Effect of exogenous essential oil treatments on the storage behaviour of apricot fruit harvested at different altitudes

Apricot (Prunus armeniaca L.) is a species of fruit tree belonging to the Rosaceae family. It is a deciduous tree that is native to China, but is now being widely cultivated in many countries including Europe, the Middle East and America (Delialioglu et al., 2022; Ugur, 2022). Türkiye is one of the largest apricot-producing countries in the world. Apricot farming is an important agricultural activity in the country, particularly in the eastern and central regions (Gecer et al., 2020; Karatas, 2022). Apricots are a rich source of vitamins, minerals and dietary fibre. They contain high levels of vitamin A, vitamin C and potassium, as well as smaller amounts of other essential vitamins and minerals (Xi and Lei, 2020; Milosevic et al., 2021). Moreover, apricots contain several organic acids, including malic acid, citric acid, ascorbic acid and tartaric acid (Karatas et al., 2021; Al-Soufi et al., 2022). These organic acids play a crucial role in the taste, preservation and nutritional aspects of apricots. Therefore, apricots are an important fruit crop, for their delicious taste, flavour and nutritional value. They are widely consumed fresh and are also used in a variety of processed food products, such as juices, jams and dried fruit. However, apricots are highly perishable and need to be handled carefully to maintain their quality and extend their shelf life. Proper postharvest handling, such as cold storage, controlled storage and modified atmosphere packing can help to preserve the levels of organic acids and other compounds in apricots (Kuchi and Sharavani, 2019; Zheng et al., 2021).

Low summer temperatures limit fruit-growing in some regions due to their high latitude or altitude, but climate change is likely to make these regions more suitable for this practice. On the other hand, hot and dry regions will become less suitable for fruit-growing (Mosedale et al., 2016). Crop models can help predict how climate change will affect the yield and quality of fruits by simulating the effects of temperature, water and CO₂ changes (Poni et al., 2006; Costa et al., 2015). However, these predictions are not simple because there are many factors that interact with each other. For example, higher CO₂ levels can increase the temperature range for photosynthesis and decrease water loss (Ewert et al., 2002; Schultz and Stoll, 2010). Climate change can also alter the soil microbes and affect how crops cope with drought (Rolli et al., 2015). Therefore, these models need to be very advanced and accurate. Besides studying the traits that help fruits adapt to climate change, we can also study how these traits vary in response to different environmental conditions (Bradshaw, 2006). Perennial fruit crops such as grapevines and other fruit species will need plant materials that can adapt to the changing environment according to the climate change projections (Nicotra et al., 2010; Van Leeuwen et al., 2019).

The altitude at which the fruits are grown can have an effect on their biochemical content. There are a few ways that altitude can impact fruit composition. Light intensity and quality: fruits grown at higher altitudes tend to receive less light and UV radiation compared to fruits grown at lower altitudes. This can impact the levels of pigments, such as carotenoids, and affect the taste and colour of the fruit. Temperature: fruits grown at higher altitudes are exposed to lower temperatures compared to fruit grown at lower altitudes. This can impact the metabolism and respiration rate of the fruit, leading to changes in the levels of organic acids and other compounds. The concentration of CO₂ decreases with increasing altitude. This can impact the rate of photosynthesis and affect the levels of carbohydrates and other compounds in the fruit. Soil characteristics, such as nutrient availability, also vary with altitude and can impact the biochemical content of the fruit. Overall, the altitude at which fruit are grown can have a significant impact on their biochemical content. The specific effects of altitude on fruit composition can depend on the specific fruit and environmental conditions (Timilsina and Tripathi, 2019; Gouvinhas et al., 2020).

The postharvest maintenance of organic acids in fruit is important for several reasons:

Flavour and taste: Organic acids play a crucial role in determining the flavour and taste of fruit. Maintaining the levels of organic acids in fruit postharvest helps preserve their taste and quality (Zhang et al., 2021).

In recent years, the use of postharvest essential oils (EOs) has become widespread to extend the shelf life of fruits and vegetables and to preserve their quality. The EOs are highly concentrated plant extracts that are rich in volatile compounds with potent antimicrobial, antifungal and antioxidant properties (Cavusoglu et al., 2021a, 2021b; Wang et al., 2023). EOs work by disrupting the cell membranes of microorganisms and inhibiting their growth and reproduction. They also act as antioxidants by eliminating free radicals and preventing oxidative damage to fruit and vegetables (Fan et al., 2023). Some of the most commonly used EOs for postharvest storage include thyme, peppermint, carob, cinnamon, clove and oregano. Thyme extract is rich in antioxidants and antimicrobial compounds and has been shown to have potential as a natural protective (Palmieri et al., 2020). Like thyme extract, peppermint extract is also rich in antioxidants and antimicrobial compounds. It has been shown to have a positive impact on the quality of fruit and vegetables and is often used in postharvest treatments to extend their shelf life (Kumar et al., 2023). Carob extract is derived from the seeds of the carob tree and is rich in polyphenols, which are potent antioxidants. It has been shown to have a positive impact on the quality and shelf life of fruits and vegetables and is often used in postharvest treatments to control decay and improve their overall quality (Brassesco et al., 2021). These oils have been shown to be effective in controlling decay and extending the shelf life of fruit and vegetables. The use of EOs in postharvest storage has several advantages, including being a natural and environmentally friendly alternative to synthetic preservatives, being cost-effective and having no negative impact on the flavour, aroma or nutritional value of fruits and vegetables (Shehabeldine et al., 2023).

To our knowledge, there have been no published studies about the effect of different samples from two apricot-growing regions and EOs (peppermint, thyme and carob oil) on organic acid levels and extending the storage performance of apricot fruit. Therefore, the purpose of the current study is to bring to light an approach that can be used to extend the storage life of apricot fruits treated with EOs and examine the effects of the two altitudes on the organic acid levels and respiration rate of apricot fruit during long-term storage.

The organic acid content in plants or tissues is determined by the interplay between the processes of acid synthesis, degradation, utilization and compartmentalization. Factors such as temperature, light, fertilization, water supply and plant-management practices can impact the source: sink ratio can, as a result, affect the organic acid content. Temperature has a significant effect on plants, which is largely mediated by changes in the plant biochemistry (Robles et al., 2019; Zhang et al., 2020). The temperature of growth influences both the titratable acidity (TA) and the stored organic acid content of the plant. The optimal temperature range for most plant physiological processes is between 0°C and 40°C. However, the ideal temperature range for the growth and development of fruit and vegetable crops is much more limited and varies depending on the species and ecological conditions (Vallarino and Osorio, 2019). Increased temperatures have a detrimental effect on photosynthesis and respiration in plants through changes in enzyme activity and the electron transport chain. Indeed, increased temperatures during fruit ripening generally give rise to a decrease in the tricarboxylic acid (TCA) cycle acids due to an increase in metabolic processes. Therefore, higher temperatures in all plant tissues result in an acceleration of metabolism, leading to increased consumption of sugars and stored TCA cycle acids that serve as metabolic substrates (Nievola et al., 2017). Changes in organic acid metabolism in response to temperature are likely caused by the impact of temperature on enzyme activities and transport systems involved in processes such as glycolysis, TCA cycle respiration, fermentation and gluconeogenesis. In other words, increased temperatures during fruit growth typically result in a decrease of TA, as seen in studies of tomato and grape fruit. The response of organic acids to temperature changes is dependent on the age of the plant or fruit, too. In the current study, higher organic acid content was found in fruit harvested at higher altitudes (Wang and Camp, 2000; Richardson et al., 2004; Vallarino and Osorio, 2019). This situation is consistent with other studies, which suggest that the maximum temperatures (<30°C) during the growth cycle lead to increased synthesis and preservation of organic acids in grape fruit (De Oliveira et al., 2019). Moreover, it was reported in other studies that organic acids are influenced by environmental conditions (Koyuncu, 2004) and that organic acid rates in the fruit are sensitive to altitude levels (Trad et al., 2013). The quality of fruit is affected by high temperatures between ripening and harvest stages. Thus, the fruit may have too much sugar, too little acid and less-fresh and complex aromas at low-altitude cultivation (Van Leeuwen and Seguin, 2006; Pons et al., 2017). The current study is consistent with the finding that apricots grown at low altitudes have fewer organic acids.

Postharvest treatment with EOs can affect the respiration rate in fruit. EOs contain volatile compounds that can modulate the respiration rate by altering the atmospheric composition around the fruit. This can be used to slow down the respiration rate and extend the postharvest life of the fruit (Shehata et al., 2020). Agricultural products with substances such as EOs and plant extracts could maintain the freshness during storage because they act as a physical barrier to reduce dehydration and to alleviate side effects of respiration (Ramezanian et al., 2016). In addition, the control of fruit ripening by EOs has been linked to their antioxidant properties. These properties reduce the diffusion of oxygen and increase the accumulation of CO₂ around the fruit surface, leading to reduced water loss and slowing down the activity of enzymes and biochemical reactions that cause pigment synthesis (Perdones et al., 2016). It was reported that the treatment of postharvest min oil (Yousefizad et al., 2015; Owolabi et al., 2021) and thyme oil (Sapper et al., 2019; Cai et al., 2020) reduced respiration rate during storage and extend the postharvest fruit life. Furthermore, the treatment of postharvest peppermint oil (Yousefizad et al., 2015; Owolabi et al., 2021) and thyme oil (Sapper et al., 2019; Cai et al., 2020) reduced respiration rate during storage and extend the postharvest fruit life in fresh fruit.

In the present study, it can be stated that apricot cultivation at high altitudes increased the amount of organic acids in the fruit. The increase in organic acids has positive effects on fruit quality, thus leading to extension of postharvest life. Based on the information mentioned, the treatment of postharvest EOs in apricot fruits has been shown to slow down the respiration rate, which in turn reduces the consumption of organic acids in the treated fruit during storage compared to untreated fruit. During storage, the highest organic acid content and the lowest respiration rate in both cultivars were observed in the fruit treated with peppermint, carob, thyme oil and control fruit, respectively.