Original Article

Chemistry in the Kitchen — Making Ground Meat More Healthful

List of authors.
  • Donald M. Small, M.D.,
  • Cheryl Oliva,
  • and Anna Tercyak, M.A.

Abstract

Background.

The National Cholesterol Education Program recommends a diet containing less than 30 percent of calories in the form of fat, less than 10 percent in the form of saturated fat, and less than 300 mg of cholesterol per day. Since Americans' diets generally exceed these recommendations, we wished to find an easy kitchen method to reduce substantially saturated fat and cholesterol in ground meat.

Methods.

Raw ground meat was heated in vegetable oil and rinsed with boiling water to extract fat and cholesterol. The fat-free broth was recombined with the meat to restore flavor. The amounts of total fat, saturated fat, and cholesterol in the meat after extraction were compared with the amounts in meat cooked as patties and in stir-fried, rinsed meat.

Results.

When raw ground beef containing 9.6 to 20.8 percent fat was cooked as patties and the fat poured off, 6 to 17 percent of the fat and 1.3 to 4.3 percent of the cholesterol were lost. In stir-fried, rinsed ground beef, 23 to 59 percent of the fat and 9.0 to 18.8 percent of the cholesterol were lost. When vegetable oil was used to extract fat and cholesterol from beef containing 20.7 percent fat, a mean (±SD) of 67.7±1.6 percent of the fat and 39.2±5.1 percent of the cholesterol were lost. The differences between conventionally cooked meat and meat prepared by the extraction of fat were significant (P<0.001). An average of 43 percent (range, 38 to 49) of cholesterol was extracted from a wide variety of ground meats. Although conventional cooking produced no change in fatty-acid composition as compared with raw meat, our extraction process greatly increased the ratio of unsaturated to saturated fat, from 1.32 in conventionally cooked meat to 2.92 to 4.56 in meat after extraction. Extraction resulted in the loss of 72 to 87 percent of saturated fat.

Conclusions.

This method produces a tasty meat product that is much lower in saturated fat and cholesterol than conventionally cooked meat, and that can be used in sauces, soups, and solid meat products. (N Engl J Med 1991;324:73–7.)

Introduction

FROM the work of Keys1 we know that populations whose diet is high in saturated fats have a higher incidence of atherosclerosis than populations eating a diet rich in unsaturated or polyunsaturated fats. Only recently, however, has it become clear that men with relatively high serum cholesterol levels actually have fewer cardiovascular events if their serum cholesterol level is lowered.2 , 3 Furthermore, patients with hypercholesterolemia who had had a myocardial infarction were able to slow the progression of the disease significantly by participating in an aggressive treatment program designed to lower their levels of low-density lipoprotein cholesterol. In fact, regression was even evident in a few cases.4 Thus, it seems prudent for middle-aged men (and perhaps women) with moderately elevated serum cholesterol levels to make moderate changes in their lifestyles, including diet. As a first step to lowering cholesterol levels, the American Heart Association and the National Cholesterol Education Program5 recommend a diet in which less than 30 percent of the calories are derived from fat, less than one third of which should be saturated fat, and providing less than 300 mg of cholesterol per day. It has been estimated that the current American diet contains an average of 350 to 500 mg of cholesterol and 35 to 40 percent of calories from fat, of which almost half is saturated. Although dairy products are a major source of cholesterol and saturated fat, meats probably are the main source.6

The middle-aged man on our team who has dabbled in kitchen chemistry in the past7 took heed of these recommendations and, by application of the basic principles of lipid physical chemistry,8 worked out a method to reduce the total fat, saturated fat, and cholesterol content of ground meat. The impulse to use organic solvents such as those used in a Folch extraction9 to remove the lipids from hamburger was squelched quickly. Clearly, that would not be a recipe for a healthful and savory dish. A simple and acceptable technique was needed by which much of the saturated fat and some of the cholesterol could be removed from meat while the basic texture and flavor were retained.

