THIN-LAYER DRYING KINETICS OF SESAME HULLS UNDER FORCED CONVECTION AND OPEN SUN DRYING

Sesame hulls are a useful by‐product of the sesame processing industry. The sesame hulls are produced at a high moisture content (68% wet basis) and need further drying to prevent deterioration. In this study, both open sun drying (OSD) and forced convection drying (FCD) at 42, 55, and 76C and 1.2 m/s air velocity were investigated. Six common thin‐layer drying models were fitted to the experimental data. Several statistical parameters were used to evaluate the performance of thin‐layer drying models, including r², x², root mean square error (RMSE) and residuals. Sesame hull drying was found to take place completely in the falling rate region. The modified Page model was found to describe OSD data well, while the Wang and Singh model was the best model for describing FCD. Effective diffusivity was found to be 1.89 × 10^‐8 m²/s and 7.36 × 10^‐10 to 1.20 × 10^‐9 m²/s for OSD and FCD, respectively. Activation energy was also found to be 12.95 kJ/mol for FCD.     

Sun drying of figs: an experimental study

In this work, the sun drying behaviour of figs was investigated. Drying experiments were conducted for figs (Ficus carica) grown in Iskenderun-Hatay, Turkey. The constant rate period is absent from the drying curve. The drying process took place in the falling rate period. The drying data were fitted to the different mathematical models such as Lewis, Henderson and Pabis, Page, Logarithmic, Two-term, Two-term exponential, Verma et al. and Wang and Singh models. The performance of these models was investigated by comparing the determination of coefficient (R²), reduced chi-square (χ²) and root mean square error (RMSE) between the observed and predicted moisture ratios. The results showed that the Verma et al. model was found to satisfactorily describe the sun drying curve of figs with a R² of 0.9944, χ² of 0.000483 and RMSE of 0.062857.     

Convective heat transfer in herb and spices during open sundrying

Tinospora cordifolia (herb), Curcuma longa L. and Zingiber officinale (spices) were dried in the open sun and their thermal behaviours investigated. Important thermal parameters, such as product temperature, temperature surrounding the product surface and the moisture removal, were studied during the open sundrying. The effect of the temperature difference between the product temperature and the temperature surrounding the product surface on the convective heat transfer coefficient was studied. The maximum values of convective heat transfer coefficient were 3.9, 3.4 and 3.3 W m^?2 K^?1 with experimental errors of 23%, 19% and 17% for T. cordifolia, C. longa L. and Z. officinale under open sundrying, respectively. The predicted values of the temperature and the moisture removal for T. cordifolia, C. longa L. and Z. officinale were close to the experimental values, the coefficients of correlation (R²) and root mean square percent errors (e) varying from 0.986 to 0.999 and 0.42 to 6.55, respectively.     

Drying of red pepper slices in a solar greenhouse dryer and under open sun: Experimental and mathematical investigations

The present work is mainly focused on the study of the solar drying of red pepper grown in the North of Tunisia. A new mixed mode solar greenhouse dryer (SGD) with forced convection was used in the drying experiments. To further understand the characteristics of the SGD, an open sun drying experiment was conducted under the same climatic condition. The results show that the constant rate period is absent from the experimental drying curves. The experimental drying curves show only the falling rate period. Thus, the drying time which was three days in the open sun decreased to two days in the SGD. The drying data were fitted to eight different mathematical models. The fit quality of the proposed models was evaluated by using the coefficient determination (R²), reduced chi-square (χ²) and root means square error (RMSE). Among the models, Modified Henderson and Pabis model for the forced solar drying and the open sun drying was found to best explain the thin-layer drying behaviour of pepper slices. The instantaneous thermal efficiency of the solar collector varied between 30% and 80%, at a mass flow rate of 0.047 kg/s. The overall energy efficiency of the solar dryer was 34%. Finally an economic evaluation was calculated using the criterion of payback period which was found very small 1.02 years compared to the life of the dryer (SGD) 20 years.     

