MATHEMATICAL MODELLING AND IMMEDIATE AND LATENT QUALITY OF NATURAL IMMATURE COFFEE UNDER DIFFERENT DRYING CONDITIONS

ABSTRACT This work aimed to study the immediate and latent effects of different relative humidities on the quality of dried coffee fruits, describe the drying kinetics of natural immature coffee (Coffea arabica L.), and evaluate the mathematical model that best fits the experimental drying data. The drying was carried out in a fixed layer dryer coupled to a composite air conditioning system in which the drying air was controlled with an air flow of 20 m3.min1.m−2, at a temperature of 40 °C, and at relative humidities of 10%, 17.5% and 32.5%. Manually harvested coffee fruits were used and dried to a mean water content of 0.120 dry basis (d.b). After drying, the kinetic curve and the physical and physiological properties were determined. The coffee was stored in permeable packs for 6 months. The electrical conductivity, potassium leaching, and colour analysis were performed every 2 months. For the modelling adjustment, the models were tested, and the Midilli model had the best fit with the drying kinetics of the immature coffee. No immediate damage was observed in the physical and physiological quality of the coffees, and latent damage was perceived after 120 days of storage for the natural immature coffees.摘要 本研究旨在探究不同相对湿度对干燥咖啡果实品质的即时与潜在影响，阐明自然未成熟阿拉比卡咖啡（Coffea arabica L.）的干燥动力学特性，并筛选出最适配实验干燥数据的数学模型。干燥实验采用复合空调系统耦合的固定床干燥装置，干燥空气流量控制为20 m³·min⁻¹·m⁻²，温度设定为40℃，相对湿度分别设置为10%、17.5%与32.5%。实验选用人工采收的咖啡果实，将其干燥至干基平均含水率为0.120（d.b）。干燥完成后，测定其干燥动力学曲线及物理、生理品质指标。随后将咖啡果实装入透气包装中储存6个月，每2个月开展一次电导率、钾离子浸出量及色泽分析。在模型拟合环节，对多款数学模型进行测试，结果显示Midilli模型（Midilli model）最适配该未成熟咖啡的干燥动力学特征。实验结果表明，供试咖啡的物理与生理品质未出现即时损伤，但自然未成熟咖啡在储存120天后出现了潜在品质劣变。