Micro- and Ultra-Structure, Cell-Wall Polysaccharide, and Water State Reveal the Mechanism of High-Humidity Hot Air Impingement Blanching Enhancing Quality and Drying Efficiency of Exocarpium Citri Grandis

Abstract

Blanching is vital during Exocarpium citri grandis (ECG) processing to obtain favorite products. The effect of high-humidity hot air impingement blanching (HHAIB) on micro- and ultra-structure, cell-wall polysaccharides, water state, color, and drying rate of ECG were investigated under various core temperatures (30-70 ℃). ECG exhibited higher softening, weight loss, and drying rate as the core temperature increased from 30 °C to 50 °C. These were related to a decrease in chelate-soluble pectin (CSP), sodium-carbonate-soluble pectin (NSP), hemicellulose content, and cellulose crystallinity, coupled with an increase in cell membrane permeability, porosity, and water freedom. However, excessive blanching (>50 °C) increased drying time and produced an unfavorable hollow structure. Moreover, blanching disintegrated chloroplasts, inhibited enzyme activity, and decreased chlorophyll content, resulting in expected dark brown color. Interestingly, chlorophyll degradation had a positive correlation with enzyme activity. This study provided new insights on blanching mechanisms for ECG to improve quality.

Keywords: High-humidity hot air impingement blanching (HHAIB), Soften, Hollow, structure, Color, Chlorophyll