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Phaleria macrocarpa (Scheff.) Boerl. or ‘Mahkota Dewa’ is a popular plant found in Malaysia as it is a valuable source of phytochemicals and therapeutic properties. Drying is an essential step in the storage of P. macrocarpa fruits at an industrial level to ensure their availability for a prolonged shelf life as well as preserving their bioactive compounds. Hence, this study evaluates the effect of different temperatures on the drying kinetics, extraction yield, phenolics, flavonoids, and antioxidant activity of P. macrocarpa fruits. The oven-drying process was carried out in this study at temperatures of 40 °C, 50 °C, 60 °C, 70 °C, and 80 °C. Six thin-layer drying models (i.e., Lewis, Page, Henderson and Pabis, two-term exponential, Logarithmic, and Midilli and Kucuk models) were evaluated to study the behaviour of oven-dried P. macrocarpa fruits based on the coefficient of determination (R2), root mean square error (RMSE), and chi-square (χ2). The quality of the oven-dried P. macrocarpa fruits was determined based on their extraction yield, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity (2,2-diphenyl-1-picrylhydrazyl) using ultrasound-assisted extraction. The results showed that the time for moisture removal correspondingly increased in the oven-dried P. macrocarpa fruits. Apparently, the Midilli and Kucuk model is the most appropriate model to describe the drying process. The range of effective moisture diffusivity was 1.22 × 10−8 to 4.86 × 10−8 m2/s, and the activation energy was 32.33 kJ/mol. The oven-dried P. macrocarpa fruits resulted in the highest extraction yield (33.99 ± 0.05%), TPC (55.39 ± 0.03 mg GAE/g), TFC (15.47 ± 0.00 mg RE/g), and DPPH inhibition activity (84.49 ± 0.02%) at 60 °C based on the significant difference (p < 0.05). A strong correlation was seen between the antioxidant activity, TPC, and TFC in the oven-dried P. macrocarpa fruits. The current study suggests that the oven-drying method improved the TPC, TFC, and antioxidant activity of the P. macrocarpa fruits, which can be used to produce functional ingredients in foods and nutraceuticals.

This study was conducted to investigate the drying kinetics and internal and external mass transfer characteristics of walnuts for an understanding of the drying mechanism. The drying characteristics, mass transfer characteristics, and color of walnut during hot air drying (HAD) were investigated under different initial moisture content (IMC) (0.35, 0.39, and 0.43 g water/g wet mass) and drying temperatures (50, 60, 70, and 80 °C). The results indicated that the IMC and drying temperature both have significant effects on the drying process of walnut, showing the higher the IMC, the longer the preheating time, the smaller the effective moisture diffusivity (Deff) and mass transfer coefficient (hm), and the longer the drying time, but reverse results for drying temperature. The values of Deff and hm for walnut ranged from 4.94 × 10−10 to 1.44 × 10−9 m2/s and 1.24 × 10−7 to 3.90 × 10−7 m/s, respectively. The values of activation energy for moisture diffusion and mass transfer ranged from 21.56 to 23.35 kJ/mol and 28.92 to 33.43 kJ/mol, respectively. Multivariate linear prediction models were also established for estimating the Deff and hm as a function of the HAD process parameters. The drying temperature has a greater effect on the walnut kernel lightness than the IMC. The Verma et al model could be used to describe the HAD process of the walnut. The findings contribute to the understanding of moisture transfer mechanisms in walnuts and have practical value for the evaluation and improvement of drying systems.

Fresh red and green cherry peppers were dehydrated under vacuum at a plate temperature: of 50 - 70 °C and bed thickness: of 3 - 7 mm for the production of cherry pepper flakes and the process was optimized using the response surface methodology (RSM). Plate temperature and bed thickness were considered as dependent variables for responses, including vitamin C, capsaicin, and total colour change, of the dehydrated cherry pepper flakes to carry out vacuum drying experiment. Optimum vacuum drying conditions for the production of quality red cherry pepper flakes were found as 60.97 °C for plate temperature and 6.4 mm of bed thickness and 59.8 °C (≈ 60 °C) plate temperature and 5.74 mm (≈ 6 mm) bed thickness for green cherry pepper flakes. The modelling of vacuum drying characteristics of red and green cherry pepper paste was done for the production of cherry pepper flakes. Midilli model was found to be the best-fit model for both types of cherry pepper paste based on statistical parameters (R2 = 1.0, χ2 = 0.007, RMSE= 0.001). The independent variables had a significant effect (p < 0.01) on effective moisture diffusivity (1.87 x 10-10 8.9-9 x 10-10 m2/s). 27.761 kJ/mol (red) and 36.465 kJ/mol (Green) were the activation energy. Due to the increased nutritional and colour retention of vacuum-dried food products, there is a greater demand for these products in the market. The findings of this research would assist in determining the ideal drying conditions for vacuum-drying red and green cherry peppers while maintaining the proper nutritional value, which in turn would benefit farmers as well as other industrial stakeholders in value addition and reduction in postharvest losses. The established optimum drying parameters of the present study reduce trial-and-error in industrial/practical applications, lowering energy costs and resource use.

