Performance of a Combined Hot-Air–Infrared Hybrid Convective Dryer for Zucchini Slices

Abstract

Drying is one of the most popular methods used in the food industry to reduce postharvest losses, extend shelf life, add value, and reduce handling. However, conventional drying methods such as hot-air (HA) dryers are time-consuming, energy-intensive, and can affect the food quality. To address these challenges, infrared (IR) drying has been added as a booster heat source, ensuring faster drying, energy saving, and quality improvement, since each method has its limitations. Therefore, combining HA and IR drying has been shown to be a more efficient technique, ensuring better drying performance. The aim of this study is to design and test the performance of using the HA and IR hybrid dryer for drying zucchini, by evaluating the zucchini quality attributes, such as moisture content (MC), water activity, rehydration ratio (RR), and shrinkage in diameter. In this study, different samples of zucchini slices were dried in a hybrid dryer under three different combinations of heat air and air speed, selected based on preliminary trials, including IR2-S1-H2, IR2-S2-H2, and IR2-S2-H1, where IR2 refers to the use of two IR tubes, S refers to the air speed and H indicates the heater level. The physicochemical properties of dried zucchini samples were analyzed and compared, including MC, moisture ratio, drying rate, water activity, rehydration, and diameter shrinkage. The results showed that IR2-S2-H2 was the fastest among the three drying combinations, reaching 10% MC within 40 min, while IR2-S1-H2 and IR2-S2-H1 required 60 and 80 min, respectively. The Midilli–Kucuk model offered the best-fit model for the MC data of IR2-S1-H2 and IR2-S1-H1 (R² = 0.9999 and 0.9999, RMSE = 1.6340 × 10⁻⁶ and 0.0011, respectively), while the logarithmic model provided the best-fit model for IR2-S2-H2 (R² = 0.9999, RMSE = 1.5421 × 10⁻⁷). All dryer combinations resulted in an RR of 4.67–5.80, and the water activity of dried zucchini samples was within the recommended food safety threshold (water activity = 0.207–0.411 < 0.6). In addition, the lowest diameter shrinkage (28.21%) was observed with the IR2-S2-H1 condition. This study recommends further research to optimize drying parameters and improve food quality as well as to evaluate the application of this dryer to other fruits and vegetables.