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Quality Characteristics, Cholesterol, and Sodium Content of Turkey as Affected by Conventional, Convection, and Microwave Heating1
Quality Characteristics, Cholesterol, and Sodium Content of Turkey as Affected by Conventional, Convection, and Microwave Heating1 K. J. PRUSA and K. V. HUGHES Department of Human Nutrition, Foods and Food Systems Management, University of Missouri, Columbia, Missouri 65211 (Received for publication April 29, 1985)
1986 Poultry Science 65:940-948 INTRODUCTION T h e relationship b e t w e e n diet a n d disease has received considerable a t t e n t i o n in recent years. Cholesterol has been implicated in t h e d e v e l o p m e n t of c o r o n a r y heart disease, a n d sodium c o n s u m p t i o n is associated with elevated blood pressure resulting in hypertension. Individuals have been advised t o lower t h e cholesterol intake in t h e diet (Senate Select C o m m i t t e e , 1977) and m o r e recently, t h e sodium i n t a k e (AMA, 1 9 8 3 ; A H A , 1 9 8 2 ; F N B , 1980). Both sodium and cholesterol are inherent c o m p o n e n t s of muscle foods. R e p o r t e d cholesterol values for t u r k e y light muscle range from 58 to 6 0 m g / 1 0 0 g for raw muscle (USDA, 1 9 7 9 ; Feeley et al., 1972) and from 6 8 t o 82 m g / 1 0 0 g for cooked muscle (USDA, 1 9 7 9 ; Karkalas et al, 1982). S o d i u m values for b o t h r a w a n d c o o k e d t u r k e y light muscle are rep o r t e d as 6 0 m g / 1 0 0 g (USDA, 1979). In t h e USDA studies, t u r k e y was roasted in a r o t a r y h e a r t h oven at 163 C t o an internal t e m p e r a t u r e of 82 C. A l t h o u g h t h e cholesterol and sodium
1 Supported by funds from the Home Economics Research Catalyst Fund.
c o n t e n t of r a w a n d c o o k e d t u r k e y has been r e p o r t e d , t h e r e is little information pertaining t o h o w these a m o u n t s are affected b y various cooking m e t h o d s . When choosing a cooking m e t h o d for muscle foods, p r o d u c t quality and energy e x p e n d i t u r e are of i m p o r t a n c e t o t h e consumer. McNeil and Penfield ( 1 9 8 3 ) indicated microwave and convection ovens were more energy efficient t h a n a conventional oven for cooking t u r k e y . O n l y o n e internal e n d p o i n t t e m p e r a t u r e (77 C) was investigated. T o t a l cooking losses were greater for microwave heated t u r k e y breasts w h e n c o m p a r e d t o those heated in a gas oven (Bowers and Heir, 1 9 7 0 ; Cipra et al, 1 9 7 1 ) . Chambers and Bowers (1981) r e p o r t e d t h a t t h e flavor of t u r k e y cooked in a conventional oven m o r e closely resembled t h a t of roast t u r k e y t h a n t u r k e y cooked in a microwave oven. Objectives of this s t u d y w e r e : 1) t o m o n i t o r energy c o n s u m p t i o n and determine relative efficiency of microwave, convection, and conventional ovens used for heating t u r k e y t o t w o different internal e n d p o i n t t e m p e r a t u r e s , and 2) t o c o m p a r e t h e three heating m e t h o d s (microwave, convection, and conventional) with respect t o t h e quality characteristics a n d changes in cholesterol and sodium c o n t e n t of t u r k e y breast muscle. Cholesterol and sodium
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ABSTRACT Six treatment combinations for evaluation of quality characteristics, sodium, and cholesterol content of turkey breast roasts were studied: three oven types (conventional, convection, and microwave) and two internal endpoint heating temperatures (77 C and 82 C). The microwave oven was the most energy efficient, and the conventional oven was the least efficient. Overall, drip loss was highest in the microwave oven, and heating to 82 C increased total cooking loss. Cook drip from the microwave oven contained less fat but the same amount of cholesterol as cook drip from the other two oven types. Instron shear values were not affected by oven type or internal endpoint temperature. Generally, when comparing raw to cooked samples, heating increased (concentrated) the cholesterol content and decreased the sodium content of the turkey. Cholesterol content of the heated roasts was not affected by type of oven; however, heating to the higher internal endpoint temperature increased (concentrated) the cholesterol. Sodium content was not affected by oven type or internal endpoint heating temperature. Cholesterol and sodium retentions of the roasts after heating were 96 and 64%, respectively, when averaged over the three oven types. (Key words: cholesterol, sodium, turkey quality)
QUALITY, CHOLESTEROL, SODIUM CONTENT IN TURKEY
retention in the turkey after heating and cholesterol content of cook drip were determined also.
