Effects of drying processes on the quality of coffee pulp

Abstract

This research aimed to evaluate the effect of sun drying, hot air drying, vacuum drying and freeze drying on moisture, water activities (aw), dry matter, energy consumption, proximate composition, chlorogenic acid, total phenolic compounds (TPCs), and 2,2- diphenyl-1-picrylhydrazyl (DPPH) of coffee pulp. Coffee pulp was collected from Thailand. Samples were placed under the sun for 15 and 18 h, hot-air drying 60 and 90 °C for 14 and 16 h, freeze drying at -18°C for 15 h or vacuum drying at 40°C for 15 h. Moisture and aw of freeze dried samples were 5.48% and 0.53, respectively. Freeze drying consumed 7.69 kW/kg lower than sun drying and hot air drying (p≤0.05). Freeze drying produced more crude ash and crude fiber than sun-drying (p≤0.05). Sun drying samples contained higher crude protein than freeze drying samples (p≤0.05). The 12.64 mg GAE/DW TPCs, 4.94 mg/DW chlorogenic acids and 2.84 mg TE/DW DPPH were detected in freeze drying samples. Freeze drying efficiently preserved bioactive compounds.