Numerical Simulation of Variable Water Diffusivity during Drying of Peeled and Unpeeled Tomato

Abstract: A mathematical model was formulated for the estimation, in conjunction with experimental measurements, of water diffusivity parameters during convective drying of peeled and unpeeled tomatoes. Fick's 2nd law of diffusion was solved numerically for a sphere, by explicit finite differences, considering shrinkage effect, variable diffusivity, and constant boundary conditions. Experiments were performed in a laboratory tunnel dryer. The equivalent radius of tomato decreased by 50% until the end of the process, which explains the necessity for shrinkage inclusion in the mass transfer model. The mean estimated diffusivities varied between 2.03 × 10^?10 and 15.1 × 10^?10 m²/s for peeled tomatoes and 0.59 × 10^?10 and 15.2 × 10^?10 m²/s for unpeeled tomatoes. The estimated water diffusivities and their variation with the tested drying temperatures (45, 55, and 65 °C) provide an insight of peeling effect during air‐drying. Peeling was beneficial since yielded greater drying rates and shortened significantly drying times, thus saving energy during drying. In all the studied cases, good agreement was found between experimental and predicted drying curves (≥ 0.99, mean relative deviation [MRD]≤ 0.12, and root mean square error [RMSE]≤ 0.03). In overall, the proposed methodology provides a reliable and easy estimation of temperature and moisture‐dependent mass transfer properties and drying simulation of shrinkable food products such as tomato. Practical Application: Water diffusivity is a food property, difficult in estimation but essential in drying processing optimization. This property was estimated as a function of moisture content and drying temperature employing a numerical simulation procedure. The peeling effect was also studied and found beneficial for lower temperature drying (<55 °C) which is useful in the energy optimization of the drying process as well as the retention of the end‐product quality.     

Evaluation of drying models of apple (var. McIntosh) dried in a convective dryer

Drying behaviour of apple particles was investigated in a laboratory type dryer. The effect of drying air temperature, airflow velocity, initial height of layer, particles shape and size on the dehydration characteristics of apples was investigated. Increase in drying air temperature and increase in the airflow velocity caused a decrease in the drying time and an increase in drying rate. Increase in initial height of layer and increase in the sample thickness caused an increase in the drying time and decrease in drying rate. Drying time of the cubes was shorter and their drying rate was higher than for slices. The experimental dehydration data of apple particles obtained were fitted to the semi‐theoretical, empirical and theoretical models. The accuracies of the models were measured using the correlation coefficient (R), mean bias error (MBE), root mean square error (RMSE), reduced chi‐square (χ²), and t‐statistic method. All models described the drying characteristics of apple particles satisfactorily (R > 0.9792). The Logarythmic model can be considered as the most appropriate (R > 0.9976, MBE = ?10^?11?4.5 × 10^?6, RMSE = 0.00287–0.01746, χ² = 8.5 × 10^?6?3.1 × 10^?4, t‐stat = 7.3 × 10^?9?1.2 × 10^?3). The effect of drying air temperature, airflow velocity, characteristic dimension of the particle and initial height of layer on the drying models parameters were also determined.     

Effect of air temperature,slice thickness and pretreatment on drying and rehydration of tomato

The effect of air temperature, pretreatment with alkaline emulsion of ethyl oleate (AEEO) and slice thickness on drying and rehydration characteristics of tomato slices was studied. Drying time decreased with pretreatment, but it increased considerably with the increase in air temperature and slice thickness of tomato. Besides, pretreatment was found to improve the rehydration ratio of tomato slices. The experimental drying curves obtained show only falling rate period. To estimate and select the suitable form of drying curves, five different mathematical models were applied to the experimental data. Among the mathematical models investigated, the Midilli et al. and logarithmic models satisfactorily described the drying characteristics of tomato slices with highest R² and lowest χ² and root mean square error. The effective moisture diffusivity varied from 3.123 to 10.03 × 10^?11 m² s^?1 over the temperature range studied, and the activation energy values varied from 59.6 to 70.2 kJ mol^?1.     

