Freeze-drying well known and developed technology for preserving food and retaining its properties such as flavor, and taste. In this study, the objectives to investigate the difference between fresh, treated, and controlled freeze-dried samples and see the effects on those samples. Browning of the samples was one of the concerns to monitor and observe. The outcomes of this study suggested that the freeze-drying is great technique in preserving the food with its properties remain intact. This was obtained by the water activity reduction from 0.96 to 0.22. Also, the structure remain undamaged that was observed from the water activity sorption isotherm where similar results were obtained in tray drying. The color change in frozen apple samples
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Materials and samples preparation Samples of apples were first peeled and cut to small round slices for easier handling. The samples were divided to two groups one just washed with water (untreated), and second group was washed with diluted citric acid (AA). Both groups were subjected to freeze-drying. Before freeze-drying step the samples were frozen in freezer to – 15-20 °C for a few hours. Both groups were taken from the freezer to the freeze-drying equipment explained next.
2.2. Drying …show more content…
When the apples were placed inside the freeze-dryer. First, the temperature was decrease below the freezing point of water 0 °C. This was to insure that the samples were frozen and all water inside the samples frozen too. The second step was applying the vacuum to start increase the temperature for the sublimation to take place from the apple samples. Increasing the temperature to 30 °C with very high vacuum allowed the sublimation for the crystals ice to evaporate and escape from the sample.
2.3. Water activity
Water activity and sorption isotherm were conducted for those both apples group. In fact, one sorption isotherm and two reading of water activity of both groups was performed. All measurements were obtained for freeze-dried apple samples, treated and controlled. Water activity sorption and desorption isotherm was conducted at 35 °C temperature. The water activity measurement conducted utilizing (AquaLab, WA, USA).
2.4. Colorimeter measurements In order to understand the treatment effectiveness of the apple colorimeter was used. One time was for the controlled samples and the other one for the treated samples after freeze-drying. Where L* is for Lightness, a* is indication from red positive to green negative, and b* is measure from yellow positive to blue negative. In the following equation (1) ∆E total color change was calculated:
∆E=√(〖∆L〗^2+〖∆a〗^2+〖∆b〗^2 )…(1)
2.5. Data
Materials and samples preparation Samples of apples were first peeled and cut to small round slices for easier handling. The samples were divided to two groups one just washed with water (untreated), and second group was washed with diluted citric acid (AA). Both groups were subjected to freeze-drying. Before freeze-drying step the samples were frozen in freezer to – 15-20 °C for a few hours. Both groups were taken from the freezer to the freeze-drying equipment explained next.
2.2. Drying …show more content…
When the apples were placed inside the freeze-dryer. First, the temperature was decrease below the freezing point of water 0 °C. This was to insure that the samples were frozen and all water inside the samples frozen too. The second step was applying the vacuum to start increase the temperature for the sublimation to take place from the apple samples. Increasing the temperature to 30 °C with very high vacuum allowed the sublimation for the crystals ice to evaporate and escape from the sample.
2.3. Water activity
Water activity and sorption isotherm were conducted for those both apples group. In fact, one sorption isotherm and two reading of water activity of both groups was performed. All measurements were obtained for freeze-dried apple samples, treated and controlled. Water activity sorption and desorption isotherm was conducted at 35 °C temperature. The water activity measurement conducted utilizing (AquaLab, WA, USA).
2.4. Colorimeter measurements In order to understand the treatment effectiveness of the apple colorimeter was used. One time was for the controlled samples and the other one for the treated samples after freeze-drying. Where L* is for Lightness, a* is indication from red positive to green negative, and b* is measure from yellow positive to blue negative. In the following equation (1) ∆E total color change was calculated:
∆E=√(〖∆L〗^2+〖∆a〗^2+〖∆b〗^2 )…(1)
2.5. Data