Ice Recrystallization in Frozen Beef

Temperature fluctuations produced during storage and transport of frozen food lead to activation of the recrystallization processes, causing enlargement of the ice crystals and diminishing advantages obtained in quick freezing of products. A model for interpreting recrystallization of ice in frozen beef was established considering that in this phenomenon the driving force is the tendency to a decrease in surface energy of the crystalline phase and that rate of movement of the grain boundary is proportional to its curvature. Meat samples were frozen and submitted to higher storage temperatures. Histological analysis of tissues immediately after freezing and of samples stored at different times made it possible to measure evolution of ice crystal size and obtain kinetic constants for proposed recrystallization model. Mechanisms for interpreting the phenomena were discussed, determining that transition of molecules occurs preferently through the liquid phase.     

Ice morphology in frozen beef

A histological study was made of pieces of meat which had been frozen from one side, in conditions where the direction of the heat flux was approximately unidirectional and perpendicular to the muscle fibres. The morphology of the ice crystals in tissue frozen under various conditions was studied, and the range of freezing velocities over which no intracellular ice existed, was established. The average diameter D , of ice crystals, measured in different experiments and at different levels in the same piece of meat was related to the characteristic freezing time t _c, by the equation:
D = a + b log t _c     

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.     

BEHAVIOR OF LISTERIA MONOCYTOGENES AND ESCHERICHIA COLI O157:H7 IN FRESH-SLICED CACTUS-PEAR FRUIT

Storage experiments were conducted to follow the behavior of Listeria monocytogenes and Escherichia coli O157:H7, deliberately inoculated on fresh‐cut cactus‐pear fruits before packaging under modified and control atmosphere and stored at four different temperatures (4, 8, 12 and 20C). L. monocytogenes was able to proliferate during storage at different temperature both in control and modified atmosphere. By comparing the sanitary‐risk values with those of shelf life, it is possible to conclude that the storage of cactus‐pear samples at temperatures greater than 4C, both in control and in modified atmospheres, could lead to a significant health‐time risk, and that this is strictly affected by temperature. E. coli O157:H7 was able to proliferate only in the sample stored at 4 and 8C in both package atmospheres. On the contrary, this species was completely suppressed at the higher temperatures. In our study, E. coli O157:H7 appeared to be much less suited for survival on the surface of the fruit than L. monocytogenes.     

Determination of Organic Acids in Dairy Products by High Performance Liquid Chromatography

A high performance liquid chromatographic method was developed for the quantitative analysis of organic acids in dairy products. A reverse-phase C8 column at room temperature, a mobile phase of 0.5% w/v buffer ((NH₄)₂HPO₄ at pH 2.24 with H₃, PO₄)-0.4% v/v acetonitrile, UV detection at 214 nm and 1.2 mL/min flow rate were utilized. Formic, acetic, pyruvic, propionic, uric, orotic, citric, lactic and butyric acids were quantitated for raw milk, yogurt, Blue, Provolone, Port Salut and Quartirolo cheeses. Recoveries greater than 85.3% were observed for all acids.     

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.