CHANGES IN HVDRATION AND CHARGES OF MUFCLE PROTEINS, DURING FREEZE‐DEHYDRATION OF MEAT^a

Abstract

Freeze-drying is the mildest method k'nown for drying meats (5,15,18,20) but even this process causes undesirable changes of meat quality. The texture of lybphilized and rehydrated meat is drier than the frozen control (17). The decrease of tenderness and juiciness produced by freeze-drying apparently is caused by a loss of the water-holding capacity of muscle proteins (3, 7). Hamdy et al (7) pointed out that the dry texture and the decrease of meat hydration is one of the principal problems in the field of lyophilization of meat.In a previous paper (4) it was shown that quick-freezing of Fuscle tissue does not decrease the hydration of muscle nor cause protein denaturation. Therefore, the influence of freeze-drying on the water-holding capacity of meat is not due to the freezing process but to the process of dehydration.The studies reported here concern the kind of biochemical changes in meat proteins caused by freeze-dehydration.It may be that dehydration causes a certain denaturation of muscle proteins since it has been shown that some proteins are denatured by lyophilization (14). The possibility of denaturation is indicated by the fact that the adenosinetriphosphatase activity of actomyosin is partially reduced by freeze dehydration of beef muscle (13). It is possible to study the denaturation of meat by means of the determination of the water-holding capacity and of the buffer capacity at different pH values and the measurement of the amount of dyes bound by the acidic and basic groups of muscle proteins (11). These methods have been adapted to study the influence of freeze-drying on meat proteins. This report concerns only the effect of freeze dehydration and not the storage of dried meat. Only the changes in muscle tissue free of extraneous connective and fatty tissue were studied. Therefore, the conditions of these experiments do not correspond exactly to the commercial application of freeze-drying of meat. METHODSThe animals used were U. S. Utility S-and 6-year old cows. Two to 3 lb of the longissimus dorsi muscle were cut out from the carcass 5 to 6 days after slaughter. Connective tissue and fat were remo?ed to the extent possible. The meat was ground or cut into cubes in the manner previously described (4).Freeze-drying. Two-hundred grams of meat, usually in cubes, were put in the 4 vessels of a laboratory free-drying apparatus. These were placed in an acetone solid carbon dioxide mixture for 15 min and then attached to the apparatus.

Effect of EDTA and pH on Properties of Freeze‐dried Pork Muscle I. Effect of pH and Magnesium and Calcium Ions on Freeze‐dried Myofibrils

“…When the pH is 5.4, the cations are not as effective in preventing the decrease in water-holding capacity. Hamm and Deatherage (1960) suggested that freeze-drying causes formation of new electrostatic and/or hydrogen bonds in the isoelectric pH range of the meat and causes cleavage of linkages between the bivalent cations and the proteins. Their observations imply that the clivalent cations do not decrease the water-binding capacity of rehydrated meat.…”

“…Rehydrated meat is often tougher and drier than the original meat, and in addition has a characteristic "woody" texture. These texture characteristics are usually ascribed to decreased ability of the meat proteins to take up moisture during rehydration (Connel, 1957;Hamdy et al, 1958;Hamm and Deatherage, 1960). Penny et al (1963) recently demonstrated that injection of adrenaline in beef and rabbits before slaughter improved rehydration, giving a rehydrated product with a more tender and juicy and less woody texture.…”

“…on Freeze-dried Myofibrils the formation of an excessive amount of electrostatic and hydrogen bonds between actin and myosin in the myofibrillar filaments (Hamm and Deatherage, 1960 ;Connel, 1957). Formation of these bonds might be counteracted by relaxation of the muscle as well as by an increase of pH away from the isoelectric point.…”

Inhibition of the Denaturation by Salt of Myosin in Baltic Herring

“…Hamm, 1955). In contrast, sodium acetate, which according to Hamm (1960) exerts a weak dehydrating effect in low concentra-Ti; J; = 0.3), has an opposite effect iiere are various mechanisms by which phosphates and citrates could inhibit the reduction of solubility of native Baltic herring myosin by sodium chloride and at the same time increase the hydration of this protein. Phosphates and citrates may, for example, be taken up directly by protein molecules, thereby increasing the numbers of polar groups in the latter.…”

“…Thus, Luijpen (1957) stated that the denaturation of fish proteins caused by freezing differs in principle from that caused by heating. There are also marked differences between the effects of freeze drying and heat denaturation (Hamm and Deatherage, 1960). In contrast, many factors indicate that there is an appreciable similarity between the denaturation of fish muscle proteins caused by freezing and that caused by salts.…”