Mass Transfer, Energy Utilization, Physical and Nutritional Properties Evaluations During Drying of Papaya (Carica papaya L.) Seeds at Low to Moderate Temperatures

Recently, papaya seeds are well recognized for their nutritional and nutraceutical properties. However, their high moisture content can trigger microbial degradation, so drying them is an essential process. This study aims to assess the drying kinetics of papaya seeds and investigate the effect of drying air temperature on the physicochemical properties of papaya seeds. The drying experiments were carried out using a natural convection oven at various drying air temperatures of 40, 55, 70, and 85 °C. The results presented that an increase in drying air temperature led to increasing the drying rate as indicated by a reduction of drying time. The results also proved that the Wang–Singh model was the most suitable model for the papaya seeds drying. Effective moisture diffusivity and mass transfer coefficient increases for drying with and without sarcotesta. A higher drying air temperature leads to more intensive energy utilization, which requires a lower energy supply. The exergy analysis resulted in significant exergy loss, which offers exergy improvement potential as indicated by the low efficiency and exergy sustainability index. Unfortunately, a lower final moisture content caused a higher shrinkage percentage and a lower rehydration ratio. In addition, higher drying air temperatures also induced a significant loss of essential nutrients, especially protein, due to denaturation processes and enzymatic autohydrolysis. The use of high air temperature speeds up the drying rate, saves drying time, and requires a low energy supply, but can severely damage the essential nutrients in the papaya seeds.