Magnetic resonance imaging study of the cold-set gelation of meat systems containing plasma powder

Abstract

The effect of rehydrated plasma powder addition to meat systems formulated with and without NaCl was evaluated by magnetic resonance imaging (MRI), texture and physico-chemical analysis. Different model systems were elaborated: rehydrated plasma powder (PPW), meat batter (ME) and ME with PPW (MEPPW) with (MEPPW2) and without (MEPPW0) NaCl addition. The effects of PPW addition to ME were different depending on the presence or absence of NaCl. The PPW addition caused high mechanical stability to ME without salt and an increase (p < 0.05) of hardness, cohesiveness, springiness and breaking force. The study of the structure of MEPPW0 by MRI showed higher T₂ (associated to larger pores), T₁ (indicating more water mobility) and apparent diffusion coefficient (ADC) values than those of ME. When salt was added (MEPPW2) there was a decrease of hardness, breaking force, T₁ and ADC and an increase of the adhesiveness and T₂ with respect to MEPPW0.

Introduction

Several commercial cold-set binding systems (alginate–calcium, transglutaminase of different origins, fibrinogen and thrombin) are available to the meat industry, especially for manufacturing restructured muscle products and for binding whole muscle pieces to resemble hams (Boles and Shand, 1998, Boles and Shand, 1999, Flores et al., 2007, Means et al., 1987, Motoki and Seguro, 1998, Trout, 1989). The use of these binding agents also offers other advantages in the manufacture of meat products such as improved emulsion/batter stability, a better yield and slicing properties (Boles and Shand, 1998, Boles and Shand, 1999, Flores et al., 2007, Jarmoluk and Pietrasik, 2003, Monahan and Troy, 1997, Ruiz-Carrascal and Regenstein, 2002). Moreover, the meat product manufactured with cold-set binding systems may reduce or eliminate the need to add sodium chloride and phosphates, which are related to cardiovascular and bone diseases (Kemi et al., 2006, Law et al., 1991). Every cold-set binding system works in a different way and can react differently to changes in ingredients and in manufacturing conditions of meat products. General information related to the practical aspects of how the binders work and how processing methods affect the finished product characteristics are required to increase the use of these binding agents. In this way, the effects of cold-set binding systems with mixtures of fibrinogen and thrombin (Fibrimex™, FNA Foods, Harimex Inc.) on consumer acceptance, physico-chemical, textural and structural properties in the manufacture of meat products have been studied (Boles and Shand, 1998, Boles and Shand, 1999, Flores et al., 2007, Herrero et al., 2007). Recently, it has been possible to utilize plasma powder as cold-set binding agent: it is obtained from bovine and porcine blood plasma and has excellent functional properties. These plasma products are prepared following the method described by Roodink and Zuijdweg (2003). With this procedure a plasma protein concentrate is obtained which contains a complex mix of proteins such as serum albumin, globulins and fibrinogen (at least 1% of the weight). Finally, the concentrate is spray-dried to form a powder (Roodink & Zuijdweg, 2003) intended for use in foodstuffs, in such a manner that the temperature of the product is maintained at less than 60 °C. These conditions allow the natural functions and activities of fibrinogen and the other proteins and enzymes of the blood plasma to be maintained. This blood plasma powder offers several advantages to the food industry when compared with other cold-set binding systems that are also of blood origin (such as the combination of fibrinogen and thrombin solutions). Plasma powder is a single-component system powder, easily stored and preserved. Previous research has indicated that the heat treatment of plasma proteins induces denaturation and aggregation, which results in a three-dimensional network forming consistent gels (Dávila et al., 2007, Hermansson, 1982, Parés et al., 1998). However, more information related to physico-chemical, textural and structural changes produced by the addition of plasma powder to meat systems is required to increase the use of this cold-set binding agent.

Raman spectroscopy has been used in a previous work (Herrero, Cambero, Ordóñez, de la Hoz, & Carmona, 2009) to evaluate the protein structural changes that occur with the addition of plasma powder to meat systems. It was established that the addition of rehydrated plasma powder to meat batter produced a decrease of α-helix and an increase of turns (sum of β and γ turns) as well as an unordered structure (Herrero et al., 2009). However, an in depth study is necessary to evaluate the structural changes that occur in the meat system formulated with the addition of this cold- set binding agent so as to completely understand the structural changes that occur in the meat system with the plasma powder addition. In this way, magnetic resonance imaging (MRI) is a non-invasive and non-destructive technique which provides structural information, mainly about water structure and its structural changes, about biological tissues through parameters such as transverse relaxation time (T₂) and longitudinal relaxation time (T₁), and the apparent diffusion coefficient (ADC). These magnetic resonance parameters are potentially sensitive to variations of bulk water (T₂), water mobility (T₁) and facility of diffusion of the water in all directions (ADC) resulting from the modification of water-macromolecule interactions and changes in tissue structure (Boulby and Rugg-Gunn, 2003, Gowland and Stevenson, 2003, Wheeler-Kingshott et al., 2003). Magnetic resonance parameters such as T₂, T₁ and ADC together provide complete information about biological tissue structures. MRI has several applications in meat science (Bertram & Andersen, 2004). In particular, some authors have indicated that MRI permits the study of carcass composition, adipose tissue distribution, connective tissue and muscle fibre type (Bonny et al., 2000, Laurent et al., 2000, Mitchell et al., 2001, Tingle et al., 1995). MRI can also help to understand the structural changes during processing and storage of meat (Bertram et al., 2004, Guiheneuf et al., 1997, Guiheneuf et al., 1996, Renou et al., 2003). Moreover, MRI parameters are also correlated with meat properties such as water content and sensory attributes (Cernadas et al., 2005, Ruiz-Cabrera et al., 2004, Shaarani et al., 2006). Recently, an MRI study has been carried out in our laboratory to identify the structural changes produce by the addition of a cold-set binding system such as fibrinogen and thrombin on meat systems (Herrero et al., 2007).

The primary aim of this work was to study the changes in the physico-chemical, textural and magnetic resonance imaging parameters produced by the incorporation of plasma powder as a cold-set binding agent to meat systems. For this reason, we have studied three model systems: rehydrated plasma powder (PPW), meat batters (ME) and meat batters supplemented with rehydrated plasma powder (MEPPW) formulated with and without NaCl addition. A secondary aim was to establish the relationship between physico-chemical, textural and MRI parameters in order to evaluate the effect of plasma powder addition to meat systems.