Shelf Life Extension of Fresh Logan Fruit by Hydrochloric Acid for Replacing Sulfur Dioxide Gas Fumigation

Abstract

Studies on the efficacy of hydrochloric acid (HCI) on prolonging storage life of fresh longan fruits as an alternative to sulfur dioxide (SO₂) fumigation were evaluated. Three experiments were conducted at the laboratory of Chiang Mai Office of Agricultural and Development Region 1 at Chiang Mai province during November, 2008-January, 2009. The first experiment was to compare dipping longan fruit with panicle attached and washing longan fruit with tap water for 1 min prior dipping in 1.5 N HCI for 20 min and air dried comparing to SO₂ usage and untreated fruit. The experiment design was CRD with 4 replications. It was found that treatment with 1.5 N HCI as well as SO₂ inhibited pericarp browning for 20 day period at ambient temperature storage. The second experiment was to compare dipping longan fruit without pinicle attached in HCI at concentration of 1.0 and 1.5 N with SO₂ and untreated fruit. The experiment design was CRD with 4 replications. The result revealed that treatment with 1.5 N HCI (pH 0.21) showed the optimum concentration to be used for bleaching fruit skin, decreasing pericarp pH and reducing fruit decay more than those treated with 1.0 N HCI (pH 0.39) during storage at 31°C with 85% RH for 32 days. For the third experimental model was a 4x2 factorial in CRD design with 3 replications comprising 4 levels of treatments: dipping the fruits in 1.5 N HCI for 20 min drained and a subsequent with or without rinsing with tap water; SO₂; and untreated fruit, Treated fruits were kept in 2 levels of storage condition in foam tray with or without wrapped with 11 m thick PVC film. The fruits were stored at 31°C with 85% RH and a subsequent chilling injuly (CI) test at ambient conditions for 24 hours prior to quality evaluation. The result indicated that the fruits without plastic wrapped significantly delayed fruit decay but increased weight loss in comparison with the wrapped fruits. The untreated fruits without plastic wrapped rapidly completed CI by 8 days whereas the untreated fruits without plastic wrapped were 30 days. The delay in CI for fruits treated with HCI and SO₂ was at least 60 days. The application of HCI and a subsequent rinse with tap water without plastic wrapped had the best treatment for replacing SO₂ usage to control CI, fruit decay and delay pulp quality loss during storage compared with the other treatments.