Effect of two stage, tray and heat pump assisted-dehumidified drying on drying characteristics and qualities of dried ginger

Desorption isotherms for sliced gingers have been measured. A non-linear regression programme was used to fit four moisture sorption isotherm models to the experimental data. The Modified Halsey and Modified Oswin models gave the best fit for X_e = f(RH_e, T) and RH_e = f(X_e, T), respectively. Tray and heat pump dehumidified drying incorporated by single and two stage drying were conducted. It was found that the modified Page model was the most effective. The drying constant was fitted to drying air temperature using the Arrhenius model. Effective moisture diffusivities were determined using the drying data. The heat pump dehumidified drying incorporated by the two stage drying could reduce the drying time at 40 °C by 59.32% and increase 6-gingerol content by 6%. Quality evaluation by 6-gingerol content, rehydration ratio and ΔE* showed the best quality for dried sliced gingers in the heat pump dehumidified drying incorporated by the two stage drying at 40 °C.     

The Development of Ginger Drying Using Tray Drying,Heat Pump–Dehumidified Drying,and Mixed-Mode Solar Drying

Mature ginger was pretreated by soaking in citric acid prior to drying in a single layer in a tray and heat pump dehumidified dryer at three temperatures of 40, 50, and 60°C and in a mixed-mode solar dryer at 62.82°C and a radiation intensity of 678 W/m². The drying data were applied to the modified Page model. Diffusivities were also determined using the drying data. Quality evaluation by color values, reabsorption, and 6-gingerol content showed best quality for ginger with no predrying treatment and dried at 40°C in a heat pump–dehumidified dryer. At drying temperature of 60 to 62.82°C, no pretreated dried ginger from mixed-mode solar dryer provided the shortest drying time and retained 6-gingerol as high as heat pump–dehumidified dryer.     

Changes during storage of dried Moringa oleifera leaves prepared by heat pump‐assisted dehumidified air drying

Moringa oleifera leaves contain phytochemicals that are retained during heat pump‐assisted dehumidified air drying. Changes in phytochemicals, antioxidant capacity and colour were evaluated at 15–35 °C, during storage of dried leaves in polypropylene (PP) or high barrier (PET/Al/PE) packaging for up to 6 months. The a_w of samples in PP increased from 0.373 to 0.669. Decreases in total phenolics were greatest at 35 °C in PP (48%) and least at 15 °C in PET/Al/PE (19%). There were few significant changes in DPPH inhibition after 2 months storage. There was little change in kaempferol and some increase in quercetin. During storage, samples became less green, suggesting breakdown in chlorophyll had occurred. The degradation of flavonoids followed first‐order kinetics. The half‐life for total flavonoids ranged from 2.13 to 1.47 months for samples stored in PP and from 2.59 to 1.83 months for samples stored in PET/Al/PE.     

Solar Drying of Bananas: Mathematical Model, Laboratory Simulation, and Field Data Compared

ABSTRACT: A mathematical model for the solar drying of bananas was developed using a numerical solution procedure to generate a computer simulation. The solution incorporated terms for solar absorption, long-wave emission, natural or forced convection, and evaporation. The model was in good agreement with laboratory results obtained under artificial lights and also field data from researchers in Thailand. The model showed drying to be insensitive to ambient relative humidity but sensitive to factors affecting banana temperature. Reducing exposure to wind was shown to increase banana temperature and so reduce drying time by typically 15%, while also lowering the final moisture content achievable. The results are potentially useful to producers.     

Kaffir Lime Leaf (Citrus hystric DC.) Drying Using Tray and Heat Pump Dehumidified Drying

Desorption isotherms of mature kaffir lime leaves are determined and a nonlinear regression program was applied to the experimental data to fit with any of the four moisture sorption isotherm models. It was found that the modified Halsey model could fit the best. Tray and heat pump–dehumidified drying of kaffir lime leaves were conducted and it was found that the modified Page model was the most effective one. The drying constant was fitted to drying air temperature using the Arrhenius model. Effective moisture diffusivities were determined using the drying data. Heat pump–dehumidified drying reduced drying time and provided dried kaffir lime leaves with higher amount of citronellal than tray drying.     

Moisture Diffusion and Desorption Isotherms for Banana

ABSTRACT: The desorption isotherms for whole peeled banana, convection dried in warm air, have been measured and fitted by the Modified-Oswin and Modified-Chung-Pfost equations. The equations agreed with the water activity observed in commercial sun-dried banana packs from Thailand. The convective drying curves for peeled banana were determined and fitted by the Newton (exponential) and Diffusion models. The Newton model was found more effective, probably due to a surface resistance that develops during drying. The drying constant, K in the Newton model, was fitted to banana temperature by the Arrhenius equation. Moisture diffusivity results agreed with previous work, including the activation energy in the Arrhenius equation.