A new semi-theoretical thin layer model for modeling the air drying of cocoa beans with overnight tempering at ambient temperature was developed. The new model was a combination of the Page and ...two-term drying model. Results showed that the new model was found best described the drying process under the conditions tested (60, 70 and 80
°C). Effective diffusivities were found between 7.46
×
10
−11 and 1.87
×
10
−10
m
2/s. The Arrhenius constant and activation energy were estimated at 8.43
×
10
−4
m
2/s and 44.92
KJ/mol, respectively. Analyses of pH and cut test for bean quality showed that beans dried at 60
°C had lower acidity and good flavour quality as compared to other drying treatments.
The present study investigated the kinetics of heat pump drying of cocoa beans under stepwise drying conditions and the heat and mass transfer analysis carried out using 3-D computer simulation. The ...fermented cocoa beans were subject to drying at constant temperature (56 °C), step up temperature (30.7 °C–43.6°C–56.9 °C) and step down temperature (54.9 °C–43.9 °C) drying profiles. Shrinkage factor was incorporated into the heat and mass transfer models. Simulation results showed that the mean relative errors determined ranged from 3.1% to 12.1% in the predicted moisture ratio profiles in both models with and without shrinkage factor. In the bean temperature profiles, results showed excellent agreement between the predicted and experimental data with mean relative errors less than 5%. The present study showed that shrinkage played a lesser role in the analysis due to the small shrinkage ratio observed before and after drying.
► Heat and mass transfer analyses were carried out using a 3-D cocoa bean model under stepwise drying condition. ► Results showed good agreement between the experimental and predicted data. ► Shrinkage could be insignificant in the model due to the mild drying conditions.
► The moisture content profile of the cotyledon and testa of cocoa was investigated. ► The moisture content of the testa was higher than the cotyledon at the end of drying. ► The heat pump dryer ...could preserve greater amount of polyphenols during drying. ► Hardness was found comparable to commercial products.
Investigation was carried out to study the drying kinetics of the individual layer of cocoa beans, namely the testa and cotyledon, during heat pump drying. The cocoa beans were dried in thin layer using dehumidified air at 28.2°C, 40.4°C and 56°C. Moisture contents of the bean, testa and cotyledon were recorded during drying. Reduction in moisture content was relatively fast at the testa as compared to the cotyledon in the initial two hours of drying. Subsequent drying showed a crossover region where the moisture content of the testa was higher than the cotyledon. The final moisture content of the testa was found to be higher than the inner cotyledon at the end of drying. This showed that moisture migrated from the cotyledon (lower moisture content) to the testa (higher moisture content) during drying. Although such transfer mechanism seems contradict but this can be further explained by the mass transfer potential concept as postulated by Luikov where the transfer of moisture is due to moisture potential difference instead of moisture content difference. Product quality analyses showed percent retention of cocoa polyphenols ranged from 44% to 73% as compared to freeze dried sample. Bean hardness was found reasonably comparable to the commercial sample and increased with decreasing moisture content.
Studies were carried out to investigate the cocoa drying kinetics and compare the quality of the dried beans produced from sun and artificial hot air drying. Currently, these are the methods commonly ...used by cocoa farmers and plantations to dry cocoa beans. Drying trials were conducted in thin layer using natural sun light and by hot air inside an air-ventilated oven at air temperatures of 60
°C, 70
°C and 80
°C. Comparison was also made against freeze-dried cocoa beans for quality assessment. The quality attributes assessed were colour (
L*,
a*,
b* and hue angle), texture (hardness and fracturability) and polyphenol content (total polyphenols, epicatechin and catechin contents). Theoretical modelling was performed on the drying kinetics using Fick's law of diffusion and to determine the effective diffusivity values. Reasonable values were obtained for the coefficient of determination (
R
2) between the experimental and predicted moisture ratio data (range 0.9845–0.9976). Effective diffusivity values were found within the range reported in literatures (range 1.61
×
10
−10
m
2
s
−1–8.01
×
10
−11
m
2
s
−1). Quality assessment showed significant differences (
p
<
0.05) among the sun dried, freeze-dried and oven dried samples in texture, colour and polyphenol content.
The current study emphasizes on the effects of four drying methods, namely, oven drying, adsorption drying, freeze-drying, and vacuum drying on the total polyphenol content and antioxidant activity ...of unfermented cocoa beans. The comparison of drying kinetics analysis showed that adsorption drying method dried faster than other methods. On comparing the results of total polyphenol contents and antioxidant activity, freeze-drying method showed the optimal results and the lowest values were recorded by oven drying. The sensory analysis of cocoa beans after drying showed low cocoa flavor and high astringency scores.
