Effects of roasting and extruding heat processes on chemical composition, degradability fractions and intestinal digestibility of dry matter and crude protein of whole soybeans

This research was undertaken to evaluate the effects of roasting and extruding heat processes on chemical composition, nitrogenous fractions, urease activity, metabolic protein, properties of degradability, and the ruminal- intestinal digestibility of dry matter and crude protein of raw and processed soybeans.

This study was carried out at the Research Farm, Faculty of Agriculture, University of Birjand, Iran. During the extrusion process, soybeans were affected for 20-30 seconds at 150-160°C in the extruder by heat and pressure and finally were dried and cooled. In the process of roasting, the soybean for 15 minutes at temperature of 145°C was heated and for 45 minutes holding tank for heat storage remained. Seeds were dried and cooled by air flow, dry and cold. Approximate analysis of samples including dry matter, crude protein, crude fat and ash was determined by AOAC. The urease activity of raw and processed soybean was determined based on ISO-3896. Degradability parameters of the samples were measured after incubation for 0, 2, 4, 8, 16, 24 and 48 hours in the rumen of two fistulated Brown Swiss cows. Also, ruminal and post ruminal digestibility were determined with the incubation of samples for 12 hours in the rumen by Daisy system. The DM and CP degradation data were fitted by exponential equation: P=a+b (1-e–ct). Effective degradability (ED) were calculated using of equation ED = a + {(cb)/(c + k)} and taking into consideration passing rate (k) 0.04, 0.06 and 0.08 per hour.

The findings of the present research revealed that roasting and extruding heat processes lead to increase of dry matter through decreasing water content and that it had no significant effect on other chemical composition. The findings showed that the process of roasting and extruding caused the amount of actual protein of the soybean to increase and was not effective on the amount of insoluble nitrogen in neutral detergent of the soybean. The non-protein nitrogen and nitrogen dissolved in the buffer soybean under the influence of roasting and extruding decreased. The amount of acid detergent insoluble nitrogen soybean decreased which might be due to the removal of some of the shells in the processing soybean has taken place or influence of roasting and extruding decreased. The urease inhibitor of the soybean became inactive by the process of roasting and extruding. Consequently, it caused intestinal protein digestibility to increase and affected by thermal process, the amount of metabolic protein of the soybean increased significantly, too. The process of roasting and extruding reduced the rapid part degradation of dry matter of the soybean (6.27 and 4.57 percent, respectively). Also, process of roasting and extruding caused the slow part of degradation to increase (of 63.75 to 74.73 and 63.25 to 85.82 percent, respectively). In addition, the rate constants degradation of dry matter of the soybean in rumen decreased (of 6.66 to 4.21 and 6.09 to 4.74 percent) under the influence of roasting and extruding. The process of roasting and extruding reduced the rapid part degradation of crude protein (38.4 and 68.4 percent, respectively) and the slow part of degradation to increase (17.3 and 26.1 percent, respectively), the rate constants degradation of crude protein of the soybean decreased (ranged from 7.61 to 3.79). Also, thermal processes reduced effective degradability of dry matter and crude protein of the soybean. Roasting and extruded with the reduction of the amount of ruminal disappearance and the increase of the post ruminal digestibility of dry matter and crude protein of soybean cased the degradability process of the soybean to be improved so that it transferred the place of the digestion of protein from the rumen to the small intestines and cased the amount of digestible of dry matter and crude protein in the intestine to increases. The increase of digestibility in the total digestive system shows that the reduction of ruminal digestion of soybean affected by the processes of roasting and extruding has been compensated by the increase of post ruminal digestibility.

The experiment results indicated that thermal processes of roasting and extrusion were an appropriate strategy for reduction the ruminal degradability of the soybean and the supply of passing protein needed by high milk producing dairy cows.