MATERIALS AND METHODS
whole breast by removing the meat (pectoralis major) from each side. The roasts were trimmed to weigh between 351 to 448 g before heating. Raw samples for cholesterol, sodium, and proximate analysis were taken by combining the trimmings from both pectoralis major breast muscles. Oven Heating. For conventional heating (Electric Premier, Model G7-B55) and convection heating (Rival, Model No. 4020), roasts were placed on racks in glass baking dishes and covered with an open aluminum foil tent. Ovens were preheated to 163 C. Oven and internal roast temperature were monitored with iron constantan thermocouples attached to an Omega Digital Thermometer (Model 2166A). Thermocouples were positioned in the geometric center of the roast. Roasts were heated to either 77 or 82 C internal temperature. For microwave heating (Sharp Model-8200), a microwave thermometer was placed in the geometric center of the roast. Roasts were placed on a rack in a glass dish, covered with
TABLE 1. Incomplete block design for assigning treatments to heating period Treatment Block (heating period) 1
Convection
Conventional 77 C
82 C
X
X
2
77 C
82 C
X
X
3 4
X
X
X
X
X
X
X X
12
15
X
X
11
14
X
X
9
13
X
X
8
10
82 C
X
6 7
77 C
X
X
5
Microwave
X X
X
X
X X
X X
X
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Treatments. Six treatment combinations for heating turkey breast roasts were studied: three oven types (conventional, convection and microwave) and two internal endpoint temperatures (77 C and 82 C). A balanced incomplete block design with five replications of each treatment was used (Table 1). Roast Preparation. Fifteen fresh, RTC (ready-to-cook) hen turkeys weighing 5.43 to 6.34 kg were obtained from a commercial supplier. The breast was removed from each of the turkeys, wrapped in plastic film, overwrapped with heavy-duty aluminum foil, and frozen (—18 C) until heating. Prior to each heating period, two whole turkey breasts were thawed approximately 3 days (60 hr) at 3 C. Two boneless roasts were made from each
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procedures (AOAC, 1980). Crude protein was determined by the Kjeldahl method described in Section 7.015. Crude fat was determined by an indirect method (Section 7.057). Moisture content was determined by an in-house method using a freeze-dryer apparatus. A 5-g sample was heated for 12 hr or until pressure fell below 10 n of Hg. Samples for sodium analysis were dry-ashed (Section 3.007 a), and determination was performed on a automated potassium instrument (Sections 2.097 to 2.101). Single analysis were made on each sample with 10% reruns to check precision and extreme values. Cholesterol content of the raw and cooked roasts and cook drip was determined according to the method of Searcy and Bergquist (1960) as described by Rhee et al. (1982). Samples (5 g) were blended with 85 ml of chloroform/methanol (2/1, v/v), made up to volume (100 ml), filtered (Whatman #1), washed with distilled water (.2 X volume), and allowed to separate (4 C) overnight (Folch et al., 1957). A 6-ml aliquot of lipid extract prepared by the Folch procedure was evaporated to dryness in a 60-C water bath under a stream of nitrogen. Lipids were saponified with 15 ml alcoholic KOH (15% KOH in 90% ethanol) for 10 min in a shaker water bath (88 C). When cool, 5-ml distilled water was added, and the unsaponifiable material was extracted with 10-ml hexane. A 5-ml aliquot of the hexane extract was dried as previously described. Cholesterol concentration was determined colorimetrically using FeS0 4 -acetic acid and concentrated H 2 S 0 4 as color developing agents. A cho-
TABLE 2. Proximate analysis, cholesterol, and sodium contents of raw turkey breast muscle1 Proximate analysis Moisture, % Protein, % Lipid, %
72.8 25.3 1.5 Cholesterol content
Wet-weight basis, mg/100 g Dry-weight basis, mg/100 g Roast-weight basis, mg/roast wt
48.13 177.12 203.77
Sodium content Wet-weight basis mg/100 g Dry-weight basis, mg/100 g Roast-weight basis, mg/roast wt 1
Mean of 15 raw values.
59.00 217.06 249.84
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waxed paper, and heated in a microwave oven on the "roast" power setting (368 W). Roasts were removed from the microwave oven when the internal temperature reached 72 to 73 C or 76 to 77 C for the desired 77- and 82-C internal endpoint temperatures, respectively. Postoven temperature rise was determined in preliminary work to be approximately 4 to 5 C for these roasts. Roasts were covered and held approximately 5 min after removal from the microwave oven to allow the final internal endpoint temperature to be reached. Energy and Oven Efficiency Measurements. For the conventional and convection ovens, power consumption during the preheating and heating period was recorded. For the microwave oven, energy consumption was recorded from the time the roast was placed in the oven until it was removed. Power consumption was measured with a Duncan portable wattmeter (Number 00013). Cooking power and oven relative efficiency were determined as described by Korschgen et al. (1980). Cooking Losses and Instron Measurements. Cooking losses (percent evaporative, drip, and total) of the roasts were determined as described by Campbell et al. (1979). For sampling, the skin was removed and the roast was sliced into four (2.54 cm) sections. The second slice (2.54 cm) was cored for shearing. Cores (1.27-cm diameter) were cut parallel to the muscle fibers in a radial fashion from the exterior (outer) portion of the muscle. A Warner-Bratzler shear attachment on the Instron Universal Testing Machine (Model 1132) was used to completely shear six roomtermperature cores from each treatment. Instron response was evaluated with a Southwest Technical Computer. The Instron Signal voltage was fed into a computer-controlled amplifier and then into a 12-bit A/D converter (resolution = 1 part in 4095). The Instron loadcell was 100 kg, the crosshead speed was 12.7 cm/min, and, for the purpose of calculating area under the force-distance curve, a simulated chartspeed of 25.4 cm/min was used. The number of data points taken was 38 ± 2/sec. Measurements recorded were area under the peak (square centimeters) and maximum peak height force (grams). Proximate Analysis, Sodium, Cholesterol Determination. Proximate analysis (protein and fat) was determined on ground (.31-cm plate) raw and cooked turkey breast samples by Association of Official Analytical Chemists
QUALITY, CHOLESTEROL, SODIUM CONTENT IN TURKEY
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TABLE 3. Heating time, heating rate, and energy values for conventional, convection, and microwave ovens1 Temperature Oven
77 C
82 C
mean
Heating time 2 (min) Conventional Convection Microwave
104.00d 81.40b 13.80a
167.20e 96.80cd 16.40a
Heating rate 2 (min/g) Conventional Convection Microwave
.24 c .19 b .03 a
.39 d .23bc .04 a
Conventional Convection Microwave
1050.56 b 1274.54° 202.24 a
1452.94 d 1419.44 d 231.06 a
Rate of consumption 2 (W-hr/g) Conventional Convection Microwave
2.47 b 3.02 c ,51a
3.40 c 3.42<: .54 a Cooking power (W)
Conventional Convection Microwave Temperature effect mean
303.73 378.20 363.63 348.52 N S
263.93 382.06 372.85 339.61NS 4
283.83 a 380.13 b 368.24 b
Relative efficiency ( ) Conventional Convection Microwave Temperature effect mean
25.85 29.76 40.23 31.95 N S
Conventional Convection Temperature effect mean
227.14 310.89 269.01NS
21.46 26.90 40.20 29.52NS
23.66 a 28.33 b 40.22 c
235.04 265.19 250.11 N S
231.09 a 288.04 b
Oven warmup (W-hr)
a c Means for an oven effect not followed by a common letter are significantly different (P-C01 for cooking power, P<.001 for relative efficiency, P<.05 for oven warmup).
Means not followed by a common letter are significantly different. 1
Means of five replications.
2
Main effect means are not reported because of significant interaction.
3
Includes power consumption for preheating conventional and convection ovens.
