Effects of different drying methods on the drying characteristics and quality of alfalfa

This study investigated low-temperature solar–heat pump hybrid drying of alfalfa. Drying kinetics, nutrient retention, color evolution, and textural properties were systematically evaluated using open sun drying as the benchmark. Compared with open sun drying, drying time was reduced by 37.04% at a hot air velocity of 3.0 m/s, by 44.44% at 3.5 m/s, and by 48.15% at 4.0 m/s. Alfalfa hay exhibited reductions in hardness and crispiness of 3.43–30.05% and 4.96–8.93%, respectively; in contrast, springiness and cohesiveness increased by 2.17–8.70% and 1.70–23.79%, respectively, while resilience increased by 20.24–28.97%. Given the multidimensional nature of texture parameters, principal component analysis (PCA) was employed to integrate multiple indicators into a comprehensive index. Optimal comprehensive texture quality was achieved under solar-heat pump hybrid drying when the hot air velocity was 4.0 m/s. The results indicated that the hybrid drying system demonstrated significant advantages. Optimal performance was consistently observed at 4.0 m/s, where nutrient loss was minimized and color retention was maximized. The empirical alfalfa drying model was optimized based on experimental data. Validation results demonstrated that the optimized Page model accurately predicted the moisture content variation during the solar-heat pump hybrid drying process. Unlike previous drying studies comparing alfalfa with existing methods, this research systematically evaluated multiple assessment indicators—including drying characteristics, color, and nutritional components—under both open sun drying and solar-heat pump hybrid drying conditions, ultimately determining optimal process parameters. Overall, the proposed low-temperature hybrid drying strategy improved drying efficiency while better preserving alfalfa quality. This study provides a theoretical basis for optimizing solar–heat pump hybrid drying and supports precise control of alfalfa drying quality.