Kinetic analysis of cooking losses from beef and other animal muscles heated in a water bath — Effect of sample dimensions and prior freezing and ageing

Abstract

Cooking loss kinetics were measured on cubes and parallelepipeds of beef Semimembranosus muscle ranging from 1 cm × 1 cm × 1 cm to 7 cm × 7 cm × 28 cm in size. The samples were water bath-heated at three different temperatures, i.e. 50 °C, 70 °C and 90 °C, and for five different times. Temperatures were simulated to help interpret the results. Pre-freezing the sample, difference in ageing time, and in muscle fiber orientation had little influence on cooking losses. At longer treatment times, the effects of sample size disappeared and cooking losses depended only on the temperature. A selection of the tests was repeated on four other beef muscles and on veal, horse and lamb Semimembranosus muscle. Kinetics followed similar curves in all cases but resulted in different final water contents. The shape of the kinetics curves suggests first-order kinetics.

Introduction

During cooking, meat can lose a large quantity of its mass, as meat juice. Ninety percent of this juice is water. Water loss determines the technological yield of the cooking operation, making it a critical factor in the industry. It affects the quality of cooked meat as it determines juiciness and is related to tenderness. Micronutrients can also flow with the cooking juice, thus reducing the nutritional quality of the end-product. Meat juice release by protein denaturation is independent of surface evaporation, as Bouton et al., 1976, Laroche, 1982 showed that even during cooking in a humidity-saturated atmosphere, 45% of product mass was still able to be expelled as meat juice. In fact cooking losses are the results of complex phenomena which depend on cooking conditions, animal properties (species, age, sex, type of muscles…), meat ageing, storage conditions and cutting before cooking.

Cooking loss is related to changes in meat protein structure caused by increasing temperature (Laroche, 1978). The myofibrillar proteins undergo denaturation and become insoluble between 50 °C and 90 °C (Table 1). The temperature increase also triggers collagen contraction (Palka and Daun, 1999, Tornberg, 2005), which exerts pressure on the myofibers it is wound around, ‘squeezing’ free water out of the matrix. The degree of myofiber shrinkage depends on both the compression force applied by the collagen and the resistance exerted by myofiber (Lepetit, Grajales, & Favier, 2000). However the respective effect of these phenomena remains under debate (Bendall and Restall, 1983, Lepetit, 2007). Traditionally the cooking losses of beef at low cooking temperatures, 50 °C to 58 °C, are linked to the denaturation of α-actinin and myosin (Palka and Daun, 1999, Tornberg, 2005) while losses observed in the range 58 °C to 65 °C are mainly attributed to collagen contraction. At higher temperatures cooking losses are often explained by both collagen and myofibers.

According to the above mechanism cooking losses should depend on animal species, animal age, type of muscle, amount of collagen, and orientation of myofibers in the meat. However there are conflicting results about these effects (Table 1). There is no simple link between cooking losses and animal age, or type of muscle or collagen content probably because these effects are often hidden by variations in crosslink numbers or in their thermal stability and solubility which can vary between animals of the same age or gender. Effect of myofiber orientation in the meat on cooking losses also leads to conflicting results all the more since experimental procedures often mix variations in fiber orientation with variations in heat transfer.

Much of the literature reports that ageing conditions and freezing/thawing meat before heating affect cooking losses, but often with conflicting results in terms of the scale of the effect (Table 1). Effect of beef ageing on cooking losses seems strongest during the first 5 days after slaughter (5% less cooking losses at D + 5 than D + 1), thereafter becoming weaker but remaining significant even at 14 days post mortem (Shanks, Wulf, & Maddock, 2002), which is the time widely considered as marking completion of the ageing process in terms of toughness. Freezing the sample at different freezing rate, storing the frozen sample for different times affect cooking losses but great variations in these effects are reported (Table 1).

Variations in cooking conditions have shown that for a given muscle and long treatment duration, cooking losses depend mainly on temperature (Bendall and Restall, 1983, Bouton et al., 1976). Translated into practice, these conditions would correspond to slow-cook stewing-type treatments over several hours. In this case, the meat temperature can be considered constant and uniform throughout the treatment, and equal to the cooking temperature. In practice though, many cooking operations last for far shorter periods of between 5 and 90 min (grilling, pan-frying, roasting, and so on), in which case average product temperature differs greatly from cooking temperature (as measured in the cooking equipment) and is dependent not only on technique but also on the equipment used and the size of the meat portion. During these treatments, there are large temperature gradients inside the product itself. This situation, associated with poorly interpreted heat transfer, leads to significant variations or even conflicting results on the effect of factors such as muscle fiber direction on cooking losses, and makes predictions impossible. These contradictions also stem from the fact that results are based on timepoint observations rather than loss kinetics.

The objective of this study was to analyze the effect of cooking time on cooking losses during short to medium-length heat treatments. A full set of experiments was performed on cuts of beef prepared under standardized conditions (muscle type, chilling, ageing, fiber orientation, freezing, thawing…) from charolais-breed cows, 1 to 4 years old. Other experiments were also performed to study the effects on cooking losses of: variations in muscle type, fiber orientation, ageing time, and pre-freezing of samples. These experiments were done to interpret the cooking losses obtained under the different scenarios liable to be encountered in practice. This also led prospective runs to test whether previous results could be generalized to younger animals (veal calves) or other ‘red’ meats than beef.

Meat temperature varies during short heat treatments. It is necessary to know accurately the temperature kinetics in order to interpret the mass transfer kinetics and to separate the effects due to the biological properties of meat and to raw meat pre-treatments from those due to cooking. Thus heat transfer was analyzed by running pre-trial heating experiments and numerical simulations designed to integrate fluid flow in the water bath and sample size and geometry.