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close this bookFood and Nutrition Bulletin Volume 06, Number 1, 1984 (UNU, 1984, 92 pages)
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View the documentAn old processing method, a new protein food
View the documentThe keeping quality of wheat flour in different packaging materials

The keeping quality of wheat flour in different packaging materials

M. Bhattacharjee and N. G. Bhole
Harvest and Post-Harvest Technology (ICAR) Scheme, Post-Harvest Technology Centre, Indian Institute of Technology, Kharagpur, India

INTRODUCTION

The quality of food either obtained from the store or preserved in the home is of prime importance to the consumer. Food packaging is the vital step to ensure product quality because it provides protection against deterioration and damage during storage, transportation, and distribution. Consumers now prefer buying products in unit packages. The criteria for quality in packaged food products include availability of wholesome, clean, unadulterated food items with minimal losses during transport, hygienic conditions, and a reasonable price for the consumer. Although packaging has no direct relation with production, storage, marketing, and distribution, it plays an important role in the safety and quality of the product once it reaches the consumer.

The present investigation was carried out to find the most suitable packaging unit for maintaining proper shelf-life of wheat flour, based on its acceptability to consumers. This is part of a research study done under the Harvest and Post-Harvest Technology Scheme of the Indian Council of Agricultural Research (ICAR) at the Post-Harvest Technology Centre, Indian Institute of Technology, Kharagpur, West Bengal.

METHODS

Flour from the Sonalika variety of wheat was chosen for the experiment. It was stored in polythene (400 pm), polythene impregnated jute, and jute bags for a period of 56 days, during which the following observations were recorded. Moisture content was determined by keeping a 25 9 sample of flour in an air oven at 130° C + 2° for one hour; the sample was then cooled, placed in a dessicator, and subsequently weighed (1). Relative humidity of the atmosphere was recorded by dry and wet bulb thermometer and was computed from the psychometric chart. Free fatty acid in the extracted wheat flour was determined by titrating it with methanolic caustic potash solution using thymol blue as the indicator (2). Insect infestation was observed only by eyesight: larvae and insects were counted in the bags while samples were being taken for the other analyses.

RESULTS AND DISCUSSION

The results of the experiment are summarized below.

Moisture content: The initial moisture content of 10.7 per cent (dry basis) increased in each type of bag with longer storage time (fig. 1). In the polythene bag, the moisture rise was within the safe limit (about 11.5 per cent) for up to 21 days, and in the polythene-impregnated jute bags it remained at a tolerable limit (about 13 per cent) under the same conditions. However, moisture in the flour stored in jute bags rose above the safe limit to 14 per cent.

Relative humidity. The rise in moisture content in the stored flour was parallel to that of the relative humidity (table 1). The highest relative humidity value (97 to 98 per cent) occurred within 28 to 35 days of storage, the point at which deterioration began, since a moisture content of 14 per cent or higher favours microbiological spoilage (3). Mahadevaiah and coworkers also reported that a lower initial moisture content (8.8 per cent) in wheat flour at a relative humidity of 65 per cent permits good storage. In the present investigation both the initial moisture content (10.75 per cent) and the relative humidity were much higher than the critical level, indicating that spoilage started quite a bit earlier.



FIG. 1. Influence of Storage Period on Moisture Content of Wheat Flour Stored in Different Packaging Materials

TABLE 1. Changes in Relative Humidity during Storage

Period (days) Average Relative Humidity (%)
Maximum Minimum
0 94.25 41.25
14 94.83 42.17
21 96.00 47.83
28 97.67 62.00
35 98.17 67.67
49 87.20 36.80
56 84.75 39.25

Free fatty acid: Development of free fatty acid in the flour stored in the three types of bags is shown in figure 2. The initial free fatty acid of 1.8 per cent rose sharply to about 7.6 per cent in flour stored in the jute bags but to only about 3 per cent in the polythene bags after 28 days of storage. The steady increase in free fatty acid in various types of wheat stored in different bins has already been reported (4). The latter study also indicated that the rate of increase in warmer surroundings was approximately twice that in cooler conditions.

Insect infestation: Infestation of the wheat flour by insects is shown in table 2. In the polythene bags the product remained safe for up to 35 days, while in the polythene impregnated jute bags it started deteriorating. Flour in the jute bags was unacceptable by day 56 because of severe infestation. The greenish-yellow to green colour, musty appearance, lumps, and obnoxious flavour and odour in the flour stored in jute and polythene-impregnated jute bags after 49 days of storage were probably due to formation of fungi and moulds (3, 4).

It is worth noting the relative cost of the packaging materials used in the experiment. The jute bags cost Rs 15 per quintal of flour stored, the polythene-impregnated jute bags Rs 21.50 per quintal, and the polythene bags Rs 18 per quintal.



FIG. 2. Influence of Storage Period on Development of Free Fatty Acid in Wheat Flour Stored in Different Packaging Meterials

TABLE 2. infestation of Wheat Flour and Condition of the Bags Used for Storage

No. of Days Polythene Bag Polythene-Impregnated Jute Bag Jute Bag
0 No infestation No infestation No infestation
14 No infestation No infestation No infestation
21 No infestation No infestation A little clot formation observed
28 No infestation A little clot formation observed Trace of infestation with moderate clot formation
35 No infestation Moderately infested; some larvae also found in bag Many larvae, heavy infestation; musty odour, lumpy appearance
49 Very little clot formation observed Heavy infestation, fungal attack, and polythene lining bored through; musty odour, yellow-green colour Heavily infested and heavy fungal attack; must odour, green-yellow colour
56 Very little infestation Heavily infested by larvae and insects; obnoxious odour, green-yellow colour Heavy fungal attack; light green colour; material rejected for consumption

CONCLUSIONS

From the standpoint of insect infestation and the development of free fatty acid in stored wheat flour, it is recommended that it can be stored safely in polythene bags for a period of up to 35 days, in polythene-impregnated jute bags up to 21 days, and in jute bags only up to 14 days.

ACKNOWLEDGEMENTS

The authors are grateful to Mr. K. K. Mishra, Junior Laboratory Assistant, HPHT (ICAR) Scheme, for his constant assistance during the investigation analyses. Thanks are also expressed to ICAR for financial support for the project.

REFERENCES

1. Association of Official Analytical Chemists, Determination of Moisture Content, W. Horowitz, ed. IAOAC, Washington, D.C., 1970), p. 211.

2. Association of Official Analyticl Chemists, Free Fatty Acids in Crude and l?efined Oils, W. Horowitz, ed. (AOAC, Washington, D.C., 1970), p. 446.

3. B. Mahadevaiah, K. R. Kumar, and Balasubrahmanyam, "Packaging Studies on Pulses and Cereal Flours in Flexible Films," Indian Food Packer, 1-7 (1977).

4. S. W. Pixton, S. Warburton, and S. T. Hill, "Long Term Storage of Wheat: 111. Some changes in the Quality of Wheat Observed during 16 years of Storage," J. Stored Prod. Res., II: 117 11975).

CLINICAL NUTRITION SYMPOSIUM

The Second International Clinical Nutrition Symposium will be held in Sydney, Australia, 3-5 October 1985. Those interested in participating should write to:

Prof. A. Stewart Truswell
Human Nutrition Unit
University of Sydney
Sydney, NSW 2006, Australia

or

Prof. Mark L. Wahlqvist
Department of Human Nutrition
Deakin University
Victoria 3217, Australia