Visualization of crust formation during hot-air-drying via micro-CT

Abstract

Nowadays, hot-air-drying (HAD) is the most common process for the production of dried fruits and vegetables till now. It is well known that HAD has a big influence on product structure leading to effects like shrinkage or case-hardening. While shrinkage has already been documented throughout the drying process, case-hardening or the formation of a crust has only been shown for the dried product. In this study, a three-step approach consisting of a HAD-, a freezing-, and a freeze-drying step is used to show the development of a crust of carrot discs throughout a HAD process. With this method, the crust structures created during HAD were preserved and could be analyzed in a dry state with cone-beam micro-CT measurements. Crust thickness increased significantly during HAD and crust formation started before a relative moisture content of X/X₀ = 0.5.

Keywords:

• Hot-air-drying
• crust formation
• case-hardening
• micro-CT
• tomography
• carrot

Acknowledgment

The authors would like to express their thanks to Kerstin Sauther for supporting the drying experiments and to Elias Hamann for supporting the micro-CT measurements.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research project was supported by the German Ministry of Economics and Energy (via AIF) and FEI (Forschungskreis der Ernährungsindustrie e.V., Bonn) in the scope of project AiF 18250 N.