Introduction
Rosa damascena Mill is a valuable cultivated plant, and for many years, essential oil has been produced from its flowers in Iran. The flower buds are generally dried by spreading them out in the shade or in the sun. Shade drying can lead to prolonged drying times, while sun drying may reduce product quality, affecting colour and essential oil. Therefore, in the current study, Rosa flower buds were dried using different drying processes and periods, and their physicochemical properties and essential oil quality were determined.
Materials and Methods
Rosa flower buds were collected from a farm located in Markazi province, Iran, in late May, 2024. Buds were dried using shade, a cabinet dryer (30 and 40 °C), an indirect solar dryer, a freeze-dryer, and a vacuum-dryer. Colour specifications (Lab) of the inner and outer petals of dried buds were measured by a colorimeter. Titratable acidity was determined by the titration method using 0.1 normal sodium hydroxide solution. Ascorbic acid was also measured by the titration method with 2 and 6 dichlorophenol indophenol. Experiments were carried out in three replications using a completely randomised design, and data were analysed using one-way ANOVA. Afterwards, the means of the data were compared using the Duncan test. The extraction of essential oil was applied by the water distillation method. After determining the essential oil yield, the compounds’ percentages were identified using GC and GC-MS devices.
Results and Discussion
The results revealed that drying in shade took too long (more than 12 days), and the shortest drying time happened in the vacuum-dryer (18 hours). The maximum colour index (L*) in the outer and inner petals of dried buds was observed in the freeze-dryer as 49.42 and 44.94, respectively. The maximum value of the a* index of 25.61 was acquired in the outer petal buds, which were dried at 50 °C in the cabinet dryer. After the fresh buds, the a* index of the inner petal buds was highest in the vacuum dryer at 16.62. The b* index of the outer and inner petal buds dried in the cabinet dryer, solar dryer, shade, and vacuum dryer did not have any significant differences. The maximum titratable acidity value was related to buds dried in the solar dryer (2.3%), and the minimum was observed in the vacuum dryer (1.23%). In the cabinet dryer (40 and 50 °C), ascorbic acid of dried buds had the highest values (1.57 and 1.49 mg per 100 g wet matter) in comparison with the other treatments. The quality of the essential oil extracted from dried buds in shade was similar to that of fresh buds. After the shade drying method, the best quality of essential oil was observed in buds dried in the cabinet dryer at 40 °C (30.4%).
Conclusion
Based on the results, applying vacuum-drying considerably shortened the drying period in comparison with shade drying. Lightness (L) is the most important specification that had the maximum value in outer and inner petals of buds dried in the freeze-dryer, and the least in the solar dryer. There were no significant differences between the lightness of inner petals of buds dried in shade and the two treatments of the cabinet dryer. Drying caused an increase in titratable acidity and a decrease in ascorbic acid of the flower buds. The maximum titratable acidity was depicted in buds dried by an indirect solar dryer, and the minimum was in the vacuum dryer. The flower buds dried in the cabinet dryer contained significantly higher levels of ascorbic acid compared to other drying methods. Cabinet drying at 50 °C yielded the highest amount of essential oil. The most aroma compounds and the lowest waxy compounds were observed in fresh buds, buds dried in shade, and buds which dried at 40 °C in the cabinet dryer, respectively.