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Effects of Air at Various Tension Levels on Storage Stability of Mechanically Deboned Poultry Meats1
Effects of Air at Various Tension Levels on Storage Stability of Mechanically Deboned Poultry Meats1 PANTIPAR JANTAWAT2 and L. E. DAWSON Food Science and Human Nutrition Department, Michigan State University, East Lansing, Michigan 48824 (Received for publication July 27, 1979) ABSTRACT Air pressures equivalent to 0, 126, 380, and 760 mm Hg were assigned to packages of mechanically deboned chicken meat (MDCM), mechanically deboned turkey meat (MDTM), and their lipid extracts. All treated samples were stored at —18 C up to 3 months. Changes in phospholipid polyunsaturated fatty acids (expressed as unsaturation ratio, C, i ^ - n i j / C , 6 : 0 ) and 2-thiobarbituric acid (TBA) absorption values were used to follow lipid oxidation reactions. Samples packaged under 0 mm Hg and samples packaged at 126 mm Hg showed similar losses of polyunsaturated fatty acids and comparable development of TBA reactive substances. After 1 month storage, TBA absorption values of MDTM samples packaged under vacuum were significantly lower than those packaged at 126, 380, and 760 mm of Hg. Significant differences in mean unsaturation ratios were observed between the lipid extracts from MDCM and the meat itself, but not between those from the lipid extract from MDTM and turkey meat. Significant differences in TBA reactive substances were found between turkey and chicken lipids. (Key words: turkey stability, chicken stability, mechanically processed, poultry vacuum level, TBA, lipid unsaturation) 1980 Poultry Science 59:1788-1794 INTRODUCTION
Oxidative rancidity or lipid oxidation has generally been accepted as one of the most serious problems involved in storage and utilization of mechanically deboned poultry meats (MDPM). Froning (1976) stated that the mechanical deboning process may cause considerable cellular disruption, protein denaturation, and increases in lipid and heme oxidation in the resulting meats. Maxon and Marion (1970) reported that both lipid oxidation and hydrolytic deteriorations occurred in lipids of mechanically deboned turkey meats (MDTM). Dimick et al. (1972) and Johnson et al. (1974) found that quality of MDPM could be maintained up to 6 days at 3 C or up to 12 to 14 weeks in frozen storage. Many attempts have been made to slow down or prevent oxidative rancidity in MDPM. In freezing preservation of ground fresh meats, the main consideration in packaging of the meat is the exclusion of oxygen. The mechanism of lipid oxidation in fresh meat is compli-
1
Michigan Agricultural Experiment Station Journal Article No. 9086. 2 Present address: 2 Pibulvatana, Rama 6, Samsen, Bangkok 4, Thailand.
cated due to the presence of heme pigments which are generally accepted as biocatalysts for meat lipid oxidation. Neill and Hastings (1925) demonstrated conversion of hemoglobin to methemoglobin at intermediate rather than at very high or very low oxygen tensions. According to Tarladgis (1961) and Watts (1961), iron in metmyoglobin or methemoglobin was highly effective in initiating the chain reaction mechanism in the lipid autoxidation process. Studying behavior of the lipids of MDPM when subjected to oxygen or air might be helpful in improving meat preservation. Specific objectives of this study were: 1) to compare effect of air at different levels on the storage stability of MDPM; and 2) to study and compare the storage stability of naturally occurring meat lipids with those extracted and stored separate from the meat. MATERIALS AND METHODS Sample Source and Preparation. Meat samples were obtained from a commercial poultry processing plant in Michigan. Mechanically deboned meats were processed through a Beehive mechanical deboning machine (Model AV 968 MF, Beehive Machinery Co., Sandy, UT). Both mechanically deboned chicken meat (MDCM) and MDTM were deboned from whole
1788
STABILITY OF MECHANICALLY PROCESSED POULTRY MEAT
carcasses. The MDCM was obtained from freshly dressed (not frozen) adult hens (fowl), and further processing (mechanical deboning) was accomplished as soon as the major muscles were removed from the carcasses. The MDTM was obtained from turkeys which had been frozen and stored. The original source and length of storage of these turkeys is unknown. Turkeys were thawed in cold water prior to hand boning major muscles and machine deboning the remaining bony portions. The MDCM and MDTM were individually mixed at medium speed in a Hobart mixer (Model K-5A) under N 2 for 2 min. After mixing, each meat item was vacuum packaged (0 mm Hg) to a 2.54 cm thickness in #13 IKD® (mylar laminated) plastic bags. After sealing, samples were held overnight at —18 C. The frozen slabs were cut into 5.08 X 5.08 X 2.54 cm blocks. Each meat block was wrapped with a piece of low density polyethylene sheet and arranged into a vacuum chamber. Lipid extracts from both meat species, stored in 30 X 3 5 mm wide mouth bottle type glass vials, were arranged within the same storage chamber. After closing, an assigned quantity of air pressure was created within each chamber. The chamber was first evacuated by using a duo-seal vacuum pump (Model 1400). After complete evacuation, a known quantity of air was injected back into the chamber, and the chamber was sealed. A U-type vacuum gauge was used to assure the appropriate quantity of air within each chamber. The closed chamber was then placed in a Cryovac bag and the bag was sealed with a Tipper Clipper bag sealer (Model 72105). Storage chambers were stored at —18 C for 3 months. Treatment diagram for this study is illustrated in Figure 1. Analytical methods. Total lipids were extracted from the MDPM by the method of Folchefa/. (1957). Thin layer chromatography was used to separate phospholipids from neutral lipids. A .5 mm layer silica gel G plate (Applied Science Laboratories) was used. Fat samples dissolved in an appropriate quantity of chloroform were applied along the bottom of the plate and the plate was developed in chloroform. After development, lipid bands were visualized by spraying with .5% iodine in methanol solution. Phospholipids were eluted with several portions of a 2:1 (v/v) chloroform-methanol solution. Methylation of the separated phospholipid samples was performed according to the method
1789
MPCM
Packaging
(mm of Hq)
I
I
126 , 380
760
Storage-18 C, 3 months
FIG. 1. Diagram of product processing and storage treatments.