Fat (triglyceride) in meat is present primarily in fat cells interspersed between the muscle cells of the meat. There is almost no cholesterol ester in meat. Most of the free cholesterol is in the muscle-cell membranes within the meat and very little in the fat itself. For this reason, it is difficult to extract the cholesterol from meat simply by cooking it and draining off the excess fat, or by subjecting meat to meticulous trimming. Although these two procedures are effective in diminishing the total amount of fat in meats, the fat that remains in the meat is largely saturated, and the cholesterol is retained. It is known that the solubility of free cholesterol in oils rich in unsaturated fat is about 2 to 3 g per 100 ml of oil at room temperature.8 The solubility of cholesterol increases enormously, however, as the temperature is raised. For instance, at 80°C about 10 g of cholesterol is soluble in 100 ml of triolein, the principal constituent of olive oil, and about 30 g at 120°C.8

The highly saturated fat in beef, pork, lamb, and veal and the somewhat less saturated fat in poultry is largely solid at room temperature, as one can tell by sight and by the feel of the waxy fat, but melts at between 50 and 65°C. Therefore, our chef decided to use as extracting fluid vegetable oils that contain nonabsorbable plant sterols but no cholesterol and large quantities of monounsaturated or polyunsaturated fat. With the use of this method, which is described below, a large proportion of the saturated fat (72 to 87 percent) was removed from ground beef or pork. Moreover, nearly half the free cholesterol was removed in this process. The steps in the method are as follows: extraction of the fat and cholesterol from the meat by heating it in vegetable oil (the meat is cooked at the same time), rinsing of the meat with boiling water or steam, separation of the oil and water (broth) from each other, and return of the broth (usually with the amount of water reduced) to the meat from which fat and cholesterol have been extracted, thus restoring any lost flavor. The reconstituted product is a low-fat, highly-unsaturated- or polyunsaturated-fat, low-cholesterol ground meat with good flavor, which can be used in spaghetti sauces, chili, meatloaf, soups, and other dishes and could be combined with binders to make a variety of solid meat products.

Methods

The method we used is as follows: An appropriate quantity (such as 1 kg [2.2 lb]) of raw ground meat (beef, pork, lamb, or poultry) is added to 500 to 1000 ml (1/2 to 1 qt) of vegetable oil and heated to about 80°C (176°F). The mixture is stirred until the temperature reaches 80 to 90°C (176 to 195°F) and then stirred for another five minutes to allow the heated oil to mix with the meat. Penetration of the oil into the meat permits the replacement of saturated fat with unsaturated fat and the partial removal of free cholesterol from cell membranes. The mixture is then heated to between 100 and 110°C (212 to 230°F) for five minutes to brown the meat, boil off excess water, and extract additional cholesterol. The meat and oil are then poured through a fine kitchen strainer, which collects the meat and allows the oil and any remaining broth to pass through to a suitable container. About 250 to 500 ml ( 1 to 2 cups) of boiling water is then poured over the meat in the strainer, removing most of the adherent oil and water-soluble material. This liquid is added to the oil and broth in the collection jar. The oil and broth are then separated —for example, by cooling in the refrigerator for about one hour, so that the fat floats, solidifies, and can be lifted off as a cake. The aqueous portion, which is a flavorful meat stock, can then be either reduced (by boiling some of the water off) or added immediately to the ground meat. The meat is now ready to be used in various recipes that call for ground or finely chopped beef, pork, veal, or lamb. Spaghetti sauce, taco filling, chili con carne, stuffed peppers, meatloaf, casseroles, and soups using meat prepared this way have been served to appreciative diners.

By chemical means, we analyzed the meat prepared by this method, the oil used for extraction (oil phase), and the broth (aqueous phase) to evaluate the efficiency of the extraction procedure and determine the composition of the meat after extraction. In the specific examples described below, safflower oil was used to extract fat and cholesterol from raw lean beef, ground sirloin, and pork. In other experiments common brands of vegetable oils such as Puritan and Crisco were used; they were equally effective and less expensive.

