Document Type : Applicable
Authors
1 PhD Student, Department of Biosystems Engineering, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran
2 Professor, Department of Biosystems Engineering, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran
3 Assistant Professor, Department of Biosystems Engineering, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran
4 Professor, Department of Horticultural Sciences, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran
Abstract
Introduction: Beetroot (Beta vulgaris) is a great source of diverse essential nutrients such as dietary fibers, betalains, vitamins and carbohydrates. Drying of fruits and vegetables is considered as an engineering strategy in food industry, pointed at applying a set of operations to enhance shelf life, ensure perennial market supply, reduce packing and transportation costs, and enhance the quality of the final product. Simultaneously this is a massive energy consumption among food industries. Numerous efforts have been made to reduce the cost of drying agricultural products through various methods, including the manufacturing of new equipment and the efficiency maximization of existing systems. In the present work, it was appraised whether by means of new drying technique of step-down mode of stepwise temperature change conditions in a vacuum dryer apparatus, could be a probable proper alternative for manufacturing new devices which tremendously, requires expenditure of time and disbursement.
Materials and Methods: In this research the impact of a laboratory infrared-vacuum dryer and a new drying technique of stepwise temperature with the same device were investigated. The new strategy was assisted by a microwave treatment using a home scale Toshiba microwave. The present study was purposed to comprehend the effects of above-mentioned drying methods on the drying behavior of 4 mm red beetroot slices in addition to physical properties including color indices of (ΔL*, Δa*, Δb*) and shrinkage; Chemical properties of vitamin C and antioxidant component; Thermal properties of effective moisture diffusivity and drying kinetics and specific energy consumption as well as environmental aspects of greenhouse gasses (GHG) emissions. Beetroot slices were exposed to three levels of temperature (45, 60 and 75 °C) and absolute pressure (20, 50 and 80 kPa) as normal drying. Also, three levels of microwave power and times (at 150, 300, and 450 W) and (0, 10, and 20s) for stepwise conditions were applied.
Results and Discussion: Results showed that R2 value of normal and stepwise drying methods were between (92.73 – 99.92%) & (94.34 – 99.92%) respectively. The high values of R2 indicates that there is a strong relationship between experimental foundlings and predicted proposed model quantities. Furthermore, the CV percentage for them was less than 6.93 and 6.16 for normal and stepwise drying methods correspondingly; that illustrates a good repeatability of related models. All studied variables demonstrate non-significant lack of fit values that exhibit a good prediction ability for dependent variables. Therefore, models offer a good reliability in all dependent variables. Temperature factor had significant effect on all studied parameters in normal vacuum drying at 0.1% level. Absolute vacuum pressure affected significantly at different levels on all variables excluding SECtotal, CO2 and NOx for both methods; Unless otherwise the effect of temperature on dependent variables was more considerable comparing to absolute vacuum pressure. Power level and duration of microwave application in stepwise strategy had significant effect at 0.1% level on all dependent variables excluding AA. Interaction effect of temperature and vacuum pressure was more significant in normal vacuum drying. Stepwise method showed more considerable effect of microwave power application time interacting with vacuum pressure and microwave power level. The desirability values were found 0.606 and 0.610 for normal vacuum and stepwise method respectively. The optimization by using the Response Surface Methodology (RSM), was detected at 65 ℃ and 20 kPa for normal vacuum drying. Besides that, pressure vacuum of 45 kPa, 360 W of microwave power and 10 s of microwave power application was found as optimum point for stepwise drying method. Compared to normal vacuum drying at optimal conditions, the stepwise method reduced NOx and CO2 emissions by 27.91% and 27.80%, respectively, and decreased specific energy consumption by 28.18%. Additionally, improvements in color parameters were observed, with Δa* and ΔL* increasing by 18.80% and 9.87%, respectively. However, Δb* showed a 14% color degradation, and shrinkage increased by 38.62%. Furthermore, reductions in vitamin C loss index and antioxidant activity were recorded at 11.31% and 11.23%, respectively.
Conclusion: Using stepwise drying strategy had a close but lower impact on quality and physical parameters; whereas, showed a great positive difference on greenhouse gasses emission and specific energy consumption. This method also needs less energy to create absolute vacuum pressure (45 kPa compared to 20 kPa for normal method) to gain the mentioned results. Therefore, stepwise strategy is recommended for drying of red beetroot, as it offers a more energy-efficient approach while maintaining product quality and reducing environmental impact. Furthermore; this technique is proposed for new research studies that can be experimented with different agricultural products.
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