described by Morrison and Smith (1964). Gas chromatographic analyses were performed by using an F & M model-810 dual column gas chromatograph, equipped with a flame ionization detector. A stainless steel column (.32 cm X 1.83 m) packed with 10% DEGS-PS on 80-100 mesh Supelcoport® (Supelco, Inc.) was used for the fatty acid separations. Helium was selected as the carrier gas at a flow rate of 30 ml/min. The hydrogen flame was fed with 35 ml/min hydrogen and 3 50/ml min compressed air. The temperature was programmed from 150 to 190 C at a rate of 4 C/min. The temperature of detectors and injection ports were kept constant at 255 C and 250 C, respectively. Fatty acid methyl esters were identified by comparing their relative retention times (relative to methyl palmitate) using a plot of logarithm of the relative retention time versus the number of carbon atoms. A fatty acid internal was not
LIPID EXTRACT
rr
< rr <
1
2
3
1
2
STORAGE TIME (Mo.) FIG. 2. Unsaturation ratios (C( s : 3 _ 2 j :
1790
JANTAWAT AND DAWSON
L
LIPID EXTRACT
MEAT
o t< rr
\\
2 O 1-
\
< rr
UNSATU
-\-o
0
V 126 \» *
c
1
2
760 380
3
0
STORAGE TIN/IE
, 1
2
*o st
0 126
-»
380
-a
760
r
3
Mo.)
FIG. 3. Unsaturation ratios (Cl s:3_22:6/Cl6-.0) of MDTM and MDTM phospholipid extract samples packaged at 0, 126, 380, 760 mm Hg and stored up to 3 months at —18 C.
found which had a r e t e n t i o n time different from t h a t of the m a n y fatty acids found in each fat sample. A quantitative external fatty acid standard m i x t u r e was used to identify all of the peaks in our sample, and t o calibrate t h e G L C
e q u i p m e n t . T w o times each day a s t a n d a r d m i x t u r e was injected into the c h r o m a t o g r a p h and the percentage of each fatty acid was calculated. Experimental samples were injected and q u a n t i t a t e d only when these s t a n d a r d m i x t u r e test results were accurate. T h e percentage of each fatty acid m e t h y l ester was calculated b y dividing t h e area of each individual peak by the total area of all peaks. Oxidation of C l g : i and C i 8 : 2 fatty acids is r e p o r t e d t o occur at a slower rate t h a n C i g : 3 "C2o:4 fatty acids. Since oxidation of p h o s p h o lipids (higher in m o r e unsaturated fatty acids) was followed in this s t u d y , only those fatty acids with m o r e t h a n t w o double b o n d s were included in these comparisons. These fatty acids included 1 8 : 3 , 2 0 : 3 , 2 0 : 4 , 2 2 : 4 , 2 2 : 5 , and 2 2 : 6 . T h e T B A absorption values for all treated m e a t samples were determined by the m e t h o d described by Tarladgis et al. ( 1 9 6 0 ) . T h e T B A a b s o r p t i o n values for lipid e x t r a c t were also
TABLE l.Mean unsaturation ratios1 for phospholipids from MDCM, MDTM, and their lipid extract samples packaged at 0, 126, 380, and 760 mm of Hg and stored at —18 C for 3 months Meat type
Storage time (month) Treatment
0
2
3 •
MDCM
Stored as meat Air pressure (mm Hg) 0 126 380 760 Stored as lipid extract Air pressure (mm Hg) 0 126 380 760
MDTM
a
Stored as meat Air pressure (mm Hg) 0 126 380 760 Stored as lipid extract Air pressure (mm Hg) 0 126 380 760
2\
1.92 a 1.92 a 1.92a 1.92a
1.42 a .65 b .86 b .53 b
.92 a .83 a ,38 b .31b
1.79 a 1.79 a 1.79a 1.79 a
1.06a 1.07 a .81° .66 b
.97 a ,82 a .62 b .53 b
1.43 a 1.43 a 1.43 a 1.43 a
.70 b 1.00a .60 b .59 b
.68 a .58 a .26 b .31b
1.42a 1.42 a 1.42 a 1.42a
.69 a .S7 a .49 b .49 b
.80 a .71a .56ab ,37 b
' Values among treatments within a column which are followed by the same letter are not significantly different (PX05). 1 Mean of 2 replicates, expressed as polyunsaturated C, s : 3 _ 2 2 : 6 fatty acids/palmitic acids. 2 Comparison among air pressure treatments for each product (meat or extract) and within each storage time.
