Experimental Investigation of Thin-Layer Dehydration Characteristics of Apple Chips

Introduction. Post-harvest preservation is currently a critical issue in agriculture. According to the UNEP Food Waste Index Report, approximately 1.05 billion tonnes of food are wasted annually at the consumption stage globally. Furthermore, approximately 14% of food products are lost during harvesting and transportation. The storage of perishable commodities is highly energy-intensive, and numerous food products are unsuitable for freezing. Dehydration effectively reduces moisture content, thereby inhibiting spoilage and reducing product weight and volume; however, the dehydration process itself is inherently energy-consuming. The objective of this study is to develop an energy-efficient drying technology using a domestic dehydrator that preserves the nutritional and organoleptic properties of the product, and to design a corresponding dehydrator prototype based on drying kinetics analysis and sensory evaluation.

Materials and Methods. The upgraded domestic dehydrator enables both the setting of averaged drying parameters and the monitoring of the residual moisture content of the product. The system architecture comprises a chassis with trays, a heating element (up to 250 W), and a fan (20–30 W); temperature (DS18B20) and humidity (BME280) sensors; an ESP32 microcontroller with Wi-Fi and Bluetooth connectivity; an ST7789VW display, and TTP223 capacitive touch buttons; and Omron G3MB-202P triac relays for heater and fan control. The modules are integrated via a common I2C bus with adjustable sensor addressing; the DS18B20 sensor is interfaced using the 1-Wire protocol with a mandatory pull-up resistor on the data line. Fuses are integrated into the power circuit: 0.15 A for the fan and 1.5 A for the heating element (incorporating a 50% overload margin), which ensures short-circuit protection and does not exceed the maximum rated current of the relays (2 A).

Research Results. During the experimental procedure, thin-layer drying of apples was performed: apple discs with a thickness of 7 mm (accuracy of ±0.1 mm) were arranged on the dehydrator trays. The initial mass was 577.2 g, decreasing to 89.4 g post-drying (mass loss of 487.8 g), while the disc thickness was reduced to 2 mm. Energy consumption was monitored using a wattmeter (1845 Wh) and evaluated indirectly based on the heater power (210 W) and the relay duty cycle; the net energy consumed for drying was 1700 Wh. Telemetry data from the sensors were transmitted to a Telegram bot in JSON format, subsequently exported to a text file, and processed utilizing Python and MATLAB. The findings are presented graphically, illustrating moisture content, moisture loss rate, specific humidity, and process efficiency.

Discussion and Conclusion. Testing of the prototype dehydrator enabled the evaluation of the drying parameters for apple chips. A comprehensive approach was employed, whereby raw material characteristics, energy consumption, and process parameters were continuously monitored using a telemetry system. The system transmitted data to a Telegram bot in JSON format, which was subsequently exported to a tabular format and analyzed utilizing MATLAB. Graphs illustrating moisture loss dynamics and other key indicators facilitated an assessment of the system's energy efficiency. Analysis of the specific efficiency allows optimization of the drying regime. The study confirmed the operability of the prototype and the efficacy of the developed methodology. The proposed data acquisition system is suitable for testing similar installations, while the obtained performance indicators can be utilized for benchmarking dehydration methods and calculating technical and economic parameters.

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