HEAT TREATMENT EFFECT ON TEXTURE CHANGES and THERMAL DENATURATION of PROTEINS IN BEEF MUSCLE

Meat tenderness is one of the most important quality criteria when evaluating results of cooking conditions. Changes in tenderness and weight losses of heat-treated meat (semitendinosus muscle) for different time-temperature combinations were analyzed; the relationship between protein denaturation and textural changes was studied.
Heat treatments of meat samples (1.5 cm in diameter, 2 cm long) were performed in a thermostatic bath in the 60–90C range. Maximum heating times were 180 min. Meat hardness was determined by Warner-Bratzler measurements using an Instron testing machine. Protein denaturation was followed by Differential Scanning Calorimetry (DSC) analyzing peaks for myosin (I and II), sarcoplasmatic proteins and collagen (II) and actin (III).
Between 60 and 64C, hardness decreased with cooking time until reaching the lowest asymptotic values. This was related to protein denaturation of peak I and II. Between 66 and 68C, hardness decreased at first but increased later due to actin denaturation; at the temperatures 81 and 90C no modifications were observed and hardness remained at its higher values.
The kinetic model proposed fit the experimental results satisfactorily. Activation energies of tenderizing and toughening processes are similar to those of protein denaturation of peak II and III. Weight losses due to cooking were also modelled increasing through the entire temperature range.     

Changes in rheological and viscoelastic properties and protein breakdown during the ripening of 'Port Salut Argentino' cheese

Changes in the rheological behaviour and viscoelastic properties during ripening at 10°C of a soft cheese (Port Salut Argentino) packaged in a plastic film (EVA-EVA) were analysed. Casein degradation was measured by electrophoresis slab gels; α_s1 casein degradation was rapid and striking compared with that of β casein. Rheological parameters obtained from uniaxial compression tests changed during ripening: hardness decreased, adhesiveness and cohesiveness increased.
An exponential decay equation with two maxwellian elements and one elastic in parallel was fitted to characterize stress relaxation curves. Viscoelastic parameters (elastic moduli and relaxation times) were obtained using non-linear regression analysis. The elastic equilibrium modulus decreased 80% during the ripening period and the viscosity of the element with the highest relaxation time decreased 20%. These parameters represented the changes observed in cheese hardness and elasticity during ageing time and were related to the extent of casein breakdown.     

Diffusion of carbon dioxide in tomato fruits during cold storage in modified atmosphere

Treatments with 20% CO₂ of tomato fruit produced a beneficial extension of storage life. The diffusion of CO₂ in tomato (Lycopersicon esculentum Mill) cv. Platense was measured chromatographically and the concentration profiles in the internal gaseous atmosphere of the fruit were determined for non-steady state conditions to establish minimum treatment times that can ensure adequate penetration of the gas.
The effective diffusivity of CO₂ in the tissue was determined by fitting concentration data, obtained from experiments with whole fruit without skin, to the non-steady state solution of the diffusion equation, assuming negligible external mass transfer resistance. The diffusivity was modelled using Maxwell-Eucken expressions, taking account of the heterogeneous structure of the tissue.
The resistance of the fruit skin was evaluated using whole fruits with the stem scar covered with paraffin and fitting experimental data to the solution in terms of mass Biot number; the specific resistance of the peel was some 200 times greater than that of the stem scar.