Convective and osmo-convective drying of aloe vera gel
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Date
2008
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MPUAT, Udaipur
Abstract
Aloe vera (Aloe barbadensis Miller), a traditional medicinal plant used in food, pharmaceutical and cosmetic industries. Aloe vera gel contains over 98-99% of water. Gel is normally dried using hot air convectional dryers. A study was undertaken on convective and osmotic-convective drying of aloe vera gel to investigate feasibility of process for making chips/powder with lower energy inputs.
Fresh aloe vera leaves were washed and cut into 12.5 × 12.5 × 12.5 mm cubes. These cubes were osmotically dehydrated in different concentration (30, 40 and 50 ºBrix) and temperature (30 and 50ºC) of syrup for 4 h duration of osmosis. The osmosed and unosmosed aloe vera cubes were dried in tray dryer at 50, 60, 70 and 80ºC drying air temperatures with air flow velocity of 1.5m/s.
The effect of process parameters during osmotic dehydration such as duration of osmosis, concentration and temperature of syrup on mass reduction, water loss and sugar gain were studied. It was found that the mass reduction, water loss and sugar gain increased with increase of syrup concentration and temperature. The water loss and sugar gain during osmosis at 30, 40 and 50 ºBrix was varied in the range of 63.07 to 71.30 and 3.98 to 6.30 per cent at 30 and 50ºC syrup temperature respectively.
It was observed that the moisture content of the product reduced with drying time and no constant rate period was observed during convective drying. The moisture diffusivity varied in the range of 2.69 to 4.59 ×10-09m²/s and 2.93 to 7.99×10-09m²/s during convective drying of unosmosed and osmosed aloe vera samples depending on the drying air temperature. The activation energy varied in the range of 16.46 to 28.13 kJ/mole during convective and osmo-convective drying process. The Exponential, Page, Modified page, Henderson and Pabis, Logarithmic and Power law models were applied to the experimentally obtained moisture loss data. The fit quality of models was evaluated using correlation coefficient (R2), standard errors estimation (SEE), reduced mean square of the deviation χ², mean bias error EMB and root mean square error ERMS. Among the drying models investigated, the Page model satisfactorily described the convective drying behaviour of aloe vera cubes. Air temperature and pretreatment as osmotic dehydration had a significant effect on the rehydration ratio, colour and water activity. The osmo-convective dehydrated samples were found more acceptable than convective dried ones.
Description
Convective and osmo-convective drying of aloe vera gel
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Citation
Pisalkar and Jain, 2008