Determination of Chemical Composition and Protein Quality of Different Commercial Samples of Soybean Meals and Corn Gluten Meal Using Biological and Chemical Assays

Introduction Plant protein sources have important role in supplying crude protein and amino acids in poultry diets and soybean meal (SBM) and are used widely in the world, including Iran. Domestic production of SBM is relatively low and most of the meal is imported from abroad. Although protein content of SBM is measured at local labs but evaluation of its protein quality is less considered and is necessary to be monitored by chemical and biological assays. Corn gluten meal (CGM) is a co-product of corn and obtained during production of starch and glucose from corn. This meal is frequently contained more than 50 percent crude protein as such is compared with the animal proteins during diet formulation.
The aim of this study was to determine of chemical composition and protein quality of some commercial samples of soybean and corn gluten meal.
Material and methods Three commercial samples of soybean meal including Brazilian, Argentinean, Iranian and one sample of corn gluten meal were provided from poultry feed plants in East Azerbaijan province. The samples were subjected to chemical analysis by standard methods and protein quality was evaluated by in vitro and in vivo assays. Urease activity index and protein solubility in KOH was used as in vitro assays. For biological evaluation of protein quality of soybean and corn gluten meal samples, 100 Ross-308 male broiler chicks fed in a completely randomized design with 5 experimented diets each 4 replicates from age 8 to 17 d with nitrogen –free basal diet and 4 semi-purified diets each of test protein samples. Feed intake and weight gain of chick after 6 h fasting was recorded and Protein efficiency ratio (PER) and Net protein ratio (NPR) was calculated according to the corresponding formulas. At end of 17 of age, two chicks in each replication was killed, blood serum collected for uric acid, total protein and glucose assessments. Breast muscles was also separated and weighted. The data was subjected to normality tests and statistically analyzed with GLM procedure of SAS.     
Results and Discussion The results of chemical analysis showed that average value of moisture, CP,EE and ash were 7.5, 7.4, 7.4, 4.7 and 46.3, 47.4, 46.4 , 65.5 and 8.6, 9.05, 12.4, 7.55 and 6.5, 6.5, 6.5, 2.15 percent in Argentinian, Brazilian, Iranian soybean and corn gluten meals, respectively. Generally, our finding on CP content was in range of CP content of soybean meal from United States, Brazil, Argentina and India (47.3, 46.9, 48.2, and 46.4% (as-fed basis), respectively). Average values of NDF and ADF were 10.93, 12, 10.43, 11.12 and 8.3, 10.9, 9.4, 10.34 percent in Argentinian, Brazilian, Iranian soybean meals and corn gluten meal, respectively.  Our data on NDF values of soy bean meal in samples of Argentina and Brazilian was higher than those values in the corresponding samples. Gross energy value for soybean meals from Brazil, Argentina, Iran and corn gluten meals were found to be 5095, 4677, 4985 and 5924 Kcal/Kg. Urease index and protein solubility in KOH for Brazilian, Argentinian and Iranian soybean meals was 0.05, 0.05, 0.07 and 88.39, 85.51, 86.82 percent, receptivity. The published acceptable data for urease index are inconsistent and generally the recommended value is less than 0.1 pH change. At present study, all value of urease index is lower than 0.1 values. KOH solubility values at this study on soy bean samples are higher than those, however, these values are acceptable from view of Araba et al and non-acceptable. The values of  PER and NPR for soybean meals from Brazil, Argentina, Iran and corn gluten meal in 17 d assay were 2.89, 3.13, 2.57, 0.36 and 3.48, 3.74, 3.14, 1.37, respectively. These biological values were comparable with PER and NPR values of different origin soybean meals. Breast muscle growth and serum blood uric acid level did not show significant difference in the meals.
Conclusion It was concluded that protein quantity and quality of domestic soybean meal was comparable with two imported samples. NDF value of domestic soybean meal, like foreign ones, is high and this can decrease its available energy and AA. CGM was rich in protein content but poor in view of protein quality.