Effects of temperature, heating time and particle size on values of rumen undegradable protein of roasted soybean

Roasted soybeans are commonly used in diets for dairy cows, but the processing conditions of roasted soybean and their effects on rumen undegradable protein (RUP) have not been fully understood. In this study, the effect of the processing of roasted soybean on RUP was examined through a factorial arrangement of treatments. The effects of roasting temperature (115 oC, 130 oC and 145 oC), time of roasting (5, 10 and 15 min) and particle size of soybean (whole, coarse and fine) on the protein fractions of roasted soybean were analysed with the Cornell Net Carbohydrate and Protein System (CNCPS) and protein dispersibility index (PDI) methods. The whole, coarsely ground and finely ground soybean had mean particle sizes of 5.30 mm, 1.15 mm and 1.05 mm. The proportion of soluble protein was reduced with increasing temperature and time of roasting. The true protein with intermediate rates of degradation decreased with escalating temperatures, but increased when the time was raised and the particle size reduced. Also, the true protein level with slow rates of degradation was raised with increasing temperature and heating time, but reduced when decreasing the particle size. The undegradable true protein level, on the other hand, was increased by decreasing the particle size. The results of CNCPS and PDI revealed that the recommended method would be to use soybeans with a particle size of 1.15 mm, and to roast them at 115 oC for 10 minutes. Furthermore, the results showed that different methods of processing used in soybean roasting could strongly affect RUP content. _______________________________________________________________________________________