In order to compare the composition of beef prepared by our extraction process with that of beef cooked conventionally, we cooked ground beef in two other ways: as hamburger patties and stir-fried and rinsed. First, 100-g hamburger patties 1 cm thick were cooked over medium-low heat until they were brown throughout. Each patty was then drained for five minutes, and all the fat was recovered from the pan. Second, we cooked 100-g portions of ground beef at 100 to 110°C, constantly crushing and stirring the beef. The beef was collected in a strainer, drained for five minutes, carefully rinsed with 50 ml of boiling water, and drained again for five minutes. Both fat and beef were analyzed chemically.

Chemical Analyses

Samples of raw lean ground beef (about 21 percent fat), ground sirloin (about 18 percent fat), and lean ground pork (about 15 percent fat) were purchased from a market and the fat and cholesterol extracted with safflower oil as described above. Samples of ground beef with a fat content ranging from 9.6 to 20.7 percent were also cooked conventionally as described above and the meat and fat analyzed. Aliquots of the raw meat, conventionally cooked meat, and meat after extraction were lyophilized (freeze-dried), the lipids were extracted into chloroform,9 and the total extracted lipids were measured gravimetrically after evaporation with solvents. Neutral glycerides were measured (kit 3320-UV; Sigma Chemicals, St. Louis), as were phospholipids.10 Aliquots of the organically extracted meat lipids and the oils used in the extraction procedure were subjected to hydrolysis in 0.5 N potassium hydroxide in ethanol at 60°C to remove the large excess of triglycerides. The neutral sterols were then extracted into hexane from the aqueous alkaline phase. Cholesterol was separated from plant sterols and quantitated by gas—liquid chromatography on a 61-cm (2-ft) 3 percent SP2500–100/120 Supelcoport glass column.11 Thin-layer chromatography was performed to identify lipid classes after charring with 50 percent sulfuric acid.12 , 13 Fatty-acid profiles of the meats and oils were determined after transmethylation and analysis of methyl esters by gas—liquid chromatography.14 An aliquot of the broth was lyophilized, and the residue was extracted by the procedure of Folch et al.9 The total lipid content was determined gravimetrically, and lipid classes were measured chromatographically.

Results

Removal of Fat and Cholesterol by Cooking

Table 1. Table 1. Loss of Fat and Cholesterol from Ground Beef Cooked as Hamburger Patties or Stir-Fried and Rinsed.*

Considerable amounts of fat and a small fraction of cholesterol can be removed by cooking. However, the fat content of the raw meat and the method of cooking influence the final result (Table 1). First, the more fat there is in the raw meat, the more fat is removed by cooking. Second, far less fat is removed if the meat is cooked as hamburger patties than if the ground meat is stir-fried and thoroughly rinsed with boiling water. Although more than 50 percent of the fat can be removed from fatty beef by the latter method, far less cholesterol is lost than with the extraction method. This difference reflects the fact that most of the cholesterol is in the muscle and therefore not readily extracted. Conventional cooking does not affect the fatty-acid composition of beef, as discussed below. If the meat is stir-fried and drained but not rinsed, considerably more fat is retained in the meat. Thus, rinsing can reduce fat up to 50 percent.

Extraction of Fat, Saturated Fat, and Cholesterol from Ground Meat with Vegetable Oil

Table 2. Table 2. Lipid Composition of Raw Ground Meat, Conventionally Cooked Ground Meat, and Ground Meat Prepared by the Extraction Method.* Table 3. Table 3. Extraction of Cholesterol from Meat with Vegetable Oil.*

