Suthaya Phimphilai, Ronald D. Galyean, and Foster B. Wardlaw

pp. 81 - 87

Abstract

Utilization of agricultural by-products as food and feed has been of increasing interest. Protein is a crucial nutrient obtained from those sources. However, in vivo method (a rat study) for protein efficiency ratio (PER) determination is time consuming and expensive. C-PER and DC-PER are in vitro assays, which
involve mathematical calculations using amino acid information from the sample. These two methods have been proven suitable for predicting protein quality of various samples with high correlation to the in vivo assay. Rapid prediction with less cost is the advantage of these methods. Theoretically, C-PER and DC-PER
of each sample should have high correlation as they are computed from the same amino acid information. However, the efficiency of the methods is probably based on a range of certain information, especially protein digestibility. This study was conducted to demonstrate one of the limitations of the in vitro assays as shown
in selected agricultural by-products. Three categories of selected agricultural by-products were feed-grade egg product (FGEP; 8 samples), distillers' dried grain (DDG; 4 samples), and defatted wheat germ (DWG;8 samples). Protein contents, amino acid profiles, in vitro protein digestibility, C-PER and DC-PER were
determined. Proteins in FGEP categories were significantly higher (P<0.05) than DWG and DDG, respectively. Both C-PER and DC-PER of all samples showed high correlation except in DWG-424. The low correlation in DWG-424 may be due to its low protein digestibility. It may also indicate the limitation of C-PER assay. The assay therefore may not be suitable for samples with low protein digestibility