Development of Golden-Dried Longan Product in Loei Province

Abstract

The objective of research was to develop the dried longan processing method in Loei Province by studying the effects of the blanching temperatures and potassium metabisulfite (KMS) concentration on the physical and chemical properties of the longan flesh. The longan flesh was blanched at temperatures of 70, 80, and 90°C and soaked in KMS solutions at concentrations of 500, 1,000, and 1,500 ppm. The results revealed that blanching at 80 °C combined with soaking in 500 ppm KMS yielded the highest L* color value; the lowest browning index; a pH of 6.46, and sulfur dioxide residual of 12.07 ppm. Then the blanched longan was subsequently dried until a final moisture content of 18% was reached. For single-stage drying, drying temperature of 60, 70, and 80°C required total drying time of 360, 330, and 300 min, respectively. For the multi-stage drying, three drying conditions were applied: (1) a first-stage temperature of 60°C followed by a second-stage temperature of 70°C, with first-stage durations of 60 and 120 min, resulting in total drying times of 330 and 300 min, respectively; (2) a first-stage temperature of 70°C followed by                 a second-stage temperature of 60°C, with first-stage durations of 60 and 120 min, yielding total drying times of 300 and 270 min, respectively; and (3) a first-stage temperature of 80°C followed by a second-stage temperature of 70°C, with first-stage durations of 60 and 120 min, corresponding to total drying times of 270 and 240 min, respectively. Sensory evaluation indicated that overall preference, including texture, color, and taste, except for odor, differed significantly at the 0.05 level. Based on the preference scores, dried longan processed with an initial drying temperature of 80°C for 60 min, followed by a second stage at 70°C received the highest score for color, odor, taste and overall preference. However, its texture ranked second, following the sample dried initially at 70°C for 60 min and followed by a second stage at 60°C.