Relationship of two in vitro assays in protein efficiency ratio determination on selected agricultural by-products

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