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The extraction and drying processes used to produce red colorant from red dragon fruit peels were optimized to yield the highest beta-cyanin content. The types of solvents (deionized water and 80% ethanol), pH, extraction time and temperature were the independent variables in the extraction process. The amount of binding medium (acetylated oxidized starch and maltodextrin) and extract, inlet temperature and feed rate were the independent variables in the spray-drying process. Based on response surface methodology, Box-Behnaken and full factorial designs were used for the experiment, while beta-cyanin was determined as the response. Antioxidant activity of the colorant powder was also tested. The optimum extraction condition giving the highest beta-cyanin content was a pH of 5.5 at 40°C for 20 min extracted by deionized water. The optimum drying condition for the production of red colorant powder was 6% binding medium at a feed rate of 6 ml/min and an inlet temperature of 140 and 160°C for acetylated oxidized starch and maltodextrin, respectively. The experimental results following the response surface methodology corresponded well to the predicted values. The optimum drying conditions yielded a red colorant powder with antioxidant properties that could be used in food products.

Lemongrass or pandan leaf extracts were used separately to improve the flavor of soy ice cream. Lemongrass or pandan leaf extracts with water in concentrations of 10:100, 15:100, and 20:100 w/w were examined using sensory evaluation for the best flavor acceptance. The best ratio was selected to spray dry using maltodextrin as the drying medium at various concentrations (2, 4, 6, 8 and 10% w/w). A ranking preference test was used to determine the flavor of the soy ice cream. Threshold testing was used to determine the sensorial quality of soy isolate protein mixed with both herb extracts, and soy ice cream mixed with both herb extracts. The flavor compound was analyzed by using headspace, solid-phase microextraction, gas chromatography, mass spectrophotometry (HS-SPME-GC-MS). The best concentration of fresh lemongrass or pandan leaf extracts for improving the sensorial flavor of soy ice cream was 10:100 (w/w). The optimum quantity of maltodextrin for spray drying was 2% (w/w). The threshold values of fresh and powdered lemongrass extracts that could mask the beany flavor in soy protein isolate solution and soy ice cream were lower than those of fresh and powdered pandan leaf extracts. The beany flavor in soy protein isolate solution and soy ice cream was mainly composed of hexanal, pentanal, benzaldehyde, 2-pentyl-furan and 1-octen-3-ol. The flavor compounds in pandan leaf extract were 2-acetyl-1-pyroline and 3-methyl-2(5H)-furanone, while those of lemongrass extract were β-myrcene, α-pinene, 3-carene, neral, geranial and geraniol. From the results of HS-SPME-GC-MS, the beany flavor was masked by these extracts. This indicated that lemongrass and pandan leaf extracts could mask the beany flavor and improve the sensorial quality of soy ice cream.