Increasing Antioxidant Compounds and Maintaining the Appearance Quality of Cherry Fruit after Harvest under the Influence of Marjoram Essential Oil

 Cherry (Prunus avium L.) is one of the most important fruit products and due to its polyphenol and antioxidant compounds, it contributes to the nutrition and health of millions of people. Due to its high perishability, this fruit suffers from post-harvest physiological losses. According to the proven antifungal activity of plant essential oils, their use as a natural substance to reduce post-harvest waste, increase shelf life and ensure the health of consumers of horticultural products.

 In the present study, the effect of marjoram essential oil in different concentrations (0, 250, 500, 750 and 1000 µl/l) on biochemical reactions of Mashhad cherry fruit var takdaneh, including phenylalanine ammonialyase enzyme activity, total anthocyanin content, ascorbic acid content, tissue color, polyphenol oxidase enzyme activity, fruit rot and browning of the tail were evaluated with three replications. The treated fruits were transferred to the refrigerator for 30 days at a temperature of 1.0 °C and a relative humidity of 90-95%. Qualitative measurements of fruits were performed during three periods before storage, on the 15th day and on the 30th day of storage. Analysis of variance (ANOVA) was performed based on factorial experiment in a completely randomized design. Mean comparison was performed based on Duncan's multiple range test using SAS software and its graphs were drawn with Excel. Finally, correlation analysis was performed using R software.

 The results of this evaluation showed that marjoram essential oil maintained the activity of phenylalanine ammonialyase enzyme, total anthocyanin content, ascorbic acid content and color significantly. It also reduced the activity of polyphenol oxidase activity, tissue color change, rot and browning of cherry fruit tail. The level of ascorbic acid in all treated samples decreased over time, but this decrease was more severe in the control sample than the other treatments. Increasing storage time and essential oil concentration improved the amount of anthocyanin in the treated fruits. The essential oil at a concentration of 750 μl/l avoided reduction of color change compared to the control. The activity of phenylalanine ammonialyase enzyme in all essential oil concentrations in both periods had an upward trend. The lowest and highest polyphenol oxidase enzyme activity were recorded in 750 μl/l essential oil treatment and control treatment, respectively. use of essential oil decreased the browning of the fruit tail in which, is probably due to the antioxidant activity of the essential oil. Also, the lowest rate of decay and the highest marketability were observed in the concentration of 750 μl/l of marjoram essential oil. On the other hand, there were significant correlations between most traits. Marketability as one of the most important traits had a positive correlation with traits such as ascorbic acid (r=0.82**) and fruit color (r=0.77**). These results clearly show that the increase of these traits leads to high marketability of cherry fruit. Also, the existence of a negative correlation between the rate of maintaining marketability with the traits of rot (r= -0.95**) and browning of the fruit tail (r= -0.89**) shows that with the increase of these traits, the marketability of the fruit decreases. Finally, according to the findings of the present study and considering the quality and durability of treated cherry fruits compared to untreated fruits, instead of harmful chemical compounds, marjoram essential oil can be recommended as an additive in cherry fruit.

 The use of plant essential oils as a natural method can be effective in increasing the shelf life of this fruit by preventing deterioration and degradation. The results of this study showed that marjoram essential oil at a concentration of 750 µl/l by increasing and maintaining ascorbic acid, anthocyanin, PAL enzyme activity, marketability and also by reducing the activity of PPO enzyme, color variability, degree of rot and browning of the fruit tail led to maintaining the internal quality and better durability of the cherry fruit during storage. The reason for this can be related to the phenolic and antioxidant compounds in marjoram essential oil. These compounds directly affect fruit spoilage and indirectly increase the host fruit's defense system and maintain fruit quality. According to the results of this study, marjoram essential oil with a concentration of 750 µl/l can be introduced as a healthy method to maintain physicochemical properties and improve the cherries quality characteristics after harvest.