- Email: [email protected]
The Effect of Dietary Fat and Tocopherol on Lipolysis and Oxidation in Turkey Meat Stored at Different Temperatures
The Effect of Dietary Fat and Tocopherol on Lipolysis and Oxidation in Turkey Meat Stored at Different Temperatures D. SKLAN, Z. TENNE, and P. BUDOWSKI
Faculty of Agriculture, Hebrew University, Rehovot 76100, Israel (Received for publication June 18, 1982)
INTRODUCTION
METHODS
Poultry meat, in particular, turkey meat, is susceptible to the development of rancidity and "warmed-over flavor" on frozen storage (Wilson et al, 1976). One of the processes contributing to this deterioration is oxidation of the polyunsaturated fatty acids of the meat (Wilson et al, 1976). Feeding different dietary fats affects the composition of triglycerides and, to less extent, that of phospholipids in turkeys (Neudoerffer and Lea, 1967; Salmon, 1976; Webb et al, 1973), and this influenced the organoleptic and storage characteristics of the meat (Webb et al, 1973; Crawford et al, 1975). High dietary tocopherol has been shown to increase tissue tocopherol levels, to retard the onset of rancidity in frozen turkey meat (Crawford et al, 1975), and to attenuate the increase in TBA values on storage (Marusich et al, 1975). We have recently shown that lipolysis of phospholipids occurs in conjunction with oxidation of lipids on frozen storage (Sklan et al, 1982). The object of the present study was to determine the effects of dietary fat supplements with different degrees of fatty acid saturation and of the addition of tocopherol on the simultaneous oxidative and hydrolytic changes in turkey meat on frozen storage.
Male turkey poults (Meleagris gallopavo) were obtained from a commercial hatchery and fed commercial diets until 15 weeks old. The poults were then randomly divided into three groups of five animals each, which received diets containing either beef tallow, soybean oil, or soybean oil with an additional 60 mg/kg all-rac-a-tocopherol, (Diets A, B, and C, respectively). All diets contained 61.3% ground sorghum, 32% defatted soybean meal (45% protein), and 3% added fat with minerals, trace minerals, and vitamins as previously described (Sklan and Hurwitz, 1980) except that total tocopherol was present at 5 mg/kg in the vitamin mix. The fatty acid profiles of the diets are shown in Table 1. Poults were fed these diets for 9 weeks before slaughtering in a commercial slaughterhouse. Meat samples were taken under sterile. conditions from pectoralis and gastrocnemius by exposure of the external surface of the meat to a red hot iron and sampling of approximately 10 g taken from deeper layers of the tissue. Samples were stored at 37, 4, or —18 C for differing periods (Sklan et al, 1982). Sterility of the samples was checked by incubating in nutrient broth at 30 C for 2 days and counting on blood agar at 15 and 37 C or by direct plating with blood agar; nonsterile
2017
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 12, 2015
ABSTRACT Turkeys were fed diets containing tallow or soybean oil with either 5 or60mg/kg all-rac-a-tocopherol for 9 weeks before slaughter. Muscle was sampled aseptically from breast or thigh and stored at 37, 4, or —18 C. Tocopherol tissue content reflected dietary levels; the fatty acid composition of muscle triglycerides was significantly affected by the dietary fat but that of phospholipids was influenced only slightly by the different diets. Both oxidative and lipolytic changes were greater in leg muscle than in breast muscle. High dietary tocopherol levels resulted in decreased oxidation on storage of meat tissues as did feeding of a more saturated fat diet. Diets did not influence the rate of hydrolysis of phospholipids, but differences in the free fatty acid concentrations were found, presumably due to increased oxidation in the soybean oil, low tocopherol diet. The concentration of conjugable oxidation products was directly correlated with initial polyunsaturated fatty acid concentrations and inversely widi tocopherol concentrations. (Key words: turkey meat storage, tocopherol, dietary fat, oxidation, lipolysis) 1983 Poultry Science 62:2017-2021
2018
SKLAN ET AL. TABLE 1. Fatty acid profiles of lipids extracted from the experimental diets 16:0'
16:1
18:0
22.4 13.9 17.0
2.4 .4 .5
18.3 3.4 3.1
18:1
18:2
18:3
30.7 28.0 26.9
24.9 51.7 49.8
1.3 2.6 2.7
\'°) ~ Tallow S o y b e a n oil Soybean oil + tocopherol 1
Number of carbon atoms: number of double bonds.
