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Effect of Pretreatments and Packaging on the Growth of Mold in Value Added Dehydrated Onion Products During Storage

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:

Total number of viable mold (TVM) in fresh onion and dehydrated processed onion packed in High density polyethylene (HDPE) and Aluminum foil (ALF) was estimated at 0, 6 and 12 month interval following storage at room temperature (RT, 20-25⁰C) and refrigerated temperature (RFT, 5⁰C). The TVM present per gm of different types of dehydrated onion samples were estimated as cfu/g. Samples tested were fresh onion (S₀), dried onion (S₁), blanched and dried (S₂), blanched + sulphited and dried (S₃), 25% salt osmosed and dried (S₄), 60% sugar osmosed and dried (S₅) and 55/15% sugar-salt osmosed dried onion (S₆). TVM count in the samples varied in ascending order such as S₆, S₃, S₅, S₂ and S_1. Sample S₁ received no pretreatment before drying and gave the highest TVM among the samples and the preservation effect was only due to reduction of a_w during drying. No mold in S₄ and 2 x 10³ to 7.5 x10⁴ in S_1.As a packaging material, ALF gave lower mold count for any sample compared to HDPE at RT or RFT and for a given packaging material RFT gave lower TVM compared to RT for a fixed storage period such as one year.

Keywords: Dehydrated onion, Pretreatment, Mold and packaging material

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

Start Date: 01-05-2009

End Date: 30-12-2009

Program Area: Postharvest and Agro-processing

Commodity: Onion

Objectives:

To find out mold in fresh and dehydrated summer onion during storage.

Methodology:

Onion used in this study were washed and sliced into 5 mm thickness and initial moisture content was determined by oven drying method. Initial weights of each of the slices were taken. Some slices osmosed in 60% sucrose, 25% salt and 55/15% sucrose-salt up to 24 hr and weighed and subsequently individually marked by using different coloured threads. After the end of each definite times 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. The pieces which were used in this study were fresh onion, dried onion, blanching in hot water for 2 min. and dried, blanching and sulphiting with 1500 ppm KMS and dried, immersed into 60% sucrose, 25% salt and 55/15% sucrose-salt solutions and dried. The fresh and processed onion were packed in high density polyethylene (HDPE) and aluminium foil (ALF) and stored at room temperature (RT, 25 ⁰C) and at refrigeration temperature (RFT, 5 ⁰C). The stored dehydrated products (treated and untreated) were observed and analyzed for growth and activity of mold at an interval of 6 months. Mold count: Mold counts of different fresh and dehydrated onions were done following the method as described by Ranganna (1991) and Harrigan (1998).

Preparation of agar media: The media for mold count was prepared by dissolving 200 g potatoes infusion, 20 g dextrose and 15 g agar in conical flask with 1000 ml distilled water. The mixture was then sterilized at 121°C (15 psi) for 15 minutes. Before pouring into Petri dishes the media was cooled to around 40⁰ C. The media kept melted keeping it in hot water bath. About 2.5 ml of 10% tartaric acid was added per 1000 ml of media to reduce pH value to 5.6 ±0.2.

Preparation of ringer solution: 2.15 g of sodium chloride, 0.075 g of potassium chloride, 0.12 g of calcium chloride and 0.5g sodium thiosulphate were taken in a conical flask and mixed with 1000 ml distilled water.

Sample preparation: The reliability of the analysis and interpretation of the results depend largely on the correct manner in which the sample was taken. The sample must be a true representative of the whole mass. For this purpose the product is thoroughly well mixed so that the sample would be the representative of the whole mass of the products. 10 g of well mixed onion were taken in 100 ml volumetric flask and the volume was made up to 100 ml with the ringer solution and mixed well by up-and-down or to-and-fro movement. At the same time to avoid contamination all the apparatus, solutions and other tools used were sterilized by heating in steam at 121° C under 15 psi atmospheric pressure for 15 minutes. The prepared sample which already become diluted to 10 times was used as stock solution. A series of dilution were made using 9 ml blanks and standard plate counts was done.

Source of Information: Bangladesh J. Crop Sci., 25: 55-63, 2014, ISSN 1018-0818

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

For long time storage ALF may be used at RT. The pretreated samples particularly 25% salt osmosed + dried onion, 55/15 % sugar/salt osmosed dried, blanched sulphited dried onion, blanched dried are recommended for drying and storage from microbial stability point of view, cost of osmosis solution etc.

Knowledge Management: Journal