The recommendation of the 96/449/EC directive for processing mammalian anim
al waste does not ensure complete inactivation of transmissible spongiform
encepalopathy (TSE) agents. The safety of the process might be ensured by a
dding alkaline treatments to the heating step. Evaluating the in vivo and i
n vitro nutritive value of meat meals produced according to 11 heat, time a
nd pressure treatments, either with or without addition of alkali was compl
eted. Meat meals were obtained from fresh soft bovine meat in a 20 kg stirr
ed displacement autoclave, resembling the standard equipment used in Italia
n rendering plants. Operating temperature and pressure were monitored conti
nuously. Meat meals were analysed for crude protein and ash contents and pH
was measured. The protein fraction was analysed for amino acids and lysino
alanine (LAL). protein quality was evaluated in vivo with the rat-based pro
tein efficiency ratio (PER) bioassay and in vitro by pepsin digestibility,
the essential amino acids composition (DC-PER) and from both essential amin
o acid composition and enzyme digestibility (C-PER) of the protein. Compare
d to the standard procedure in use before 96/449/EC directive (NM,), implem
enting of the EC treatment did not reduce the nutritive value of the meat m
eal (MM), whereas negative effects were observed when the length of treatme
nt was increased to 180 min or when adding an alkaline step to the MM prepa
ration. In particular, addition of alkali reduced the nutritive value of th
e MM as suggested by the PER bioassay, and increased the (LAL) content of t
he protein fraction. Data suggests that LAL content of the protein fraction
could be used as an indicator of protein quality of meat meals. In vitro a
nd in vivo results demonstrate the inadequacy of the in vitro technique (pe
psin digestibility, C-PER and DC-PER) for evaluating the nutritive value of
meat meals. (C) 2001 Elsevier Science B.V. All rights reserved.