Condensed tannin and gossypol concentrations in cottonseed and in processed cottonseed meal

Experimental varieties of cottonseed and of industrial cottonseed meal (CSM) were analysed for extractable and bound condensed tannin (CT) and free gossypol. CT was present in the hulls of all varieties, with higher concentrations recorded for high tannin and glandless selections (55 and 58 g kg-1 DM) than for the multiple host plant resistant and high gossypol selections (38 g kg-1 DM). CT was present in trace amounts in the kernels (meats) of high tannin selections, but was not detected in the kernels of all other selections. Industrial CSM contained 8-15 g kg-1 CT, due to contamination of meats with hull components. On average, for the hulls of all varieties, approximately 22, 60 and 18% of total CT was present in the extractable, protein-bound and fibre-bound forms, respectively. Total CT content in the hulls was positively correlated with the lignin content of kernels (r = 0.67, P < 0.01). Free gossypol was mainly found in the kernels, with negligible amounts being found in the hulls of the experimental varieties. Kernels of high gossypol selections contained higher concentrations of free gossypol (18 g kg-1 DM) than kernels of multiple host plant resistant, high tannin and commercial selections (10-12 g kg-1 DM), with free gossypol concentration being very low (0.8 g kg-1 DM) in the kernels of glandless cottonseed and in Australian industrial CSM. A negative correlation (R = -0.50, P < 0.05) between free gossypol in the kernels and total CT in the hulls was found. The kernels of multiple host plant resistant selections were lower in neutral detergent fibre, acid detergent fibre and lignin, whilst those of the glandless selection were higher in oil, than the mean for all other selections. The results are discussed in relation to plant defence mechanisms against insect attack and in relation to the nutritive value of CSM for ruminant and monogastric livestock.