Gossypol

Gossypol is a plant antinutritive that would probably have remained unnoticed as a food hazard, if the seeds of the plant concerned had not gained importance as a dietary oil and protein source, especially in tropical and subtropical countries. This antinutritive is a yellow pigment present in all parts of the cottonplant. The highest levels are found in cottonseed.

Gossypol exists in three tautomeric forms (Figure 3.2): phenolic quinoid tautomer (I), aldehyde (II), and hemiacetal (III).

HCOH OH

OH HCOH

HCOH OH

OH HCOH

CHO OH

OH CHO

CHO OH

OH CHO

CH3 II H3C CH3

CH3 II H3C CH3

HCOH O

O HCOH

HCOH O

O HCOH

CH3 III H3C'

CH3 III H3C'

Gossypol

Figure 3.2 The three tautomeric forms of gossypol.

Gossypol is an antimineral as well as an antiprotein. It forms insoluble chelates with many essential metals, such as iron, and binds to amino acid moieties in proteins, espe-

cially to lysine. The protein binding suggests that gossypol can reduce the availability of food proteins and inactivate important enzymes.

Processing removes 80 to 99% of the gossypol. The pigment is extracted with the oil and subsequently removed by refining and bleaching. About 0.5 to 1.2% of the total gossypol generally remains in the processed meal. Less than 0.06% is free gossypol. The free gossypol concentration in cottonseed meal can also be lowered considerably by the formation of insoluble metal-gossypol complexes. The use of additives such as FeSO4 and Ca(OH)2 prevents the reaction of gossypol with lysine, even during heat treatment. Breeding of cotton with gossypol-free seeds has been succesful and this cotton variety is now planted commercially. In the US, the maximum allowable gossypol content of cottonseed products for use in human food has been set at 0.045%.

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