Abstract:
The purposes of this research were study on the dried longan production, reduction of sulfur dioxide content in dried longan and food safety for dried longan tea drink. Flesh longan was soaked in 0.3% (w/v) potassium metabisulfite, and heated at 60°C for 12-15 hours to produce dried longan in laboratory. It was found that moisture content of dried longans in the range of 12.49-15.19% and sulfur dioxide content in the range of 662.66-711.42 ppm, respectively. Dried longan process from a manufacturer in Lumphun were prepared from flesh longan, soaked in 10-40 ppm sodium metabisulfite solution, and dried at 60°C for 11-13 hours. The moisture content of dried longan was 17.52% and sulfur dioxide (SO₂) content were 22.77 ppm, respectively. The quality and food safety of 18 dried longan samples were collected from various markets and retailers in Bangkok and Metropolitan Region, Chaing Mai and Lumphun in the year 2017 (10 samples) and 2018 (8 samples). Moisture content was found in the range of 12.42-16.99% and 13.60-19.52%. SO₂ content, detected in the range of 9.40-229.19 ppm. and 9.96-444.15 ppm., were not exceeded the permitted level. The results showed that 16 samples (88.89%) from local market without manufacturers detected SO₂ content exceeded safety standard at 10 ppm. Reduction of SO₂ content in dried longan using microwave, hot air oven, hot water dipping and sun drying methods were studied. The results revealed that microwave could not reduce SO₂ content but hot water dipping reduced SO₂ content in dried longan and product has high moisture content. Hot air oven at 90°C, 30 minutes and sun drying could decrease SO₂ at 84.12 ppm or 21.27% and 39.75 ppm or 10.05%, respectively. The appearance of dried longan after reducing showed the same quality dried longan as control. Dried longan was used as a raw material in the preparation of dried longan tea added citric acid for older-people and studied consumer safety after drinking tea. Consumers, over 40 year olds, accepted dried longan tea added citric acid in the ratio of 10:0.125 g and SO₂ content was not detected in dried longan tea drink. The finding of this research showed that SO₂ content in dried longans from manufacturer and retailer followed accordance with regulation according to Thai Notification of the Ministry of Public Health no. 389 B.E 2561. However, consumer, who are allergic or sensitive to sulfur dioxide, can be harmful and health effect. Therefore, these reducing sulfur dioxide methods are alternative way for consumption dried longan to safety from sulfur dioxide.