1977). This technique invokes the following spectrometric measurements: 1) oxodiene value (OV), which represents diene conjugation after reduction of the keto groups of oxodiene fatty acids, to hydroxy groups; 2) conjugable oxidation products (COP) obtained by dehydration of fatty acids hydroperoxides, oxodienes, and hydroxydienes; and 3) the conjugated oxidation products ratio (COPR), which is a measure of the relative amounts of conjugated tri- and tetraenes formed in the dehydration mixture. All oxidation product values are expressed
TABLE 2. Fatty acid composition of breast and leg muscle triglycerides (TG), phospholipids (PL), and free fatty acids (FFA) of turkeys fed diets A (tallow), B (soybean oil), or C (soybean oil + tocopherol). Results are mean ± SD. 16:0
Diet A Breast
Leg
18:2
18:0
9.1 25.6 29.5 13.4 28.9 28.5
± ± ± ± ± ±
1.1 3.6 4.7 1.5 3.7 3.0
32.0 30.0 18.4 30.5 23.7 19.5
± + + ± ± ±
2.1 5.2^ 4.1 3.2 4.1a 2.1
14.5 11.0 9.0 14.3 17.4 9.4
+ + + ± ± ±
3.0a 4.1 2.1a 2.9a 3.2 2.3a
9.2 27.8 28.0 9.3 37.5 27.3
± ± ± ± ± ±
2.3 4.7 4.5 4.2 4.7 5.0
29.6 20.4 18.0 30.0 11.0 13.5
+ ± ± ± ± ±
3.2 3.5b 2.5 4.5 4.5D 4.3
26.0 14.3 14.0 25.5 17.8 15.2
+ ± ± ± ± ±
2.5b 2.5 4.3ab 4.3b 2.6 4.0b
9.5 27.0 26.1 10.1 37.0 26.0
± ± ± ± + +
3.7 6.9 4.7 1.8 4.2 4.0
27.7 26.1 18.8 29.0 15.7 15.2
± ± ± ± + ±
4.0 4.0ab 3.7 4.0 3.7b 4.0
30.3 15.6 18.5 27.5 20.2 17.0
± ± ± ± ± ±
3.5b 5.0 2.5b 2.5b 5.2 3.7b
TG PL FFA TG PL FFA
37.5 28.5 39.0 36.0 25.1 36.6
± ± ± + ± ±
5.2 3.5 4.7 4.7 4.0 3.7
6.0 ± 3.1
TG PL FFA TG PL FFA
31.4 29.5 37.0 32.2 27.5 39.5
± ± ± + + ±
1.7 4.3 4.1 2.3 4.5 4.5
3.0 ± 2.7
TG PL FFA TG PL FFA
28.3 + 27.0+ 35.4 ± 31.0 + 19.3 ± 37.5 ±
3.0 1.9 2.7 4.0 4.3 1.9
2.0 ± 1.8
3.0 ± 2.7 6.0 ± 2.5 5.0 + 2.5
18:1
20:4
16:1
0 4.0 + 1.5 0 0 4.7 + 2.0 0
DietB Breast
Leg
Diet C Breast
Leg
3.0 + 1.0 3.0 ± 3.3 3.5 ± 2.5
. 6 ± .2 2.4 ± 1.5 3.7 + 1.9
7.0 ± 2.5
5.4 ± 3.5
4.1 ± 1.9
7.8 ± 3.3
Values within fatty acid within lipid class not followed by the same letter differ significantly (P<.05).
