Definition, composition and methods of analysis for vegetable and animal proteins competing with milk proteins.
1995
Viroben G.
In the animal or human feeding field, protein content of raw materials and elaborated products is estimated from nitrogen determination at which a conversion factor is applied. For a given product, this factor depends especially on amino acid composition, but also non-protein (NPN) content. Therefore, there is some doubt about the protein content owing to the lack of precision in the different determinations required: total nitrogen (variations due to the mineralization step), amino acids (variations due to the hydrolysis step), NPN (variations due to extraction step). Even though there is an official method for nitrogen determination (Kjeldhal method), no reference method is yet available either for amino acids or for NPN. This fact explains the variability of the conversion factor used for protein estimation. According to the origin of the product, it may change from 5.3 to 6.4. Nevertheless, in trading relations, a single factor is required, but it may favour some protein sources rather than others. In a first part, the main characteristics (protein fractions, limiting amino acids, calculated conversion factor, digestibility) are given for vegetable and animal protein sources, pointing out those competing with milk proteins both in animal (calf, pig) and human nutrition. It is proved that the conventional factor 6.25, usually used in animal feeding, favours vegetable proteins compared with animal ones. In a second part, the NPN problem is discussed for qualitative and quantitative aspects according to the different extraction procedures available. With a 25 per cent ethanol extraction followed by utrafiltration, NPN appears slightly higher for vegetable proteins. Amino acids in the free form and small peptides would represent 10-30 per cent of NPN, regardless of the type of protein.
Afficher plus [+] Moins [-]Mots clés AGROVOC
Informations bibliographiques
Cette notice bibliographique a été fournie par Wolters Kluwer
Découvrez la collection de ce fournisseur de données dans AGRIS