The Effect of Chitosan Edible Coating on Physicochemical Properties and Enzymatic Activity of Grape Fruit Cultivar Fakhri in Cold Storage Conditions

Chitosan, as a bio-polymer, has many applications in agriculture. Coating fruits and vegetables with chitosan plays a positive role in increasing their shelf-life, since the chitosan coating reduce growth of fungi and preserves the quality of the fruits longer.

This study was conducted to evaluate the effect of chitosan treatments (0, 0.25, 0.5 and 1%) and storage time (0, 20, 40 and 60 days) on maintaining quantitative and qualitative parameters and shelf life of grape fruit of Fakhri cultivar. The experiments were factorial based on a completely randomized design with three replications. The fruits were stored for 2 months. Some characteristics of fruits including percentage of weight loss, percentage of berries abscission, percentage of decay of berries, browning of berries and biochemical characteristics including titratable acidity, ascorbic acid content, total phenol, enzymes activity including peroxidase (POD), phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO) were measured in order to investigate the best treatment.

 The results showed that the traits under study were affected by different concentrations of chitosan, with the lowest percentage of weight loss associated with the concentration of 0.5% chitosan. Chitosan, by forming a semi-permeable membrane, regulates gases,and reduces the transfer of water from fruit tissues. The lowest amount of browning of berries was observed in the concentration of 0.5% chitosan. Chitosan is partly prevented from increasing the activity of brown-peroxidase in chitosan-treated fruits. There was no significant difference in concentration of 0.5% chitosan with 1% concentration. The lowest percentage of contamination and percentage of berries abscission was observed in 1% chitosan concentration. It seems that these treatments prevent the effects of ethylene levels and the formation of a swab layer at the site of fruit attachment to the cluster. The slightest increase in the titratable acidity and the lowest decrease of ascorbic acid was observed in the concentration of 1% chitosan. Higher levels of ascorbic acid in fruits that are coated with chitosan may be due to decreased oxygen levels and respiration inhibition. The highest total phenol was related to the control treatment, which may be due to the loss of chlorophyll and the onset of synthesis of phenolic compounds. The highest level of activity of PAL enzyme was observed in the concentration of 0.5% chitosan and the control. This enzyme is stimulated by various live and non-living stresses. In general, the highest activity of peroxidase enzyme was observed in the concentration of 0.5% chitosan and the highest activity of polyphenol oxidase in 1% concentration of chitosan.

 It seems that the concentration of 1% chitosan can improve the quality of fruits for a longer time while increasing the shelf life of fruit.