Dynamic changes of drying behavior, physicochemical quality, and volatile oil of <i>Exocarpium citri grandis</i> under different drying temperatures

Drying is the primary processing step in Exocarpium citri grandis (ECG), yet its quality changes throughout the drying process have not been elucidated. Dynamic changes of drying behavior, structure, color, active components, antioxidant properties, and volatile oil in ECG under different drying temperatures (50, 60, 70, and 80°C) were investigated, and the quality change mechanism was revealed. Results showed that the moisture ratio decreased rapidly and that structural damage occurred as moisture content decreased from 1.0000 to 0.2175 g/g (on a dry basis, d.b.), which accelerated flavonoids, polysaccharides, volatile oil, and antioxidant activity degradation, whereas levels of naringin and rhoifolin were increased. The above quality change process was accelerated with the increasing temperature. Correlation analysis revealed that active components had a synergistic effect on antioxidant activity, and the total color difference (ΔE) value and that active components could be well fitted by a linear mathematical model with correlation coefficient (R²) of 0.7749-0.9781. Moreover, all the indicators were uniformly quantified using comprehensive evaluation method to obtain a comprehensive score, which was the highest (0.57) at 70°C, with high drying efficiency, well quality, and low energy consumption. The biosynthesis pathway verified that the species of volatile oil components increased, including newly terpenes, alcohols, aldehydes, esters, and others after 0.2175 g/g. This study revealed that the total content of active components in ECG decreased before 0.2175 g/g, and then the metabolite content and species increased during drying, as well as obtained the optimal drying temperature (70°C).