FLAVOR COMPOUNDS RELATED TO THE WARMED-OVER FLAVOR OF TURKEY

E. L. RUENGER, G. A. RElNECCIUSand D. R. THOMPSON

ABSTRACT Organoleptic evaluation Taste panel results indicated that the warmedaver flavor of turkey meat was readily detectable and was equally detectable in both white and dark meat. Statistical analysis of gas chromatographic flavor pro- files comparing fresh and reheated turkey meat selected three com- ponents of the profile as being correlated to the warmed-over flavor. The three components were found to increase due to reheating. Two of the three were identified as heptanal and n-nona-3,6-dienal. The re- maining compound could not be identified. The two known com- pounds are typical end-products of lipid oxidation which further sup- ports the hypothesis that warmed-over flavor is due to lipid oxidation.

A flavor panel was held weekly for 12 wk to compare freshly cooked to reheated turkey meat. The panel consisted of 6 male and 9’ female untrained members, 10 of which took part in each testing ses- sion. A triangle test was used to compare fresh to reheated turkey meat. The order of sample examination and sample numbering was random- ized. Samples were served warm (60”(Z), and apple juice was used to rinse the mouth between samples. Extraction methods

INTRODUCTION

CHANGING SOCIAL PATTERNS and eating habits have greatly increased the demand for precooked foods. The acceptance of some precooked foods, especially meat prod- ucts, is diminished due to a flavor defect which develops dur- ing reheating. The off-flavor is often described as warmed-over, stale, reheated, or institutional. The problem often makes nutritionally acceptable products unpalatable. Turkey, is especially subject to the development of a warmed-over flavor (WOF) (Wilson et al., 1976).

WOF is generally accepted to be the result of autoxidation of tissue lipids. Initial workers (Hirano and Olcott, 197 1; Kendrick and Watts, 1969; Younathan and Watts, 1960) sug- gested that the oxidation was heme catalyzed; however, more recent data (Love and Pearson, 1974; Sato and Hegarty, 1971) have shown nonheme iron to be the major proxidant. Wilson et al. (1976) suggested that the phospholipids play a major role in the formation of WOF in turkey, beef and chicken while total lipids were most important to WOF in pork.

The purpose of our study was to determine if a relationship existed between taste panel responses to WOF and volatile flavor constituents in turkey.

Samples were evaluated within 20 min of finish cooking of the’ samples. Three hundred grams of white meat (or 275g of dark meat) were ground in a Waring Blendor in 3L of distiued water. The slurry ~ was poured into a S-L round bottom flask and distilled using steam vacuum distillation. Ice water was used to cool the condensers and liquid nitrogen was used in three Dewar traps. A vacdum (50 mm Hg) was drawn by the vacuum pump, and the steam generator was kept between 40” and 45°C. After about 2 hr, 180 ml of distillate had been collected and the distillation stopped. The distillate was then trans- ferred to a lighter-than-water continuous extractor (Ace Glass Inc.,’ Vineland, NJ) for extraction with pentane which had been purified by the method of Murray and Keller (1969). The Dewar traps were rinsed with pentane before and after distillation. The pentane rinse containing flavor compounds was poured into the distillation reservoir of the con- tinuous extractor. Enough pentane was added to have a reservoir of 20 ml in the side flask. The extraction was conducted for 3% hr after which the side flask was removed and the pentane was dried with 0.2g of anhydrous MgSO, _ The pentane was filtered and filtrate placed into a screw capped test tube. The volume of the sample was then reduced to 0.1 ml under a stream of N, gas. Gas liquid chromatography I

A Hewlett-Packard model 7620A research gas chromatograph

METHODS

equipped with a hydrogen flame ionization detector was used in this study. Separation of the concentrated volatile material was accom- plished using a 3m by 0.32 cm o.d. stainless steel column packed with ( 10% Carbowax 20 M on 80/100 Gas Chrom P. The column was pro- grammed from SO-195’C at 4”/min with a 2-min post injection hold and a 15 min hold at final limit. A Hewlett-Packard 3370B electronic integrator was used to determine peak areas. Mass spectrometry

Source of turkeys Turkeys were purchased from a commercial processor (Richland

Foods, Faribault, MN) as frozen, unadulterated birds. Twelve to four- teen-pound hen turkeys were used. Each was halved, wrapped and stored at -29°C to allow paired comparisons. Cooking method

One-half of a bird was thawed at room temperature and wrapped in aluminum foil. It was then placed in a preheated oven (177°C) until an internal temperature of 82°C was reached. If the meat were to be reheated, it was then cooled at room temperature followed by refrigera- tion at 4°C. After storage for 48 hr, the bird was reheated in an oven preheated to 177°C until an internal temperature of 82°C was reached.