4
NS = Not significant.
lesterol standard curve was c o n s t r u c t e d according t o Searcy and Bergquist ( 1 9 6 0 ) . Statistical Analysis. Least squares analysis of variance using t h e general linear m o d e l procedure (PROC GLM) was used t o determine t r e a t m e n t and block differences a m o n g o b -
jective data (SAS, 1 9 8 2 ) . Adjusted m e a n s derived from t h e balanced i n c o m p l e t e block design were calculated w h e n a p p r o p r i a t e . RESULTS AND DISCUSSION P r o x i m a t e analysis, cholesterol c o n t e n t , and
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Total energy2'3 (W-hr)
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PRUSA AND HUGHES
TABLE 4.. Cooking losses for turkey and fat and cholesterol content of the cook drip of turkey heated in conventional, convection, and microwave ovens' Temperature Oven
77 C
82 C
Oven effect mean
Evaporative loss2 (%]I Conventional Convection Microwave
18.78 a 19.92a 19.94a
27.66 c 23.78° 23.02 b Drip loss (%)
3.14 3.82 6.31 4.42NS 3
3.06 3.46 6.13 4.22NS
3.10a 3.64a 6.22b
Total loss2 (%) a
Conventional Convection Microwave
22.43 23.44a 26.55 b c
Conventional Convection Microwave Temperature effect mean
74.69 53.72 33.69
30.72 d 26.25 b 29.34 c d
Cook drip lipid content: (%) 72.58 69.29 33.46 58.11 N S 54.03NS
73.64b 61.51b 33.08a
Drip that is cholesterol (%) Conventional Convection Microwave Temperature effect mean
.040 .036 .025
.050 .047 .028
.034NS
.042NS
.045° .042b .027a
ab ' Means for an oven effect not followed by a common letter (a,b) are significantly different (P<.001) for drip loss and cook drip lipid content, P<.01 for drip that is cholesterol. a—d Means not followed by a common letter are significantly different. 'Means of five replications. 2
Main effect means are not reported because of significant interaction.
3
NS = Not significant.
sodium c o n t e n t of t h e raw t u r k e y breast muscle are presented in Table 2. T h e moisture, p r o t e i n , and fat c o n t e n t s were comparable to t h e reported values of 7 3.57% for moisture, 2 3 . 6 4 % for protein, and 1.66% for fat (USDA, 1979). T h e cholesterol c o n t e n t of t h e raw t u r k e y light meat was slightly lower t h a n reported values of 6 0 m g / 1 0 0 g (Feeley, 1 9 7 2 ) and 58 m g / 1 0 0 g (USDA, 1979). T h e sodium c o n t e n t was comparable t o t h e r e p o r t e d value of 6 0 m g / 1 0 0 g of t u r k e y light meat (USDA, 1979). T u r k e y roasts heated in t h e microwave oven had t h e shortest heating times, and conven-
tionally cooked roasts t o o k t h e longest t o heat (Table 3). T h e effect of heating t o a higher internal t e m p e r a t u r e was d e p e n d e n t o n oven t y p e . Cooking t o a high internal t e m p e r a t u r e decreased t h e rate of heating in t h e conventional oven; however, roasts heated in t h e convection or microwave oven (within oven) heated at t h e same rate t h r o u g h t h e entire heating process, regardless of internal e n d p o i n t t e m p e r a t u r e . T h e lower heating times and m o r e rapid rate of heating t u r k e y in t h e microwave oven is in agreement with past studies (Cipra et al, 1 9 7 1 ; McNeil and Penfield, 1 9 8 3 ) .
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Conventional Convection Microwave Temperature effect mean
QUALITY, CHOLESTEROL, SODIUM CONTENT IN TURKEY
More total energy was required to cook the turkey to 77 C in the convection oven than in the conventional and microwave ovens. This may be attributed to more energy being used by the convection oven during the preheating period. Total energy values were similar between conventional and convection ovens when roasts were heated to 82 C. The microwave oven used less total energy than the conventional or convection ovens, regardless of endpoint temperature. Rate of energy consumption was greatest for the convection oven and least for the micro-
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wave oven for roasts cooked to 77 C. When comparing the cooking power, or amount of energy required for cooking the turkey, less energy was required for the conventional oven than for either the convection or microwave ovens. However, relative efficiency was greatest for the microwave oven and lowest for the conventional oven. This is in agreement with the findings of McNeil and Penfield (1983) and Korschgen et al. (1980). As pointed out by Korschgen et al. (1980), more energy is used in the operation of the appliance than in the actual cooking of the food. In this study, the
Temperature Oven
77 C
Oven effect 82 C
Moisture 3 (%) Conventional Convection Microwave
65.20 a 65.80 a b 65.40 a
68.60 c 66.10 a b 67.00 b Lipid (%)
Conventional Convection Microwave Temperature effect mean
1.87 1.49 1.83 1.73NS
1.12 1.64 1.87 1.54NS4
1.50* 1.57 a 1.85 a
Protein (%) Conventional Convection Microwave Temperature effect mean
30.10 32.24 31.06
33.00 32.52 32.90
31.13**
32.81**
31.55 a 32.38 a 31.98 a
Instron areas under the peak (cm^) Conventional Convection Microwave Temperature effect mean
8.96 8.41 10.01 9.I3NS
8.86 10.13 10.32 9 77NS
8.91 a 9.27a 10.17 a
Instron maximum force (g) Conventional Convection Microwave
1860.48 2041.74 2144.48
2061.58 2044.5 3 2212.80
Temperature effect mean
20!5.57NS
2106.30 N S
' ' Means not followed by a common letter are significantly different. 1
Means of five replications.
2
No significant differences for oven effect for lipid, protein, and Instron values.
3 4
Main effect means are not reported because of significant interaction. NS = Not significant.
