NUTRITIONAL CHARACTERISTICS OF
DIFFERENTLY PROCESSED VARIETIES OF BACTERIAL PROTEIN MEAL
H.F. Schoyen, J.R.K. Froyland, S. Sahlstrom, S. Knutsen, A. Skrede
Bacterial protein meal grown on
natural gas shows promise towards use as protein source in fish
feeds. Several product varieties, with different nutritional features, have
been developed from basic bacterial protein meal (BBP). Differently
processed varieties of BBP were investigated in terms of
chemical characterization of the protein fraction and digestibility, using
mink (Mustela vison) as model animal. BBP, autolysate,
autolysate extract, hydrolysate, and the insoluble rests of
the latter two, revealed great differences in protein solubility and molecule
size. Crude protein (CP) content varied from about 54 to 73%, but amino acid
composition
of the CP was similar. True digestibility of CP in BBP, autolysate and the
hydrolysate rest was about 85%, while digestibility of CP in autolysate
extract and hydrolysate was significantly higher (93.1 and 98.7%, respectively). The
digestibility of the autolysate rest CP was significantly lower (77.1%)
than that of BBP. There was a relationship between protein digestibility and
protein molecule size, i.e. reduced size of protein molecules resulted
in higher digestibility. Arginine and lysine in BBP showed high
digestibility ('94%) while phenylalanine, tryptophan, cysteine and tyrosine
were rather poorly digested (-80%).
The hydrolysate and the autolysate
extract revealed very high digestibility of all amino acids.
(Department of Animal and
Aquacultural Sciences, The Agricultural University of Norway, P.O.
Box 5025, N-1432 As, Norway, e-mail: hilde.faaland-schoyen@iha.nlh.no)