STABILITY OF MECHANICALLY PROCESSED POULTRY MEAT
1791
measured by following the method described by Tarladgis et al. (1960), except that a quantity of lipid extracts equivalent to lOg of MPPM (2.0g for turkey lipid extract and 2.3g for chicken lipid extract) was used for each determination. Statistical Analysis. Analysis of variance was performed by using a Michigan State University computer program and Tukey's multiple comparisons of means were calculated according to Gill (1978).
RESULTS AND DISCUSSION
In this study the total lipid content of MDCM was 23% and of MDTM, 20%. Changes in phospholipid unsaturation ratios ( C i 8 : 3 -2 2:6/C 1 6 : o ) for MDCM, MDTM, and their lipid extracts are shown in Figures 2 and 3. Significant differences in unsaturation ratios were found for MDCM and MDTM and the phospholipid extracts over storage time and at different air tensions (Table 1). Significance of two- and 3-way interactions for all treatment combinations were found in both MDCM and MDTM phospholipid unsaturation ratios. A marked decrease in unsaturation ratios was found in samples from all treatments at the end of 3 months storage. Significant differences in unsaturation ratios were found among means of samples stored under different air tensions (Table 1). For MDCM, at the end of 3 months storage, the quantities of unsaturated molecules (Ci 8:3—22:6) left i° the phospholipids were comparable between samples stored at 0 and at 126 mm of air and between those stored at 3 80 and 760 mm of air. Similar results were observed in MDCM lipid extract samples and in MDTM samples. When MDCM samples were stored as lipid extracts, significantly higher quantities of polyunsaturated fatty acids (Ci 8 : 3 —2 2 :6 ) were found in their phospholipids when compared to those found in their corresponding meat samples. The TBA absorption values obtained for variously treated MDCM and MDTM samples are shown in Figures 4 and 5 and Table 2. Analyses of variance and the significance of differences in means are also presented in Table 3. The TBA absorption values for all treated samples increased as storage time increased. The induction period for the development of TBA reactive substances occurred between 0 to 2 months of storage for MDCM samples stored at 0 and 126 mm of air. The MDCM samples stored
STORAGE TIME (Mo.)
FIG. 4. TBA absorption values of MDCM and MDCM phospholipid extract samples, packaged at 0, 126, 380, and 760 mm Hg and stored up to 3 months at -18 C.
at 3 80 and 760 mm of air showed a rapid increase in TBA absorption values between 0 and 1 to 2 months of storage and then slowed down; MDCM lipid extract samples showed similar changes. The TBA absorption values, however, behaved differently for MDTM samples. Rapid increases were observed in all treatments of MDTM early in the storage. After 2 months frozen storage, TBA absorption values of MDTM samples increased to approximately 1.4 to 1.6 nm, and thien with subsequent storage periods, some of these values dropped. This increase and decline in TBA absorption values,
I-
02 ' 0
' 1
' 2
'— ' 3 0
' 1
-^ 2
'— 3
STORAGE TIME (Mo.) FIG. 5. TBA absorption values of MDTM and MDTM phospholipid extract samples, packaged at 0, 126, 380, and 760 mm Hg and stored up to 3 months at —18 C.
1792
JANTAWAT AND DAWSON
TABLE 2. Mean TBA absorption values' forMDCM, MDTM, and their lipid extract samples packaged at 0, 126, 380, and 760 mm of Hg and stored at -18 C for 3 months Meat type
Storage t i m e ( m o n t h ) Treatment
0
2
1
3 \2
MDCM
MDTM
Stored as meat Air pressure ( m m Hg) 0 126 380 760
.089a .089a .089a .089a
.072b .070b .076b .454a
.lllb .173b .762ab 1.106a
.235b ,304b ,885ab 1.173a
Stored as lipid extract Air pressure ( m m Hg) 0 126 380 760
.059a .059a .059a .059a
.116b .132b .270ab .444a
.185b .421ab .700a ,727a
.293b .454ab ,632a .625a
Stored as meat Air pressure ( m m Hg) 0 126 380 760
.426a .426a .426a .426a
.600c .819bc 1.168ab 1.335a
Stored as lipid extract Air pressure ( m m Hg) 0 126 380 760
,365a .365a .365a .365a
.330b .394b .485b .723a
1.000 b 1.258a 1.571a 1.492 a
.214b .300b .600ab .780a
1.150b 1.318a 1.398a 1.383a
.400b .460b .710ab .939a
a
' ' Like letters among treatments within a column denote no significant difference (P>.05). Mean of 2 replicates with 6 determinations. 2 Comparison among air pressure treatments for each product (meat or extract) within each storage interval and extraction treatment. 1
however, were not observed in MDTM lipid extract samples. A rather steady increase in TBA absorption values was observed for samples from most treatments within this group. Tukey mean separations indicated that at the end of the first month, there were no significant differences in TBA absorption values among MDCM samples stored at 0, 126, and 380 mm of air. At the end of the second month, however, significant differences in mean TBA absorption values were found between samples stored at 0 and 126 mm of air and those stored at 380 and 760 mm of air. These differences were still observed at the end of the 3 month storage period. For MDTM samples, significant differences in TBA absorption values among samples stored under vacuum and those stored at 126, 380, and 760 mm of air were observed after the first month of storage. At the end of 3 months, these results were still observed among
various treatments within this group. The results obtained from TBA tests indicate that air at 126 mm Hg had the same effect as air at 0 mm or vacuum storage with respect to the development of TBA reactive substances in MDCM for a 3 month storage period. For MDTM samples, 126 mm of air in their packages resulted in differences in TBA absorption values from those stored under vacuum after the first month of storage. Lipid extract samples were expected to develop oxidative deterioration more slowly and to a lesser degree than their corresponding meat samples upon frozen storage. Extraction of muscle lipids with chloroform methanol and purification of the crude extracts with an aqueous solution should provide meat fats which were free from most other water soluble components including the meat pigments and nonheme iron which have been reported to be
STABILITY OF MECHANICALLY PROCESSED POULTRY MEAT
1793
TABLE 3. Analyses of variance of the unsaturation ratios, TBA absorption values, and total phospholipid phosphorus Unsaturation ratio
TBA number
Source of variation
d.f.
