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Effect of Osmotic Solution Concentration on Drying Time and Development of Value Added Summer Onion Products

Md. Masud Alam
Senior scientific officer
Spices Research Center, Bangladesh Agricultural Research Institute, Shibganj, Bogura

Md. Nazrul Islam
Professor
Department of Food Technology and Rural Industries, Bangladesh Agricultural University, Mymensingh

Abstract/ Executive Summary:

The osmotic solutions were 60% sugar, 45/15, 50/15 and 55/15% sugar-salt and 15, 20 and 25% salt solution. The immersion time was 6 hr. The drying time (8.52 hr) was found by nonosmosed (fresh) onion and the 2^nd drying time (7.53 hr) is given by 60% sugar osmosed onion and were successively followed by 25% salt osmosed dried onion with 7.45 hr, 20% salt osmosed dried onion with 6.28 hr, 15% salt osmosed dried onion with 5.95 hr, 55/15% sugar-salt osmosed dried onion with 4.96 hr, 50/15% sugar-salt osmosed dried onion with 4.68 hr, while the lowest drying time (4.27 hr) was observed by 45/15% sugar-salt osmosed dried onion. The highest salt content (38.23%) was found in 25% salt osmosed dried onion and the 2^nd highest salt content (34.11%) was given by 20% salt osmosed dried onion while the lowest salt content (17.78%) was given by 55/15% sugar-salt osmosed dried onion. It was also seen that 50/15% sugar-salt osmosed onion gave the highest throughput 4.01 and was followed by 55/15% sugar-salt osmosed with 3.95, 45/15% , while the lowest throughput, 1.94 was given by 60% sugar osmosed dried onion.

Keywords: Osmotic dehydration, Drying time, Value added onion products

Location: Department of Food Technology and Rural Industries of Bangladesh Agricultural University, Mymensingh, Bangladesh

Start Date: 01-01-2009

End Date: 30-04-2009

Program Area: Postharvest and Agro-processing

Commodity: Onion

Objectives:

To find out the effect of different osmotic solutions on drying time and dryer throughput of 5mm thick osmosed onion slices and development of value added summer onion products.

Methodology:

Summer onion used in this study were washed and sliced into 5 mm thickness and initial moisture content was determined by oven drying method. Slices was weighed and subsequently individually marked by using different coloured threads. Pieces were immersed into 15, 20, 25% salt and of 45/15, 50/15 and 55/15% sucrose-salt and 60% sucrose solutions at room temperature (25°C) for different period of times, such as ½ hr, 1 hr, 2 hr, 4 hr, 6hr. After the end of each definite time interval the slices were removed and quickly rinsed in water. Subsequently, surface water was removed by gently blotting with tissue-paper. The ratio of sugar to onion slices was 5:1 w/w. After weighing the slices at definite time interval, moisture content of each individual sample was determined by oven drying method. From the weight loss due to osmotic dehydration of each sample, percentage of water loss (%WL), solid gain (%SG), total solids (%TS) and Normalized solid content (NSC) were determined according to the standard formula reported by Hawkes and Flink (1978).

To analyze the experimental data, Fick’s 2^nd law of diffusion has used (Brooker et al. 1974 and Islam, 1980). Thickness dependence of drying rate was analyzed by plotting ‘log’ of drying rate constant (m) against ‘log’ of sample thickness (L); the relationship was derived from the solution of Fick’s 2^nd law of diffusion (Islam, 1980).

Source of Information: Bangladesh J. Crop Sci., 25: 45-53, 2014

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Higher dryer throughput (2.40 to 4.01) obtained by drying onion in 25, 20, 15 % salt, 55/15 and 50/15 % salt-sugar than non osmosed onion. Higher dryer throughput will reduced cost of production particularly when low cost salt was used as solute for value added onion products. Another advantage in using salt in osmosis solution was that disruption for short period due to power breakdown and inclement weather (for solar drying), might not be disadvantageous towards product stability.

Knowledge Management: Journal