**For temperature effect significant differences (P<.01).
1961.03 a 2043.14 a 2178.64 a
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TABLE 5. Proximate analysis and Instron measurements of turkey heated in three oven types1
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PRUSA AND HUGHES TABLE 6. Cholesterol retention and cholesterol content of turkey heated in conventional, convection, and microwave ovens1 Temperature
Oven
77 C
82 C
Oven effect mean
Cholesterol (rag/100 g)
Conventional Convection Microwave Temperature effect mean
58.50 59.60 64.06
64.32 63.48 65.83
60.72*
64.54*
61.41a 61.54a 64.95a
Cholesterol, dry basis (mg/100 g) 185.07 176.34 197.68 186.36NS 2
184.84 184.66 189.67
184.96a 180.50a 193.68a
186.39 N S
Cholesterol, roast weight basis (mg)
Conventional Convection Microwave Temperature effect mean
189.95 197.23 195.67
191.60 194.32 200.54
194.28 N S
195.49 N S
190.78a 195.78a 198.11a
Cholesterol retention in roast (%)
Conventional Convection Microwave Temperature effect mean
92.90 93.64 97.50
95.65 97.90 98.80
94.68NS
97.45NS
94.28a 95.77a 98.15a
No significant difference for oven effect for any cholesterol variable. Means of five replications. 2 NS = Not significant. *For temperature effect significant differences (P<.05). 1
convection oven required more energy for preheating than the conventional oven. Cooking losses for turkey and fat and cholesterol content of the cook drip are presented in Table 4. For all roasts cooked to 77 C, evaporative losses were similar, regardless of oven type. Evaporative losses were greatest for roasts cooked to 82 C in the conventional oven. Drip loss was greatest in the microwave oven, regardless of endpoint temperature, which is in agreement with the finding of McNeil and Penfield (1983). In contrast with McNeil and Penfield, total cook loss was greater for turkey cooked to 77 C in the microwave when compared to both conventional and convection heating, which did not differ. In roasts cooked to 82 C, total cook loss was lowest for the convection oven when compared to conventional and microwave heating, which did not
differ. This may be attributable to the combined effects of evaporative losses for conventionally cooked 82-C roasts and drip losses for microwave cooked roasts. Lipid content of the cook drip was lower for roasts cooked in the microwave oven. Causes may include the shorter time for fat to be lost from the roasts cooked in the microwave and also little time for evaporation of moisture in the drip. The amount of cholesterol in the drip was lowest for roasts cooked in the microwave oven, regardless of endpoint temperature. This parallels the amount of fat contained in the cook drip as well as the retention of cholesterol in the roast (Table 6). Proximate analysis of the turkey roasts heated in the three oven types are presented (Table 5). The effect of internal endpoint temperature on the amount of moisture present
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Conventional Convection Microwave Temperature effect mean
QUALITY, CHOLESTEROL, SODIUM CONTENT IN TURKEY
microwave and conventional gas ovens. McNeil and Penfield (1983) found that shear values for turkey cooked in the conventional oven did not differ from microwave and convection heated roasts; however, roasts cooked in the convection oven had lower shear values than did roasts heated in the microwave oven. No differences in cholesterol content and retention of cholesterol were found in turkey cooked in the conventional, convection, and microwave ovens to the two endpoint temperatures (Table 6). This would indicate that, of the heating methods used in this study, none were advantageous in minimizing the amount of cholesterol in the finished meat product. However, the amount of cholesterol in the roasts was dependent on internal endpoint
TABLE 7. Sodium retention and sodium content of turkey heated in conventional, and microwave ovens1 Temperature Oven
77 C
82 C
convection,
Oven effect mean
Sodium (mg/lOOg) Conventional Convection Microwave Temperature effect mean
47.0 50.0 54.0 50.3NS 2
50.0 51.0 52.0 51.0NS
48.5 a 50.5 a 53.0 b
Sodium, dry basis (mg/100 g) Conventional Convection Microwave
149.60 147.25 163.89
143.75 149.54 150.70
Temperature effect mean
15 3.58 N S
148.00 N S
146.67 a 148.39 a 157.30a
Sodium, roast weight basis (mg) Conventional Convection Microwave Temperature effect mean
156.58 163.97 162.29
149.18 156.97 157.27
160.95 N S
154.47 N S
152.88 a 160.47 a 159.78 a
Sodium retention in roast (%) Conventional Convection Microwave
63.43 65.30 68.24
56.98 64.92 64.13
Temperature effect mean
65.66NS
62.01NS
60.21 a 65.13 a 66.19 a
a ' b Means for an oven effect not followed by a common letter are significantly different (P<.05 sodium). 1
Means of five replications.
2
NS = Not significant.
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in the cooked samples was dependent on oven type. The moisture content decreased in the conventional and microwave oven when heated to the higher internal endpoint temperature. There were no moisture differences found in roasts cooked to 82 C in the three oven types. In general, protein content increased and was inversely related to percent moisture when turkey, cooked to 82 C, was compared to that cooked at 77 C. There was no difference in percent lipid or protein for any oven type or endpoint temperature. No differences in shear values were detected for turkey heated to different endpoint temperatures in the three oven types. These results agree with Cipra et al. (1971) who reported similar shear values for turkey cooked in
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REFERENCES American Heart Association, 1982. Rational of the diet-heart statement of the American Heart Association. Dallas, TX. American Medical Association, 1983. Sodium in processed foods. Council on Scientific Affairs, J. Am. Med. Assoc. 249:784. Association of Offical Analytical Chemists, 1980. Official Methods of Analysis. 13 ed. Assoc. Offic. Anal. Chem., Washington, DC. Bowers, J. A., and M. Heier, 1970. Microwave cooked turkey: heating patterns, eating quality, and
histological appearance. Microwave Energy Application Newsletter. 3(6): 3—5. Campbell, A. M., M. P. Penfield, and R. M. Griswold, 1979. The experimental Study of Food. Houghton Mifflin Co., Boston, MA. Chambers, E. IV., and J. A. Bowers, 1981. Sensory characteristics of postmortem papain injected turkey cooked conventionally or by microwaves. J. Food Sci. 46:1627-1628. Cipra, J. E., J. A. Bowers, and A. S. Hooper, 1971. Precooking and reheating of turkey. J. Am. Diet. Assoc. 58:38-40. Feeley, R. M., P. E. Criner, and B. K. Watt, 1972. Cholesterol content of foods. J. Am. Diet. Assoc. 61:134-149. Food and Nutrition Board, 1980. Toward Healthful Diets. Food and Nutrition Board, Natl. Acad Sci., Natl. Res. Council, Washington, DC. Folch, J., M. Lees, and G.H.S. Stanley, 1957. A simple method for the isolation and purification of total lipids from animal tissues. J. Biol. Chem. 226: 497-509. Karkalas, J., A. E. Donald, and K. M. Clegg, 1982. Cholesterol content of poultry meat and cheese determined by enzymatic and gas-liquid chromatography methods. J. Food Technol. 17: 281-283. Korschgen, B. M., J. M. Berneking, and R. E. Baldwin, 1980. Energy requirements for cooking beef rib roasts. J. Food Sci. 45:1054-1055. McNeil, M., and M. P. Penfield, 1983. Turkey quality as affected by ovens of varying energy costs. J. Food Sci. 48:85 3-855. Rhee, K. S., T. R. Dutson, G. C. Smith, R. L. Hostetler, and R. Reiser, 1982. Cholesterol content of raw and cooked beef longissimus muscles with different degrees of marbling. J. Food Sci. 47:716-719. Searcy, R. L., and L. M. Bergquist, 1960. A new color reaction for the quantification of serum cholesterol. Clin. Chim. Acta 5:192-199. Senate Select Committee on Nutrition and Human Needs, US Senate, 1977. Dietary Goals for the United States. 2nd ed. US Govt. Printing Office, Washington, DC. Statistical Analysis System, 1982. SAS User's Guide: Statistics. SAS Inst. Inc., Raleigh, NC. USDA, 1979. Composition of Foods, Agriculture Handbook 8-5. US Dept. Agric, Washington, DC.
