J. Sci. Res. Chula. Univ., Vol. 25., No. 2 (2000) 237 Process Improvement to Preserve the Color of Instant Pennywort Centella asiatica (Linn.) Urban Saiwarun Chaiwanichsiri, 1 Narongchai Dharmsuriya, 1 Nirachara Sonthornvit 1 and Theeranun Janjarasskul 1 Method to maintain color of instant Pennywort [Centella asiatica (Linn.) Urban or Buo-Bok] during processing was investigated. Two methods of preparation before juice extraction were studied: blanching the Buo-Bok at 95- 100 o C for 0 to 10 minutes or blanching Buo-Bok at 95-100 o C and then immersing it in 0.005% citric acid solution (pH 4.5) before extracting the juice and adding ZnCl 2 75 ppm to the juice. The color of the juice was measured and the overall acceptability of the juice was tested organoleptically. The effect of the temperature on the color of Buo-Bok during spray drying was investigated by varying the inlet temperature of the hot air over 150-225 o C. The powder was analyzed for moisture content and the rehydrated juice was evaluated for color. The optimum hydration ratio was determined by varying the ratio of the Buo-Bok mix to water from 1:5 to 1:25 (w/v). The rehydrated juice was then evaluated for color, flavor, and overall acceptability using the Ranking test. The powder was kept in laminated aluminum foil or KOP packages for two months at room temperature and was taken every 15 days to be analyzed for moisture content and evaluated for overall acceptability using the Triangle test. The results showed that blanching Buo-Bok at 95-100 o C for 1.5 minutes helped maintaining the color of fresh Buo-Bok juice. A hot inlet air temperature of at least 200 o C gave the powder having moisture content less than 2%. The optimum rehydration ratio of 1:10 gave rehydrated juice having the fresh Buo-Bok juice color. During storage of the mix in both packages it was found that the difference in color of the Buo-Bok mix and the fresh one increased while the overall acceptability of the product decreased with storage time. However, the product was still acceptable. The type of packaging materials had no effect on the quality of the product during two months of storage. Key words: color, Pennywort juice, preservation, spray drying. 1 Department of Food Technology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand.