T h e quality of meat includes many factors such as wholesomeness, appearance, composition, tenderness, flavor, juiciness, and nutritive value, most of which must be further subdivided. Development of adequate methods for measuring characteristics of meat has been and, in certain respects, continues to be a difficult problem. Breeding, age, sex, feeding, rate of growth, and other animal production factors have important effects on quality. Examples are presented, supplemented with a
brief discussion of the significance of commercial meat grades. Of great influence on quality in meat are the following factors: processing, preservation, and preparation which involve methods of chilling, ripening, curing, smoking, freezing and freezer storage, dehydration, cooking, and other operations. Significant relations in this respect are discussed in some detail. Emphasis is placed on recent developments, particularly on those involved in the dehydration and freezing of meat.
QUALITY IN MEAT AND MEAT PRODUCTS 0.G. Hankins BUREAU OF ANIMAL INDUSTRY U. 9. DEPARTMENT OF AGRICULTURE, WASHINGTON 25, D. C.
HE opinion is widely held that meals should be built arouud T m e a t The high degree of palatability of this food, ita ability to satisfy hunger, and important nutritive assets are largely responsible for this belief. The normal per capita consumption of meat in the United States is about 135 pounds per year, and it Ir emong the foods regarded as relatively high priced. That intereat in the quality of meat should be general, continuous, and intense is readily understandable. Quality as applied to meat is a term too broad to have real significance. When it is broken down into its component parts, a number of factors are derived, such as wholesomeness, appearance, composition, tenderness, flavor, juiciness, and nutritive value, most of which must be further subdivided. Each of these characteristics is at least moderately well understood by the consuming public, and quality in any instance is determined by a conscious or subconscious consideration of all of them. Basically, however, differences in composition, tenderness, and other characteristics of meat may be due to any one or more of a number of causes.
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WHOLESOMENESS
Although far from being unique in that respect, meat consumption could involve many dangers with respect to health. It is unnecewary to point out the risks that would be taken in eating meat from diseased animals or those harboring certain parasites, and meat that has been kept too long with the result that i t has crossed the line between “fresh” and “spoiled”. However, no large proportion of consumers in the United States is confronted with the necessity of taking such risks. Inspection services furnish protection to the bulk of our population. Notable among these services is the Meat Inspection Division of the War Food Administration, until February, 1943, a division of the Bureau of Animal Industry of the Department of Agriculture. It was established to administer the Meat Inspection Act passed by Congress on the same day in 1906 m the Food and Drug Act with which Harvey W. Wiley was so prominently identified. There is, however, an unwholesome condition that may exist but is not detectable by present known practical methods of inspection. Reference is made to the possible infection of pork with trichinae (Trichinella spiralis). Unless destroyed in the processing or preparation of the meat, these parasites may cause (he disease known as trichinosis. However, certain procedurea 220
in freezer storage and curing are now known to kill the organism. Cooking the pork to a n internal temperature of 137’ F. is likewise effective. Pork products which are usually eaten without cooking by the consumer are required at federally inspected establishments to be treated by one of these methods. Except in farm and home curing and canning, spoilage of meat does not present a serious problem in the United States. This is due to a general understanding that meat is highly perishable and to the extensive use of good refrigeration facilities. APPEARANCE
Although not necessarily a p;llide to quality in meat, appearance is always a psychological factor, and in some cases it is associated with characteristics of real importance to the consumer. Color is probably outstanding among those elements contributing to appearance. White fat, for example, is generally regarded as an asset in this respect and yellow fat a liability. Yet the latter, as often found in fr&h beef, is caused in large measure by the deposition of carotene from the feed, carotene being the p m cursor of vitamin A. Therefore, yellow color of fat in beef may well indicate a higher vitamin A potency than white color and in that respect be an advantage, not a disadvantage. The development of rancidity in fat is accompanied by a change to a yellowish color. Pork is especially predisposed to such changes. This color characteristic of fat that has acquired a n objectionable flavor undoubtedly has much to do with the fact that meat consumers seek white fat. There is considerable variation in the color of muscle or lean meat, especially in beef. The causes are not well established, except that i t is rather clear that older cattle have darker-colored ineat than younger cattle. However, it has not been shown that even dark-cutting beef, the extreme that meets with marked discrimination on the market, is necessarily low in palatability or other factors of quality important to consumers. Another interesting example of change in appearance that may occur is that due to desiccation in low-temperature storage or freezer burn. Unless meat is well protected to prevent drying out, it loses moisture when stored a t freezing temperatures, becomes pithy and spongy in appearance, and tends to lose the reddish color. There is little doubt that these changes are accompanied by undesirable changes in important factors of palatability.
March, 1945
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY COMPOSITION
Subsequent to the attainment of “chemical maturity”, which comes early in life, there is little change in the composition of the muscle tissue of meat animals when considered on the fat-free basis. Nevertheless, the meat of cattle, hogs, and sheep, as they come to market, varies strikingly in both physical and chemical composition. Breeding iu one important basic cause of variation in composition. I n one study (fd),for example, the edible meat of steers of one type within a breed contained about 50% water, 35% fat, 14% protein, and 0.69% ash, whereas the meat of steers of another type within the same breed had about 56,27,18,and 0.74%, respectively. Even differences in composition of the meat from progeny of different sires within the same breed and type have been reported (27). There is actually prospect now of differentiation between such sires in terms of yield of the preferred cuts by their progeny (16). As age and weight increase, meat animals in general tend to have more and more fat, with decreasing proportions of water, protein, and ash, under normal conditions of feeding. For example, it has been shown (9) that in hogs ranging from 50 to 325 pounds in empty body weight the fat content increased from about 20 to 55% whereas the water content decreased from approximately 60 to 35%, the protein from 16 to lo%, and the ash from about 3 to 2%. When animals of widely differing ages but of approximately equal fatness are fed under uniform conditions for the same period of time, the fat content of the meat tends to vary with age. Work a t a number of research institutions, apecially with cattle, has indicated this to be true. The dressed carcasses of heifers contain higher proportions of fat and total edible meat, with lower proportions of lean meat and bone, than the carcasses of steers of the same breeding, age, and feeding. Wether lambs tend to be fatter, although slightly lighter in weight,. than comparable ram Iambs. Results of different studiec on the comparative composition of barrows and gilts, however, are inconsistent. Different feeds, feed combinations, and levels of feeding or daily allowances are rather generally known to have distinct effects on the composition of meat of the animals to which they are fed. Perhaps the outstanding example in this country is the relatively strong tendency of corn feeding to result in the deposition of fat. I n one notable stuuy (IJ), four combinations of levels were compared in the feeding of pigs. They were as follows: high followed by high, high followed by low, low followed by high, a n d low followed by low. Each animal was slaughtered when it attained the weight of 200 pounds. The separable fat content of the carcasses was 38, 33,44,and 27% for the high-high, highlow, low-high, and low-low groups, respectively. Correspondand 49,and of bone, ing percentages of lean tissue were 40,45,36, 11, 11, 10,and 12. The variation that occurs in the composition of the meat fat itself is influenced by the characteristics and proportion of the fat in the feed. This influence, exemplified by the fat of such feeds as soybeans and peanuts, is responsible for the production of most of the soft pork in this country. The war created an urgent need for meat, as well as other foods, in space and weightsaving form for long-distance shipment. Dehydration was the answer, but much research was required and has been conducted during the emergency on this method of food preservation. The chemical composition of dehydrated meat is influenced by the composition of the raw material, the extent of the removal of moisture, and any losses or removal of other constituents, such as fat, that occur during processing. A typical analysis for fresh, closely trimmed pork ready for drying is moisture 65.3,ash 0.9,protein 18.8,and fat 15.0%. Dehydrated to 10% moisture content, but with no fat or other loss in the processing, meat of this composition should yield a finished product containing approximately 2.3% ash, 48.7% protein, and
221
39% fat. This would be in line with WFA specifications for this product, which provide in part that it shall not exceed 10% in moisture and 40% in fat. GRADES
The numerous factors that affect quality and the extremely wide variation in the quality of meats and meat products as they are offered on United States markets make it essential that the grading system be the best possible for recognizing differences. Beginning with beef in 1927, the United States Department of Agriculture made available a meat grading and stamping service. The undertaking was expanded to include lamb and mutton in 1930 and veal in 1931. I n December, 1942,the federal grading and stamping of meat became mandatory in connection with the application of price ceiling regulations. All meats, except pork, expected to go into commercial channels were soon covered by this program. Considerable Department of Agriculture research has been directed toward the characterization of meat grades’ in definite, measurable terms. Noteworthy progress has been made, particularly in establishing the composition of the different grades. Highly useful values are now available, for example, not only for the mean composition of dressed lamb carcasses of any of the six recognized grades-prime, choice, good, commercial, utility and cull-but also for the primary cuts from such carcasses. TENDERNESS
Excepting unwholesomeness, there is no attribute of meat more of a liability than toughness. There is insufficient knowledge on which to base a fully satisfactory statement as to the basic factora responsible for toughness. However, the following inherent factors, at least, are now considered by many to have a bearing on toughness or tenderness: diameter of muscle fibers and of muscle-fiber bundles that give the grainy appearance to meat, proportion and distribution of connective fissue, fatness in the gross and, wpecially, the proportion and distribution of fat within the muscle. Several objective methods for the determination of tenderness have been developed. The method in successful use by the Department of Agriculture and a number of other research institutions was described in its original form in a Department publication (3)and later improved cooperatively by the Bureau of Animal Industry and the Kansas Agricultural Experiment Station. Values obtained with the apparatus represent resistance of cooked meat to shearing action. The tenderness of meat is influenced by many factors. Breeding of the animal may logically be mentioned first. As a n example of this influence, it was found in a study of first-generation lambs of Lincoln X Rambouillet, Corriedale X Rambouillet, Columbia X Rambouillet, and Romney X Rambouillet breeding that the meat of the Lincoln-sired animals was clearly the least tender. Among the second-generation crossbred lambs, those of Romney X Rambouillet breeding ranked lowest in this respect (6). Generally speaking, sigiiificant differences in tenderness of meat have not been produced experimentally by different feeds or rations, when the feeding was such as to result in about the same rate of gain and the same degree of fatness in the animals. Yet feeding can be responsible for significant differences. A good illustration i s found in the case of paired lambs, given B certain feed combination by the Department so that one animal of each pair made a normal gain whereas the other made no appreciable gain in weight. The cooked meat of the normal gaining lambs was approximately 25% the more tender (I). I t is not necessarily true that the meat of the young animal is tender and the meat of the old animal tough. However, there is a general tendency for tenderness to vary inversely with age. Research has indicated, surprisingly, that the meat of exercised cattle is more tender than that of cattle which have little op-
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cidontll?,
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Val. 31, No. 3
lii3i'iiil ( I S ) . O w r l l i d d lxwr is, *nitill, int h i ~ tt h w e are viiristioni i n I C ~ ~ P I . I I~~n~ iI o ~ nthe ~
CUI* and IIIIISCIBS of thr snme ilriimi~l. MakiLtg use of aneymes that occur i n i h e iiiei~tirndf is ii widely k i a w n I I I P I I L O ~ of tenderieine. This ripmina may involve II period n l some plied t o m a t slid aausnge casings. Tenderized ready-tcreal hams, which have become so popular in recent years, sre smoked under i u e h conditions that they are really cooked at fhe same time. The tenderizing that occurs in the processing is believrd to be primarily due to t,he heat of the cooking, not to the curinx ni.
