FOOD. Science. Technology. Quality

Food. SCIENCE. Technology. Quality

Food. Science. TECHNOLOGY. Quality

Food. Science. Technology. QUALITY




The effect of temperature on some selected properties of convective-dried and freeze-dried apples


The objective of this work was to investigate the impact of temperature on the rehydration and sorption properties of the convective-dried and freeze-dried apples. The effect of temperature on mass increase and soluble leakage during the re-hydration of convective-dried fruits was insignificant. However, it was stated that the higher temperature of drying air caused the smaller increase in mass of apples being dried. While analyzing the increase in the mass of apples being dried, it was stated that the impact of temperature was more apparent in a case when the freeze dried material was watered. The apple mass increased stronger in the material being dried at higher temperatures (at 40°C – more than 5 times; at 10°C – more than 4 times), i.e. differently (inversely) than in case of convective-dried apples. The water vapor sorption analysis served as a confirmation of the results obtained: it proved that the freeze-dried apples absorbed a higher quantity of water vapor ranging from 0.33 (at a temperature of 10°C) to 0.56 g/g d.m. (at a temperature of 40°C) when the temperature of a heating plate increased. Changes generated in the bio-polimers by a higher temperature of the drying process could be a reason that the water bonding ability of convectivedried material became reduced. The material absorbed water vapor amounting from 0.03 (temperature of 80°C) up to 0.15 g/g d.m. (temperature of 60°C).


freeze-drying, convection drying, temperature, rehydration, sorption properties