Effects of drying processes on the quality of coffee pulp

This research aimed to evaluate the effect of sun drying, hot air drying, vacuum drying, and freeze drying on moisture, water activities (a(w)), 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 at 60 and 90 degrees C for 14 and 16 h, freeze drying at -18 degrees C for 15 h, or vacuum drying at 40 degrees C for 15 h. Moisture and a(w) 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. Novelty impact statement The high content of antioxidant capacity of coffee pulp was found in vacuum and freeze drying. Regarding its ability to highly preserve bioactive compounds, freeze drying was recommended for producing a higher quality of dried coffee pulp.