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 12, 2015
samples were discarded. At least four samples were taken from each bird and examined separately. At intervals during the storage period samples were homogenized and extracted with chloroform-methanol (Bligh and Dyer, 1959) and aliquots of the chloroform taken for the different analyses. Because of difficulties in obtaining reproducible TBA values, oxidative changes in fatty acids were estimated by the method of Parr and Swoboda (1976; also Fishwick and Swoboda, 1977; Streiff et al.,
LIPOLYSIS AND OXIDATION IN TURKEY MEAT BREAST
80
THIGH
60 40 20
3 7 0 3 DAYS OF INCUBATION AT 37 °C
0 60
15
30 45 60 0 15 DAYS OF STORAGE AT 4 °C
30
45
60
RESULTS Growth of the turkeys on the three diets were similar during the 9 weeks of the feeding period; final weights were 13.3, 13.6, and 13.6 kg for Diets A, B, and C, respectively. Fatty acid profiles of lipid fractions from breast and thigh muscles are shown in Table 2. Triglycerides in both muscles reflect the dietary fatty acid composition, especially the linoleic acid content, whereas phospholipids and free fatty acids were less influenced by the diet. No significant compositional differences are apparent between fatty acids in Diets B and C, which differ only in tocopherol supply level. On storage of the meat at different temperatures, COP values increased slightly in breast muscle and considerably in thigh muscle (Fig. 1). Meat from poults of Diet B (soybean oil, low tocopherol) had significantly greater COP than other treatments. The OV values (not shown) also increased on storage, in particular in the thigh muscle, but no differences between treatments were observed. The COPR values decreased in leg muscle from .58 at slaughter to .32 in A and C meat and to .25 in B meat after 24 months storage at —18 C. This indicates enhanced oxidation of dienes in B meat. Tocopherol levels decreased in all tissues on storage but remained consistently higher in group C than in groups A and B (Fig. 2). After 24 months storage at —18 C, tocopherol was no longer detectable in the meat. Concentrations of lipid phosphorus decreased and that of free fatty acids increased in all meat samples on storage, but changes were of greater magnitude in thigh than in breast muscle (Fig. 3). Triglyceride concentrations did not change significantly. No treatment dif-
12 18 24 0 6 12 MONTHS OF STORAGE AT-18 °C
FIG. 1. The conjugable oxidation products (COP) in breast and thigh muscles of turkeys fed diets A (o), B (•), and C (A) during storage at 37, 4, and — 18 C. The SD are shown when they do not fall within the circles. The COP were significantly greater (P<.05) in the thigh muscle stored at 37 C for 7 days, at 4 C for 60 days, and at 24 months at —18 C in Treatment B.
ferences in phospholipid concentrations were observed, but free fatty acid concentrations were lower in meat from B turkeys than in A and C meat in both tissues (P<.05 for breast stored at 4 C and P<.05 for both tissues at —18 C). The COP values were negatively correlated with tocopherol content in both tissues (R 2 = .74 and .54 in breast and leg muscles, respectively) and in leg muscle were also negatively correlated with phospholipid concentrations (R 2 = .74). In addition, in both tissues, COP values at different storage times were shown by multiple regression analysis to be correlated to tissue tocopherol (negative regression coefficient) and polyunsaturated fatty acid concentrations at the time of slaughter (R 2 = .88 and .91 in breast and thigh muscle, respectively).
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 12, 2015
as changes in optical density per gram meat. In an additional aliquot of chloroform extract, concentrations of phospholipids, free fatty acids, and triglycerides were determined after addition of internal standards of triheptadecanoin and heptadecanoic acid, separation by thin layer chromatography, and gas chromatography (Sklan et al, 1982). Tocopherol concentrations were determined after saponification and thin layer chromatography as described by Strum et al. (1966). Significance of differences between the treatments was determined by standard methods (Snedecor and Cochran, 1968) using the multiple range test (Duncan, 1955).
2019
2020 2
0
SKLAN ET AL. BREAST
r
6
2
r
THIGH
12 18 24 0 6 12 MONTHS OF STORAGE AT -18 °C
18
24
DISCUSSION This study was designed to follow the lipolytic and oxidative changes occurring in stored turkey meat, as affected by the type of dietary fat and tocopherol. Feeding saturated fat resulted in triglyceride fatty acid composition that closely reflected that of the dietary fat, in confirmation of previous work (Salmon, 1976; Neudoerffer and Lea, 1967). Increased tocopherol intake enhanced tissue tocopherol levels, also as expected (Crawford et al,, 1975; Marusich et al., 1975; Streiff eta/., 1977). Oxidative changes in the meat on storage, as indicated by the COP values, depended on the initial polyunsaturated fatty acid concentrations in the tissues and on the tocopherol levels. However, the rate of oxidation also appeared to be influenced by the extent of lipolysis, which is greater in thigh than breast (Fig. 3). Oxidative changes were much more extensive in leg muscle than in breast muscle (Marion and Forsythe, 1964; Sklan et al., 1982), possibly due to the higher phospholipid and polyunsaturated fatty acid concentrations, but a contributory factor may be the faster rate of lipolysis in thigh muscle. Free fatty acids appear to be oxidized at a faster rate than esterified acyl fatty acids (Labuza et al., 1969; Govindarajan et al., 1977). The negative correlation found between phospholipid concentration and COP values implies that hydrolysis of phospholipids with release of fatty acids is followed by oxidation of the free fatty acids. This is consistent with the lower concentrations of free fatty acids and the higher
FIG. 3. Concentrations of phospholipids and free fatty acids (FFA) of breast (upper panel) and thigh muscle (lower panel) from turkeys fed diets, A, B, and C and stored for 60 days at 4 C or 24 months at —18 C. Shorter bars represent FFA concentrations and are superimposed on the higher bars, which represent phospholipid concentration. The SD are shown for both FFA and phospholipids. The FFA were significantly lower (P<.05) in breast muscle from chicks fed diet B and stored at 4 C and in both breast and thigh muscle of chicks fed diet B and stored at —18 C for 24 months.