smoking. One of the most signifiexrit Findings of recont years in relatimi to tenderness of meat is the effect oi freezing. It was s h o w (81, for exnmplo, that, beef frown at +20" F. w&$ approximatd? 12% more tender than unfrozen beef. When the freezing temperature was -10" or -40" the effect was about IS%. I n SEIother etudy (iff), beef ripened 5 days at, 34" F. and then froztlii nt - 10' wx6 fully 8s tender as beef ripened 35 days. Cooking undoubtedly is a major factor influencinR tendernea-. Kcsesrch has shown, among other things, that when meat i s suspected oi h k i n g tendernew, the use of B low cooking temperature fora relativcly ion~timeisnppropriate. FLAVOR AND IUICIXESS
The components which together impart the ohilraetoristie
frwh meat flavor BE not accurately identified, although they are
belicvod to consist of water-soluble extractives, lipid-, small amounts of csrbohydratea and salts, or compounds produced from these products and proteins by cooking, enzyme action, or both (11). Of course there are several modified meat flsvon meli as thoseoi ripened iresh meet, cured meat in both the ireshly processed and aged forms, snd even rsncidity wsoeiated with fat breakdown. Reseesrch workers &re atill largely dependent upon organoleptic methods for determination of differences in this characteristic of meat. An exsmplo of difference in iresh mest flavor is found between beef from young animals and that from more mature cattle. Tho latter is imuaily more intense in flavor. Perhsps an even more striking difference is found between I m b and mutton. In B closely controllcd study by the I>cpartment of Agriculture, the meat of full-fed lambs w&s not materially different from that of limitdied lambs in tho intensity of flavor of lean ( I ) . However, the iormor was rrtted significantly hiaher in desirability of flavor. In emergency research by the Department on methods for dehydration of meat, flavor of the product was B point of major importsnce. Pork, frozeen, ground, and then dehydrated in moving sir st 120" F., had B definitely better flavor rating in the freshly processed state than similar mest that was preoooked and subsequently dried at higher temperatures in air 01 VBCUUm. The former product, however, presented a somewhatseriouakeeping quality problem ( 6 ) . In 8 particular instance the problem reiating to juiciness may be stated as follows: Haw juicy i a the meat and how rich is the juice? A serious obstacle to research on thin eharaeteristio of meat slso has been the lack of Bdequste technique. However,
wiI,h respect to the quantitative phase ui the problem, this obstscle is now rat,her well over~omethrough the development of
certain mcchsnicel methods. The method offeredby the Bureau of Animal Industry produced values which gave coefficienta of correlation of spproximately f0.W with committee judgmentn (15). Eliminetion of the pencnsl factor in evelusting juiciness of meat would seem to be justified. A satisfactory method for replscing subjective determinations of qunliiy is yet to be de-
vised. Only limited research hsa been done to detehine the fsetom rcsponsible for variations in juiciness. As an exemple of red t s , B direct relation between fat content of beef and qusntity of juice has been reported (e). On the other hand, the letter nm found to decrease with increase in degree oi donen- in roasting (4, 14, 15). Fatness oi meat has also been reported to h e x a highly siynifieant effeot on riehrievs of the juice (e), although it is probable that eampanent,s other thsn the fat oi the juice also have aheering on this factor of !mlutabilily. LIUTRITIONAL PROPERTIES
Mest is generally'regarded as a high-protein iood. Therefore, qnations may logioally be =ked 8s follom: How does the hiologiesl value of meat protein oompare with that of other foods? Does it vary significantly among the different kinds oi mest? What i s the supplemental value to the proteins of cereala and cereal products? Present knowledge on these points is to the effect that the proteins of lean meat are superior to those of cered8 and cereal products, st least equsl to milk prot,eins, and prrssibly somewhat inferior to egg proteins. When the meats do not vary meteridly in connective t.issue content, the proteins of lean beef, pork, veal, and mutton appear to have praotienlly the asme biological value. In proper combination with the proteins of cereala and cered products, the use of meat proteins results in the biological value of the combination equsling that of the meat proteins
themselvcs. In research on dehydrated meats, it was observed (6) that the protein was most nutritious when the rsw meat conbitled 8 minimum proportionof connective tissue and when the processing
INDUSTRIAL A N D ENGINEERING CHEMISTRY
March, 1945
was carried out as rapidly and at as low a temperature as practicable. Moreover, for the most part, the digestive coefficients for the protein in the dehydrated product compared favorably with those previously reported for meat in general. With respect to certain vitamins, meat and some meat products are now known to be good sources. I n fact, vitamin A is abundantly supplied by liver. Of the B vitamins, riboflavin is found in extremely large amounts in liver, heart, and kidneys. Niacin also occurs in large amounts in these products, especially in liver and kidneys. Thiamine is supplied to an intermediate extent by these same three products, to only a slightly lesser extent by beef, lamb, and veal muscle, and very liberally by pork muscle. LITERATURE CITED
Barbella, N. G., Hankins, 0,G,, and Alexander, L, M., proc, Am. SOC.Animal Production, 29, 289-94 (1936).
Barbella, N. G.; Tannor, B., and Johnson, T. G., Ibid., 32,3204 (1939) I
Black, W. H., Warner, K. F., and Wilson, C. V., U. S. Dept. Agr., Tech. Bull. 217 (1931). Child, A. M., and Esteros, Gertrude, J . Home Econ., 29, 183-7 (1937).
[ G d4 s
223
(5) Committee on Dehydration of Meat, U. 8. Dept. Agr., Circ.