Mean square
d.f.
MDCM Storage Extraction Air Extraction-storage Extraction-air Storage-air Extraction-storage-air
2 1 3 2 3 6 6
6.88a .02° .34a .05a .04a ,09a .05°
MDTM Storage Extraction Air Extraction-storage Extraction-air Storage-air Extraction-storage-air
2 1 3 2 3 6 6
3.82a .01b .12a ,10a .02° .04a .01b
Phospho lipid phosphc Drus Mean square
d.f
Mean square
3 1 3 3 3 9 9
.95a .01a .65a .03a .09a .lla .03a
3 1 3 3 3 9 9
.50a .32a .07a .15a .03b ,03a .13a
3 1 3 3 3 9 9
1.04 a 4.43a .44a .48a .02b .05a .02a
3 1 3 3 3 9 9
.36a .026a .06a .08a ,01b .02b .llb
Significant at .01% level. Significant at .05% level.
present as trace components in MPPM. Thus, the autoxidation reactions which occur in isolated lipids should be entirely different from those which occur when these lipids are in the meat samples. However, when lipids are in the meat tissues, some of them might bind with proteins and be present in the form of lipoprotein complexes. Protein and water in meat tissues together might partially protect the lipids from being reached by 0 2 molecules which surround the meat blocks. Lipid extract samples, in contrast, were exposed directly to 0 2 molecules. This factor might have some compensation effect on losses of prooxidant substances found in lipid extract samples. Hence, at the end of 3 months storage, there either were no significant differences in fatty acid oxidation of MDTM and MDTM lipid extract samples or only lower level significant differences in mean unsaturation ratios between MDCM and MDCM lipid extract samples. Significant differences in TBA absorption values were observed among MDCM, MDTM, and their lipid extract samples after 3 months storage. These results were not in good agreement with results obtained from changes in phospholipid unsaturation ratios. One factor is
the difference in response to TBA test which might occur between these two types of products. The TBA analyses were applied directly to meat samples without extraction of the meat lipids. Handling of meat at elevated temperatures during the distillation processes might result in a favorable condition for catalytic action of natural meat prooxidant substances on meat lipid oxidation. Thus, different forms of samples might respond differendy to this particular testing method. This difference also might contribute to the highly significant difference in TBA absorption values found between these two treatment groups. From analyses of data obtained from changes in phospholipid polyunsaturated fatty acids and TBA absorption values, several conclusions can be drawn. A partial vacuum (air at 126 mm Hg) was comparable to vacuum packaging for MDCM products stored up to 3 months, while vacuum packaging was significantly better than other treatments for MDTM. Significant differences among MPPM samples stored as meat and as lipid extract were observed in most treatment groups and testing methods with the only exception being changes in unsaturation ratio of MDTM samples. In all significant cases, samples stored as meats exhibited higher and
1794
JANTAWAT AND DAWSON
faster lipid oxidation reaction than did their corresponding lipid extract samples.
REFERENCES Dimick, P. S., J. H. Mac Neil, and L. P. Grunden, 1972. Poultry product quality: Carbonyl composition and organoleptic evaluation of mechanically deboned poultry meat. J. Food Sci. 37:544— 546. 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. Froning, G. W., 1976. Mechanically deboned poultry meat. Food Technol. 30(9):50-63. Gill, J. L., 1978. Design and analysis of experiments. Vol. 1. Iowa State Univ. Press, Ames, IA. Johnson, A. G., F. E. Cunningham, and J. A. Bowers, 1974. Quality of mechanically deboned turkey meat: Effect of storage time and temperature. Poultry Sci. 53:732-736.