This research investigated the effects of convective air drying on the quality of raw and cooked chicken breast meats at 60, 70, and 80°C. Raw samples were cut into sizes of 20 mm × 20 mm × 7 mm and ...cooked samples were precooked in hot water and cut into similar sizes. It was observed that cooked samples had a lower initial moisture content and dried faster than the raw samples. The thicknesses of raw samples were observed to increase in the first 2 h due to internal water vapor generation. The rigid structure of the cooked samples resulted in a lower degree of shrinkage compared to the raw samples. Rehydration capacity was lower in the cooked samples, which could be due to the rigid structure resulting from the precooking process. This further reduced the imbibition of water into the sample. Effective diffusivity values were determined in the order of magnitude of 10
−11
m
2
/s and comparable to those from the literature. Hardness values of dried cooked samples were significantly higher (p < 0.05) than the dried raw samples, whereas elasticity was significantly lower (p < 0.05).
Sun drying is perhaps one of the oldest methods of food preservation that has been practiced for centuries. The direct usage of solar radiation which is renewable and abundant favours farmers that ...harvest and process at small quantity. As technology advances, an alternative to sun drying evolves to maximize the potential of solar radiation and this technology is known as solar drying. Solar drying has several inherent advantages over sun drying namely faster drying rate, better protection of products, reduce risk of prolonged drying, lesser risk of product spoilage and improvement in product quality. Various studies have reported the application of solar drying for fruits, vegetables, grains, seeds, beans, herbs, spices and medicinal plants. Product quality improvement is definitely associated with solar dried products as compared to sun dried and to some extent oven/hot air dried products. However, uptake of this technology especially among farmers in developing countries are still low despite the many years of research and technology advancement. Nonetheless, some successful application of solar drying have been reported in countries such as Indonesia, Laos, Zimbabwe, Tanzania, Brazil, Uganda, Kenya and Senegal.
Abstract
Convective drying is typically used to dry shallot (
Allium cepa
) commercially. However, a long drying time with a relatively low efficiency has led to the pursuit of new and improved ...drying methods. Microwave drying was chosen to be used due to its numerous advantages such as improved drying time, high drying efficiency and better product quality. In this research, three microwave power (180 W, 300 W, 450 W) and convective drying at 100°C were used. Results showed that drying kinetics (moisture content and drying rates) decreased the fastest at higher microwave power and the slowest using convective drying. In order to determine the best model to describe the thin-layer drying kinetics, four semi-empirical models were used namely Newton, Page, Logarithmic and Two-term models. Page model was found to be the best in describing the thin-layer microwave drying kinetics. Effective diffusivity values increased with higher microwave power and were found to be in the range of 6.62 × 10
−6
m
2
/s to 3.69 × 10
−5
m
2
/s with convective drying being the lowest (6.62 × 10
−6
m
2
/s) and 450W being the highest (3.69 × 10
−5
m
2
/s). Microwave drying is therefore able to improve drying kinetics compared to convective drying.
Drying is a significant step in the production of carrageenan. However, current drying process still deals with too long drying time and carrageenan quality degradation. The foam mat drying is an ...option to speed up drying process as well as retaining carrageenan quality. In this case, the carrageenan was mixed with egg white (albumin) as foaming agent and methyl cellulose for foam stabilizer. The foam will break the carrageenan gels and creates the porous structure resulting higher surface area for water transfer. This research studied the effect of egg white and methyl cellulose on carrageenan drying at various air temperature, and thickness. As a response, the water content versus time was observed and the drying rate was estimated. Meanwhile, the carrageenan texture was verified by X-RD (X-Ray Diffraction) and TEM (Transmission Electron Microscopy). Results showed that the presence of egg white stablized by methyl cellulose can speed up drying rate as well as retaining the crystalline structure of carrageenan. The higher albumin content, the faster drying rate. However, the addition of albumin and methyl cellulose restricted not more than 30 % in the mixture for keeping carrageenan quality and purity. By adding egg white 20 % and methyl cellulose 10 %, the water diffusion and drying rate can be two fold compared with carrageenan drying without foam. The improvement can be higher at the higher temperature and thinner carrageenan sheets.
Kedondong is an underutilized fruit cultivated in a small scale in Malaysia and it contains nutrients that can be preserved through drying. The dried product can be sold as a premium fruit snack that ...could generate revenue for the producer. We studied the drying of peeled and unpeeled kedondong fruits using hot air (60-80°C). This study aims to investigate the drying kinetics (drying rates and effective diffusivities) of kedondong fruits and model the drying curves using thin layer models. Ten thin layer models were employed and solved using non-linear regression. Drying kinetics showed that only falling rate periods were observed, which implied that internal diffusion was the dominant mechanism for moisture release. Mathematical models showed that Modified Hii et al. (I) and (II) models were able to predict the drying curve well with the highest R2 (0.9992-0.9999), the lowest RMSE (8.0 x 10-4 - 2.5 x 10-3) and the lowest χ2 (4.0 ×10-5 - 2.0 x 10-4). Peeled samples showed higher effective diffusivities (average 3.2 x 10-11 m2/s) than unpeeled samples (average 2.7 x 10-11 m2/s). The activation energy was lower in peeled samples (25.8 kJ/mol) as moisture diffusion could occur more easily than unpeeled samples (32.1 kJ/mol). Results from this study provide kinetic information that can be used in scaling up of dryer and optimizing dryer performances.
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