COP values in B meat (soybean oil, low tocopherol). Increased tissue tocopherol (group C) reduced the magnitude of these changes, and higher saturated fatty acid concentration (group A) in the muscles likewise reduced oxidative changes. It thus appears that lipolysis and oxidation interact, that both processes contribute to the deterioration of turkey meat on frozen storage, and that the oxidative changes on storage can be reduced by dietary means. ACKNOWLEDGMENTS This study was supported in part by a grant from the Poultry Marketing Board. Skilled technical assistance was provided by O. Kedar. REFERENCES Bligh, E. G., and W. J. Dyer, 1959. A rapid method of total lipid extraction and purification. Can. J. Biochem. Physiol. 37:911-917. Crawford, L., M. J. Kretsch, D. W. Peterson, and A. L. Lilyblade, 1975. The remedial and preventative
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 12, 2015
FIG. 2. Tocopherol concentrations in breast and thigh muscle of chicks fed diets A (o), B (•), and C (A) on storage at -18 C. The tocopherol content of muscles from chicks fed diet C was significantly greater (P<.05) than in the other dietary treatments.
LIPOLYSIS AND OXIDATION IN TURKEY MEAT
turkeys following a change in fat source. Poultry ScL 55:201-208. Sklan, D., and S. Hurwitz, 1980. Protein digestion and absorption in young chicks and turkeys. J. Nutr. 110:139-144. Sklan, D., Z. Tenne, and P. Budowski, 1982. Simultaneous lipolytic and oxidative changes in turkey meat stored at different temperatures. J. Sci. Food Agric. 34:93-99. Snedecor, G. W., and W. G. Cochran, 1968. Statistical Methods. Iowa State Univ. Press, Ames, IA. Streiff, K., L. Volker, and H. Friesecke, 1977. Dietary vitamin E and rancidity of poultry tissue. Pages 335-340 in Growth and Poultry Meat Production. K. N. Boorman and B. J. Wilson, ed. Br. Poult. Sci. Ltd, Edinburgh. Strum, P., R. M. Parkhurst, and W. A. Skinner, 1966. Quantitative determination of individual tocopherols by thin layer chromatographic separation and spectrophotometry. Anal. Chem. 38:1244-1247. Webb, J. E., C. C. Brunson, and J. D. Yates, 1973. Effects of feeding fish meal and tocopherol on flavor of precooked and frozen turkey meat. Poultry Sci. 52:1029-1034. Wilson, B. R., A. M. Pearson, and F. B. Shorland, 1976. Effect of total lipids and phospholipids on warmed over flavor in red and white muscle from several species as measured by thiobarbituric acid analysis. J. Agric. Food Chem. 24:7-11.
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 12, 2015
effect of dietary tocopherol on the development of fishy flavor in turkey meat. J. Food Sci. 40:751-755. Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics 11:1—42. Fishwick, M. J., and P.A.T. Swoboda, 1977. Measurement of oxidation of polyunsaturated fatty acids by spectrophotometric assay of conjugated derivatives. J. Sci. Food Agric. 28:387-393. Govindarajan, S., H. O. Hultin, and A. W. Kotula, 1977. Myoglobin oxidation in ground beef: mechanistic studies. J ; Food ScL 40:571—577. Labuza, T. P., W. Tsuyuki, and M. Karel, 1969. Kinetics of linoleate oxidation in model systems. J. Am. Oil Chem. Soc. 46:409-416. Marion, W. W., and R. H. Forsythe, 1964. Autoxidation of turkey lipids. J. Food Sci. 24:530-534. Marusich, W. L., E. De Ritter, E. F. Ogrinz, J. Keating, M. Mitrovic, and R. H. Bunnell, 1975. Effect of supplemental vitamin E in control of rancidity in poultry meat. Poultry Sci. 54:831-844. Neudoerffer, T. S., and C. H. Lea, 1967. Effects of dietary polyunsaturated fatty acids on the composition and individual lipids of turkey breast and leg muscle. Br. J. Nutr. 21:691-714. Parr, L. J., and P.A.T. Swoboda, 1976. The assay of conjugable oxidation products applied to lipid deterioration in stored foods. J. Food Technol. 11:1-12. Salmon, R. E., 1976. The effect of age and sex on the rate of change of fatty acid composition of
2021
Faculty of Agriculture, Hebrew University, Rehovot 76100, Israel (Received for publication June 18, 1982)
INTRODUCTION
METHODS
