406
0. B. COWEY AND J. R. SAROENT
and P is the per cent protein calories in the diet. I n the absence of
standard conditions for determining NPU by fish, equations of this
type for different food proteins might provide the best relative measure
of their quality for fish,
The relative protein quality for plaice of a selection of feedstuffs is
shown in Table V. NPU was measured at dietary protein levels of 50%
by weight. The proportion of dietary calories present as protein was
similar in all cases. The interesting features are the relatively high
value of the single cell protein (B.P. protein concentrate) and the low
value for the fish protein concentrate (a commercial product, probably
a solvent extracted fish meal).
TABLE V. NET PROTEIN UTILIZATION (NPU) OB
SOME FEEDSTUFY PROTEINS BY PLAICE
Food protein
yo protein calories in N P U
the diet fed
Freeze dried cod muscle
76
42
B.P. protein concentrate
White fish meal
73
34
Promine D (Soya protein
A commercial sample of a fiah protein
(supplemented With methionine)
69
38
supplemented with methionine)
76
33
concentrate
76
23
Protein content of all diets was 60% by weight (Cowey, Adron and Blair,
unpublished data).
TABLE VI. NET PROTEIN UTILIZATION (NPU) OF PROTEIN MIXTURES BOR
RAINBOW TROUT SHOWINU THE EEPECT OE AMINO ACID SUPPLEMENTATION
(Data of Nose, 1963.)
Protein mkztzcre
NPU
Casein-gelatin
37.9
Casein-gelatin + methionine
+ tryptophan
44.7
Gluten-gelatin
35.2
Zein-gelatin
4.6
+ tryptophan
26.1
Zein-gelatin + lysine