Heating of meat causes certain physical chemical changes in muscle proteins which affect the quality of cooked meat and meat products. Changes in protein solubility, in the adenosinetriphosphatase activity of myosin, or in the contractibility of the muscle fiber have been used by others to determine the extent of denaturation of meat proteins. In this study the changes in the hydration of muscle were studied because this factor is more directly correlated with the quality of meat (28,31, 66, 67). It is known that heating releases juice, that the amount of juice depends on the temperature, and that this loss of water influences juiciness and texture of meat (4,28,36, 43, 66, 68). In this study we have investigated in some detail the influence of different temperatures on the hydration of beef muscle.An investigation of the influence of temperature on the pH-dependence of water-holding capacity will give information concerning changes in meat quality and also the mechanism of denaturation. This is because changes in protein net charge and in steric conditions affect meat hydration in a pH range from pH 3.0 to 7.5 (34).In addition we have determined the acidic and basic groups in muscle and the solubility of the globular and structural muscle protein after heating at different temperature. METHODSUtility cows from 4 to 6 years of age were used. Two to 3 lb of the longissimus dovsi muscle were cut from the carcass 5-6 days after slaughter. Connective tissue and fat were removed as far as possible. The muscle was ground twice in a cooled meat grinder.Influence of pH on the water-holding capacity of meat after heating at different temperatures.One hundred g of ground meat at 20" C was minced in a homogenizer with 30 ml ice water at high speed for 30 sec. During mincing the metal homogenizer vessel was cooled by ice.For heating meat, the covered metal vessel of a homogenizer, filled with 110 g of ground meat, was placed in a water bath of the desired temperature.The meat was heated with occasional stirring until it was at the temperature of the water bath and was kept there for 30 min. [Other authors have shown that after 30 min heating at 70-90" C protein hydration changed very little (43, 6011. Then the vessel with meat was put in ice for about 15 min. Thirty-three ml ice water was added to bring the added water to 30%. The mixture was minced in an ice-cooled homogenizer in the same way as the fresh meat. It was considered that the different texture of heated muscle has an influence on the extent of mincing and, therefore, oh the water-holding capacity; however, we found that this effect has no influence on the relative difference of hydration produced by heating.

The relation between the changes of hydration and the changes in charge of muscle during the heating of meat has been reported previously (13). This investigation showed that it is possible to study the protein denaturation of meat by means of the determination of its water-holding capacity and its buffer capacity at different pH values and of the amount of dyes bound by the acidic and basic groups of the proteins. In the present paper these methods are used to determine whether freezing and thawing cause denaturation. This problem was of interest because of the undesirable changes in meat proteins brought about by freeze drying (10). In this process the meat is frozen before drying and the question arises whether changes caused by freeze drying are due to the freezing procedure itself or to other factors.It is known that freezing immediately after slaughter presents special problems because of the presence of adenosinetriphosphate (ATP) and the accelerated decomposition of the ATP during thawing resulting in "thaw rigor." In order to prevent such influences of ATP, for all experiments meat was used 5 to 6 days post mortem, after resolution of rigor mortis.

SUMMARY Sarcoplasmic proteins from beef skeletal muscle were fractionated by chromatography on ion‐exchange cellulose (cellulose phosphate and diethyl‐aminoethyl cellulose) at pH 5 and 9.3. From effluent diagrams of sarcoplasma from muscle immediately after slaughter, at least 14 fractions were recognized, and some of them were identified with known proteins by assays for enzymic activities. The numbers and levels of eluted peaks in the effluent diagram were found to decrease with storage (aging) of muscle and freeze‐drying of sarcoplasma; these decreases are perhaps due to denaturation. Proteins in solutions appear to be more completely separated by chromatography when different combinations of ion‐exchange cellulose are used.

