Effects of delayed cooling and sulphur dioxide pads on storage of 'Hicaznar' cultivar of pomegranate

This study investigated the effects of different cooling delays and sulphur dioxide (SO2) generating pads treatments containing different concentrations of sodium metabisulfite (Na2S2O5) on the storage of 'Hicaznar' pomegranate. For this purpose, the pomegranates were harvested at optimal harvest maturity (total soluble solids, titratable acidity). The first, second and third groups of fruits were kept for cooling delays of 48, 96 and 144 h at 18-20 °C and 65-70% relative humidity. The fourth, fifth and sixth groups were treated with sulfur dioxide generating pads containing different concentrations of Na2S2O5 (1.5 g, 3 g and 4.5 g) placed on top of the fruits. The seventh group was control which received no treatment. All the treatments were packaged under modified atmosphere packages (MAP) and stored at 6 °C and 90-95% relative humidity. Both experiments were conducted for two years between 2020 and 2022. In delay cooling experiment, during both years the fruit samples for quality analysis were taken at 45, 90 and 120 days of cold storage. After each removal, the fruits from each treatment were kept at 20 °C for additional 3 days to simulate the shelf life performance. The extension in storage duration showed increase in weight loss, hue angle (h°) value, total flavonoid content, carbon dioxide (CO2) levels and decay incidence while decrease in brightness (L*), chroma (C*), sensory evaluation (appearance and taste) scores, total soluble solids (TSS) content, titratable acidity (TA), total phenolic content, total antioxidant acitivity, total anthocyanin content, ascorbic acids, organic acids (citric, malic, succinic and oxalic acids), phenolic compounds (Gallic, protocatechuic and chlorogenic acids) and oxygen (O2) levels. No chilling injury was recorded throughout the storage. At the end of cold storage and shelf life period, the minimum weight loss, CO2 levels, decay incidence with maximum appearance and taste scores, total phenolic content, total antioxidant activity, ascorbic acid content, protocatechuic acid content and O2 levels were recorded in control. There were no significant effects of cooling delays on citric acid and succinic acid contents. Delayed cooling for 48, 96 and 144 h significantly reduced the storage time of pomegranates. According to the results obtained it was concluded that the 'Hicaznar' cultivar should be stored directly at 6 °C and 90-95% relative humidity without any delay in cooling in order to prevent postharvest quality losses. Based on the results obtained it can be concluded that 'Hicaznar' pomegranate should be directly cooled at 6 °C and 90-95% relative humidity without any delays in cooling to avoid significant quality losses during postharvest storage. In SO2 generating pads experiment, during both years the fruit samples for quality analysis were taken at 45, 90, 120, 150 and 180 days of cold storage. After each removal the fruits from each treatment were kept at 20 °C for additional 3 days to determine shelf life performance. Prolonging storage duration resulted increase in weight loss, h° values, total flavonoid content, CO2 levels and decay incidence while decrease in L*, C* values, appearance and taste scores, TSS content, TA, total phenolic content, total antioxidant activity, total anthocyanin content, ascorbic acid content, organic acids (citric, malic, succinic and oxalic acids) contents, phenolic compounds (Gallic, protocatechuic and chlorogenic acid), O2 levels and sulphur dioxide production in MAP. During both years of experiment, SO2 generating pads reduced weight losses. No chilling injury and SO2 residues in arils were found throughout the storage. The highest L* value and total phenolic content were recorded in 3.0 and 4.5 g SO2 generating pads in both years. During first year of experiment, at the end of storage the highest appearance, taste scores, O2 levels with lowest CO2 levels were recorded in 3.0 g SO2 generating pads. The highest h° value and total anthocyanin contents were in 1.5 and 4.5 g SO2 generating pads respectively. SO2 generating pads reduced the decay incidence with minimum decay incidence was in 3.0 g SO2 generating pads. During second year of experiment, at the end of storage the maximum C* and h° values were in 3.0 and 4.5 g SO2 generating pads. The highest appearance, taste scores, O2 levels with lowest weight loss, CO2 levels were in 4.5 g SO2 generating pad. The highest succinic acid content was in 1.5 and 4.5 g SO2 pads. SO2 generating pads treatments increased total antioxidant activity with highest total antioxidant activity was in 4.5 g SO2 generating pad. SO2 generating pads successfully reduced decay incidence with minimum decay incidence was in 4.5 g SO2 generating pad. It can be concluded based on the results obtained that SO2 generating pads containing 3.0 and 4.5 g Na2S2O5 maintained better postharvest quality of 'Hicaznar' pomegranates for 180 days of cold storage. KEYWORDS: Pomegranate, Delayed cooling, Sodium Metabisulfite, SO2 Generating Pads, Quality.