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Letter to the editor

A process to lower the free gossypol content of cottonseed cakes

The recent "Guideline for Edible Cottonseed Protein Flours and Related Products" (Food and Nutrition Bulletin, vol. 2, no. 3) provided up-to-date information on cottonseed products and processes for their production.

A technical article describing a very simple process to lower the free gossypol content of cottonseed cakes-H. Mayorga, J. Gonzalez, J.F. Menchu, and C. Rolz, "Preparation of a Low Free Gossypol Cottonseed Flour by Dry and Continuous Processing," J. Food Sci., 40: 1270 (1975) was unfortunately overlooked by the experts who prepared the Guideline. The process was developed at the Instituto Centroamericano de Investigación y Tecnología Industrial (ICAITI) and tested on a pilot-plant scale. Unfortunately, because of the fixed price structure existing in Central America for cottonseed products, the industrial consortium that had decided to undertake production on a commercial scale shelved the project until the situation changes. However, we have received inquiries about it from many parts of the world and believe that a description of the process could be of interest to your readers as complementary information to the Guideline.

A laboratory study was carried out to determine the kinetics of gossypol reduction in cottonseed meal mixed with 0.5 per cent ferrous sulphate and 1 per cent calcium hydroxide at several temperatures. It was found that the reaction followed first-order kinetics and that the variation of the rate constant with temperature could be described well with the Arrhenius equation. A similar study was done for the thermal available Iysine destruction in cottonseed meal samples heated for 1 hour at 100°, 125° ,150°, and 170° C. It was found that the available Iysine content decreased significantly after heating for 40 minutes at 170°C. No significant difference was found at lower temperatures.

A pilot plant was built for the continuous processing of cottonseed meal to achieve gossypol reduction. Two arrangements for solids were tested, one using a bag collector and the other using a cyclone separator. The arrangement using the cyclone worked well, while the other method was less satisfactory. Several runs were made at different temperatures and flow rates. It was found possible to obtain a homogeneous product with a final gossypol content of 0.04 per cent. Trying to reduce it further by increasing the temperature is not recommended because of a higher lysine loss. Gossypol reduction was a function of temperature, residence time, initial gossypol content, and amount of chemical additives, but not of meal flow rate.

The dry continuous process has the following advantages over the new technologies that the Guideline makes reference to (liquid cyclone, acetone, membrane, aqueous extraction):

i. it can be adapted to existing commercial processes;
ii. the investment is minimal relative to the alter natives; and
iii. it does not need special solvents, special equipment, or a new plant.

Carlos Rolz
Head, Applied Research Division
Instituto Centroamericano de Investigatión y Tecnología Industrial

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