| Summary: | 碩士 === 國立臺灣大學 === 食品科技研究所 === 94 === Three processing methods including hot-air drying, semi-withering processing and scented tea making were used to investigate the effect of processing methods on the quality of rose tea. The taste, aroma and color quality of rose tea infusion was emphasized. Two cultivars of Rosa Hybrid Grand Gala and Double Delight, were tested.
In the hot-air drying, result showed that the drying time for rose petals is decreased as the temperature increased. The equilibrium moisture content of Grand Gala and Double Delight were about 12.5 % and 5.0 % respectively. Furthermore, higher heating temperatures（80~100℃）resulted in less content of contents of anthocyanins, carotenoids, total polyphenol and reducing sugar than lower heating temperatures （40~60℃）. In wind velocity（0.5 m/s, 1.2 m/s, 2.0 m/s）caused no significantly differences on the content of chemical compounds in rose. The redness（a value）of Grand Gala rose tea infusion decreased as heating temperature increased. The yellowness （b value）of Double Delight rose tea infusion increased as heating temperature increased. The pH value of Double Delight and Grand Gala rose tea decreased as the heating temperature increased. However, the rose tea infusions of Grand Gala and Double Delight roses dried in 80℃ showed significantly better sensory scores than the others heating temperature. The high heating temperature might cause some chemical changes of rose petals and lead to new flavor compound formation. The optimum hot air drying condition recommended for making rose tea was drying at 80℃、1.2 m/s for 4 hr.
In the scented tea experiment, the effect of moisture content（12.5 %, 25 %, 40 %, 55 %, 65 %）on the total fragrances adsorption of Grand Gala were evaluated. The result showed that 25 % moisture content of Grand Gala was the best. In addition, the effect of adsorption conditions including adsorption time（5 hr, 10 hr）, flower amount（25 g fw , 55 g fw, 85 g fw） and drying methods（60℃hot-air drying, 30℃vacuum drying ） on the total fragrances adsorption of Grand Gala were also tested. The results showed that the condition for maximum total fragrances adsorption of Grand Gala was 25% moisture contents, 8 hr adsorption time with 85 g fw of Double Delight petals, using vacuum drying method.
Double Delight was chosen in the semi-withering processing to investigate the best conditions of hot-air withering temperature and panning time for the making of rose tea. Our results showed that 42℃ hot-air withering for 30 mins led to the maximum activity of polyphenol oxidase. The moisture content of Double Delight petals decreased slightly during withering. However, the total polyphenol oxidase activity increased during withering. The panning process at 250℃、4 mins destroyed peroxidase activity successfully. The optimum semi-withering processing condition recommended for making rose tea was 42℃hot-air withering for 30 mins 、250℃ panning for 4 mins 、70℃ drying for 4 hr. However the sensory evaluation found that Double Delight rose tea from semi-withering process showed no significantly better than hot-air drying method in the quality of tea infusion prepared.
|
|---|