To illustrate the use of the extraction procedure, samples of lean beef (20.7 percent fat, 59 percent water), ground sirloin (18.2 percent fat, 62 percent water), and lean pork (14.5 percent fat, 63 percent water) were heated with safflower oil and rinsed as described in Methods. In addition, lean beef was also cooked by the stir-fry—rinse method (Table 1), and its composition was compared with that of raw meat and samples of meat after extraction. Analysis of the lipid composition of the raw and treated meats (Table 2) indicated that even after marked fat loss the principal lipid was triacylglycerol (triglyceride), which accounted for more than 92 percent of the total fat. Small percent-ages of phospholipid and very small percentages of cholesterol were also present. After conventional cooking, lean beef lost a mean (±SD) of 59.0±2.8 percent of the fat (number of samples measured [n] = 6) and 18.3±6.9 percent of the cholesterol (n = 12), whereas the same lean beef prepared by the extraction method lost 67.7± 1.6 percent of the fat (n = 6) and 39.2±5.1 percent of the cholesterol (n = 12). These differences between conventionally cooked meat and meat prepared by extraction are significant at the P<0.001 level. The extraction of cholesterol with vegetable oil from several different meat samples uniformly produced a reduction of about 43 percent in cholesterol (range, 38 to 49 percent) (Table 3).

Table 4. Table 4. Fatty-Acid Composition of Raw Ground Meat, Conventionally Cooked Ground Meat, and Ground Meat Prepared by the Extraction Method, Fat from Cooked Beef, and Extracting Oil.

The distributions of fatty acids in raw and conventionally cooked ground beef and pork and in ground beef and pork after extraction are compared with each other and with those in the extracting oil in Table 4. As expected, cooking did not change the fatty-acid composition of meat. In fact, the composition of the raw meat, cooked meat, and removed fat is virtually identical (Table 4). In contrast, extraction results in a marked decrease in saturated fats. For instance, the proportion of stearic acid (18:0) was reduced from 13.3 to 6.5 percent in lean beef, from 13.2 to 4.7 percent in ground sirloin, and from 14.2 to 5.1 percent in pork. Marked decreases also occurred in the proportion of palmitic acid (16:0). Conversely, the proportion of linoleic acid (18:2), the principal fatty acid in the extracting oil, increased substantially from less than 3 percent to 39 to 59 percent. The replacement of triglyceride fatty acids can be estimated from marker fatty acids such as myristic acid (14:0) and heptadecanoic acid (17:0), which are not present in safflower oil. The degree to which triglyceride fatty acids were replaced can be calculated as the sum of the fat reduction and the absolute replacement. Thus, when raw meat is compared with meat after extraction, about 72 percent of the triglycerides were replaced in pork and 78 to 87 percent in beef. Comparing ground meat cooked conventionally and rinsed thoroughly with boiling water with beef prepared by extraction shows that about two thirds (64 to 70 percent) of the saturated triglyceride left in the conventionally cooked beef was replaced by other fats in the meat prepared by the extraction method. These remarkable changes resulted in a reduction in saturated fatty acids from about 43 percent in raw ground sirloin and lean pork to 18 percent and from 43 percent in conventionally cooked lean beef to 25 percent in lean beef prepared by extraction. The ratio of unsaturated to saturated fatty acids increased from 1.32 in raw ground sirloin to 4.44, from 1.31 in raw ground pork to 4.56, and from 1.32 in conventionally cooked beef to 2.92. The ratio of polyunsaturates to saturates also markedly increased (Table 4).

The fatty-acid content of the safflower oil used in the extraction process reflects moderate increases in saturated fatty acids (for example, stearic acid increased from 2.0 percent to 3.9 percent and 3.6 percent in oil used to extract fat from beef and pork, respectively) and moderate decreases in polyunsaturates. The linoleic acid level fell from 77.3 percent to 65.9 percent (for beef) and 67.7 percent (for pork). (Complete data on the fatty-acid composition of the oils after extraction are available elsewhere.*) The small increase in highly saturated triglycerides, coming from the meat, is adequate to cause the crystallization of these triglycerides, which have high melting points, when they are refrigerated and permits the separation of the solidified oil mass from the aqueous phase. Before its use in extraction the safflower oil is a clear, light yellow and is liquid even at 5°C (41°F); after the saturated triglycerides are extracted and the oil is cooled to 5°C, it is a semisolid cake resting on top of the aqueous broth. Microscopical examination under crossed polarizing lenses shows that even at room temperature the oil is full of small spherulites of partially crystallized triglycerides. At refrigerator temperature (about 5°C) these relatively saturated triglycerides form a highly intricate crystalline mesh that allows the whole mass of fat, which is

*See NAPS document no. 04829 for one page of supplementary material. Order from NAPS c/o Microfiche Publications, P.O. Box 3513, Grand Central Station, New York, NY 10163–3513. Remit in advance (in U.S. funds only) $7.75 for photocopies or $4 for microfiche. Outside the U.S. and Canada add postage of $4.50 ($1.50 for microfiche postage). There is an invoicing charge of $15 on orders not prepaid. This charge includes purchase order.

still more than 60 percent liquid, to be removed as a cake from the broth. Since the extracting oil contains a comparatively small amount of cholesterol (20 to 30 mg per 100 ml) and small amounts of saturated triglyceride, it can be recovered and used for three or four more extractions, with results nearly as good. Reuse of the oil greatly increases the efficiency of the process. Less oil can be used in the original extraction, but the results are not as good. In experiments with a ratio of raw meat to oil of 5:1 (wt:vol), the proportion of linoleic acid increased from 2 percent to 19 percent after extraction and that of stearic acid fell from 13 percent to 9 percent; only about 40 percent of the saturated fat was replaced.

The broth resulting from the extraction of fat from beef had 16.6 mg of lipid and that from pork had 31.9 mg of lipid — only 0.09 percent and 0.22 percent, respectively, of the total fat in the raw meat. Thus, the amount of lipid recovered in the broth was insignificant. Virtually all this lipid was triglyceride and was probably adsorbed to the small particulate fraction of meat that passed through the strainer.

Discussion

The method of cooking ground meat is clearly an important factor in how much fat is contained in the final product. For instance, if raw ground meat is added directly to a chili, a spaghetti sauce, or a meatloaf — especially one made with bread crumbs, which absorb the fat — then all the fat present in the raw meat remains in the final product. If hamburger patties are cooked and drained, only a small fraction of fat is removed (Table 1). However, if ground meat is stirred and crushed during cooking and then rinsed carefully with a large volume of boiling water and drained for five minutes, 23 to 59 percent of the fat and 9 to 19 percent of the cholesterol can be removed (Table 1). This method is probably not widely employed, as it takes more effort than other methods and the resulting meat is relatively dry and tasteless. The procedure described here also requires somewhat more effort than conventional methods and a good supply of vegetable oil (although it can be reused), but the product has markedly reduced saturated fat content and a considerably lower percentage of cholesterol than raw or conventionally cooked meat.

The vegetable-oil extraction procedure can be used with beef, pork, lamb, and other forms of red meat and with poultry (ground turkey or chicken). The recombination of the recovered (and reduced) fat-free broth to the meat enhances the flavor. The product can be used in many preparations, from tacos to chili, soups to casseroles, spaghetti sauces to lasagna. Such foods could become an important part of a dietary regimen, replacing a fair share of red meat cooked conventionally. If a "usual American" eating a diet in which 35 to 40 percent of total calories are derived from fat and 15 to 18 percent of calories from saturated fat were to prepare just one third of his or her red meat in this fashion, it would lower the consumption of saturated fats by about 3 percent of calories. The National Cholesterol Education Program has estimated that for every increase of 1 percent of calories ingested in the form of saturated fat, the serum cholesterol level rises an average of 0.07 mmol per liter (2.7 mg per deciliter). Thus, if one third of dietary red meat were replaced by meat prepared by extraction of fat, the serum cholesterol level might be reduced by as much as 0.16 to 0.18 mmol per liter (6 or 7 mg per deciliter). Furthermore, the total cholesterol intake and the total percentage of calories derived from fat would decrease, which could reduce the serum cholesterol level an additional 0.03 to 0.05 mmol per liter (1 to 2 mg per deciliter). Overall, this modest dietary change could conceivably reduce the average serum cholesterol level by 0.18 to 0.23 mmol per liter (7 to 9 mg per deciliter). In a relatively large population group over several years, this decrease might have an important effect on the prevalence of cardiovascular disease.