Hot-air drying characteristics of Aloe vera (Aloe barbadensis Miller) and influence of temperature on kinetic parameters

The aim of this research was to study and model the kinetics of the hot-air drying of Aloe vera (Aloe barbadensis Miller) and to evaluate the influence of temperature on the kinetic parameters for the proposed models. A convective dryer was used at 50, 60, 70, 80 and 90 °C with an air flow of 2.0±0.2 m/s. The sorption isotherm of the fresh product was mathematically described by the Guggenheim, Anderson and de Boer (GAB) model, giving as a result monolayer moisture of 0.20 g water/g d.b. The mathematical models evaluated in the kinetic research included five empirical equations (Newton, Henderson-Pabis, Page, modified Page and Fick's diffusional model). The fit quality of the proposed models was evaluated by using the linear regression coefficient (r²), sum square error (SSE), root mean square error (RMSE) and Chi-square statistic (χ²). The diffusivity coefficient increased with the temperature from 5.30 to 17.73×10⁻¹⁰ m²/s, for a range of temperatures between 50 and 90 °C, with an estimated activation energy of 30.37 kJ/mol. When comparing the experimental moisture values with those estimated by the proposed models, the modified Page model provided the best to fit of the data, showing that this equation correctly simulates the Aloe vera drying process and represents an excellent tool for estimating its drying time.     

Effect of temperature on antioxidant capacity during drying process of mortiño (Vaccinium meridionale Swartz)

The mortiño fruit (Vaccinium meridionale Swartz) has been recognized as an excellent source of antioxidants, phenolic compounds, and anthocyanins. Drying conditions, particularly temperature, often lead to food quality degradation. The present study investigated the influence of drying temperature (40, 50, and 60°C) on antioxidant activity, anthocyanin, and phenol content of mortiño. Four different thin layer drying models of drying kinetics (Modified page, Newton, Henderson & Pabis and, two-terms) were fitted to the experimental data. For antioxidant capacity determination, oxygen radical absorbance capacity and ferric ion reducing antioxidant power assays were used. The results showed that antioxidant capacity, and phenolic and anthocyanin content all decreased with increasing temperature and drying time. It was observed that phenols and anthocyanins were conserved in greater amounts at 60°C with 34% (5.85 mg gallic acid/g dm) and 32% (2.36 mg Cyanidin-3-glucoside/g dm) preservation of initial content, respectively. Drying kinetics models were compared based on their R² and root mean square error values between the experimental and predicted moisture ratios. The two-terms model was found to satisfactorily describe the drying curves for all temperatures evaluated, with a determination coefficient (R²) above 0.9987 and root mean square error lower than 0.0201.     

Thin-layer drying characteristics of kurut, a Turkish dried dairy by-product

Kurut, which is made in villages of Eastern part of Turkey, is a sun‐dried dairy product. Thin‐layer drying behaviour of kurut at a temperature range of 35–60 °C, with 5 °C increments, and constant thickness of 0.5 cm and drying air velocity of 1.5 m s^?1 was determined in a convective type dryer. The data of sample weight, dry and wet‐bulb temperatures were recorded continuously during each experiment and drying curves obtained. The drying process took place in the falling rate period. Drying curves were then fitted to eleven mathematical models available in the literature to estimate a suitable model for drying of kurut. Two‐term model gave better predictions than other models and satisfactorily described the thin‐layer characteristics of kurut. The effective diffusivity varied from 2.444 × 10^?9 to 3.597 × 10^?9 m² s^?1 over the temperature range. The temperature dependence of diffusivity coefficient was described by the Arrhenius‐type relationship. The activation energy for moisture diffusivity was found to be 19.88 kJ mol^?1.     

Finite Element Modeling of Moisture Transfer During Storage of Mixed Multicomponent Dried Foods

A finite element model is described that can be used for predicting moisture transfer in mixed food products during storage. Two of three components (raisins, roasted peanuts, banana chips, and roasted almonds) were packed in a well sealed cup. The rate of moisture transfer between the components was assumed to be limited by the component with the Lowest effective diffusion coefficient divided by the square of half of smallest dimension (i.e., D_effLo²) value. The surface moisture content of the rate determining component was assumed to be in equilibrium with the other component(s) at all times. The mean error between the experimental and predicted moisture values with time ranged from 0.28% to 0.84% as a percentage of moisture content.     

