results were reported for delayed ascorbic acid in melatonin-treated plums by Ball in 2019, which suggested that the effect of melatonin treatment on preserving ascorbic acid content could be attributed to the reduction or delay of ascorbate oxidase activity. Melatonin treatment in orange fruit preserved total phenolics during storage (Ma et al., 2021).
Conclusion: In general, different levels of melatonin had a significant effect on most of the evaluated traits and improved the of quality traits of cornelian cherry fruit. According to the results obtained the use of melatonin at a concentration of 250 μM on cornelian cherry fruit increased the quality traits of the fruit.Therefore, melatonin can be used as a suitable and effective hormone in maintaining the quality traits of cornelian cherry fruit.