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t e m p e r a t u r e , with t u r k e y cooked t o 82 C having greater a m o u n t s of cholesterol regardless of m e t h o d of p r e p a r a t i o n . Previous studies (Feeley et al, 1 9 7 2 ; R h e e et al., 1982) have indicated t h a t cholesterol is c o n c e n t r a t e d in t h e tissue during cooking. Work d o n e at t h e University of Nebraska (unpublished) o n t u r k e y m e a t c o o k e d with t h e skin indicated t h a t cholesterol was n o t lost in t h e drip (Feeley et al, 1972). T u r k e y roasts c o o k e d in t h e microwave oven had m o r e sodium t h a n roasts cooked in t h e conventional and convection ovens (Table 7 ) . This m a y be explained b y t h e shorter cooking t i m e required for t h e microwave oven as compared to t h e conventional and convection ovens. T h e r e were no differences for percent sodium r e t e n t i o n a n d sodium on a dry-weight or roast-weight basis. When comparing sodium and cholesterol values for raw (Table 2) and cooked (Tables 6 and 7) turkey, sodium retention was lower t h a n cholesterol r e t e n t i o n after heating w h e n averaged over oven t y p e . This m a y b e explained b y t h e relatively low degree of b o n d i n g of sodium in t h e tissues and its solubility in t h e drip as c o m p a r e d to cholesterol, which is b o u n d in t h e m e m b r a n e structures (Feeley et al, 1972).
1986 Poultry Science 65:940-948 INTRODUCTION T h e relationship b e t w e e n diet a n d disease has received considerable a t t e n t i o n in recent years. Cholesterol has been implicated in t h e d e v e l o p m e n t of c o r o n a r y heart disease, a n d sodium c o n s u m p t i o n is associated with elevated blood pressure resulting in hypertension. Individuals have been advised t o lower t h e cholesterol intake in t h e diet (Senate Select C o m m i t t e e , 1977) and m o r e recently, t h e sodium i n t a k e (AMA, 1 9 8 3 ; A H A , 1 9 8 2 ; F N B , 1980). Both sodium and cholesterol are inherent c o m p o n e n t s of muscle foods. R e p o r t e d cholesterol values for t u r k e y light muscle range from 58 to 6 0 m g / 1 0 0 g for raw muscle (USDA, 1 9 7 9 ; Feeley et al., 1972) and from 6 8 t o 82 m g / 1 0 0 g for cooked muscle (USDA, 1 9 7 9 ; Karkalas et al, 1982). S o d i u m values for b o t h r a w a n d c o o k e d t u r k e y light muscle are rep o r t e d as 6 0 m g / 1 0 0 g (USDA, 1979). In t h e USDA studies, t u r k e y was roasted in a r o t a r y h e a r t h oven at 163 C t o an internal t e m p e r a t u r e of 82 C. A l t h o u g h t h e cholesterol and sodium
1 Supported by funds from the Home Economics Research Catalyst Fund.
c o n t e n t of r a w a n d c o o k e d t u r k e y has been r e p o r t e d , t h e r e is little information pertaining t o h o w these a m o u n t s are affected b y various cooking m e t h o d s . When choosing a cooking m e t h o d for muscle foods, p r o d u c t quality and energy e x p e n d i t u r e are of i m p o r t a n c e t o t h e consumer. McNeil and Penfield ( 1 9 8 3 ) indicated microwave and convection ovens were more energy efficient t h a n a conventional oven for cooking t u r k e y . O n l y o n e internal e n d p o i n t t e m p e r a t u r e (77 C) was investigated. T o t a l cooking losses were greater for microwave heated t u r k e y breasts w h e n c o m p a r e d t o those heated in a gas oven (Bowers and Heir, 1 9 7 0 ; Cipra et al, 1 9 7 1 ) . Chambers and Bowers (1981) r e p o r t e d t h a t t h e flavor of t u r k e y cooked in a conventional oven m o r e closely resembled t h a t of roast t u r k e y t h a n t u r k e y cooked in a microwave oven. Objectives of this s t u d y w e r e : 1) t o m o n i t o r energy c o n s u m p t i o n and determine relative efficiency of microwave, convection, and conventional ovens used for heating t u r k e y t o t w o different internal e n d p o i n t t e m p e r a t u r e s , and 2) t o c o m p a r e t h e three heating m e t h o d s (microwave, convection, and conventional) with respect t o t h e quality characteristics a n d changes in cholesterol and sodium c o n t e n t of t u r k e y breast muscle. Cholesterol and sodium
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ABSTRACT Six treatment combinations for evaluation of quality characteristics, sodium, and cholesterol content of turkey breast roasts were studied: three oven types (conventional, convection, and microwave) and two internal endpoint heating temperatures (77 C and 82 C). The microwave oven was the most energy efficient, and the conventional oven was the least efficient. Overall, drip loss was highest in the microwave oven, and heating to 82 C increased total cooking loss. Cook drip from the microwave oven contained less fat but the same amount of cholesterol as cook drip from the other two oven types. Instron shear values were not affected by oven type or internal endpoint temperature. Generally, when comparing raw to cooked samples, heating increased (concentrated) the cholesterol content and decreased the sodium content of the turkey. Cholesterol content of the heated roasts was not affected by type of oven; however, heating to the higher internal endpoint temperature increased (concentrated) the cholesterol. Sodium content was not affected by oven type or internal endpoint heating temperature. Cholesterol and sodium retentions of the roasts after heating were 96 and 64%, respectively, when averaged over the three oven types. (Key words: cholesterol, sodium, turkey quality)
QUALITY, CHOLESTEROL, SODIUM CONTENT IN TURKEY
retention in the turkey after heating and cholesterol content of cook drip were determined also.