Thermodynamic properties of moisture adsorption of whole wheat flour. Calculation of net isosteric heat

The moisture sorption isotherms of whole wheat flour were determined at 10, 20 and 30 °C over a relative humidity range of 10–90%. Two models were applied to the sorption experimental data: the Guggenheim–Anderson–de Boer (GAB) and the Caurie models. The goodness of fit of the mathematical models was statistically evaluated by means of the root mean square per cent error (%RMS), obtaining values between 1.44 and 1.05 for GAB, and between 2.69 and 2.57 for the Caurie model. Hence, both models provided a good fit to the experimental data. The isosteric heat of sorption was calculated using two methods: the Clausius–Clapeyron expression and the Caurie equations, showing in both cases maximum values (11.03 and 12.39 kJ mol^?1, respectively) when moisture content was minimum (2.5 g H₂O per 100 g dry matter), and gradually diminishing to the value of the heat of vaporisation of pure water when moisture content reached a maximum value.     

Direct and Simultaneous Quantification of Tannin Mean Degree of Polymerization and Percentage of Galloylation in Grape Seeds Using Diffuse Reflectance Fourier Transform‐Infrared Spectroscopy

The direct and simultaneous quantitative determination of the mean degree of polymerization (mDP) and the degree of galloylation (%G) in grape seeds were quantified using diffuse reflectance infrared Fourier transform spectroscopy and partial least squares (PLS). The results were compared with those obtained using the conventional analysis employing phloroglucinolysis as pretreatment followed by high performance liquid chromatography‐UV and mass spectrometry detection. Infrared spectra were recorded in solid state samples after freeze drying. The 2nd derivative of the 1832 to 1416 and 918 to 739 cm^?1 spectral regions for the quantification of mDP, the 2nd derivative of the 1813 to 607 cm^?1 spectral region for the degree of %G determination and PLS regression were used. The determination coefficients (R²) of mDP and %G were 0.99 and 0.98, respectively. The corresponding values of the root‐mean‐square error of calibration were found 0.506 and 0.692, the root‐mean‐square error of cross validation 0.811 and 0.921, and the root‐mean‐square error of prediction 0.612 and 0.801. The proposed method in comparison with the conventional method is simpler, less time consuming, more economical, and requires reduced quantities of chemical reagents and fewer sample pretreatment steps. It could be a starting point for the design of more specific models according to the requirements of the wineries.     

Mathematical Modelling of Thin Layer Dried Cashew Kernels

In this paper mathematical models describing thin layer drying of cashew kernels in a batch dryer were presented. The range of drying air temperature was 70 – 110°C. The initial moisture content of the cashew kernels was 9.29% (d.b.) and the final moisture content was in the range of 3.5 to 4.6% dry-basis. Seven different thin layer mathematical drying models were compared according to their coefficients of determination (R²) mean square error (MSE) and mean relative deviation modulus (P) to estimate drying curves. The effects of the drying air temperature and time on the drying model constants and coefficients were predicted by multiple regression analysis using linear and non-linear type models. The results have shown that among the models, the Page model was found to be the best for describing the drying behaviour of cashew kernels with R², MSE and P values of 0.9830, 0.00311 and 5.046 respectively.     

Vacuum drying kinetics of Asian white radish (Raphanus sativus L.) slices

In this study, radish slices were dried as single layers with thickness of 4 and 6 mm in the ranges of 40-60 °C of drying air temperature in a laboratory scale vacuum dryer. The effect of drying air temperature and slice thickness on the drying characteristics was determined. Moisture transfer from radish slices was described by applying the Fick's diffusion model, and the effective diffusivity changes between 6.92 × 10⁻⁹ and 14.59 × 10⁻⁹ m²/s within the given temperature range. Effective diffusivity increased with increasing temperature. An Arrhenius relation with activation energy values of 16.49 and 20.26 kJ/mol for the thickness of 4 and 6 mm expressed the effect of temperature and sample thickness on the diffusivity. A non-linear regression procedure was used to fit nine thin-layer drying models available in the literature to the experimental moisture loss data. The models were compared based on the coefficient of determination, mean relative percent deviation, root mean square error, and the reduced chi-square between the observed and predicted moisture ratios. The logarithmic model has shown a better fit to the experimental drying data as compared to other models.     