Research background. Traditionally, open sun drying method serves to dry the products for long time preservation. Solar drying is also employed to minimise the drying time to achieve the required moisture content. This method inherently contains complex heat and mass transfer mechanism, which makes difficult to describe drying kinetics at the micro level. Experimental approach. In this present paper, research is carried out to investigate the drying of 5 mm thick slices of red banana (Musa acuminata “Red Dacca”) in a single slope solar dryer based on natural and forced convection. Based on the experiments, a new semi-empirical thin layer drying kinetics is proposed and compared with other existing models. The proposed model with the correlation coefficient (R2) of 0.997 is in very good agreement with other well-known models. Based on the model, we calculated the moisture diffusivity and activation energy of the red banana drying process. Results and conclusions. It is found that the moisture diffusivity of the red banana samples was in the range of 8.74·10-10-1.56·10-9 m2/s for natural convection solar drying and 8.43·10-9-2.61·10-8 m2/s for forced convection solar drying. The activation energy of the red banana varied from 24.58 to 45.20 kJ/mol for passive and 22.56 to 35.49 kJ/mol for active drying. Besides, we carried out energy and exergy analysis of red banana in the dryers and found that the average exergy losses for the forced and natural convections were 16.1 and 6.63 kJ/kg and the average exergic efficiency of the natural and forced convection dryers was 57.7 and 70.9 %, respectively. Novelty and scientific contribution. A single slope direct solar dryer was designed and built to maintain the desired temperature for a specified period in both natural and forced convection mode. A novel drying kinetics model with higher correlation coefficient (R2) than the other drying kinetic models is proposed for the preservation of red bananas.

Performance of a tractor mounted solar-biomass hybrid dryer which utilise combined energy of solar and biomass was investigated. Drying behaviour of maize grains in the dryer was also investigated using 10 thin-layer mathematical models. The models were compared based on coefficient of determination (R2) and root mean square error (RMSE) values between experimental and predicted moisture ratios. Moisture content (MC) of grains in the dryer reduced from 19 ± 0.86% to 13 ± 0.4% (w.b.) in 5 h, compared to grains dried in open-sun which reached same MC in 15 hours. This resulted in average drying rate of 1.2 %.h-1 compared to 0.4 %.h-1 for grains dried in the open-sun leading to net savings in drying time of 67%. Overall mean temperature, 41.93 ± 2.7 °C in the dryer was 15.3 °C higher than the ambient temperature. Midilli Kucuk model was best to describe the thin-layer drying kinetics of maize in the dryer. It showed a good fit between the predicted and experimental data. The effective moisture diffusivity of grains dried in the dryer ranged between 1.45 × 10-11 m2.s-1 - 3.10 × 10-11 m2.s-1. An activation energy of 96.83 kJ.mol-1 was determined based on the Arrhenius-type equation.

The objective of the present study was to determine the influence of air temperature on the drying kinetics of sage leaves at temperatures of 45, 50, 55, 60, and 65 °C in a cabinet dryer. The drying time was significantly affected by temperature. Eight thin-layer drying models were used to describe the changes in moisture ratio as a function of time. The applicability of the models was determined regarding determination coefficient (R2), reduced chi-square (χ2) and root mean square error (RMSE) values. The Midilli & Kucuk model showed the highest R2, and lowest χ2 and RMSE and was selected as the best model to describe drying characteristics of the sage leaves. Fick’s second law was used to determine the effective moisture diffusivity (Deff) at each temperature. Deff values were significantly affected by temperature and ranged from 1.62×10-9 to 5.73×10-9 m2/s. Temperature dependence parameters of Deff was described by the Arrhenius equation. Ea value was 52.52 kJ/mol for the given temperatures. Drying temperature significantly affected total phenolic content (TPC) and antioxidant activity (AA). Highest TPC and AA values were found from the samples dried at temperature 45 °C. This study suggested that sage leaves should be dried at a lower temperature due to lower phenolic degradation and colour change.

