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Acta Universitatis Sapientiae, Agriculture and Environment

The Journal of "Sapientia" Hungarian University of Transylvania

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2068-2964
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Evaluation of freezing pre-treatments for the lyophilisation of apple

Tamás Antal / László Sikolya / Benedek Kerekes
Published Online: 2014-05-30 | DOI: https://doi.org/10.2478/ausae-2014-0004

Abstract

The effect of freezing rate on the quality of dried Jonagold and Idared (Malus domestica Borkh.) was studied. Apple slices underwent various pre-treatments, i.e. freezing in household freezer (freezing speed/rate: 0,5◦C/min), contact plate freezing (2◦C/min) and vacuumfreezing (3◦C/min). The quality of the freeze-dried product was then evaluated in terms of water activity (aw), hardness, color and rehydration. The texture and color experiments were carried out with texture analyser and colorimeter. The aw of apple slices was measured by aw apparatus. It was found that drying time was influenced by freezing rate. The freezing in household freezer (slow freezing rate) significantly reduces the duration of the freeze-drying process and consequently the process costs. The slow freezing rate allows the growth of large ice crystals at the beginning of the freeze-drying process; this fact should consequently lead to larger pores and injured cell walls and thus to shorter freeze-drying time. Quality of the freezing in household freezer product was assessed as higher than the quality of the other freezing pre-treated material. Slow freezing rate resulted softer texture and higher rehydration capacity than that of other pre-treated samples. In all cases, slow freezing speed lead to lower final moisture content, total color difference and water activity. Freeze-dried samples prepared with higher freezing rates (3◦C/min) were the most white in color because small pores, originated by sublimation of small ice crystals formed by fast freezing.

Keywords: lyophilisation; vacuum-freezing; rehydration

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About the article

Published Online: 2014-05-30

Published in Print: 2013-12-01


Citation Information: Acta Universitatis Sapientiae, Agriculture and Environment , Volume 5, Issue 1, Pages 56–68, ISSN (Online) 2068-2964, DOI: https://doi.org/10.2478/ausae-2014-0004.

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© 2014. This article is distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. BY-NC-ND 3.0

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