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vol. 12, nr. 3 (2008)
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Influence of osmotic dehydration on changes in structure of freeze-dried strawberries
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Agnieszka Ciurzyńska, Andrzej Lenart:
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Department of Food Engineering and Process Management, Faculty of Food Sciences, Warsaw University of Life Sciences (SGGW), ul. Nowoursynowska159c, 02-787 Warszawa |
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vol. 12 (2008), nr. 3,
pp. 613-624
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abstract:
The aim of this work was to investigate the effect of osmotic dehydration on changes in structure of freeze–dried strawberries. A study was undertaken to define pre-treatment conditions before freeze-drying of strawberries which could affect their structure. Strawberries cv. Senga Sengana were freeze-dried heating shelves temperature of 30°C for 24 hours. The analysis of changes in structure was made with the use of scanning microscopy in zoom 50 and 100x. Average value of area, circumference and Feret diameter of individual cell of freeze-dried strawberries, osmotically and without osmotic dehydration, were determined. Photographs which were made with the use of bi-refraction interferometry permitted observation of the degree of saturation of the tissue of freeze-dried strawberries by sugars. It was demonstrated that osmotic dehydration strengthened the structure of freeze-dried strawberries, causing an increase in the thickness of cell walls. The biggest changes were observed on the surface, where cells were glued together and partly disrupted due to saturation with sugars, what created big spaces. The changes depended on the kind of osmotic solution used. For glucose solution, the spaces which were created after cell wall cracking were almost 2-times smaller than in the case of sucrose solution. On the photographs which were made with the use of bi-refraction interferometry, fiber forms of glucose crystals were found.
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keywords:
freeze-drying, strawberries, osmotic dehydration, structure
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original in:
Polish
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