Maxon, S. T., and W. W. Marion, 1970. Lipids of mechanically deboned turkey. Poultry Sci. 49:1412-1413. Morrison, W. R., and L. M. Smith, 1964. Preparation of fatty acid methyl esters and dimethylacetals from lipids with boron fluoride methanol. J. Lipid Res. 5:600-608. Neill, J. M., and A. B. Hastings, 1925. The influence of the tension of molecular oxygen upon certain oxidations of hemoglobin. J. Biol. Chem. 63: 479-492. Tarladgis, B. G., 1961. An hypothesis for the mechanism of the heme catalyzed lipid oxidation in animal tissues. J. Amer. Oil Chem. Soc. 38: 479-483. Tarladgis, B. G., B. M. Watts, M. T. Younathan, and L. R. Dugan, Jr., I960. A distillation method for the quantitative determination of malonaldehyde in rancid foods. J. Amer. Oil Chem. Soc. 37: 44-48. Watts, B. M., 1961. The role of lipid oxidation in lean tissue in flavor deterioration of meat and fish. Page 38 in Proc. Flavor Chem. Symp., Campbell Soup Co., Camden, NJ.
Oxidative rancidity or lipid oxidation has generally been accepted as one of the most serious problems involved in storage and utilization of mechanically deboned poultry meats (MDPM). Froning (1976) stated that the mechanical deboning process may cause considerable cellular disruption, protein denaturation, and increases in lipid and heme oxidation in the resulting meats. Maxon and Marion (1970) reported that both lipid oxidation and hydrolytic deteriorations occurred in lipids of mechanically deboned turkey meats (MDTM). Dimick et al. (1972) and Johnson et al. (1974) found that quality of MDPM could be maintained up to 6 days at 3 C or up to 12 to 14 weeks in frozen storage. Many attempts have been made to slow down or prevent oxidative rancidity in MDPM. In freezing preservation of ground fresh meats, the main consideration in packaging of the meat is the exclusion of oxygen. The mechanism of lipid oxidation in fresh meat is compli-
1
Michigan Agricultural Experiment Station Journal Article No. 9086. 2 Present address: 2 Pibulvatana, Rama 6, Samsen, Bangkok 4, Thailand.
cated due to the presence of heme pigments which are generally accepted as biocatalysts for meat lipid oxidation. Neill and Hastings (1925) demonstrated conversion of hemoglobin to methemoglobin at intermediate rather than at very high or very low oxygen tensions. According to Tarladgis (1961) and Watts (1961), iron in metmyoglobin or methemoglobin was highly effective in initiating the chain reaction mechanism in the lipid autoxidation process. Studying behavior of the lipids of MDPM when subjected to oxygen or air might be helpful in improving meat preservation. Specific objectives of this study were: 1) to compare effect of air at different levels on the storage stability of MDPM; and 2) to study and compare the storage stability of naturally occurring meat lipids with those extracted and stored separate from the meat. MATERIALS AND METHODS Sample Source and Preparation. Meat samples were obtained from a commercial poultry processing plant in Michigan. Mechanically deboned meats were processed through a Beehive mechanical deboning machine (Model AV 968 MF, Beehive Machinery Co., Sandy, UT). Both mechanically deboned chicken meat (MDCM) and MDTM were deboned from whole
1788
STABILITY OF MECHANICALLY PROCESSED POULTRY MEAT
carcasses. The MDCM was obtained from freshly dressed (not frozen) adult hens (fowl), and further processing (mechanical deboning) was accomplished as soon as the major muscles were removed from the carcasses. The MDTM was obtained from turkeys which had been frozen and stored. The original source and length of storage of these turkeys is unknown. Turkeys were thawed in cold water prior to hand boning major muscles and machine deboning the remaining bony portions. The MDCM and MDTM were individually mixed at medium speed in a Hobart mixer (Model K-5A) under N 2 for 2 min. After mixing, each meat item was vacuum packaged (0 mm Hg) to a 2.54 cm thickness in #13 IKD® (mylar laminated) plastic bags. After sealing, samples were held overnight at —18 C. The frozen slabs were cut into 5.08 X 5.08 X 2.54 cm blocks. Each meat block was wrapped with a piece of low density polyethylene sheet and arranged into a vacuum chamber. Lipid extracts from both meat species, stored in 30 X 3 5 mm wide mouth bottle type glass vials, were arranged within the same storage chamber. After closing, an assigned quantity of air pressure was created within each chamber. The chamber was first evacuated by using a duo-seal vacuum pump (Model 1400). After complete evacuation, a known quantity of air was injected back into the chamber, and the chamber was sealed. A U-type vacuum gauge was used to assure the appropriate quantity of air within each chamber. The closed chamber was then placed in a Cryovac bag and the bag was sealed with a Tipper Clipper bag sealer (Model 72105). Storage chambers were stored at —18 C for 3 months. Treatment diagram for this study is illustrated in Figure 1. Analytical methods. Total lipids were extracted from the MDPM by the method of Folchefa/. (1957). Thin layer chromatography was used to separate phospholipids from neutral lipids. A .5 mm layer silica gel G plate (Applied Science Laboratories) was used. Fat samples dissolved in an appropriate quantity of chloroform were applied along the bottom of the plate and the plate was developed in chloroform. After development, lipid bands were visualized by spraying with .5% iodine in methanol solution. Phospholipids were eluted with several portions of a 2:1 (v/v) chloroform-methanol solution. Methylation of the separated phospholipid samples was performed according to the method
1789
MPCM
Packaging
(mm of Hq)
I
I
126 , 380
760
Storage-18 C, 3 months
FIG. 1. Diagram of product processing and storage treatments.