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Studies on the biochemistry of meat during post niortem aging has shown that the muscle plasma plays an important role in the changes in the chemical and physical properties of the meat (6,15,16,17,25,26, 27,25). Arnold et al. (3) reported that during post niortem aging, sodium and calcium were continuously released by the muscle protein while potassium was absorbed after the first 24 hours. They also stated that the cationic shifts during post mortem ging appears to increase the electrical charge of the protein molecules of meat esulting in a measurable increase of hydration accompanied by improved mderness. N'ierbicki et al. (26,29) established that the water holding capac-.y of meat may be altered by modifying the ionic atmosphere in meat. Again hese authors (29,30) stated that ion protein interactions are taking place uring post niortem aging of meat and also during cooking process. Preparations, properties, and histological, histochemical and some chemical haracteristics of freeze-dehydrated meat have been described (7,19,20,21, '2). Harper and Tappel ( 2 4 ) stated that the texture of the freeze-dried meat s drier than the frozen control and that this dry texture is one of the principal iroblenis which remains to be solved in the field of lyophilization of meat.The studies to be reported here were directed to an improvement in the 'euture and toughness of cooked reconstituted freeze-dehydrated meat. Since the rehydrated meat tends to be tough and woody upon cooking, it was thought 'hat modification of meat through vascular infusion of various salts to improve the water holding properties of the muscle protein prior to freeze-dehydration might be carried over to the cooked rehydrated meat and thereby improve the acceptability of the product. In order to evaluate the effect of modification of the meat it was also necessary to study in some detail the relationship of post mortem aging and of cooking prior to freeze-dehydration to the quality of the meat as eaten. MATERIALS A N D M E T H O D STwenty-eight cattle were used in this work; most of them were comparable to lower half of U. S. good grade. The sampling techniques and methods used have been previously reported from this laboratory (3,6,17,28,29).Modification of meat: Three different methods were used for modification of meat under investigation : 1 ) Modificatiolt of groztnd meat: Aliquot samples of ground meat were weighed and modifier solutions were added to the ground meat using one part of additive to 10 '

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.

The chemistry of flavor development during the roasting of coffee is not well understood. Acidity is often considered an important factor in the flavor of brewed coffee. Consequently, a study of the acidic compounds of coffee might contribute to a better understanding of the taste and flavor of coffee beverages. Kaufman (8) made water extracts of both green coffee and successive samples withdrawn during roasting, and observed that the p H fell about one pH unit, and then began to rise. These changes were confirmed here. The optimum roast is often considered to terminate shortly after the p H of the water extract begins to increase. The titratable acidity is nearly doubled at this point (12,16). Kaufman (8) suggested that these changes were due to the formation and volatilization of acetic acid from decomposition of sugars, decarboxylation of acids formed by rearrangement of sugars and decarboxylation of chlorogenic acid. In a heavy roast approximately 50% of the original chlorogenic acid was reported to be destroyed (14). Since partition chromatography on silica gel was particularly adaptable for a separation of organic acids in coffee (9,11,19) a quantitative study of several organic acids in coffee during roasting has been carried out. EXPERIMENTALCoffee samples were obtained from the Coffee Brewing Institute, New York. The samples were vacuum packed in one-pound cans as whole beans and stored at -20" C. Table 1 describes the samples and gives the code.Methods. The weight of 100 beans was obtained as a mean value, weighing 4 groups of 200 beans each. One hundred grams of coffee beans were ground coarsely with a laboratory mill. Moisture was determined by drying 2 g. for 5 hours at 105'-110" C. Thirty-gram samples were shaken 5 minutes with 400 ml. distilled water of 95" C. in a 1000-ml. Erlenmeyer flask. Next, 100 nil. of distilled water was added by rinsing the walls of the flask; the flask was then cooled under running tap water. The extract was centrifuged for 20 minutes and the solution transferred to a 500-ml. volumetric flask and filled to the mark. Using 25 ml. of this extract the titratable acidity was detrmined by titrating with 0.1 N sodium hydroxide to pH 8.2 as indicated by a Beckman pH meter model G. The remaining extract was brought to pH 7.9 with 0.1 sodium hydroxide and after filling again to the mark 20 ml. aliquots were freeze-dried. The weight of solids was recorded and then the solid extract after acidifying to pH 1 was transferred to the top of a column of silica gel. The organic acids were then separated into 6 bands by a method similar to that reported from this laboratoe (11). The purity of these bands was checked by paper chromatographic methods using the Ri values of Table 2 in the case of phenolic acids. Some of the compounds were identified by physico-chemical methods.The individual fractions from the column were evaporated to dryness. If the presence of volatile acids was suspected, the fractions were neutralized with ammonia before drying. The residues were dissolved in ethanol or ...