AGREEMENT BETWEEN THE PROTEIN DIGESTIBILI TY OF ANIMAL AND VEGETABLE PROTEINS MEASURED IN-VIVO AND IN-VITRO AND ITS EFFECT ON THE CHEMICAL SCORE

Protein digestibility is a key factor in the determination of protein quality using the chemical score. Since there are several methods avai lable for determining protein digestibility the purpose of this study was to compare three methods in vitro (pH drop, pH stat and pepsin dig estibility) and two methods in vivo (true and apparent digestibility i n rats) in the determination of the protein digestibility of: casein, soy protein isolate, fish meal, black beans, corn meal and wheat flour . The results showed that in the case of highly digestible proteins al l methods agreed very well. However, this agreement was much less appa rent in the case of proteins with digestibilities below 85%. As a resu lt, the chemical score of these proteins varied substantially dependin g upon the method used to determine its digestibility. Thus, when the chemical score of the proteins analyzed was corrected by the true prot ein digestibility measured in rats, they ranked as: casein 83.56, soy 76.11, corn-beans mixtures (1:1) 58.14, fish meal 55.25, black beans 4 7.93, corn meal 46.06 and wheat flour 32.77. In contrast, when the che mical score of these proteins was corrected by the pepsin digestibilit y method, the lowest quality was assigned to fish meal. In summary, th is results pointed out that for non conventional proteins of for known proteins which have been subjected to processing, protein digestibili ty should be measured in vivo.