MATERIALS AND METHODS
whole breast by removing the meat (pectoralis major) from each side. The roasts were trimmed to weigh between 351 to 448 g before heating. Raw samples for cholesterol, sodium, and proximate analysis were taken by combining the trimmings from both pectoralis major breast muscles. Oven Heating. For conventional heating (Electric Premier, Model G7-B55) and convection heating (Rival, Model No. 4020), roasts were placed on racks in glass baking dishes and covered with an open aluminum foil tent. Ovens were preheated to 163 C. Oven and internal roast temperature were monitored with iron constantan thermocouples attached to an Omega Digital Thermometer (Model 2166A). Thermocouples were positioned in the geometric center of the roast. Roasts were heated to either 77 or 82 C internal temperature. For microwave heating (Sharp Model-8200), a microwave thermometer was placed in the geometric center of the roast. Roasts were placed on a rack in a glass dish, covered with
TABLE 1. Incomplete block design for assigning treatments to heating period Treatment Block (heating period) 1
Convection
Conventional 77 C
82 C
X
X
2
77 C
82 C
X
X
3 4
X
X
X
X
X
X
X X
12
15
X
X
11
14
X
X
9
13
X
X
8
10
82 C
X
6 7
77 C
X
X
5
Microwave
X X
X
X
X X
X X
X
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Treatments. Six treatment combinations for heating turkey breast roasts were studied: three oven types (conventional, convection and microwave) and two internal endpoint temperatures (77 C and 82 C). A balanced incomplete block design with five replications of each treatment was used (Table 1). Roast Preparation. Fifteen fresh, RTC (ready-to-cook) hen turkeys weighing 5.43 to 6.34 kg were obtained from a commercial supplier. The breast was removed from each of the turkeys, wrapped in plastic film, overwrapped with heavy-duty aluminum foil, and frozen (—18 C) until heating. Prior to each heating period, two whole turkey breasts were thawed approximately 3 days (60 hr) at 3 C. Two boneless roasts were made from each
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procedures (AOAC, 1980). Crude protein was determined by the Kjeldahl method described in Section 7.015. Crude fat was determined by an indirect method (Section 7.057). Moisture content was determined by an in-house method using a freeze-dryer apparatus. A 5-g sample was heated for 12 hr or until pressure fell below 10 n of Hg. Samples for sodium analysis were dry-ashed (Section 3.007 a), and determination was performed on a automated potassium instrument (Sections 2.097 to 2.101). Single analysis were made on each sample with 10% reruns to check precision and extreme values. Cholesterol content of the raw and cooked roasts and cook drip was determined according to the method of Searcy and Bergquist (1960) as described by Rhee et al. (1982). Samples (5 g) were blended with 85 ml of chloroform/methanol (2/1, v/v), made up to volume (100 ml), filtered (Whatman #1), washed with distilled water (.2 X volume), and allowed to separate (4 C) overnight (Folch et al., 1957). A 6-ml aliquot of lipid extract prepared by the Folch procedure was evaporated to dryness in a 60-C water bath under a stream of nitrogen. Lipids were saponified with 15 ml alcoholic KOH (15% KOH in 90% ethanol) for 10 min in a shaker water bath (88 C). When cool, 5-ml distilled water was added, and the unsaponifiable material was extracted with 10-ml hexane. A 5-ml aliquot of the hexane extract was dried as previously described. Cholesterol concentration was determined colorimetrically using FeS0 4 -acetic acid and concentrated H 2 S 0 4 as color developing agents. A cho-
TABLE 2. Proximate analysis, cholesterol, and sodium contents of raw turkey breast muscle1 Proximate analysis Moisture, % Protein, % Lipid, %
72.8 25.3 1.5 Cholesterol content
Wet-weight basis, mg/100 g Dry-weight basis, mg/100 g Roast-weight basis, mg/roast wt
48.13 177.12 203.77
Sodium content Wet-weight basis mg/100 g Dry-weight basis, mg/100 g Roast-weight basis, mg/roast wt 1
Mean of 15 raw values.
59.00 217.06 249.84
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waxed paper, and heated in a microwave oven on the "roast" power setting (368 W). Roasts were removed from the microwave oven when the internal temperature reached 72 to 73 C or 76 to 77 C for the desired 77- and 82-C internal endpoint temperatures, respectively. Postoven temperature rise was determined in preliminary work to be approximately 4 to 5 C for these roasts. Roasts were covered and held approximately 5 min after removal from the microwave oven to allow the final internal endpoint temperature to be reached. Energy and Oven Efficiency Measurements. For the conventional and convection ovens, power consumption during the preheating and heating period was recorded. For the microwave oven, energy consumption was recorded from the time the roast was placed in the oven until it was removed. Power consumption was measured with a Duncan portable wattmeter (Number 00013). Cooking power and oven relative efficiency were determined as described by Korschgen et al. (1980). Cooking Losses and Instron Measurements. Cooking losses (percent evaporative, drip, and total) of the roasts were determined as described by Campbell et al. (1979). For sampling, the skin was removed and the roast was sliced into four (2.54 cm) sections. The second slice (2.54 cm) was cored for shearing. Cores (1.27-cm diameter) were cut parallel to the muscle fibers in a radial fashion from the exterior (outer) portion of the muscle. A Warner-Bratzler shear attachment on the Instron Universal Testing Machine (Model 1132) was used to completely shear six roomtermperature cores from each treatment. Instron response was evaluated with a Southwest Technical Computer. The Instron Signal voltage was fed into a computer-controlled amplifier and then into a 12-bit A/D converter (resolution = 1 part in 4095). The Instron loadcell was 100 kg, the crosshead speed was 12.7 cm/min, and, for the purpose of calculating area under the force-distance curve, a simulated chartspeed of 25.4 cm/min was used. The number of data points taken was 38 ± 2/sec. Measurements recorded were area under the peak (square centimeters) and maximum peak height force (grams). Proximate Analysis, Sodium, Cholesterol Determination. Proximate analysis (protein and fat) was determined on ground (.31-cm plate) raw and cooked turkey breast samples by Association of Official Analytical Chemists
QUALITY, CHOLESTEROL, SODIUM CONTENT IN TURKEY
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TABLE 3. Heating time, heating rate, and energy values for conventional, convection, and microwave ovens1 Temperature Oven
77 C
82 C
mean
Heating time 2 (min) Conventional Convection Microwave
104.00d 81.40b 13.80a
167.20e 96.80cd 16.40a
Heating rate 2 (min/g) Conventional Convection Microwave
.24 c .19 b .03 a
.39 d .23bc .04 a
Conventional Convection Microwave
1050.56 b 1274.54° 202.24 a
1452.94 d 1419.44 d 231.06 a
Rate of consumption 2 (W-hr/g) Conventional Convection Microwave
2.47 b 3.02 c ,51a
3.40 c 3.42<: .54 a Cooking power (W)
Conventional Convection Microwave Temperature effect mean
303.73 378.20 363.63 348.52 N S
263.93 382.06 372.85 339.61NS 4
283.83 a 380.13 b 368.24 b
Relative efficiency ( ) Conventional Convection Microwave Temperature effect mean
25.85 29.76 40.23 31.95 N S
Conventional Convection Temperature effect mean
227.14 310.89 269.01NS
21.46 26.90 40.20 29.52NS
23.66 a 28.33 b 40.22 c
235.04 265.19 250.11 N S
231.09 a 288.04 b
Oven warmup (W-hr)
a c Means for an oven effect not followed by a common letter are significantly different (P-C01 for cooking power, P<.001 for relative efficiency, P<.05 for oven warmup).
