Study on technological development for reducing the sulfur dioxide residue problem in fresh longan for exporting

The objective of this study was to test some alternative ways to decrease sulfur dioxide (SO₂) residue problem and prolong storage life in fresh longan for export. The Office of Agricultural Research and Development Region 1, Chiang Mai province conducted the research and development from 2016 to 2018. The results found that the possible treatments were 1.5% SO₂ + ozone (O₃) 1 h and 5% hydrochloric acid (HCl) + 1% sodium metabisulfite (SMS), respectively, and prevented pericarp browning for 80 days at 5°C. There were no significant changes in some parameters in any treatments; 1.5% SO₂ + O₃ 1 h and 1.5% SO₂ during storage, i.e., pericarp browning, flesh discoloration, disease incidence (%) and sensory evaluation during storage. Application 1.5% SO₂ + O₃ 1 h had a tendency for less both SO₂ residue in fruit and disease incidence (%) including brighter pericarp color as compared with commercial 1.5% SO₂ alone. Moreover, HCl 5% + SMS 1% showed the least SO₂ residue in whole fruit below Codex tolerance at 50 mg kg^‑1 throughout a period of time. The fruit treated with 1.5% SO₂ + O₃ 1 h, 1.5% SO₂, 5% HCl + 1% SMS, O₃ 2 h + 1.5% SO₂, and 1.5% SO₂ + SO₂ pad (Uvasys^®) could prolong storage life for 40, 40, 40, 30 and 30 days, respectively, at 5°C, 90% RH. Thus, application of 1.5% SO₂ + O₃ 1 h and/or 5% HCl + 1% SMS could be used for extending shelf life of fresh longan exported to restricted countries due to less SO₂ residue and fruit quality was maintained as compared with the conventional method.