Effect of temperature, pressure and alkaline treatments on meat meal quality

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.