Means not followed by a common letter are significantly different. 1
Means of five replications.
2
Main effect means are not reported because of significant interaction.
3
Includes power consumption for preheating conventional and convection ovens.
4
NS = Not significant.
lesterol standard curve was c o n s t r u c t e d according t o Searcy and Bergquist ( 1 9 6 0 ) . Statistical Analysis. Least squares analysis of variance using t h e general linear m o d e l procedure (PROC GLM) was used t o determine t r e a t m e n t and block differences a m o n g o b -
jective data (SAS, 1 9 8 2 ) . Adjusted m e a n s derived from t h e balanced i n c o m p l e t e block design were calculated w h e n a p p r o p r i a t e . RESULTS AND DISCUSSION P r o x i m a t e analysis, cholesterol c o n t e n t , and
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Total energy2'3 (W-hr)
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TABLE 4.. Cooking losses for turkey and fat and cholesterol content of the cook drip of turkey heated in conventional, convection, and microwave ovens' Temperature Oven
77 C
82 C
Oven effect mean
Evaporative loss2 (%]I Conventional Convection Microwave
18.78 a 19.92a 19.94a
27.66 c 23.78° 23.02 b Drip loss (%)
3.14 3.82 6.31 4.42NS 3
3.06 3.46 6.13 4.22NS
3.10a 3.64a 6.22b
Total loss2 (%) a
Conventional Convection Microwave
22.43 23.44a 26.55 b c
Conventional Convection Microwave Temperature effect mean
74.69 53.72 33.69
30.72 d 26.25 b 29.34 c d
Cook drip lipid content: (%) 72.58 69.29 33.46 58.11 N S 54.03NS
73.64b 61.51b 33.08a
Drip that is cholesterol (%) Conventional Convection Microwave Temperature effect mean
.040 .036 .025
.050 .047 .028
.034NS
.042NS
.045° .042b .027a
ab ' Means for an oven effect not followed by a common letter (a,b) are significantly different (P<.001) for drip loss and cook drip lipid content, P<.01 for drip that is cholesterol. a—d Means not followed by a common letter are significantly different. 'Means of five replications. 2
Main effect means are not reported because of significant interaction.
3
NS = Not significant.
sodium c o n t e n t of t h e raw t u r k e y breast muscle are presented in Table 2. T h e moisture, p r o t e i n , and fat c o n t e n t s were comparable to t h e reported values of 7 3.57% for moisture, 2 3 . 6 4 % for protein, and 1.66% for fat (USDA, 1979). T h e cholesterol c o n t e n t of t h e raw t u r k e y light meat was slightly lower t h a n reported values of 6 0 m g / 1 0 0 g (Feeley, 1 9 7 2 ) and 58 m g / 1 0 0 g (USDA, 1979). T h e sodium c o n t e n t was comparable t o t h e r e p o r t e d value of 6 0 m g / 1 0 0 g of t u r k e y light meat (USDA, 1979). T u r k e y roasts heated in t h e microwave oven had t h e shortest heating times, and conven-
tionally cooked roasts t o o k t h e longest t o heat (Table 3). T h e effect of heating t o a higher internal t e m p e r a t u r e was d e p e n d e n t o n oven t y p e . Cooking t o a high internal t e m p e r a t u r e decreased t h e rate of heating in t h e conventional oven; however, roasts heated in t h e convection or microwave oven (within oven) heated at t h e same rate t h r o u g h t h e entire heating process, regardless of internal e n d p o i n t t e m p e r a t u r e . T h e lower heating times and m o r e rapid rate of heating t u r k e y in t h e microwave oven is in agreement with past studies (Cipra et al, 1 9 7 1 ; McNeil and Penfield, 1 9 8 3 ) .
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Conventional Convection Microwave Temperature effect mean
QUALITY, CHOLESTEROL, SODIUM CONTENT IN TURKEY
More total energy was required to cook the turkey to 77 C in the convection oven than in the conventional and microwave ovens. This may be attributed to more energy being used by the convection oven during the preheating period. Total energy values were similar between conventional and convection ovens when roasts were heated to 82 C. The microwave oven used less total energy than the conventional or convection ovens, regardless of endpoint temperature. Rate of energy consumption was greatest for the convection oven and least for the micro-
945
wave oven for roasts cooked to 77 C. When comparing the cooking power, or amount of energy required for cooking the turkey, less energy was required for the conventional oven than for either the convection or microwave ovens. However, relative efficiency was greatest for the microwave oven and lowest for the conventional oven. This is in agreement with the findings of McNeil and Penfield (1983) and Korschgen et al. (1980). As pointed out by Korschgen et al. (1980), more energy is used in the operation of the appliance than in the actual cooking of the food. In this study, the
Temperature Oven
77 C
Oven effect 82 C
Moisture 3 (%) Conventional Convection Microwave
65.20 a 65.80 a b 65.40 a
68.60 c 66.10 a b 67.00 b Lipid (%)
Conventional Convection Microwave Temperature effect mean
1.87 1.49 1.83 1.73NS
1.12 1.64 1.87 1.54NS4
1.50* 1.57 a 1.85 a
Protein (%) Conventional Convection Microwave Temperature effect mean
30.10 32.24 31.06
33.00 32.52 32.90
31.13**
32.81**
31.55 a 32.38 a 31.98 a
Instron areas under the peak (cm^) Conventional Convection Microwave Temperature effect mean
8.96 8.41 10.01 9.I3NS
8.86 10.13 10.32 9 77NS
8.91 a 9.27a 10.17 a
Instron maximum force (g) Conventional Convection Microwave
1860.48 2041.74 2144.48
2061.58 2044.5 3 2212.80
Temperature effect mean
20!5.57NS
2106.30 N S
' ' Means not followed by a common letter are significantly different. 1
Means of five replications.
2
No significant differences for oven effect for lipid, protein, and Instron values.
3 4
Main effect means are not reported because of significant interaction. NS = Not significant.
