Effect of microwave and air-borne ultrasound-assisted air drying on drying kinetics and phytochemical properties of broccoli floret

Abstract

The drying kinetics and detailed phytochemical profile of broccoli under microwave drying (500 and 900 W) and air-borne ultrasound (125.2 and 180.1 W/dm²) assisted air drying at 70 °C were compared. The results show that, together with the faster drying speed, microwave performed better than ultrasound for the protection of chlorophylls and ascorbic acid. On the other hand, ultrasound-dried broccoli samples showed higher contents of carotenoids (lutein, zeaxanthin, α-carotene, and β-carotene), glucosinolates (glucoraphanin, glucobrassicin, and 4-methoxyglucobrassicin), and sulforaphane compared to the microwave-dried samples. The contents of lutein, glucoraphanin, glucobrassicin, and sulforaphane in the ultrasound-dried samples at 180.1 W/dm² were 56.5%, 13.7%, 24.9%, and 53.0% higher than that in microwave-dried samples at 900 W. Taking the aforementioned results and literature survey into consideration, it can be concluded that microwave drying has a higher drying efficiency, whereas ultrasound-assisted drying could be a better technology for the preservation of phytochemicals in fruits and vegetables.

Keywords:

• Broccoli drying
• microwave
• air-borne ultrasound
• drying kinetics
• phytochemicals

Disclosure statement

No potential conflict of interest was reported by the authors.

Geolocation information

This paper’s study area is Nanjing, Jiangsu Province, China.

Additional information

Funding

This work was sponsored by Jiangsu Agricultural Science and Technology Innovation Fund (No. CX(17)2017); National Natural Science Foundation of China (No. 31701616); Natural Science Foundation of Jiangsu, China (No. BK20170714); National Key Research and Development Program of China (No. 2017YFD0400900); Fundamental Research Funds for the Central Universities (No. KJQN201824); Open Fund from Fruit and Vegetable Processing Key Laboratory Affiliated to Ministry of Agriculture and Rural Affairs, China (No. FVKF2018007); Natural Science Foundation of Tibet Autonomous region (No. XZ2017ZRG -31).