Ma. Gutierrez et al., Comparison of egg-yolk protein hydrolysate and soyabean protein hydrolysate in terms of nitrogen utilization, BR J NUTR, 80(5), 1998, pp. 477-484
Egg-yolk protein hydrolysate (YPp) is an alternative protein source in form
ulas for infants with intolerance to cow's milk or soyabean protein, or for
patients with intestinal disorders. However, the nutritional value of YPp
has never been investigated. YPp, was prepared by enzymic hydrolysis of del
ipidated yolk protein, which led to an average peptide length of 2.6 residu
es. Three experiments were performed. In Expt 1, we compared the intestinal
absorption rate of YPp and soyabean protein hydrolysate (SPp) in rats. YPp
and SPp solutions were injected into the duodenum of anaesthetized rats an
d blood samples were taken from the portal vein at 7, 15, 30, 60, and 120 m
in. A higher amino acid concentration in the serum of the YPp group demonst
rated that YPp was absorbed faster than SPp. In Expt 2, the effects of diet
ary YPp and SPp on bodyweight gain, protein efficiency ratio (PER) and feed
efficiency ratio (FER) were determined. At the end of the experiment, body
weight had increased in both groups, while PER and FER were significantly
higher in rats fed on YPp. In Expt 3, to investigate the effects of dietary
YPp and SPp on N metabolism, we determined the biological value and net pr
otein utilization. Yolk protein was the reference protein. Biological value
and net protein utilization values were very similar between animals fed o
n yolk protein and YPp diets, and significantly higher than in rats fed on
the SPp diet. The present findings demonstrate that there is no adverse eff
ect of hydrolysis of yolk protein on N utilization, and that the nutritive
value:of YPp is similar to that of yolk protein and superior to that of SPp
.