706 (1944). (6) Gorman, J. A,, Hultz, F. S., Hiner, R. L., Hankins, 0. G., and Spencer, D. A., Wyo. Agr. Expt. Sta., Bull. 254 (1942). (7) Griswold, R.M., and Wharton, M. A,, Food Research, 6,517-28 (1941). (8) Hankins, 0. G., and Hiner, R. L., Proc. Am. SOC.Animal Production, 31,260 (1938): Food Ind., 12,49-51 (1940). (9) Hankins, 0.G., and Titus, H. W., Yearbook of Agriculture, U. S. 'Dept. Agr., 1939. (10) Hiner, R. L., and Hankins, 0. G., Refrig. Eng., Sept., 1941. (11) Howe, P. E.,and Barbella, N. G., Food Research. 2. 197-202 (1937). (12) Howe, P. E., and Hankins, 0. G., Proc. Am. Soc. Animal Pmduction, 27,79 (1934). (13) McMeekan, C. P.,and Hammond, J., J . Ministry Agr. (Eng.), 46 (3).238-43 (1939). (14) Noble, 1. T., Halliday, E. G., and-Klass, K. K., J . Home Econ., 26,238-42 (1934). (15) Tannor. Bernard, Clark, N. G.t and Hankins, 0.G., J. ABr. Research, 66,403-12 (1943). (16) U. 5. Bur. of Animal Ind.. unpublished results. (17) U. S.Bur. of Animal Ind., Rept. of Chief of Bur., p. 14 (1941). (18) Univ. of Ill. Agr. Expt. Sta., Ann. Rept. of Director, pp. 85-8 (1930-31).
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Predicting Volume Increase of Perbunan Compounds in Petroleum Products R. M. HOWLETT Esso Laboratories, Standard Oil Development Company, Eliaabeth, N. J .
I
N T H E formulation of oil-resisting synthetic rubber stocks, it is frequently desirable to know what will be the approximate volume increase of the proposed compound in a certain immersion medium under specific test conditions. If available volume increase data on a synthetic rubber compound could be used in formulating the new recipe, the amount of work required to establish the new stock could be considerably reduced. The purpose of this paper is to show the development of a relatively simple system to predict the volume increase of Perbunan compounds. Catton and Fraser (8)reported that the swelling of neoprene compositions depends on the volume of neoprene in the compounds. A subsequent paper (4) showed how the volume increase of a compound may be calculated if the oil immersion medium is used as a softener in the compound. Aniline point, viscosity-gravity constant, and Diesel index @,4,6,7)may beused tomeasure the propertiesofpetroleumproducts which govern the swelling characteristics of synthetic rubber compounds. plso, the swell of Perbunan compounds (IO) is a function of the aromatic content of the gasoline. These factors will not be considered in this discussion; rather, specific values will be presented for a variety of petroleum products, and an attempt will be made to relate the effect of various compound changes on the resistance of Perbunan compounds to petroleum products. If, as previously stated, the swelling of a synthetic rubber compound is due to swelling of the polymer, V = KP/100 where V = Q volume increase of compound K volume swell of cured polymer P = polymer by volume in compound
%
(1)
A s t u d y has been made of the volume increase of Perbunan compounds immersed in various petroleum products. As a result of this work a method has been developed for calculating the volume swell of a P e r b u n a n compound when it is immersed in a given petroleum product under certain test conditions. The work of prediction or calculation of volume increase has been simplified by the construction of two graphs which m a y be used w i t h experimentally determined constants of swell and extraction.
Volume increase results were obtained in duplicate by A.S. T.M. method D471-43" (I), except that a Jolly balance was used in weighing. Table I shows volume increase data for Perbunan compounds containing various amounts of carbon black. The polymer swell values for each gasoline were calculated, and the deviation from the average was found to be small. Additional K values, or percentage volume swell of the polymer, are reported in Table 11. Two concentrations of black were used, and the K values for the different polymer concentrations were found to be nearly equivalent. The data cited appear to demonstrate that the swell of Perbunan compounds in various immersion media is due tu the swell of the polymer, the compounding ingredients serving to dilute the Perbunan and thus reduce the swell of the total compound. This conclusion.assumes that all the compounds have approximately the same state of cure and that there are no extractable softeners in the compound. I n this work the same accelerator, sulfur concentration, and time of cure were used. The recipes are the type in which the state of cure should be similar, even though the amyunt of loading is widely varied.
