Aloe vera (Aloe barbadensis Miller) cubes of 12.5 × 12.5 × 12.5 mm thick were osmosed for 4 h in sugar syrup of 30, 40 and 50°Brix concentration and temperatures of 30 and 50°C at constant syrup to fruit ratio of 5:1. Osmosed and unosmosed aloe vera samples were hot air dried at 50, 60, 70 and 80°C with constant air velocity of 1.5 m/s. The water loss, solid gain and convective drying behaviour were recorded during experiments. It was observed that water loss and solid gain ranged from 39.2 to 71.3 and 2.7 to 6.3%, respectively during osmo-drying. The moisture diffusivity varied from 2.9 to 8.0 × 10−9 m²/s and 2.7 to 4.6 × 10−9 m²/s during air drying of osmosed and unosmosed aloe vera samples, respectively. Drying air temperature and osmosis as pre-treatment affected the water loss, solid gain, diffusivity at −p ≤ 0.01
The effect of different pre-treatments (i.e. osmotic dehydration in 10, 15 and 20°Brix NaCl solution and drying air temperature of 50, 60 and 70°C) on drying behaviour of onion slices were investigated. The onion slices were dried in a laboratory model tray dryer. Drying of onion slices occurred in falling rate period. Five thin-layer drying models (Exponential, Page, Henderson and Pabis, Logarithmic and Power law) were fitted to the moisture ratio data. Among the drying models investigated, the Page model satisfactorily described the drying behaviour of onion slices. The effective moisture diffusivity of pre-treated samples was higher than that of non-treated samples
Background
The study of sorption isotherm is the most important for prediction of shelf life, selection of packaging materials, drying characteristics, etc., of any food and agricultural materials. Gum is hygroscopic in nature, so finding of moisture sorption is crucial. Equilibrium moisture content of babool gum at 30, 40, 50 and 60 °C temperatures under relative humidity ranging from 11 to 95% was determined.
Results
Maximum equilibrium moisture content (EMC) of babool gum (33.6%, db) was recorded with the set of highest relative humidity (92.3%) at lowest temperature (30 °C), and minimum (2.8%, db) was obtained with the set of lowest relative humidity (10.9%) at highest temperature (60 °C) under the experimental conditions. The EMC data were employed in five well-identified sorption models, namely GAB, Iglesias and Chirife, Caurie, Halsey and BET model. GAB model best interpreted the data in a reasonable way as per statistical parameters of goodness of fit. The monolayer moisture content Mo was found to be 8.46 and 7.49 g/100 g at 30 and 60 °C, respectively.
Conclusion
The sorption behaviours of babool gum were classified as type-II curves. It was obviously perceived that the isosteric heat decreases with the boost in moisture content.
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