Variability of physical and phytochemical criteria of pot marigold (Calendula offıcinalis L.) flowers under different drying methods and plant nutrient source

With considering importance of post harvest operation on quality criteria of pot marigold (Calendula offıcinalis L.), the effect of flower nutrient source (organic inputs such as cattle manure (25 t ha-1), municipal waste compost (20 t ha-1), spent mushroom compost (15 t ha-1), vermicompost (15 t ha-1) and control) as well as different drying methods including microwave (300, 600 and 900 W), oven (60, 70 and 80oC) and natural-shade drying in room temperature were investigated on physical and phytochemical characteristics of flowers in a factorial experiment based on completely randomized design with three replications in Research Laboratories ofUniversity College of Agriculture and Natural Resources, University of Tehran and Shahid Beheshti University during 2010 and 2011 growing seasons. Criteria such as drying kinetic, antioxidant activity, total flavonoid content, total phenolic compounds and total carotenoid were evaluated. Results indicated that organic inputs had no significant effects on quality criteria of pot marigold except of total flavonoid content while drying methods significantly affected phytochemical criteria. Application of microwave 300, 600 and 900 W resulted in highest amount of total flavonoid content, total phenolic compounds and antioxidant activity, respectively. However, oven drying caused the lowest amount of phytochemical criteria. Interaction effect of nutrient source and drying method significantly affected antioxidant activity in which the highest amount of antioxidant activity was obtained in combination of vermicompost and microwave 900 W. In addition, application of vermicompost combined with oven drying at 60oC caused the lowest amount of antioxidant activity. Based on results of drying curves trend, drying of flowers by microwave showed a faster drying rate than oven and natural-shade drying in which by increasing microwave power and oven temperature, time of flower drying decreased whereas slope of moisture content reduction curve showed accelerated trend. In general, selection of optimum drying method depends on several factors and also it should be considered based on optimum use of energy and effective cost.