**For temperature effect significant differences (P<.01).
1961.03 a 2043.14 a 2178.64 a
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TABLE 5. Proximate analysis and Instron measurements of turkey heated in three oven types1
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PRUSA AND HUGHES TABLE 6. Cholesterol retention and cholesterol content of turkey heated in conventional, convection, and microwave ovens1 Temperature
Oven
77 C
82 C
Oven effect mean
Cholesterol (rag/100 g)
Conventional Convection Microwave Temperature effect mean
58.50 59.60 64.06
64.32 63.48 65.83
60.72*
64.54*
61.41a 61.54a 64.95a
Cholesterol, dry basis (mg/100 g) 185.07 176.34 197.68 186.36NS 2
184.84 184.66 189.67
184.96a 180.50a 193.68a
186.39 N S
Cholesterol, roast weight basis (mg)
Conventional Convection Microwave Temperature effect mean
189.95 197.23 195.67
191.60 194.32 200.54
194.28 N S
195.49 N S
190.78a 195.78a 198.11a
Cholesterol retention in roast (%)
Conventional Convection Microwave Temperature effect mean
92.90 93.64 97.50
95.65 97.90 98.80
94.68NS
97.45NS
94.28a 95.77a 98.15a
No significant difference for oven effect for any cholesterol variable. Means of five replications. 2 NS = Not significant. *For temperature effect significant differences (P<.05). 1
convection oven required more energy for preheating than the conventional oven. Cooking losses for turkey and fat and cholesterol content of the cook drip are presented in Table 4. For all roasts cooked to 77 C, evaporative losses were similar, regardless of oven type. Evaporative losses were greatest for roasts cooked to 82 C in the conventional oven. Drip loss was greatest in the microwave oven, regardless of endpoint temperature, which is in agreement with the finding of McNeil and Penfield (1983). In contrast with McNeil and Penfield, total cook loss was greater for turkey cooked to 77 C in the microwave when compared to both conventional and convection heating, which did not differ. In roasts cooked to 82 C, total cook loss was lowest for the convection oven when compared to conventional and microwave heating, which did not
differ. This may be attributable to the combined effects of evaporative losses for conventionally cooked 82-C roasts and drip losses for microwave cooked roasts. Lipid content of the cook drip was lower for roasts cooked in the microwave oven. Causes may include the shorter time for fat to be lost from the roasts cooked in the microwave and also little time for evaporation of moisture in the drip. The amount of cholesterol in the drip was lowest for roasts cooked in the microwave oven, regardless of endpoint temperature. This parallels the amount of fat contained in the cook drip as well as the retention of cholesterol in the roast (Table 6). Proximate analysis of the turkey roasts heated in the three oven types are presented (Table 5). The effect of internal endpoint temperature on the amount of moisture present
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Conventional Convection Microwave Temperature effect mean
QUALITY, CHOLESTEROL, SODIUM CONTENT IN TURKEY
microwave and conventional gas ovens. McNeil and Penfield (1983) found that shear values for turkey cooked in the conventional oven did not differ from microwave and convection heated roasts; however, roasts cooked in the convection oven had lower shear values than did roasts heated in the microwave oven. No differences in cholesterol content and retention of cholesterol were found in turkey cooked in the conventional, convection, and microwave ovens to the two endpoint temperatures (Table 6). This would indicate that, of the heating methods used in this study, none were advantageous in minimizing the amount of cholesterol in the finished meat product. However, the amount of cholesterol in the roasts was dependent on internal endpoint
TABLE 7. Sodium retention and sodium content of turkey heated in conventional, and microwave ovens1 Temperature Oven
77 C
82 C
convection,
Oven effect mean
Sodium (mg/lOOg) Conventional Convection Microwave Temperature effect mean
47.0 50.0 54.0 50.3NS 2
50.0 51.0 52.0 51.0NS
48.5 a 50.5 a 53.0 b
Sodium, dry basis (mg/100 g) Conventional Convection Microwave
149.60 147.25 163.89
143.75 149.54 150.70
Temperature effect mean
15 3.58 N S
148.00 N S
146.67 a 148.39 a 157.30a
Sodium, roast weight basis (mg) Conventional Convection Microwave Temperature effect mean
156.58 163.97 162.29
149.18 156.97 157.27
160.95 N S
154.47 N S
152.88 a 160.47 a 159.78 a
Sodium retention in roast (%) Conventional Convection Microwave
63.43 65.30 68.24
56.98 64.92 64.13
Temperature effect mean
65.66NS
62.01NS
60.21 a 65.13 a 66.19 a
a ' b Means for an oven effect not followed by a common letter are significantly different (P<.05 sodium). 1
Means of five replications.
2
NS = Not significant.
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in the cooked samples was dependent on oven type. The moisture content decreased in the conventional and microwave oven when heated to the higher internal endpoint temperature. There were no moisture differences found in roasts cooked to 82 C in the three oven types. In general, protein content increased and was inversely related to percent moisture when turkey, cooked to 82 C, was compared to that cooked at 77 C. There was no difference in percent lipid or protein for any oven type or endpoint temperature. No differences in shear values were detected for turkey heated to different endpoint temperatures in the three oven types. These results agree with Cipra et al. (1971) who reported similar shear values for turkey cooked in
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REFERENCES American Heart Association, 1982. Rational of the diet-heart statement of the American Heart Association. Dallas, TX. American Medical Association, 1983. Sodium in processed foods. Council on Scientific Affairs, J. Am. Med. Assoc. 249:784. Association of Offical Analytical Chemists, 1980. Official Methods of Analysis. 13 ed. Assoc. Offic. Anal. Chem., Washington, DC. Bowers, J. A., and M. Heier, 1970. Microwave cooked turkey: heating patterns, eating quality, and
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t e m p e r a t u r e , with t u r k e y cooked t o 82 C having greater a m o u n t s of cholesterol regardless of m e t h o d of p r e p a r a t i o n . Previous studies (Feeley et al, 1 9 7 2 ; R h e e et al., 1982) have indicated t h a t cholesterol is c o n c e n t r a t e d in t h e tissue during cooking. Work d o n e at t h e University of Nebraska (unpublished) o n t u r k e y m e a t c o o k e d with t h e skin indicated t h a t cholesterol was n o t lost in t h e drip (Feeley et al, 1972). T u r k e y roasts c o o k e d in t h e microwave oven had m o r e sodium t h a n roasts cooked in t h e conventional and convection ovens (Table 7 ) . This m a y be explained b y t h e shorter cooking t i m e required for t h e microwave oven as compared to t h e conventional and convection ovens. T h e r e were no differences for percent sodium r e t e n t i o n a n d sodium on a dry-weight or roast-weight basis. When comparing sodium and cholesterol values for raw (Table 2) and cooked (Tables 6 and 7) turkey, sodium retention was lower t h a n cholesterol r e t e n t i o n after heating w h e n averaged over oven t y p e . This m a y b e explained b y t h e relatively low degree of b o n d i n g of sodium in t h e tissues and its solubility in t h e drip as c o m p a r e d to cholesterol, which is b o u n d in t h e m e m b r a n e structures (Feeley et al, 1972).