Poultry meat, in particular, turkey meat, is susceptible to the development of rancidity and "warmed-over flavor" on frozen storage (Wilson et al, 1976). One of the processes contributing to this deterioration is oxidation of the polyunsaturated fatty acids of the meat (Wilson et al, 1976). Feeding different dietary fats affects the composition of triglycerides and, to less extent, that of phospholipids in turkeys (Neudoerffer and Lea, 1967; Salmon, 1976; Webb et al, 1973), and this influenced the organoleptic and storage characteristics of the meat (Webb et al, 1973; Crawford et al, 1975). High dietary tocopherol has been shown to increase tissue tocopherol levels, to retard the onset of rancidity in frozen turkey meat (Crawford et al, 1975), and to attenuate the increase in TBA values on storage (Marusich et al, 1975). We have recently shown that lipolysis of phospholipids occurs in conjunction with oxidation of lipids on frozen storage (Sklan et al, 1982). The object of the present study was to determine the effects of dietary fat supplements with different degrees of fatty acid saturation and of the addition of tocopherol on the simultaneous oxidative and hydrolytic changes in turkey meat on frozen storage.
Male turkey poults (Meleagris gallopavo) were obtained from a commercial hatchery and fed commercial diets until 15 weeks old. The poults were then randomly divided into three groups of five animals each, which received diets containing either beef tallow, soybean oil, or soybean oil with an additional 60 mg/kg all-rac-a-tocopherol, (Diets A, B, and C, respectively). All diets contained 61.3% ground sorghum, 32% defatted soybean meal (45% protein), and 3% added fat with minerals, trace minerals, and vitamins as previously described (Sklan and Hurwitz, 1980) except that total tocopherol was present at 5 mg/kg in the vitamin mix. The fatty acid profiles of the diets are shown in Table 1. Poults were fed these diets for 9 weeks before slaughtering in a commercial slaughterhouse. Meat samples were taken under sterile. conditions from pectoralis and gastrocnemius by exposure of the external surface of the meat to a red hot iron and sampling of approximately 10 g taken from deeper layers of the tissue. Samples were stored at 37, 4, or —18 C for differing periods (Sklan et al, 1982). Sterility of the samples was checked by incubating in nutrient broth at 30 C for 2 days and counting on blood agar at 15 and 37 C or by direct plating with blood agar; nonsterile
2017
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 12, 2015
ABSTRACT Turkeys were fed diets containing tallow or soybean oil with either 5 or60mg/kg all-rac-a-tocopherol for 9 weeks before slaughter. Muscle was sampled aseptically from breast or thigh and stored at 37, 4, or —18 C. Tocopherol tissue content reflected dietary levels; the fatty acid composition of muscle triglycerides was significantly affected by the dietary fat but that of phospholipids was influenced only slightly by the different diets. Both oxidative and lipolytic changes were greater in leg muscle than in breast muscle. High dietary tocopherol levels resulted in decreased oxidation on storage of meat tissues as did feeding of a more saturated fat diet. Diets did not influence the rate of hydrolysis of phospholipids, but differences in the free fatty acid concentrations were found, presumably due to increased oxidation in the soybean oil, low tocopherol diet. The concentration of conjugable oxidation products was directly correlated with initial polyunsaturated fatty acid concentrations and inversely widi tocopherol concentrations. (Key words: turkey meat storage, tocopherol, dietary fat, oxidation, lipolysis) 1983 Poultry Science 62:2017-2021
2018
SKLAN ET AL. TABLE 1. Fatty acid profiles of lipids extracted from the experimental diets 16:0'
16:1
18:0
22.4 13.9 17.0
2.4 .4 .5
18.3 3.4 3.1
18:1
18:2
18:3
30.7 28.0 26.9
24.9 51.7 49.8
1.3 2.6 2.7
\'°) ~ Tallow S o y b e a n oil Soybean oil + tocopherol 1
Number of carbon atoms: number of double bonds.