described by Morrison and Smith (1964). Gas chromatographic analyses were performed by using an F & M model-810 dual column gas chromatograph, equipped with a flame ionization detector. A stainless steel column (.32 cm X 1.83 m) packed with 10% DEGS-PS on 80-100 mesh Supelcoport® (Supelco, Inc.) was used for the fatty acid separations. Helium was selected as the carrier gas at a flow rate of 30 ml/min. The hydrogen flame was fed with 35 ml/min hydrogen and 3 50/ml min compressed air. The temperature was programmed from 150 to 190 C at a rate of 4 C/min. The temperature of detectors and injection ports were kept constant at 255 C and 250 C, respectively. Fatty acid methyl esters were identified by comparing their relative retention times (relative to methyl palmitate) using a plot of logarithm of the relative retention time versus the number of carbon atoms. A fatty acid internal was not
LIPID EXTRACT
rr
< rr <
1
2
3
1
2
STORAGE TIME (Mo.) FIG. 2. Unsaturation ratios (C( s : 3 _ 2 j :
1790
JANTAWAT AND DAWSON
L
LIPID EXTRACT
MEAT
o t< rr
\\
2 O 1-
\
< rr
UNSATU
-\-o
0
V 126 \» *
c
1
2
760 380
3
0
STORAGE TIN/IE
, 1
2
*o st
0 126
-»
380
-a
760
r
3
Mo.)
FIG. 3. Unsaturation ratios (Cl s:3_22:6/Cl6-.0) of MDTM and MDTM phospholipid extract samples packaged at 0, 126, 380, 760 mm Hg and stored up to 3 months at —18 C.
found which had a r e t e n t i o n time different from t h a t of the m a n y fatty acids found in each fat sample. A quantitative external fatty acid standard m i x t u r e was used to identify all of the peaks in our sample, and t o calibrate t h e G L C
e q u i p m e n t . T w o times each day a s t a n d a r d m i x t u r e was injected into the c h r o m a t o g r a p h and the percentage of each fatty acid was calculated. Experimental samples were injected and q u a n t i t a t e d only when these s t a n d a r d m i x t u r e test results were accurate. T h e percentage of each fatty acid m e t h y l ester was calculated b y dividing t h e area of each individual peak by the total area of all peaks. Oxidation of C l g : i and C i 8 : 2 fatty acids is r e p o r t e d t o occur at a slower rate t h a n C i g : 3 "C2o:4 fatty acids. Since oxidation of p h o s p h o lipids (higher in m o r e unsaturated fatty acids) was followed in this s t u d y , only those fatty acids with m o r e t h a n t w o double b o n d s were included in these comparisons. These fatty acids included 1 8 : 3 , 2 0 : 3 , 2 0 : 4 , 2 2 : 4 , 2 2 : 5 , and 2 2 : 6 . T h e T B A absorption values for all treated m e a t samples were determined by the m e t h o d described by Tarladgis et al. ( 1 9 6 0 ) . T h e T B A a b s o r p t i o n values for lipid e x t r a c t were also
TABLE l.Mean unsaturation ratios1 for phospholipids from MDCM, MDTM, and their lipid extract samples packaged at 0, 126, 380, and 760 mm of Hg and stored at —18 C for 3 months Meat type
Storage time (month) Treatment
0
2
3 •
MDCM
Stored as meat Air pressure (mm Hg) 0 126 380 760 Stored as lipid extract Air pressure (mm Hg) 0 126 380 760
MDTM
a
Stored as meat Air pressure (mm Hg) 0 126 380 760 Stored as lipid extract Air pressure (mm Hg) 0 126 380 760
2\
1.92 a 1.92 a 1.92a 1.92a
1.42 a .65 b .86 b .53 b
.92 a .83 a ,38 b .31b
1.79 a 1.79 a 1.79a 1.79 a
1.06a 1.07 a .81° .66 b
.97 a ,82 a .62 b .53 b
1.43 a 1.43 a 1.43 a 1.43 a
.70 b 1.00a .60 b .59 b
.68 a .58 a .26 b .31b
1.42a 1.42 a 1.42 a 1.42a
.69 a .S7 a .49 b .49 b
.80 a .71a .56ab ,37 b
' Values among treatments within a column which are followed by the same letter are not significantly different (PX05). 1 Mean of 2 replicates, expressed as polyunsaturated C, s : 3 _ 2 2 : 6 fatty acids/palmitic acids. 2 Comparison among air pressure treatments for each product (meat or extract) and within each storage time.
STABILITY OF MECHANICALLY PROCESSED POULTRY MEAT
1791
measured by following the method described by Tarladgis et al. (1960), except that a quantity of lipid extracts equivalent to lOg of MPPM (2.0g for turkey lipid extract and 2.3g for chicken lipid extract) was used for each determination. Statistical Analysis. Analysis of variance was performed by using a Michigan State University computer program and Tukey's multiple comparisons of means were calculated according to Gill (1978).
