Effect of Postharvest Treatments of Phenylalanine and Hydrogen Sulfide on Maintaining Quality and Enhancing Shelf life of Eggplant (Solanum melongena L.)

Eggplant (Solanum melongena L.) is an important non-climacteric fruit grown in tropical and subtropical regions. The total production in Iran and world for eggplants in 2018 were estimated 54077210 and 666838 tons, respectively, and Iran ranked fifth in the production of this product. The health-promoting attributes of eggplant are derived from the phytochemicals with good source of antioxidants (anthocyanin and phenolic acids), dietary fiber and vitamins. Fruit deterioration during long term storage is associated with appearance quality reduction, calyx discoloration, softening and pulp browning caused by the oxidation of phenolic compounds. Hydrogen Sulfide (H2S) is a flammable and colorless gas, that similar to carbon monoxide and nitric oxide, is known as third leading signaling molecule. It has been reported that H2S play an imperative role in the postharvest physiology and chilling injury of various fruits and vegetables. In recent years, exogenous phenylalanine (PA) application has been employed as a beneficial procedure for enhancing quality in fruits and vegetables by promoting higher phenols and flavonoids accumulation arising from higher PAL enzyme activity and proline accumulation exhibiting higher ROS scavenging capacity. Thus, the aim of this study was to investigate the postharvest application of H2S and PA on quality and postharvest storage of eggplant fruit during storage at 7 °C for 21 days. Eggplant fruits (Solanum melongena cv. Hadrian) were harvested at commercially maturity stage in Jun 2019 from a greenhouse in Hashtgerd city, Iran. Fruit selected for uniform size, shape, and color, and immediately transported to the laboratory. They were divided into seven parts for the following treatments: control (0), hydrogen Sulfide (H2S) at 0.1, 0.2 or 0.3 mM and phenylalanine (PA) at 2.5, 5 or 7.5 mM. Each treatment was done in three replicates, consists of 24 fruits from each replicate, and then randomly divided into four groups include six fruits. One group was analyzed 24 hrs. after harvesting and another groups stored at 7 ± 1 °C and 85% RH for 21 days. At 7-day intervals, one group was taken at random and transferred for one day at 20 °C (shelf-life), and subjected to physicochemical analysis. For H2S fumigation, fruit was placed at the bottom of a sealed 15 L container with different aqueous sodium hydrosulfide (NaHS) solution concentrations for 10 min, and for PA treatments, the fruits were immersed in 10 L of fresh phenylalanine solution for 10 min and in distilled water as a control. The fruits were allowed to completely dry at room temperature before storage. The results showed that fruits treated by PA and H2S exhibited higher fruit firmness, chlorophyll, anthocyanin, total soluble solids (TSS), vitamin C, pH and titratable acidity (TA) accompanied by lower weight loss and chilling indices during storage at 7 ºC for 21 days. In control eggplant fruits, fruit firmness (24.2%), chlorophyll (45.8%), vitamin C (34.1 %), anthocyanin content (66.2 %) and TA (44.8) decreased, and weight loss (7.5 %), TSS (8.2%) and chilling indices (4.5 %) increased during 21 storage time. The maximum fruit firmness (1.37 and 1.34 kg cm-2), anthocyanin content (5.02 and 4.2 mg L-1) and TA (18.67 and 1.37 %), and the lowest weight loss (3.67 and 3.7 %) and chilling index (1.6 and 1.3 %) was found in fruits treated with H2S at 3 mM and PA at 7.5 mM during storage at 7 °C for 21 days, respectively. It has been reported that texture correlates with firmness and higher firmness is a characteristic indicator of good texture during postharvest storage of fresh products. Soluble solid contents, titratable acidity (TA) and sugars have been known as important attributes contributing in overall sensory quality of fruits and vegetables. Development of the chilling injury disorder significantly reduces quality of fruits and vegetables due to diminished consumer’s acceptance. So, start of chilling injury symptoms eventually becomes economically critical postharvest constraint that defines the storage life potential of the products. Decline chilling injury in responses to H2S and PA treatments may resulted from higher ROS scavenging enzymes SOD, CAT, APX and POD activity and proline, phenols and flavonoids accumulation giving rise to conferring chilling tolerance. According to results, PA at 7.5 mM and H2S at 3 mM had the highest positive effect on maintain firmness and fruit quality and reducing weight loss and chilling, therefor postharvest treatment of PA and H2S can be proposed to improve fruit quality and postharvest life during storage period.