THIN LAYER DRYING STUDY ON FOAMED AONLA PULP
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Date
2011-09
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jau,junagadh
Abstract
Indian gooseberry (Emblica officinalis Geartn. Syn. Phyllanthus emblica L.) fruit, commonly known as Aonla or Amla is one of the oldest minor fruits of India.The ascorbic acid content of fresh Amla fruit can range from 500 to 1500 mg per 100 gm of pulp, which is said to be highest among all fruits next only to Barbados cherry. The fresh Aonla fruits are not popular as a table fruit due to their high astringency taste. Its storability after harvesting is also limited due to its high perishable nature. But it has a great potential in processed forms.
Generally, drying rates are comparatively higher in foamed pulps because of increased surface area at the liquid-gas interface thus allowing rapid drying through internal moisture movement within the pulp. The dehydrated powder/flakes are superior to drum dried and spray dried products because of its honeycomb structure and better reconstitution properties.
The Aonla pulp was prepared and foam was produced using two foaming agents i.e. Glycerol monostearate (5, 10 and 15 %) and Egg albumin (5, 10 and 15 %), while methylcellulose (0.5 %) was used as a stabilizing agent throughout the experiment. For getting uniform foam and its proper expansion, the Aonla pulp was whipped with hand blender for 25 minutes for all the treatments and replications were taken. Thereafter, each treatment sample was analyzed for the determination of foaming behaviour for all the treatments undertaken in terms of foam expansion, foam stability and foam density
Amongst both the foaming agent (Egg albumin and Glycerol monostearate) at all the concentration taken (5%, 10% and 15 %) and whipping time (5, 10, 15 20 and 25 minutes), Glycerol monostearate with 10 % concentration gives the maximum foam expansion as 142.00 %, after 15 minutes of whipping, maximum foam density (0.42 g/cm3) and maximum foam stability (70.59 %) amongst all the foam characteristics treatments. Hence the further research was carried using Glycerol monostearate with 10 % concentration.
The foamed Aonla pulp was dried in Industrial tray dryer. The drying was carried out in three level of temperature (50, 60 and 70 °C) and three level of thickness (4mm, 6mm and 8 mm). The observations on reduction in weight were taken regularly with increase in time during the experiment. All the drying runs were evaluated in terms of drying characteristics.
The Exponential model and Modified Page’s model which are commonly used grain models were tested for their validity to foamed Aonla pulp drying. For all the drying treatments taken the value of drying constants k and n were varying from 0.06 to 0.56 hr-1 and 1.73 to 2.62 respectively. Considering the average drying rate, drying time, drying constant, fitness of models and cost of drying, foamed Aonla pulp should be dried at 60 °C air temperatures with either 6 or 8 mm thickness of foam.
From the observations on functional properties it was observed that lowest solution time (39.77), maximum solubility (60.00 %) and maximum water holding capacity (355.0 %) was found in the powder produced with 50 0C and 4 mm thickness, 60 °C with 6 mm thickness and 60 °C with 8 mm thickness. Both the maximum bulk density (0.41 g/ml) and minimum porosity (13.79 %) was found in the samples prepared by drying at 60 0C temperature with 8 mm and 6 mm foam bed thickness respectively indicating good quality powder. The foam dried Aonla powder obtained from the different treatments was biochemically analyzed in terms of moisture content, pH, ascorbic acid, titratable acidity and ash content.
The foam dried Aonla powder obtained from the different treatments was stored at room temperature in plastic coated aluminum foil bag. During storage different observations in terms of moisture content, ascorbic acid, visual colour change and microbial count were recorded at 15 days interval for 2 months. The samples of powder dried at 50 °C inducing microbial growth even during the short term storage of two months and therefore the drying temperature should be more than 50 °C.
From the analytical and statistical observations it was concluded that for effective drying and quality retention during the foam drying of Aonla pulp, foam of Aonla pulp should be produced by using Glycerol monostearate with 10 % concentration as foaming agent added with methylcellulose (0.5 % concentration) as stabilizing agent followed by 15 minutes whipping and then the produced foam of Aonla pulp should be dried at 60 °C air temperature with 6 or 8 mm bed thickness in tray dryer.
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agriculture