RESULTS AND DISCUSSION
In this study the total lipid content of MDCM was 23% and of MDTM, 20%. Changes in phospholipid unsaturation ratios ( C i 8 : 3 -2 2:6/C 1 6 : o ) for MDCM, MDTM, and their lipid extracts are shown in Figures 2 and 3. Significant differences in unsaturation ratios were found for MDCM and MDTM and the phospholipid extracts over storage time and at different air tensions (Table 1). Significance of two- and 3-way interactions for all treatment combinations were found in both MDCM and MDTM phospholipid unsaturation ratios. A marked decrease in unsaturation ratios was found in samples from all treatments at the end of 3 months storage. Significant differences in unsaturation ratios were found among means of samples stored under different air tensions (Table 1). For MDCM, at the end of 3 months storage, the quantities of unsaturated molecules (Ci 8:3—22:6) left i° the phospholipids were comparable between samples stored at 0 and at 126 mm of air and between those stored at 3 80 and 760 mm of air. Similar results were observed in MDCM lipid extract samples and in MDTM samples. When MDCM samples were stored as lipid extracts, significantly higher quantities of polyunsaturated fatty acids (Ci 8 : 3 —2 2 :6 ) were found in their phospholipids when compared to those found in their corresponding meat samples. The TBA absorption values obtained for variously treated MDCM and MDTM samples are shown in Figures 4 and 5 and Table 2. Analyses of variance and the significance of differences in means are also presented in Table 3. The TBA absorption values for all treated samples increased as storage time increased. The induction period for the development of TBA reactive substances occurred between 0 to 2 months of storage for MDCM samples stored at 0 and 126 mm of air. The MDCM samples stored
STORAGE TIME (Mo.)
FIG. 4. TBA absorption values of MDCM and MDCM phospholipid extract samples, packaged at 0, 126, 380, and 760 mm Hg and stored up to 3 months at -18 C.
at 3 80 and 760 mm of air showed a rapid increase in TBA absorption values between 0 and 1 to 2 months of storage and then slowed down; MDCM lipid extract samples showed similar changes. The TBA absorption values, however, behaved differently for MDTM samples. Rapid increases were observed in all treatments of MDTM early in the storage. After 2 months frozen storage, TBA absorption values of MDTM samples increased to approximately 1.4 to 1.6 nm, and thien with subsequent storage periods, some of these values dropped. This increase and decline in TBA absorption values,
I-
02 ' 0
' 1
' 2
'— ' 3 0
' 1
-^ 2
'— 3
STORAGE TIME (Mo.) FIG. 5. TBA absorption values of MDTM and MDTM phospholipid extract samples, packaged at 0, 126, 380, and 760 mm Hg and stored up to 3 months at —18 C.
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TABLE 2. Mean TBA absorption values' forMDCM, MDTM, and their lipid extract samples packaged at 0, 126, 380, and 760 mm of Hg and stored at -18 C for 3 months Meat type
Storage t i m e ( m o n t h ) Treatment
0
2
1
3 \2
MDCM
MDTM
Stored as meat Air pressure ( m m Hg) 0 126 380 760
.089a .089a .089a .089a
.072b .070b .076b .454a
.lllb .173b .762ab 1.106a
.235b ,304b ,885ab 1.173a
Stored as lipid extract Air pressure ( m m Hg) 0 126 380 760
.059a .059a .059a .059a
.116b .132b .270ab .444a
.185b .421ab .700a ,727a
.293b .454ab ,632a .625a
Stored as meat Air pressure ( m m Hg) 0 126 380 760
.426a .426a .426a .426a
.600c .819bc 1.168ab 1.335a
Stored as lipid extract Air pressure ( m m Hg) 0 126 380 760
,365a .365a .365a .365a
.330b .394b .485b .723a
1.000 b 1.258a 1.571a 1.492 a
.214b .300b .600ab .780a
1.150b 1.318a 1.398a 1.383a
.400b .460b .710ab .939a
a
' ' Like letters among treatments within a column denote no significant difference (P>.05). Mean of 2 replicates with 6 determinations. 2 Comparison among air pressure treatments for each product (meat or extract) within each storage interval and extraction treatment. 1
however, were not observed in MDTM lipid extract samples. A rather steady increase in TBA absorption values was observed for samples from most treatments within this group. Tukey mean separations indicated that at the end of the first month, there were no significant differences in TBA absorption values among MDCM samples stored at 0, 126, and 380 mm of air. At the end of the second month, however, significant differences in mean TBA absorption values were found between samples stored at 0 and 126 mm of air and those stored at 380 and 760 mm of air. These differences were still observed at the end of the 3 month storage period. For MDTM samples, significant differences in TBA absorption values among samples stored under vacuum and those stored at 126, 380, and 760 mm of air were observed after the first month of storage. At the end of 3 months, these results were still observed among
various treatments within this group. The results obtained from TBA tests indicate that air at 126 mm Hg had the same effect as air at 0 mm or vacuum storage with respect to the development of TBA reactive substances in MDCM for a 3 month storage period. For MDTM samples, 126 mm of air in their packages resulted in differences in TBA absorption values from those stored under vacuum after the first month of storage. Lipid extract samples were expected to develop oxidative deterioration more slowly and to a lesser degree than their corresponding meat samples upon frozen storage. Extraction of muscle lipids with chloroform methanol and purification of the crude extracts with an aqueous solution should provide meat fats which were free from most other water soluble components including the meat pigments and nonheme iron which have been reported to be
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TABLE 3. Analyses of variance of the unsaturation ratios, TBA absorption values, and total phospholipid phosphorus Unsaturation ratio
TBA number
Source of variation
d.f.