1977). This technique invokes the following spectrometric measurements: 1) oxodiene value (OV), which represents diene conjugation after reduction of the keto groups of oxodiene fatty acids, to hydroxy groups; 2) conjugable oxidation products (COP) obtained by dehydration of fatty acids hydroperoxides, oxodienes, and hydroxydienes; and 3) the conjugated oxidation products ratio (COPR), which is a measure of the relative amounts of conjugated tri- and tetraenes formed in the dehydration mixture. All oxidation product values are expressed
TABLE 2. Fatty acid composition of breast and leg muscle triglycerides (TG), phospholipids (PL), and free fatty acids (FFA) of turkeys fed diets A (tallow), B (soybean oil), or C (soybean oil + tocopherol). Results are mean ± SD. 16:0
Diet A Breast
Leg
18:2
18:0
9.1 25.6 29.5 13.4 28.9 28.5
± ± ± ± ± ±
1.1 3.6 4.7 1.5 3.7 3.0
32.0 30.0 18.4 30.5 23.7 19.5
± + + ± ± ±
2.1 5.2^ 4.1 3.2 4.1a 2.1
14.5 11.0 9.0 14.3 17.4 9.4
+ + + ± ± ±
3.0a 4.1 2.1a 2.9a 3.2 2.3a
9.2 27.8 28.0 9.3 37.5 27.3
± ± ± ± ± ±
2.3 4.7 4.5 4.2 4.7 5.0
29.6 20.4 18.0 30.0 11.0 13.5
+ ± ± ± ± ±
3.2 3.5b 2.5 4.5 4.5D 4.3
26.0 14.3 14.0 25.5 17.8 15.2
+ ± ± ± ± ±
2.5b 2.5 4.3ab 4.3b 2.6 4.0b
9.5 27.0 26.1 10.1 37.0 26.0
± ± ± ± + +
3.7 6.9 4.7 1.8 4.2 4.0
27.7 26.1 18.8 29.0 15.7 15.2
± ± ± ± + ±
4.0 4.0ab 3.7 4.0 3.7b 4.0
30.3 15.6 18.5 27.5 20.2 17.0
± ± ± ± ± ±
3.5b 5.0 2.5b 2.5b 5.2 3.7b
TG PL FFA TG PL FFA
37.5 28.5 39.0 36.0 25.1 36.6
± ± ± + ± ±
5.2 3.5 4.7 4.7 4.0 3.7
6.0 ± 3.1
TG PL FFA TG PL FFA
31.4 29.5 37.0 32.2 27.5 39.5
± ± ± + + ±
1.7 4.3 4.1 2.3 4.5 4.5
3.0 ± 2.7
TG PL FFA TG PL FFA
28.3 + 27.0+ 35.4 ± 31.0 + 19.3 ± 37.5 ±
3.0 1.9 2.7 4.0 4.3 1.9
2.0 ± 1.8
3.0 ± 2.7 6.0 ± 2.5 5.0 + 2.5
18:1
20:4
16:1
0 4.0 + 1.5 0 0 4.7 + 2.0 0
DietB Breast
Leg
Diet C Breast
Leg
3.0 + 1.0 3.0 ± 3.3 3.5 ± 2.5
. 6 ± .2 2.4 ± 1.5 3.7 + 1.9
7.0 ± 2.5
5.4 ± 3.5
4.1 ± 1.9
7.8 ± 3.3
Values within fatty acid within lipid class not followed by the same letter differ significantly (P<.05).
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 12, 2015
samples were discarded. At least four samples were taken from each bird and examined separately. At intervals during the storage period samples were homogenized and extracted with chloroform-methanol (Bligh and Dyer, 1959) and aliquots of the chloroform taken for the different analyses. Because of difficulties in obtaining reproducible TBA values, oxidative changes in fatty acids were estimated by the method of Parr and Swoboda (1976; also Fishwick and Swoboda, 1977; Streiff et al.,
LIPOLYSIS AND OXIDATION IN TURKEY MEAT BREAST
80
THIGH
60 40 20
3 7 0 3 DAYS OF INCUBATION AT 37 °C
0 60
15
30 45 60 0 15 DAYS OF STORAGE AT 4 °C
30
45
60
RESULTS Growth of the turkeys on the three diets were similar during the 9 weeks of the feeding period; final weights were 13.3, 13.6, and 13.6 kg for Diets A, B, and C, respectively. Fatty acid profiles of lipid fractions from breast and thigh muscles are shown in Table 2. Triglycerides in both muscles reflect the dietary fatty acid composition, especially the linoleic acid content, whereas phospholipids and free fatty acids were less influenced by the diet. No significant compositional differences are apparent between fatty acids in Diets B and C, which differ only in tocopherol supply level. On storage of the meat at different temperatures, COP values increased slightly in breast muscle and considerably in thigh muscle (Fig. 1). Meat from poults of Diet B (soybean oil, low tocopherol) had significantly greater COP than other treatments. The OV values (not shown) also increased on storage, in particular in the thigh muscle, but no differences between treatments were observed. The COPR values decreased in leg muscle from .58 at slaughter to .32 in A and C meat and to .25 in B meat after 24 months storage at —18 C. This indicates enhanced oxidation of dienes in B meat. Tocopherol levels decreased in all tissues on storage but remained consistently higher in group C than in groups A and B (Fig. 2). After 24 months storage at —18 C, tocopherol was no longer detectable in the meat. Concentrations of lipid phosphorus decreased and that of free fatty acids increased in all meat samples on storage, but changes were of greater magnitude in thigh than in breast muscle (Fig. 3). Triglyceride concentrations did not change significantly. No treatment dif-
12 18 24 0 6 12 MONTHS OF STORAGE AT-18 °C
FIG. 1. The conjugable oxidation products (COP) in breast and thigh muscles of turkeys fed diets A (o), B (•), and C (A) during storage at 37, 4, and — 18 C. The SD are shown when they do not fall within the circles. The COP were significantly greater (P<.05) in the thigh muscle stored at 37 C for 7 days, at 4 C for 60 days, and at 24 months at —18 C in Treatment B.
