CONICET | Buscador de Institutos y Recursos Humanos

Changes in meat fat composition, mainly a reduction of saturated fatty acids together with an increase of mono and polyunsaturated fatty acids, have been persistently recommended by nutritionists for the positive effects that such changes appear to have on the serum balance between low and high density lipoproteins and on blood cholesterol levels. There is an increasing interest in improving the nutritional quality of food by means of manipulation of the fatty acid composition, for example, it is possible to increase the proportion of unsaturated fats by incorporation of marine origin oils, primary source for long chain n-3 PUFA, into very popular meat products such as sausages. However, replacing solid fats by liquid oils in the batters affects rheological and textural characteristics of the products. Moreover, when low lipid sausages are formulated, fat is mostly replaced by water, consequently, additives have to be incorporated to improve not only texture but water holding capacity of the matrix as well. We selected several frequenty used hydrocolloids (hydroxypropylmethylcellulose (HPMC), methylcellulose (MC), a mixture of 2k:1i carrageenans (C), and a mixture of 2:1 xanthan-locust bean gums (XL) to compare the effect of a 1 % addition to meat sausages formulated with 5% fish oil as lipid source. Two control formulations, one with beef tallow fat and another with fish oil without any binder added were included in the study. Batters and frankfurters sausages were prepared using lean beef meat (adductor femoris and semimembranosus muscles) as previously described by Andrés et al. (2009). As fat sources, commercial beef tallow or deodorized refined fish oil (Omega Sur S.A., Mar del Plata, Argentina) were used. Analytical grade sodium chloride (1.4 %), sodium tripolyphosphate (0.2 %), sodium erythorbate (0.045 %), sodium nitrite (0.015 %) and cold distilled water were employed. The addition of gums compensated for the potential loss of some water binding properties when water was added to the formulation, and process yields ranged between 80.9 % and 98.2 %. Oil control (OC) had slightly lower process yield than fat control (FC) suggesting the formation of a less stable emulsion. Texture Profile Analysis (TPA) was performed on chilled (4 °C) sausages. Samples (1.5 cm thick and 1.7 cm diameter) were cut from the centre of the links and compressed twice to 30% of their original height between flat plates using a TAXT2i Texture Analyzer (Stable Micro Systems, UK). The replacement of fat with fish oil had a strong impact on sausages texture. A reduction of 40.2% of hardness occurred when solid fat was replaced by fish oil. Addition of xanthan-locust bean gums, or mix of carrageenans gave the highest hardness, similar to fat control while adhesiveness was higher for oil control, MC, and HPMC formulations. All rheological measurements were performed using a controlled stress rheometer (Haake RS600, Thermoelectron, Germany) provided with a temperature control unit, using serrated parallel plates (35 mm diameter). Two types of assays were performed: i) Temperature sweeps on raw batter, from 25ºC to 70ºC at a heating rate of 1ºC/min in linear deformation oscillatory mode, at a fixed frequency of 6.28 rad/s with a stress of 5.0 Pa (gap 1mm). ii) Frequency sweeps at 25ºC: Precooked samples (gap 1.4 mm height) were used to study their rheological behaviour in oscillatory shear in the linear range (stress = 5 Pa). Storage modulus (G´), loss modulus (G´´), and tan δ were recorded in the frequency range of 0.0628 ? 62.8 rad/s. Temperature sweep curves showed a typical behaviour of thermal gelation of meat systems where the main component corresponds to the denaturation of myosin. G´ was always higher than G´´ and loss tangent less than 0.25, showing a predominantly elastic behaviour characteristic of weak gels even for the raw batters. As temperature increased bond-making led to structural changes that affected rheological properties increasing elastic moduli and decreasing loss tangent. Denaturation temperatures observed by temperature sweeps appeared in the same range (55ºC - 65ºC) of those found by modulated differential scanning calorimetry (Marchetti et al., 2011). Cooked batters behaved as viscoelastic solids at 25 °C. G´ had values greater than G´´ in the tested frequency range, with a minimum of the latter at intermediate frequencies and a plateau region in G´ ; loss tangent in the plateau zone presented values between 0.08 and 0.25. Formulations containing the mixture of carrageenans or xanthan-locust bean gums showed the highest elastic moduli, reflecting the formation of an important three-dimensional network with even more solid-like characteristics than beef tallow formulation (FC); OC always had the less elastic behavior of all the formulations than the oil control (OC) . The viscoelastic behaviour of the cooked systems was modelled according to the broadned Baumgaertel - Schausberger - Winter (BSW) equation, to predict the mechanical relaxation spectra. The plateau moduli (GN0) predicted by the broadened BSW model were in general agreement with those calculated directly from dynamic experiments, since GN0 was also estimated as G´ when the loss tangent is minimum. An empirical superposition method was applied, using the inverse of the plateau moduli GN0 as normalization factors. All data fell into a single master-curve in reasonable approximation which implies that the different additives did not modify the overall microstructural pattern of systems, but mainly influenced the level of interactions among macromolecular components. It is interesting to mention that small strain results could be linked to the textural properties of the samples measured by TPA; a good correlation between the plateau modulus and hardness was found. The addition of k:i-carrageenan, xanthan/locust bean gums, produced systems with adequate rheological and physicochemical characteristics, similar to the traditional formulation containing beef tallow.