Effects of ultrasound pretreatment followed by far-infrared drying on physicochemical properties, antioxidant activity and aroma compounds of saffron (Crocus sativus L.)

Abstract In the current study, the influence of ultrasound pretreatment followed by far-infrared drying on the drying rate, color difference and microstructure of saffron was investigated. The effect of pretreatment duration (30 and 60 s) and drying temperature (50, 60, 70 and 80 °C) on the main chemical composition, total flavonoid, antioxidant activity and volatile flavor compounds in saffron was also evaluated. The results indicated that the total drying time decreased with the increase of pretreatment duration. Especially at 50 °C, the drying time was reduced by 21.05% after 60 s pretreatment. It could also be found that 30 s ultrasound pretreatment with far-infrared drying at 50 °C was the best combination to obtain a good quality of the dried saffron. Under this condition, the samples had the highest chemical properties and volatile compounds, including crocin Ⅰ (20.78%), crocin Ⅱ (10.41%), flavonoid content (10.84 mg/g), antioxidant scavenging activity (58.92%), and major volatile flavor components (54.52%), as well as the acceptable drying time (35 min) and low color difference (26.32). The results of this study confirmed that ultrasound pretreatment had obvious effects and could be recommended for far-infrared drying of saffron.