The Effect of Pre-Drying Treatment and Drying Conditions on Quality and Energy Consumption of Hot Air-Dried Celeriac Slices: Optimisation

Tina Nurkhoeriyati; Boris Kulig; Barbara Sturm; Oliver Hensel

doi:10.3390/foods10081758

The Effect of Pre-Drying Treatment and Drying Conditions on Quality and Energy Consumption of Hot Air-Dried Celeriac Slices: Optimisation

Foods. 2021 Jul 29;10(8):1758. doi: 10.3390/foods10081758.

Authors

Tina Nurkhoeriyati^{1

2}, Boris Kulig¹, Barbara Sturm^{3

4}, Oliver Hensel¹

Affiliations

¹ Department of Agricultural Engineering, Faculty of Organic Agricultural Sciences, University of Kassel, 37213 Witzenhausen, Germany.
² Study Program of Food Technology, Faculty of Life Sciences, International University Liaison Indonesia, Tangerang 15345, Indonesia.
³ Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB), 14469 Potsdam, Germany.
⁴ Albrecht Daniel Thaer Institute for Agricultural and Horticultural Sciences, Humboldt Universitӓt zu Berlin, 10115 Berlin, Germany.

Abstract

Celeriac is a good source of fibre, trace minerals, and phenolic compounds; it has a pleasant aroma but is a perishable material, prone to discolouration. This research investigated the optimisation of the quality and energy demand in hot-air dried celeriac slices. The experiment utilised the I-optimal design of response surface methodology with 30 experiment runs. Pre-drying treatments (blanching at 85 °C, three minutes; dipping in 1% citric acid solution, three minutes; no pre-drying treatment), drying temperatures (50, 60, and 70 °C), air velocities (1.5, 2.2, and 2.9 m/s), and thickness (three-, five, and seven-mm) were applied. The drying conditions affected drying time significantly (p < 0.0001). The model by Midilli and others and the logarithmic model fitted best with celeriac slices drying kinetics. Blanched samples had a higher ΔE*_ab (total colour difference) and BI (browning index) but lower WI (whiteness index) than samples with other pre-drying treatments. The rehydration ratio decreased with the increase of sample thickness and blanching (p < 0.0001). A quadratic model described the specific energy consumption (E_s) best. The dried samples compared with fresh samples had increased antioxidant activity but decreased total phenolic compound value. The optimisation solution chosen was 58 °C drying temperature, 2.9 m/s air velocity, and 4.6 mm sample thickness with acid pre-drying treatment.

Keywords: antioxidant activity; browning index; celeriac; energy demand; hot air drying; optimisation; rehydration ratio; total colour difference; total phenolic compound.