The use of tray rotating dryer for tomato drying significantly improved the overall drying performance by influencing both drying rate and product quality. This was due to the fact that the use of tray rotation drastically reduced temperature variation within the drying chamber from 2 to 0.2 C. Tray rotation had an important contribution on the variability of the tomato quality indicators used in this work: lycopene content (23.1%), ascorbic acid content (2.5%) and the a* color value (7%). For example, ascorbic acid was better preserved at temperatures of 45 and 50 C with the use of tray rotation. On the other hand, total polyphenols content was primarily affected by air velocity, whereas rehydration rate was not dependent on any of the operating conditions. In general, the contribution of the process variables to drying time was as follows: temperature > tray rotation > air velocity. The Page model resulted in a good fit to the experimental data. Deff had a good positive correlation with the chemical composition variables (0.82e0.85). This implies that the increase in the water diffusion rate from the interior of the tomato slice reduced the degradation of lycopene, ascorbic acid and total polyphenols. This paper reports for the first time, the high correlation between the a* CIELAB color value and both lycopene (0.90) and ascorbic acid (0.91) during tomato thermal treatments. Therefore, color determination, in addition to lycopene and ascorbic acid content, can be used as excellent tomato quality indicators in drying processes.
The use of tray rotating dryer for tomato drying significantly improved the overall drying performance by influencing both drying rate and product quality. This was due to the fact that the use of tray rotation drastically reduced temperature variation within the drying chamber from 2 to 0.2 C. Tray rotation had an important contribution on the variability of the tomato quality indicators used in this work: lycopene content (23.1%), ascorbic acid content (2.5%) and the a* color value (7%). For example, ascorbic acid was better preserved at temperatures of 45 and 50 C with the use of tray rotation. On the other hand, total polyphenols content was primarily affected by air velocity, whereas rehydration rate was not dependent on any of the operating conditions. In general, the contribution of the process variables to drying time was as follows: temperature > tray rotation > air velocity. The Page model resulted in a good fit to the experimental data. Deff had a good positive correlation with the chemical composition variables (0.82e0.85). This implies that the increase in the water diffusion rate from the interior of the tomato slice reduced the degradation of lycopene, ascorbic acid and total polyphenols. This paper reports for the first time, the high correlation between the a* CIELAB color value and both lycopene (0.90) and ascorbic acid (0.91) during tomato thermal treatments. Therefore, color determination, in addition to lycopene and ascorbic acid content, can be used as excellent tomato quality indicators in drying processes.
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