Changes in some quality parameters of red and white pitaya fruits after ripening, storage and drying

In this thesis, the effects of ripening stages, storage conditions, and different drying methods on the physical and chemical quality parameters of red (Hylocereus polyrhizus) and white (Hylocereus undatus) pitaya species grown in Turkey were investigated. Changes in indicators such as pH, titratable acidity, color, vitamin content, organic acids, betanin, total and individual phenolic compounds, antioxidant capacity, HMF were evaluated depending on the maturity level, storage type, and drying methods. Drying processes were analyzed by mathematical modeling, and the effects of drying on the fruit texture were evaluated in detail by scanning electron microscopy (SEM). pH, titratable acidity, phenolic substance, antioxidant activity, and malic acid contents of red and white pitaya fruits at different ripening stages were determined to be highest at the color turning stage. A decrease in vitamin contents was observed with ripening. Betanin content in fully ripe red pitaya fruit was determined as 128,22±0,76 mg/100g DM. A decrease in phenolic compounds, vitamins, and organic acids was observed during storage at the color turning stage (25 °C, 65% RH). An increase in betanin content was detected in red pitaya fruit during storage at the color turning stage. During drying of pitaya fruits, an increase in the effective diffusion coefficient was observed due to the increase in drying temperature. The highest effective diffusion coefficients were calculated with hot air-assisted microwave (50, 60 and 70 °C+200 W) methods. For both pitaya species, the highest R², lowest RMSE, and chi-square (χ²) values were determined with the parabolic model in hot air and vacuum drying, and with the Page model in hot air-assisted microwave and microwave drying. High temperature and microwave power caused losses, especially in heat-sensitive compounds such as ascorbic acid. Vacuum drying was found to be more successful in preserving vitamins and phenolic compounds. The highest HMF amount was determined as 4,89 mg/kg at 70°C+200W drying. Increasing temperature and microwave power caused structural cracks to become more evident in SEM images.