ferences in phospholipid concentrations were observed, but free fatty acid concentrations were lower in meat from B turkeys than in A and C meat in both tissues (P<.05 for breast stored at 4 C and P<.05 for both tissues at —18 C). The COP values were negatively correlated with tocopherol content in both tissues (R 2 = .74 and .54 in breast and leg muscles, respectively) and in leg muscle were also negatively correlated with phospholipid concentrations (R 2 = .74). In addition, in both tissues, COP values at different storage times were shown by multiple regression analysis to be correlated to tissue tocopherol (negative regression coefficient) and polyunsaturated fatty acid concentrations at the time of slaughter (R 2 = .88 and .91 in breast and thigh muscle, respectively).
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 12, 2015
as changes in optical density per gram meat. In an additional aliquot of chloroform extract, concentrations of phospholipids, free fatty acids, and triglycerides were determined after addition of internal standards of triheptadecanoin and heptadecanoic acid, separation by thin layer chromatography, and gas chromatography (Sklan et al, 1982). Tocopherol concentrations were determined after saponification and thin layer chromatography as described by Strum et al. (1966). Significance of differences between the treatments was determined by standard methods (Snedecor and Cochran, 1968) using the multiple range test (Duncan, 1955).
2019
2020 2
0
SKLAN ET AL. BREAST
r
6
2
r
THIGH
12 18 24 0 6 12 MONTHS OF STORAGE AT -18 °C
18
24
DISCUSSION This study was designed to follow the lipolytic and oxidative changes occurring in stored turkey meat, as affected by the type of dietary fat and tocopherol. Feeding saturated fat resulted in triglyceride fatty acid composition that closely reflected that of the dietary fat, in confirmation of previous work (Salmon, 1976; Neudoerffer and Lea, 1967). Increased tocopherol intake enhanced tissue tocopherol levels, also as expected (Crawford et al,, 1975; Marusich et al., 1975; Streiff eta/., 1977). Oxidative changes in the meat on storage, as indicated by the COP values, depended on the initial polyunsaturated fatty acid concentrations in the tissues and on the tocopherol levels. However, the rate of oxidation also appeared to be influenced by the extent of lipolysis, which is greater in thigh than breast (Fig. 3). Oxidative changes were much more extensive in leg muscle than in breast muscle (Marion and Forsythe, 1964; Sklan et al., 1982), possibly due to the higher phospholipid and polyunsaturated fatty acid concentrations, but a contributory factor may be the faster rate of lipolysis in thigh muscle. Free fatty acids appear to be oxidized at a faster rate than esterified acyl fatty acids (Labuza et al., 1969; Govindarajan et al., 1977). The negative correlation found between phospholipid concentration and COP values implies that hydrolysis of phospholipids with release of fatty acids is followed by oxidation of the free fatty acids. This is consistent with the lower concentrations of free fatty acids and the higher
FIG. 3. Concentrations of phospholipids and free fatty acids (FFA) of breast (upper panel) and thigh muscle (lower panel) from turkeys fed diets, A, B, and C and stored for 60 days at 4 C or 24 months at —18 C. Shorter bars represent FFA concentrations and are superimposed on the higher bars, which represent phospholipid concentration. The SD are shown for both FFA and phospholipids. The FFA were significantly lower (P<.05) in breast muscle from chicks fed diet B and stored at 4 C and in both breast and thigh muscle of chicks fed diet B and stored at —18 C for 24 months.
