The effect of screw‐press and hydraulic‐press processing conditions on pigment glands in cottonseed

Abstract

SummaryA procedure is given for estimating the amount of intact pigment glands in cottonseed kernels and meal.The amounts of intact pigment glands, free gossypol, and total gossypol in uncooked meats, cooked meats, and press cake samples from commercial hydraulic‐press mills, a screw‐press mill, and laboratory‐scale tests were determined. It was observed that when meats were cooked with adequate moisture present, as is common in hydraulic‐press mills, most of the free gossypol was converted to bound gossypol during the cooking operation and further conversion during the pressing stage was of slight magnitude. The trend of the change in percentage of recoverable glands was roughly parallel to that of the free gossypol. By contrast, in the screw‐press mill where cooking was carried out without the addition of moisture, little change in either component occurred during cooking, but both were reduced to very low levels during passage of the cooked meats through the screw press.In laboratory tests cooked cottonseed meats were subjected to hydraulic pressures at levels of 2,000 and 20,000 pounds per sq. in. of cake surface. When meats were cooked at low moisture content, no significant change in either free gossypol or recoverable glands occurred during cooking, but hydraulic pressing at both 2,000 and 20,000 pounds per sq. in. reduced the percentage of recoverable glands. No corresponding decrease in free gossypol during pressing could be found. Wet cooking of meats decreased the percentages of free gossypol and intact glands and, although hydraulic pressing failed to further reduce the free gossypol, the percentage of recoverable glands was sharply reduced by pressing at both levels of pressure.It is suggested that the high degree of effectiveness of the screw press in rupturing and disintegrating pigment glands in cottonseed meats is due to the development of shearing forces in combination with direct or compressive type pressure. It is believed that a shearing action is more effective for this purpose than compressive force of similar magnitude.