Advanced blanching technology for Exocarpium citri grandis: Optimizing processes and unraveling the enhancement mechanism of drying efficiency

Abstract

In the quest for higher drying efficiency and quality of large-size Exocarpium citri grandis (ECG, a large citrus fruit), cutting-edge blanching technology has been unlocked as a pre-treatment. The effects of high-humidity hot air impingement blanching (HHAIB), vacuum-steam pulse blanching (VSPB), and hot water blanching (HWB) on the drying characteristics, and physicochemical quality of ECG at various core temperatures (30–70 ℃) were evaluated, and the drying promote mechanism was elucidated. Results showed that the average heating rates of HHAIB (4.73 %) and VSPB (4.84 %) were lower than those of HWB (6.99 %), but they were not significantly different. HHAIB effectively improved the ECG’s drying rate, flavonoid content, and color while reducing peroxidase activity, shrinkage, and hardness. In contrast, HWB and VSPB resulted in unfavorable nutrient loss and crumpling. Cell-wall polysaccharides and crystallinity properties analysis revealed that HHAIB induced deterioration of chelate-soluble pectin (CSP), Na₂CO₃-soluble pectin (NSP), and hemicellulose content, along with cellulose crystallinity. These changes in the molecular level led to disrupted cell wall stability, cell membrane permeability, and cell expansion pressure as well as increased porosity, which improved water diffusion, resulting in enhanced drying efficiency. However, over-blanching (>50 °C) severely damaged structures which prolonged the drying process and formed an undesirable hollow structure. Furthermore, ECG yielded the lower drying time (52 h) and shrinkage (10 %), and higher flavonoid content (115.69 mg/g) and hardness (26.78 N) at 50 ℃ under HHAIB. This study provides innovative blanching technologies and reveals information on drying promotion for large-size materials.