基于净初级生产力的春小麦生产潜力及估产研究——以甘肃省白银区为例--测试文章

利用2010年白银区春小麦生长季（4—7月）空间分辨率为250 m的MODIS影像和气象站点的气象数据,通过CASA模型建立了基于MODIS数据的春小麦净初级生产力遥感估算模型,估算出白银区春小麦生长季的净初级生产力（NPP）,通过春小麦NPP与干物质转换关系计算出春小麦生产潜力。结果表明：白银区南部春小麦的NPP和生产潜力均大于北部地区,其NPP最小值为42 gC·m^-2·a^-1,最大值为402 gC·m^-2·a^-1,且春小麦的生产潜力有明显的季节性规律。根据春小麦生产潜力与实际产量的拟合关系建立了产量估测模型,并对该模型做了精度验证与实用性评价,结果显示该估产模型均方根误差RMSE为76.33 g·m^-2,相对均方根误差RMSEr为23.51%。     

Non-destructive determination of fat,moisture and protein in salmon fillets by use of near-infrared diffuse spectroscopy

Near infrared (NIR) diffuse spectroscopy was used to determine the fat, moisture and protein contents in whole and ground farmed atlantic salmon fillets. A remote fibre-optic probe was used for NIR measurements on 50 whole salmon fillets. The constituent ranges were: 91-205 g kg^?1 fat, 599-709g kg^?1 moisture and 186-209 g kg^?1 protein. Principal component regression resulted in the following prediction errors for ground salmon fillets, expressed as root mean square error of cross validation: 6.6 g kg-1 fat, 3.8 g kg^?1 moisture and 2.0 g kg^?1 protein. The corresponding prediction errors for non-destructive measurements on whole salmon fillets were 10.8 g kg^?1 fat, 8.5 g kg^?1 moisture and 3.7 g kg^?1 protein. Regression models using the 760-1100 m range gave lower prediction errors than models using the 1100-2500 mm or 760-2500 nm ranges. The results show that fibre-optic probe NIR instruments are suited to determine fat and moisture in whole salmon fillets non-destructively.     

广式腊肉热泵薄层干燥数学模型研究

为提高广式腊肉干燥过程中能源利用效率和物料水分控制准确度,通过测定广式腊肉不同温度、风速条件下的热泵干燥水分比(MR),选用11种常用的薄层干燥数学模型进行拟合比较,根据模型的决定系数(R2)、均方根误差(RMSE)和卡方(χ2)值确定了最佳模型;采用回归分析拟合了干燥模型常数、系数与干燥温度、风速之间的关系。结果表明：Two term模型比其他模型能更好地反映广式腊肉的热泵干燥规律,含水率的预测值与实际值吻合较好,在干燥温度50～60℃和风速0.4～1.0m/s的范围内,可以用来描述广式腊肉的热泵干燥进程。     

Suitable drying model for far infrared drying of taegeuk ginseng

In this study we have elucidated the suitable drying model for the far infrared drying of taegeuk ginseng. Thin layer drying tests of taegeuk ginseng were conducted at 3 temperature levels of 45, 55, and 65°C, and 3 taegeuk ginseng size levels of large, medium, and small. Four thin layer drying models were used to estimate drying curves. The goodness-of-fit of the drying models were evaluated using the coefficient of determination (R²), root mean square error (RMSE), mean relative deviation modulus (P_e), and reduced chi-square (χ²). In the mean time, the influences of drying temperature and taegeuk ginseng size on drying behavior were also determined. The results revealed that the Page model, which can describe the far infrared drying behavior of taegeuk ginseng with a great accuracy, was the best model to fit adequately most of the drying conditions for the far infrared drying of taegeuk ginseng.     

Drying kinetics and effective moisture diffusivity of bamboo shoot slices undergoing microwave drying

Effect of microwave power on moisture content, moisture ratio, drying rate, drying time and effective moisture diffusivity (D_eff) of bamboo shoot was investigated using microwave drying. To study the effect of microwave power on drying, bamboo shoot samples (250 g) were dried at different power levels ranging from 140 to 350 W. To determine the kinetic parameters, drying data were fitted to various models based on the ratios of differences between initial and final moisture contents and equilibrium moisture content. Among the models proposed, Wang and Singh model gave a better fit for all drying conditions used. By increasing microwave output power, the D_eff values increased from 4.153 × 10^?10 to 22.835 × 10^?10 m² s^?1. A third‐order polynomial relationship was found to correlate the D_eff with moisture content. Further scope of this research work would include the effect of certain factors (shrinkage, case hardening, distortion of product and shape of bamboo shoot samples as an infinite slab) of practical significance to improve the model.