Abstract
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. Keywords: Processing, roasted soybean grain, rumen undegradable protein
Highlights
Soybean seeds contain 19.2% oil and 39.2% protein (NRC, 2001)
The particle size decreased with increased roasting temperatures and holding times, because soybeans roasted at 145 oC or held for 15 min in the roaster had lower mean particle size (MPS) compared with other roasting temperatures and holding times
dry matter (DM), organic matter (OM) and neutral detergent insoluble CP (NDICP) were increased and neutral detergent fibre (NDF) and acid detergent insoluble CP (ADICP) were decreased in the roasted soybean, in comparison with the raw soybean
Summary
Soybean seeds contain 19.2% oil and 39.2% protein (NRC, 2001). Soybean is regarded as an economical and convenient source of dietary fat and protein (Dhiman et al, 1997). Raw soybean contains several anti-nutritional factors that reduce its nutritional value, among which are antitrypsin, urease and hemagglutinins. To eliminate these anti-nutritional substances, soybean seeds are processed. Heating results in cross linking between the peptide chain (free amino acid groups) and carbohydrate (sugar aldehyde groups), decreasing protein solubility and increasing the rumen bypass protein (Reddy et al, 1993; Dhiman et al, 1997). The processing temperature must be controlled carefully to ensure that the beans are heated sufficiently to eliminate anti-nutritional factors, but not excessively as this could increase processing costs and reduce protein quality. High temperatures damage the nutritional value of soybean seeds, because they reduce the degradability of protein in the rumen and small intestine (Reddy et al, 1993)
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