COP values in B meat (soybean oil, low tocopherol). Increased tissue tocopherol (group C) reduced the magnitude of these changes, and higher saturated fatty acid concentration (group A) in the muscles likewise reduced oxidative changes. It thus appears that lipolysis and oxidation interact, that both processes contribute to the deterioration of turkey meat on frozen storage, and that the oxidative changes on storage can be reduced by dietary means. ACKNOWLEDGMENTS This study was supported in part by a grant from the Poultry Marketing Board. Skilled technical assistance was provided by O. Kedar. REFERENCES Bligh, E. G., and W. J. Dyer, 1959. A rapid method of total lipid extraction and purification. Can. J. Biochem. Physiol. 37:911-917. Crawford, L., M. J. Kretsch, D. W. Peterson, and A. L. Lilyblade, 1975. The remedial and preventative
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 12, 2015
FIG. 2. Tocopherol concentrations in breast and thigh muscle of chicks fed diets A (o), B (•), and C (A) on storage at -18 C. The tocopherol content of muscles from chicks fed diet C was significantly greater (P<.05) than in the other dietary treatments.
LIPOLYSIS AND OXIDATION IN TURKEY MEAT
turkeys following a change in fat source. Poultry ScL 55:201-208. Sklan, D., and S. Hurwitz, 1980. Protein digestion and absorption in young chicks and turkeys. J. Nutr. 110:139-144. Sklan, D., Z. Tenne, and P. Budowski, 1982. Simultaneous lipolytic and oxidative changes in turkey meat stored at different temperatures. J. Sci. Food Agric. 34:93-99. Snedecor, G. W., and W. G. Cochran, 1968. Statistical Methods. Iowa State Univ. Press, Ames, IA. Streiff, K., L. Volker, and H. Friesecke, 1977. Dietary vitamin E and rancidity of poultry tissue. Pages 335-340 in Growth and Poultry Meat Production. K. N. Boorman and B. J. Wilson, ed. Br. Poult. Sci. Ltd, Edinburgh. Strum, P., R. M. Parkhurst, and W. A. Skinner, 1966. Quantitative determination of individual tocopherols by thin layer chromatographic separation and spectrophotometry. Anal. Chem. 38:1244-1247. Webb, J. E., C. C. Brunson, and J. D. Yates, 1973. Effects of feeding fish meal and tocopherol on flavor of precooked and frozen turkey meat. Poultry Sci. 52:1029-1034. Wilson, B. R., A. M. Pearson, and F. B. Shorland, 1976. Effect of total lipids and phospholipids on warmed over flavor in red and white muscle from several species as measured by thiobarbituric acid analysis. J. Agric. Food Chem. 24:7-11.
Downloaded from http://ps.oxfordjournals.org/ at UCSF Library on April 12, 2015
effect of dietary tocopherol on the development of fishy flavor in turkey meat. J. Food Sci. 40:751-755. Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics 11:1—42. Fishwick, M. J., and P.A.T. Swoboda, 1977. Measurement of oxidation of polyunsaturated fatty acids by spectrophotometric assay of conjugated derivatives. J. Sci. Food Agric. 28:387-393. Govindarajan, S., H. O. Hultin, and A. W. Kotula, 1977. Myoglobin oxidation in ground beef: mechanistic studies. J ; Food ScL 40:571—577. Labuza, T. P., W. Tsuyuki, and M. Karel, 1969. Kinetics of linoleate oxidation in model systems. J. Am. Oil Chem. Soc. 46:409-416. Marion, W. W., and R. H. Forsythe, 1964. Autoxidation of turkey lipids. J. Food Sci. 24:530-534. Marusich, W. L., E. De Ritter, E. F. Ogrinz, J. Keating, M. Mitrovic, and R. H. Bunnell, 1975. Effect of supplemental vitamin E in control of rancidity in poultry meat. Poultry Sci. 54:831-844. Neudoerffer, T. S., and C. H. Lea, 1967. Effects of dietary polyunsaturated fatty acids on the composition and individual lipids of turkey breast and leg muscle. Br. J. Nutr. 21:691-714. Parr, L. J., and P.A.T. Swoboda, 1976. The assay of conjugable oxidation products applied to lipid deterioration in stored foods. J. Food Technol. 11:1-12. Salmon, R. E., 1976. The effect of age and sex on the rate of change of fatty acid composition of
2021