Effect of postharvest treatment of gamma-amino butyric acid on some biochemical and antioxidant properties of sweet cherry cv. Tak Daneyeh Mashhad

Sweet cherry fruit due to high water content and respiration rate is rotten in post-harvest period and hence has a short storage life. So, reducing of respiration rate and delaying of senescence process are required for increasing of storage life. Gamma amino butyric acid (GABA) is a non-protein amino acid with low content in the cell in normal state. No study has taken into account the effect of GABA on the storage life of sweet cherry fruit and also, increasing of shelf life by natural compounds seems essential to maintain the quality. Therefore, this study was conducted with the aim of improving the post-harvest quality of sweet cherry fruit, increasing biochemical and antioxidant properties and improving fruit appearance using GABA with the purpose of replacing it with synthetic chemicals. Fruits of sweet cherry cv. Tak Daneyeh Mashhad were harvested at commercial maturity from a commercial orchard in Urmia (Iran) and transported to laboratory immediately. GABA was used in three concentrations (5, 10 and 20 mM). Titration method was used for determination of Titratable acid (TA) and pH was determined by pH meter. TSS was determined by refractometer. Total antioxidant capacity was determined by ferric ions reducing antioxidant power assay (FRAP). Total phenolic content was determined by Folin ciocalteu method and total flavonoid content was determined by the aluminum chloride colorimetric method. The results showed that TA content remains constant with treatment of GABA during storage. GABA treatment leads to an increase in total antioxidant activity, total phenol, total flavonoid and activity of catalase and guaiacol peroxidase enzymes in the treated fruits compared to control fruit after 30 days of storage. The pH value in treated fruits compared to untreated fruits was decreased during storage. Also, GABA at 10 mM level compared with other concentrations had the highest effect on total antioxidant capacity after 30 days of storage. The increasing of organic acids in treating fruits can be probably due to increasing of antioxidant capacity by GABA treatment, hence the damage to membrane was prevented and the organic acids were used less frequently. Treatment of fruits with GABA decreased the pH during storage, which may be due to its role in reducing of respiration rate in harvested fruits. The mechanism of the effect of GABA on increasing of total phenol and flavonoid content may be due to stimulating the production of Phenylalanine ammonia lyase (PAL) which can trigger phenylpropanoid pathway and hereby, syntheses of phenolic compounds such as flavonoids compounds were occurred. Catalase is one of the key enzymes to protect the cells and cause the conversion of hydrogen peroxide to water and oxygen. Therefore, probably the GABA treatment via the increasing the antioxidant system such as catalase leads to scavenge free radicals thereby protecting plants against oxidative stress.