Effects of Chlorine Dioxide from Hydrochloric Acid Mixed with Sodium Chlorite and Ozone Prior to Sulfur Dioxide Fumigation on Color of Longan Fruit Pericarp Browning

Abstract

This study was aimed to find out the suitable methods to substitute sulfur dioxide (SO2) fumigation and the methods to reduce SO2 residue in exported longan fruit. The experiments were done at the laboratories of Office of Agricultural Research and Development region 1 (OARD1), Chiang Mai province and Postharvest Innovation Center, Chiang Mai University during 2016-2020. The experiment 1 was studies the effects of hydrochloric acid (HCl), sodium chlorite (NaClO2), sodium chloride (NaCl) and Sulfur dioxide (SO2) fumigation (commercial method) on fruit browning. Longan fruit were packed in 3 kilograms and then dipped into various treatment solutions of HCl mixed with NaClO2 for 5 minutes. After that, the treated fruit were stored for 14 days, at 5oC 85% RH for 7 days (the same condition as transportation method for exporting longan) and then stored at room temperature (25oC) for another 7 days. They were found that ClO2 1.5% and HCl 6.4% + NaCl 1% treatments could prevent fruit browning for 14 days which were equaled to the commercial method, SO2 fumigation. While the study of methods to reduce SO2 use by ozone (O3) fumigation for 60 and 120 minutes prior to SO2 fumigation at 3 levels concentrations (0.6, 0.9 and 1.2%). They were found that O3 fumigation 120 minutes before SO2 fumigation with a concentration of 0.9 and 1.2% could prevent pericarp browning for 14 days compared with SO2 fumigation commercial was 11 days. Experiments 2 was aimed to prolong shelf life of longan fruit and residue of ClO2 and SO2 after storage at 5oC 85% RH. They were founded that ClO2 1.0, 1.25, and 1.5% for 5 min. could extended shelf life for 28 days compared to the commercial method (SO2 fumigation) and untreated fruit which had 21 and 7 days of shelf life respectively. The ClO2 residue in the aril was less than the pericarp. However, the residue of all ClO2 treatments were less than 3 mg/kg. The study of reducing SO2 by O3 fumigation. They found that O3 120 min. prior to SO2 1.2% could extend shelf life of 28 days compared with commercial SO2 fumigation was 21 days. SO2 residue in the aril of all SO2 treatments were lower than 50 mg/kg. Experiment 3 was aimed to study the effects of ClO2 and SO2 on some biochemical changes of aril and pericarp of longan fruit. They were founded that ClO2 and SO2 treatments could reduce Polyphenol oxidase (PPO) and Peroxidase (POD) activities but the total phenolic content in pericarps were increased by storage time. The pH of pericarp of ClO2 treated fruit were lower than the SO2 fumigation and untreated treatments. Total anthocyanin contents in the pericarp in all treatments were varied between 0.00-646.02 mg/kg. The anthocyanin was not found in the abnormal aril, pinked aril but 1,2-benzoquinone, 6-deoxfagomine, L-phenylalnine, L-isoleucyl-proline and pyrrolidone-5-carboxylic acid were founded. There were 31 volatile compounds founded which (E)-3-7-dimethylocta-1,3,6-triene or β-ocimene was the most founded volatiles in all treatments.