| Abstrakt: |
The present study deals with the dehydrofreezing of apples. Fresh samples (700 % db) and samples dehydrated up to different water contents (200, 100, and 30 % db) were frozen at high practical freezing rate (PFR) and low practical freezing rate (PFR). The effects of water content ( W) and practical freezing rate (PFR) were investigated in terms of freezing characteristics: initial freezing temperature (IFT), practical freezing time (PFT), specific freezing time (SFT), thaw exudate water (TEW), and texture (maximum puncture force as index of firmness). Only high W samples (700 and 200 % db) had a significant impact of PFR in terms of PFT, SFT, and TEW. IFT decreased sharply with the decrease in the sample W. PFT greatly depended on PFR for fresh apples. PFT varied from 86 to 329 min for fresh apples at PFR and PFR, respectively, whereas it was lower than 32 min for samples with W = 30 % db. SFT decreased, equally, with sample W decrease. The TEW of fresh frozen samples, during thawing, was approximately 12 g/100 g water for low PFR (PFR), whereas it was lower than 3 g/100 g water for samples with W = 200 % db at the same PFR. Moreover, the impact of PFR on TEW was significant and very important for high W samples. Finally, the firmness increased when W decreased for both PFR and PFR. Nevertheless, an insignificant impact of PFR on apple firmness was found. Thus, partial removal of water constitutes a promising solution to prevent the negative impacts of freezing on apple fruit firmness. [ABSTRACT FROM AUTHOR] |
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