Drying and disinfection of off-ground harvested almonds using step-down temperature hot air heating

• DOI: 10.13031/aim.202100267
• Publication Date: 2021-07-06T12:55:41Z
• Authors: Chang Chen; Chao Liao; Ivan Wongso; Wenbin Wang; Ragab Khir Abd El...; Zhaokun Ning; Guangwei Huang; Franz Niederholzer; Luxin Wang; Zhongli Pan
• Keywords: 0404 agricultural biotechnology; 04 agricultural and veterinary sciences

Abstract This study aimed to develop a simultaneous drying and disinfection method for off-ground harvested almonds to improve drying efficiency and product safety. Almonds were dried in a column dryer (0.57 m-height) with hot air under constant temperature (ambient, 40, 50 and 60 °C) or step-down temperature (preheating with 80 °C and 90 °C, holding for 1–3 h, then stepping down to complete drying at 60 °C) and 1.0 m/s velocity. The drying time ranged from 240 to 2160 min to dry almonds from initial moisture content of 0.41 kg water/kg wet mass to a targeted 0.12 kg water/kg wet mass. Specific energy consumption ranged from 14.3 to 22.0 MJ/kg. No cavity, significant color change, concealed damage or oil quality deterioration were observed under all tested conditions. Step-down temperature drying with holding achieved up to 0.8 log CFU/g total bacterial counts reduction of in-shell almonds. Drying in-shell almonds saved up to 75% drying time and 78.6% specific energy consumption compared to drying in-hull almonds under the same temperature, with more uniform final moisture distribution. The findings suggested off-ground harvested almonds should be sorted and de-hulled prior to drying, which could significantly improve the drying efficiency, moisture uniformity and throughput of the drying process.