Kiwifruit slices were dried at four different air drying temperatures of 50, 55, 60 and 70ºC and at 2 m s-1 air velocity by using a cabinet dryer in this study. The drying, rehydration and colour characteristics were significantly influenced by pretreatment and drying temperature. The drying time decreased with the increase in drying temperature. The drying rate curves showed that the entire drying process took place in the falling rate period. Five well-known thin-layer models were evaluated for moisture ratios using nonlinear regression analysis. The results of regression analysis indicated that the Midilli & Kucuk model the best to describe the drying behaviour with the lowest c2 and RMSE values, and highest R2 value. The effective moisture diffusivity of the dried kiwifruit slices was calculated with Fick’s diffusion model, in which their values varied from 4.19×10–10 to 6.99×10-10 m2 s-1 over the mentioned temperature range. The dependence of effective diffusivity coefficient on temperature was expressed by an Arrhenius type equation. The calculated values of the activation energy of moisture diffusion were 10.37 and 19.08 kJ mol-1 for citric acid and control samples, respectively

The objective of the present study was to investigate microwave-assisted drying of Jerusalem artichoke tubers to determine the effects of the processing conditions. Drying time (DT) and effective moisture diffusivity (EMD) were determined to evaluate the drying process in terms of dehydration performance, whereas the rehydration ratio (RhR) was considered as a significant quality index. A pretreatment of soaking in a NaCl solution was applied before all trials. The output power of the microwave oven, slice thickness and NaCl concentration of the pretreatment solution were the three investigated parameters. The drying process was accelerated by altering the conditions while obtaining a higher quality product. For optimization of the drying process, response surface methodology (RSM) and genetic algorithms (GA) were used. Model adequacy was evaluated for each corresponding mathematical expression developed for interested responses by RSM. The residual of the model obtained by GA was compared to that of the RSM model. The GA was successful in high-performance prediction and produced results similar to those of RSM. The analysis and results of the present study show that both RSM and GA models can be used in cohesion to gain insight into the bioprocessing system. --Keywords: Jerusalem artichoke, microwave-assisted drying, effective moisture diffusivity, response surface methodology, genetic algorithm--

The water cycle over the Amazon basin is a regulatory mechanism for regional and global climate. The atmospheric moisture evaporated from this basin represents an important source of humidity for itself and for other remote regions. The deforestation rates that this basin has experienced in the past decades have implications for regional atmospheric circulation and water vapor transport. In this study, we analyzed the changes in atmospheric moisture transport towards tropical South America during the period 1961–2010, according to two deforestation scenarios of the Amazon defined by Alves et al. (Theor Appl Climatol 100(3-4):337–350, 2017). These scenarios consider deforested areas of approximately 28% and 38% of the Amazon basin, respectively. The Dynamic Recycling Model is used to track the transport of water vapor from different sources in tropical South America and the surrounding oceans. Our results indicate that under deforestation scenarios in the Amazon basin, continental sources reduce their contributions to northern South America at an annual scale by an average of between 40 and 43% with respect to the baseline state. Our analyses suggest that these changes may be related to alterations in the regional Hadley and Walker cells. Amazon deforestation also induces a strengthening of the cross-equatorial flow that transports atmospheric moisture from the Tropical North Atlantic and the Caribbean Sea to tropical South America during the austral summer. A weakening of the cross-equatorial flow is observed during the boreal summer, reducing moisture transport from the Amazon to latitudes further north. These changes alter the patterns of precipitable water contributions to tropical South America from both continental and oceanic sources. Finally, we observed that deforestation over the Amazon basin increases the frequency of occurrence of longer dry seasons in the central-southern Amazon (by between 29 and 57%), depending on the deforestation scenario considered, as previous studies suggest.

A laboratory scale microwave-convection dryer was used to dry the eggplant fruit, applying microwave power in the range of 270–630 W, air temperature in the range of 40–70°C and air velocity in the range of 0.5–1.7 m/s. Six mathematical models were used to predict the moisture ratio of eggplant fruit slices in thin layer drying. The results showed that the Midilli et al. model had supremacy in prediction of turnip slice drying behavior. Minimum and maximum values of effective moisture diffusivity (Deff) were 1.52 × 10–9 and 3.39 × 10–9 m2/s, respectively. Activation energy values of eggplant slices were found between 13.33 and 17.81 kJ/mol for 40°C to 70°C, respectively. The specific energy consumption for drying eggplant slices was calculated at the boundary of 86.47 and 194.37 MJ/kg. Furthermore, in the present study, the application of Artificial Neural Network (ANN) for predicting the drying rate and moisture ratio was investigated. Microwave power, drying air temperature, air velocity and drying time were considered as input parameters for the model.