Effect of heat treating defatted soyflakes on nutrient digestibilities at the end of the small intestine and over the total digestive tract of growing swine

Abstract

The effect of cooking time on nutrient digestibilities of soy-flakes determined at the end of the small intestine and over the total digestive tract of growing pigs was studied. Raw defatted soyflakes, with an initial moisture content of 23%, were cooked at atmospheric pressure for a total of 25, 35, 45, 65 and 105 min in a 57 cm diameter French cooker with a horizontal sweep. Twenty-five min of cooking were required for the soyflakes to reach a temperature of 100C. Soyflake temperatures ranged from 100 to 107C after 25 min of cooking. Soybean meal quality was determined by the following in vitro measurements: trypsin inhibitor activity measured by the methods of Kakade and Hamerstrand, urease activity, protein dispersibility index (PDI), nitrogen solubility index (NSI) and Hunterlab color values L, +a and b. Thirty-six barrows, weighing between 25 and 45 kg initially, were surgically fitted with simple T-cannula at the end of the small intestine and used in 6 experimental periods with 6 different pigs per period. Corn starch-soyflakes diets were formulated to provide .70% dietary lysine. Measured at the end of the small intestine and over the total digestive tract, digestibilities of all nutrients were lower (P < .01) for raw than for cooked soyflakes. Soyflakes cooked for different periods of time had similar digestibilities for nitrogen, amino acids and energy measured at the end of the small intestine and over the total tract. Using least squares procedures, maximum digestibility of nitrogen at the end of the small intestine was predicted to occur at the following levels of in vitro measurements: trypsin inhibitor measured by the methods of Kakade equal to 19.3 ug TI/mg of protein and Hamerstrand equal to 4.0 mg TI/g sample; urease activity equal to .15 (DELTA)pH; PDI equal to 22%; NSI equal to 18%; Hunterlab color values L, +a and b equal to 68, 3.5 and 31, respectively. Hunterlab color values L, +a and b could detect differences in soybean meal quality. Correlation coefficients between in vitro measurements and nutrient composition of soyflakes and nutrient digestibilities were also calculated.