Effect of Drying Temperature on Nutritional Quality and Availability of Amino Acids in Normal and Opaque-2Corn for Rats

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Abstract
Four experiments with weanling rats were conducted to determine the effect of increasing drying temperature on (1) the nutritional quality of corn protein and (2) the availability of several amino acids (AA), especially lysine and tryptophan. A comparison of methods for calculating AA availabilities using growth, plasma AA and fecal AA responses was also made. Normal (NC) and opaque-2 corn (OC) with initial moisture levels of 28 and 21%, respectively, were dried at 50, 75, 100 or 125 C to a moisture level of approximately 12%. These corn treatments were fed along with naturally dried and prolong-dried (50 C, 42 hr) corn to rats. A marked decrease in the quality of corn was observed with increasing drying temperatures. Prolonged drying at 50 C was as detrimental to protein quality and AA availabilites as was drying at 125 C. The nutritional quality of NC was impaired to a greater extent than that of OC at all temperatures, apparently due to the higher initial moisture of NC. The availability of all AA decreased with increasing drying temperatures. The AA most affected by drying temperatures was lysine which showed losses of 22 and 11% in NC and OC, respectively, when corns were dried at 125C. Comparable losses of available lysine were noticed with prolonged heating at 50 C. The next essential AA affected most of drying temperature in decreasing order (same order in both corn varieties) were: threonine, isoleucine, methionine, valine, tryptophan, phenylalanine and leucine. Among the non-essential AA, glycine was the most and glutamic acid the least affected by drying temperature. No difference in true nitrogen digestibility of corn due to treatment of drying or corn variety was observed. Average nitrogen digestibility was 91.8 and 90.6% for NC and OC, respectively. The results obtained for AA availabilities using growth, plasma AA or fecal AA parameters indicated that the fecal method was more convenient and produced more reliable results than the other two. Copyright © 1978. American Society of Animal Science . Copyright 1978 by American Society of Animal Science.