Document Type : Full Paper

Authors

• maryam karbasi ¹
• Forouzandeh Soltani ²
• Siamak Kalantari ¹

¹ Department of Horticuitural Science, Faculty of Agricultural & Natural Resources, University of Tehran, Karaj, Iran

² Department of Horticuitural Science, Faculty of Agricultural & Natural Resources, University of Tehran, Karaj, Iran

Abstract

Keywords

• Active oxygen
• Chilling
• Hybrid
• Melon
• Storage

Extended Abstract

Introduction

Melons (Cucumis melo L.) are a type of vegetable belonging to the Cucurbitaceae family. They are particularly sensitive to chilling injuries, which can occur during storage at low temperatures. Chilling injuries can manifest in various ways, including discoloration, pitting, water-soaked areas, surface decay, and flavor loss.The severity of chilling injury depends on several factors, including the cultivar, maturity stage at harvest time, duration of exposure to chilling temperatures, and post-harvest handling practices. Some melon varieties are more susceptible to chilling injuries than others. Chilling stress can lead to the accumulation of reactive oxygen species (ROS) in plants, including melons. ROS are highly reactive molecules that can cause oxidative damage to various cellular components, including proteins and lipids. The excess production of ROS during chilling stress can disrupt normal cellular functions and contribute to chilling injury in plants. Malondialdehyde (MDA) is a commonly used biomarker to assess lipid peroxidation, which is a result of oxidative damage to lipids. Lipid peroxidation occurs when reactive oxygen species (ROS) attack and oxidize polyunsaturated fatty acids in cell membranes, leading to the formation of MDA. To counteract the harmful effects of ROS, plants have developed antioxidant defense systems. Antioxidant activity in plants, can be attributed to both enzymatic (superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and non-enzymatic antioxidants (including ascorbic acid, carotenoids and phenolic compounds).

Material and methods

In this research, the antioxidant activity of different melon samples was investigated under low temperature conditions. Seven genotypes of melon were studied, including four parents (Abadan, Khatouni, Dudaim, Japan) and three hybrids (Khatouni×Abadan, Dudaim×Khatoni, Japan × Khatouni) in the years 2018 and 2019. Seeds were cultivated at the Horticultural Science Research Center, karaj according to completely randomized design with three replicates. After harvesting, the fruits were stored at three different temperatures (1, 4, and 13°C) for a duration of thirty days. The quality characteristics included texture firmness, total soluble solids, percentage of weight loss, chilling index, content of malondialdehyde and catalase, peroxidase and superoxide dismutase enzymes were evaluated on harvest time and during storage.

Results and discution

The results demonstrated that firmness and total soluble solids (TSS) were higher in the samples of Japan and Japan×Khatouni compared to the other genotypes. These also exhibited a lower chilling index after thirty days at temperatures of 1 and 4°C. On the other hand, Dudaim × Khatouni and Khatouni × Abadan hybrids showed the lowest degree of firmness and TSS amount, along with the highest percentage of weight loss, chilling index and malondialdehyde content. During storage, particularly at elevated temperatures, a noticeable reduction in firmness and TSS, along with an increase in weight loss was observed across all melon samples. it has been observed that the decomposition of polysaccharides, particularly hemicellulose and pectin, contributes to the softening and reduction in stiffness of fruit tissue during ripening. Additionally, it has been noted that the firmness of fruit decreases at lower temperatures, albeit at a slower rate. TSS is an important indicator of fruit quality, particularly in terms of sweetness. However, during storage, especially at higher temperatures, there can be a decrease in TSS content due to various factors such as enzymatic activity, respiration, and metabolic changes. Weight loss is another common observation during fruit storage. Fruits naturally lose moisture through processes such as transpiration and respiration. Higher temperatures can enhance these processes, leading to increased water loss and subsequent weight loss in melons. MDA increased with time, and the highest increase was observed in the Abadan and Dudaim×Khatouni genotypes at temperatures of 1 and 4°C. It is generally known that chilling stress can lead to an elevation in MDA levels in plants. Chilling stress can induce oxidative damage and lipid peroxidation, resulting in the accumulation of MDA as a byproduct. The extent of MDA accumulation can vary depending on factors such as the specific fruit cultivar, storage conditions, the duration of chilling stress, and environmental factors. Furthermore, it has been observed that melons with a lower chilling index exhibit higher activity of antioxidant enzymes, including catalase, peroxidase, and superoxide dismutase. Specifically, Japan and Japan×Khatouni genotypes have shown the highest activity levels of these antioxidant enzymes.

Conclution

The activity of antioxidant enzymes plays a crucial role in improving cold resistance. Melons with a lower chilling index tend to have higher levels of antioxidant enzymes. Japan and Japan×Khatouni are recommended as genotypes with high durability (up to 30 days) at low temperatures condition.