Osmotic Dehydration of Apples Under Reduced Pressure Conditions
Abstract The aim of the study was to determine the effect of reduced pressure on the osmotic dehydration of apples. Tests were performed under vacuum of 8 kPa, 67 kPa, 80 kPa and under the atmospheric pressure (100 kPa). The samples were dehydrated in a sucrose solution with a concentration of 30°Bx, 50°Bx and 70°Bx. It has been shown that the effect of low pressure application depends significantly to the concentration of the osmotic solution. It has been found that the overall weight change significantly depend on the concentration of the solution, and after 3 hours of dehydration at a pressure of 80 kPa at solutions of 30°Bx, 50°Bx and 70°Bx total weight loss increased by 65%, 12% and 25% respectively, when compared to samples dehydrated at atmospheric pressure. From the studied variants of reduced pressure, the pressure of 80 kPa seems to be the optimal one, as evidenced by the lowest values of weight gain to water loss ratios for apples dehydrated in solutions of 50°Bx and 70°Bx.
The impact of the osmotic dehydration process and its parameters on the mass transfer and quality of dried apples
Abstract The aim of the study was to evaluate the effect of different assisting conditions (i.e., ultrasounds, vacuum, microwaves) during osmotic dehydration (OD) on the mass transfer kinetics and quality of dehydrated apple slices. The results of the study showed that the applied process conditions had a significant influence on the mass transfer with highest water loss obtained for ultrasound-assisted OD and highest solid gain for standard OD. Also, considerably higher total phenolic compounds content and antioxidant capacity measured by ABTS and FRAP methods were observed for all applied variants after osmotic dehydration process. It was concluded that joint use of ultrasounds and vacuum (OD-U-V) had the highest impact on quality improvement of dehydrated apple slices.
Antioxidant capacity changes of bird chili (Capsicum frutescens Linn.) during hot air drying.
The antioxidant capacity of bird chili (Capsicum frutescens Linn.) during hot air drying at 70, 100 and 121°C was analyzed by three different methods: ferric-reducing, antioxidant power (FRAP) assay; improved, ABTS, radical cation decolorization assay; and DPPH, free radical scavenging activity, together with the analysis of total phenolic content and browning pigment formation. It was found that total phenolic content might decrease at the beginning of the drying process, but that it would increase when the browning pigments were developed. Phenolic compounds of fresh, red bird chili were less heat stable than the ones of fresh, green bird chili. In addition, the antioxidant capacity of dried bird chili was dependent on the degree of browning and the drying temperature. All the antioxidant capacities of the dried products were higher than for the fresh ones, except after drying at 70°C, when the reducing power, FRAP value, of dried green and red chili was lower than the fresh one, and the values of the free radical scavenging activities, ABTS and DPPH of dried red bird chili did not change.