This technique of meat preparation was worked out in the kitchen by someone who enjoys good food. Those who wish to use this procedure in their own kitchens will find it quite simple and not expensive. Many Americans, however, prefer the convenience of fast foods, which offer breathing room in overcrowded schedules and relief for working parents. Food companies and fast-food chains could probably scale up this technique to produce a variety of more healthful fast foods and other products.

Funding and Disclosures

We are indebted to Kathryn Small for her assistance and for graciously recognizing that the kitchen can be a laboratory. We are also indebted to Cynthia Curry for her help with the lipid measurements and to Margaret Gibbons and Irene Miller for their assistance in the preparation of the manuscript.

Author Affiliations

From the Department of Biophysics, Housman Medical Research Center, Boston University School of Medicine, 80 E. Concord St., Boston, MA 02118–2394, where reprint requests should be addressed to Dr. Small.

References (14)

  1. 1. Keys AB. Seven countries: a multivariate analysis of death and coronary heart disease. Cambridge, Mass.: Harvard University Press, 1980

  2. 2. Lipid Research Clinics Program. . The Lipid Research Clinics Coronary Primary Prevention Trial results. I. Reduction in incidence of coronary heart disease . JAMA 1984; 251:351–64

  3. 3. Frick MH, Elo O, Haapa K, et al. . Helsinki Heart Study: primary-prevention trial with gemfibrozil in middle-aged men with dyslipidemia: safety of treatment, changes in risk factors, and incidence of coronary heart disease . N Engl J Med 1987; 317:1237–45

  4. 4. Blankenhorn DH, Nessim SA, Johnson RL, Sanmarco ME, Azen SP, Cashin-Hemphill L. . Beneficial effects of combined cholestipol-niacin therapy on coronary atherosclerosis and coronary venous bypass grafts . JAMA 1987; 257:3233–40

  5. 5. Report of the National Cholesterol Education Program expert panel on detection, evaluation, and treatment of high blood cholesterol in adults . Arch Intern Med 1988;48:36–69

  6. 6. Gurr MI. Dairy fats: nutritional nasties or dietary delights? In: Cambie RC, ed. Fats for the future! Chichester, England: Ellis Horwood, 1989:41–61

  7. 7. Small DM, Bernstein M. . Doctor in the kitchen: experiments on sauce Béarnaise . N Engl J Med 1979; 300:801–2

  8. 8. Small DM. The physical chemistry of lipids — from alkanes to phospholipids. Vol. 4 of Handbook of lipid research. New York: Plenum Press, 1986

  9. 9. Folch J, Lees M, Sloane Stanley GH. . A simple method for the isolation and purification of total lipids from animal tissue . J Biol Chem 1957; 226:497–509

  10. 10. Bartlett GR. . Phosphorous assay in column chromatography . J Biol Chem 1959; 234:466–8

  11. 11. Supelco Chromatographic supplies catalogue #17. Belefonte, Pa.: Supelco, 1980:25

  12. 12. Downing DT. . Photodensitometry in the thin-layer Chromatographie analysis of neutral lipids . J Chromatogr 1968; 38:91–9

  13. 13. Katz SS, Shipley GG, Small DM. . Physical chemistry of the lipids of human atherosclerotic lesions: demonstration of a lesion intermediate between fatty streaks and advanced plaques . J Clin Invest 1976; 58:200–11

  14. 14. Morrison WR, Smith LM. . Preparation of fatty acid methyl esters and dimethylacetals from lipids with boron fluoride-methanol . J Lipid Res 1964; 5:600–8

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