Mean square
d.f.
MDCM Storage Extraction Air Extraction-storage Extraction-air Storage-air Extraction-storage-air
2 1 3 2 3 6 6
6.88a .02° .34a .05a .04a ,09a .05°
MDTM Storage Extraction Air Extraction-storage Extraction-air Storage-air Extraction-storage-air
2 1 3 2 3 6 6
3.82a .01b .12a ,10a .02° .04a .01b
Phospho lipid phosphc Drus Mean square
d.f
Mean square
3 1 3 3 3 9 9
.95a .01a .65a .03a .09a .lla .03a
3 1 3 3 3 9 9
.50a .32a .07a .15a .03b ,03a .13a
3 1 3 3 3 9 9
1.04 a 4.43a .44a .48a .02b .05a .02a
3 1 3 3 3 9 9
.36a .026a .06a .08a ,01b .02b .llb
Significant at .01% level. Significant at .05% level.
present as trace components in MPPM. Thus, the autoxidation reactions which occur in isolated lipids should be entirely different from those which occur when these lipids are in the meat samples. However, when lipids are in the meat tissues, some of them might bind with proteins and be present in the form of lipoprotein complexes. Protein and water in meat tissues together might partially protect the lipids from being reached by 0 2 molecules which surround the meat blocks. Lipid extract samples, in contrast, were exposed directly to 0 2 molecules. This factor might have some compensation effect on losses of prooxidant substances found in lipid extract samples. Hence, at the end of 3 months storage, there either were no significant differences in fatty acid oxidation of MDTM and MDTM lipid extract samples or only lower level significant differences in mean unsaturation ratios between MDCM and MDCM lipid extract samples. Significant differences in TBA absorption values were observed among MDCM, MDTM, and their lipid extract samples after 3 months storage. These results were not in good agreement with results obtained from changes in phospholipid unsaturation ratios. One factor is
the difference in response to TBA test which might occur between these two types of products. The TBA analyses were applied directly to meat samples without extraction of the meat lipids. Handling of meat at elevated temperatures during the distillation processes might result in a favorable condition for catalytic action of natural meat prooxidant substances on meat lipid oxidation. Thus, different forms of samples might respond differendy to this particular testing method. This difference also might contribute to the highly significant difference in TBA absorption values found between these two treatment groups. From analyses of data obtained from changes in phospholipid polyunsaturated fatty acids and TBA absorption values, several conclusions can be drawn. A partial vacuum (air at 126 mm Hg) was comparable to vacuum packaging for MDCM products stored up to 3 months, while vacuum packaging was significantly better than other treatments for MDTM. Significant differences among MPPM samples stored as meat and as lipid extract were observed in most treatment groups and testing methods with the only exception being changes in unsaturation ratio of MDTM samples. In all significant cases, samples stored as meats exhibited higher and
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faster lipid oxidation reaction than did their corresponding lipid extract samples.
REFERENCES Dimick, P. S., J. H. Mac Neil, and L. P. Grunden, 1972. Poultry product quality: Carbonyl composition and organoleptic evaluation of mechanically deboned poultry meat. J. Food Sci. 37:544— 546. 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. Froning, G. W., 1976. Mechanically deboned poultry meat. Food Technol. 30(9):50-63. Gill, J. L., 1978. Design and analysis of experiments. Vol. 1. Iowa State Univ. Press, Ames, IA. Johnson, A. G., F. E. Cunningham, and J. A. Bowers, 1974. Quality of mechanically deboned turkey meat: Effect of storage time and temperature. Poultry Sci. 53:732-736.
Maxon, S. T., and W. W. Marion, 1970. Lipids of mechanically deboned turkey. Poultry Sci. 49:1412-1413. Morrison, W. R., and L. M. Smith, 1964. Preparation of fatty acid methyl esters and dimethylacetals from lipids with boron fluoride methanol. J. Lipid Res. 5:600-608. Neill, J. M., and A. B. Hastings, 1925. The influence of the tension of molecular oxygen upon certain oxidations of hemoglobin. J. Biol. Chem. 63: 479-492. Tarladgis, B. G., 1961. An hypothesis for the mechanism of the heme catalyzed lipid oxidation in animal tissues. J. Amer. Oil Chem. Soc. 38: 479-483. Tarladgis, B. G., B. M. Watts, M. T. Younathan, and L. R. Dugan, Jr., I960. A distillation method for the quantitative determination of malonaldehyde in rancid foods. J. Amer. Oil Chem. Soc. 37: 44-48. Watts, B. M., 1961. The role of lipid oxidation in lean tissue in flavor deterioration of meat and fish. Page 38 in Proc. Flavor Chem. Symp., Campbell Soup Co., Camden, NJ.