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Studies on the Rehydration Properties of Dried Green Beans (lablab Purpureus)

M. Shams-Ud-Din
Professor
Dept. of Food Technology & Rural Industries, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

M. Huzur Ali
Graduate students, respectively
Dept. of Food Technology & Rural Industries, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

M. Ziaul Hassan
Graduate students, respectively
Dept. of Food Technology & Rural Industries, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

Abstract/ Executive Summary:

Green beans ( Lablab purpureus ) were sun-dried and dehydrated in cabinet drier. The dried beans were reconstituted in water, one percent salt solution, one percent sugar solution and one percent salt plus one percent sugar solution at different intervals of time. The products were also reconstituted in waters made hard by addition of several concentrations ( 62.5 - 1000 ppm ) of calcium chloride and in distilled water for comparison. Effects were noted as rehydration ratio, co-efficient of reconstitution, moisture contents in rehydrated products and sensory characteristics. Considerable differences were observed as to the effects of the different solvents and water hardness. Noodles prepared with dehydrated green beans showed varied degrees of acceptability with different reconstitution media used for rehydration of the dried products.

Keywords: Green beans, Sun drying, Mechanical drying, Rehydration properties

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

Start Date:

End Date:

Program Area: Postharvest and Agro-processing

Commodity: Lablab bean

Objectives:

To study the reconstitution of dried green beans, obtained from sun drying and mechanical drying procedures, in different solutions (namely salt, sugar and their combinations) and waters made hard by addition of different concentrations of calcium chloride to simulate hard waters.

Methodology:

The tips and stem portions of the green beans were cut-off by knife. The snipped beans were washed and cut crosswise by knife into 2 cm long pieces. The cut beans were blanched for 6 min in boiling water to inactivate the enzyme systems.The blanched beans were soaked in 0.5% potassium metabisulphite (KMS) solution for 5 min using 0.5 kg of KMS solution per kg of the beans to fix up the natural green colour of the beans by preventing enzymatic and non-enzymatic browning reactions. The blanched and sulphited beans were dried in the sun on stainless steel tray with tray load of 0.75 lb/ft² using day temperatures ranging from 26 to 34°C for about 19 hours. The dried beans were packed in medium density polyethylene bags (200 gm per bag) and kept at room temperature until used. For mechanical drying, the previously blanched and sulphited green beans, as done for sun drying, were dried in a cabinet drier (Model No. OV -165: Gallenkamp). A tray load of 1 lb/ft² was used for drying and the drying temperature and the time were 85°C for 1 hr, 70°C for 2.5 hr and 60°C for 4 hr. After drying, the dried samples were cooled, packed in medium density polyethylene bags (200 gm per bag) and kept at room temperature until further studies.Rehydration means refreshing (reconstitution) the dried products in water. Six beakers of each 500 ml capacity were taken and 150 ml of water and 5 grams of dried sample were poured into each beaker. The contents were boiled for 10, 15, 20, 25, 30 or 35 min respectively. Dried samples were added to the water when boiling started and counting of time began after that. It was necessary to add 20-30 ml of extra water for the last two tests to maintain the liquid level than for shorter boiling duration. After the expiry of the calculated boiling time. the liquid portion was drained off and the solid contents were transferred to a 4 inch dia Buchner funnel separately fitted with filter paper and excess water was removed by applying a gentle suction for a few seconds.

Source of Information: Joint IntI. Conf on Agril. Engg. & Tech. Exhibition, '97, Dhaka

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

This study has demonstrated that mechanical drying process significantly increased dehydration ratio. rehydration ratio and co-efficient of reconstitution of dried green beans than those obtained from of sun-dried method. Pre-soaking for 1 hr and boiling of mecahnically-dried sample for 25 or 30 min in water or salt solution improve the rehydration properties of the dried beans than those of boiling in sugar solution or salt plus sugar solution. While sun-dried beans after pre-soaking for 1 hr and boiled with water or sugar solution yielded with improved reconstituted products than the sun drying procedures using same solutions. The mechanically-dried green beans yielded with improved reconstituted products in terms of colour, flavour and texture. Considerable differences were found as the effect of water hardness on the rehydration ratio and co-efficient of reconstitution for both mechanically-dried and sun-dried samples. Studies on the organoleptic properties of mechanically dried green beans when prepared with instant noodles showed that noodles when incorporated with beans reconstituted in 1 % salt plus 1 % sugar solution had significantly overall acceptability than those noodles incorporating beans reconstituted in water, 1 % salt or 1 % sugar solution.

Knowledge Management: Report/Proceedings