Influence of thermoplastic extrusion on the nutritive value of bovine rumen protein Ana Carolina Conti e Silva a , Robison José da Cruz b , José Alfredo Gomes Arêas a, * a Departamento de Nutrição, Faculdade de Saúde Pública, Universidade de São Paulo. Av. Dr. Arnaldo, 715, Cerqueira César, São Paulo/SP 01246-904, Brazil b Faculdade de Medicina, Universidade de São Paulo. Av. Dr. Arnaldo, 455, Cerqueira César, São Paulo/SP 01246-904, Brazil article info Article history: Received 25 April 2009 Received in revised form 2 September 2009 Accepted 17 September 2009 Keywords: Bovine rumen Thermoplastic extrusion Food composition Amino acid In vivo assay True digestibility abstract This study investigated the impact of thermoplastic extrusion on the nutritive quality of bovine rumen protein. Proximal composition, amino acid profile and in vivo true protein digestibility among rats were determined in raw (RBR) and extruded (EBR) rumen. Raw and extruded bovine rumen presented high percentages of protein (more than 95% on dry basis). Neither raw nor extruded proteins had any limiting amino acid, and the RBR and EBR amino acid scores were, respectively, 1.28 (leucine) and 1.25 (methio- nine plus cystine). Extrusion reduced significantly true protein digestibility from 97.7% to 93.1% (p < 0.001), but protein digestibility-corrected amino acid scores for both proteins (RBR and EBR) were 100%. Animal growth presented comparable profiles using raw and extruded rumen. In conclusion, ther- moplastic extrusion did not affect the protein quality of bovine rumen, and this does not hinder the use of this material as a food ingredient. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Slaughterhouse by-products are parts of animals that are not consumed either for cultural reasons or because they are unappeal- ing to one of the senses. Bovine rumen, the first compartment of bovine stomach, is considered to be a slaughterhouse by-product for esthetic reasons such as flavor and texture (Mittal & Lawrie, 1984) and, particularly, for cultural reasons, because of the repul- sion that people feel when the stomach is mentioned as human food. After mincing, lyophilization and milling, the protein content of bovine rumen is 85% on a dry basis (Conti & Arêas, 2001). This nutritive characteristic makes bovine rumen a material that can be used in food formulations, since proteins are added into a wide variety of products because of their nutritive value and functional properties (Giese, 1994). Therefore, using bovine rumen as a food ingredient would be a way of providing a new use for a meat cut that is currently underused. One way to develop bovine rumen as a food ingredient is through thermoplastic extrusion. This process subjects the mate- rial to high temperature and a high shear rate for a short period of time, thereby restructuring it into a fiber-like product, improv- ing the functional properties of the protein and enabling its use as an ingredient for human foods (Arêas, 1992; Camire & Belbez, 1996; Reifsteck & Jeon, 2000; Vaz & Arêas, 2010). On the other hand, in spite of the positive changes promoted by extrusion (such as structure and texture), this thermal processing may reduce the nutritive value of the protein, as observed in other bovine by-products (Campos & Arêas, 1993). Thus, reinstatement of bovine rumen use by improving its functional properties through thermo- plastic extrusion needs to be achieved with as little loss of nutritive value of the protein as possible. Therefore, the aim of this study was to investigate the effect of thermoplastic extrusion on the nutritive quality of bovine rumen protein, under the processing conditions for achieving an extruded product with appropriate protein functional properties. 2. Materials and methods 2.1. Bovine rumen Bovine rumen was supplied by Sadia S/A (Toledo, PR, Brazil). It was removed from healthy animals under conditions appropriate for human consumption, as certified by SIF (Federal Inspection Ser- vice, Brazilian Ministry of Agriculture). The material was minced and frozen immediately after the animals had been slaughtered (kept at À30 °C until use), and then lyophilized by Nutribrás S/A (São Paulo, SP, Brazil). The bovine rumen needed prior defatting, in order to produce enough barrel resistance during the process and achieve proper texturization. The dried material was defatted using a mixture of 0309-1740/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2009.09.009 * Corresponding author. Tel.: +55 11 30617858; fax: +55 11 30617705. E-mail address: jagareas@usp.br (J.A.G. Arêas). Meat Science 84 (2010) 409–412 Contents lists available at ScienceDirect Meat Science journal homepage: www.elsevier.com/locate/meatsci