A LKB model 9000 combined gas chromatograph-mass spectro- meter was used to identify unknown flavor compounds. Separation of the flavor compounds was obtained using the same Carbowax column as described. The LKB 9000 has, as a detection system, a total ion current recording of the gas chromatographic eluants. Flash heater and molecular separator temperatures were 280°C. Mass spectra were ob- tained with a constant accelerating voltage of 3,500 volts with 70 ev energy, and a scanning time of 5 set over a m/e range of 10-300. Compounds were considered identified when mass spectra and gas chromatographic retention times of known compounds were corn- patible with those of the unknown compounds. Statistical analysis

Author Ruenger is with the Dept. of Environmental Health & Safety, University of Minnesota, Minneapolis, MN 55455. Author Reineccius is with the Dept. of Food Science & Nutrition, University of Minnesota, St. Paul, MN 55108. Author Thompson is with the Dept. of Agricul- tural Engineering, University of Minnesota, St. Paul, MN 55108.

0022-1147/78/0004-1198$02.25/O 0 1978 Institute of Food Technologists

Fractional values for each chromatographic peak were obtained by dividing each peak area by total chromatogram peak area. Statistical analysis was conducted in two steps. First, meats were grouped into categories: fresh white meat, reheated white meat, fresh dark meat and reheated dark meat. The mean and standard deviation of each fractional value (6 trials) were determined for each category. No attempt was made to compare the bird half which was fresh to the-corresponding half which was reheated. The average fractional value (X,) for 6 fresh ,birds was compare_ to the average fractional value of 6 warmed-over birds (XR). (H,: XF = XR, H,: XF # X,). The results were analyzed using the student’s T test. Those peaks which had statistically signiti- 1 cant differences in their averages were analyzed in the second phase. In this second phase of analysis, a comparison was made between frac- tional values of peaks in the individual fresh birds to their corre-

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sponding reheated halves. The differences between the individual frac- tional values (d) were analyzed for whether there was (Ho:d = 0) or was not (H,:d # 0) a significant difference in fractional value.

Identification of flavor compounds An LKB model 9000 combined gas chromatograph-mass spectro-

Table I-Organolepric derecrion of freshly cooked and reheared rur- key meat

Sample

White meat Dark meat

No. of No. samplings Correct

76 41 77 42

Significance

p < 0.001 p < 0.001

Table P-Paired comparison srudenr’s r-resra of turkey flavor com- ponents which were found to be significantly different /ar = 0.15) following rehearing

Peakb Average

differencec Standard deviation t Value

4 -0.1149 0.0792 5.025 p < 0.001 5 -0.1282 0.1272 3.491 p < 0.01 6 +0.0800 0.1534 1.806 8 -0.1020 0.1476 2.394 p <0.05

11 -0.5733 1.302 1.525 15 -0.0692 0.1660 1.444 16 -0.1761 0.3095 1.971

a The paired comparison student’s t-test was computed as follaws:

lY=12 i=l2 1

L‘. . 77-J n-l

where .Sd = standard deviation, n = number of samples, D = differ- ence in fractional value.

b See Fig. 1 C Average difference, fresh meat fractional value minus reheated

meat fractional value.

WARMED-OVER FLAVOR OF TURKEY.. .

meter was used to identify unknown compounds for which a significant difference was found between the gas chromatogram of freshly cooked and reheated turkey meat.

Separation of the flavor compounds was obtained using the same Carbowax column and temperature program as described earlier. Com- pounds were considered identified when mass spectra and gas chro- matographic retention times of known compounds were compatible with those of the unknown compounds.

RESULTS & DISCUSSION

TASTE PANEL DATA (Table 1) indicate that the panel could distinguish between fresh and reheated turkey samples (p < * 0.001).

Wilson et al. (1976) reported that red muscle consistently had higher TBA numbers than white muscle. Since several workers have shown a correlation between TBA and WOF, their data would suggest that the WOF is more intense and easier to detect in the red muscle than the white muscle. Our results do not support this hypothesis for our panel had equal success in selecting the WOF in dark and light muscle.

A typical gas chromatogram of the volatile constituents of turkey is presented in Figure 1. Visual inspection of the chromatograms of freshly roasted and reheated turkey yielded no obvious differences between the two samples. Peaks were labeled and area computed for use in statistical analysis. In the first phase, computer analysis, comparing by groups (white meat or dark) each peak of the chromatograms from freshly cooked turkey to its corresponding peak in chromatograms from reheated turkey meat, found peaks 4, 5,6, 8, 11, 15 and 16 (Fig. 1) to be significantly different ((u = 0.15). Paired comparison (Student’s t-test) was conducted on these seven peaks. Peaks 4, 5 and 8 were found to be statistically signifi- cant (Table 2) using (11= 0.05.

A paired analysis (Student t-test) of white meat (individual fresh half vs corresponding reheated half) and dark meat (individual fresh half vs corresponding reheated half) was con- ducted (Table 3). Statistically significant differences (a = 0.10) were observed for peaks 4, 5 and 8 in dark meat, but only for peak 4 in white meat.

All three compounds increased in concentration in the re- heated sample (Table 3). This would suggest that the WOF is

Ir LA TIME

Fig. l-Gas chromarographic profile of rhe volatile consriruenrs in turkey.

Table 3-Comparison of paired analyses of indi- vidual fresh ro reheated white meat halves and individual fresh to reheated dark meat halves.

Pea ka White meat Dark meat

4 iY = -0.1236 b = -0.1062 Sd = 0.0991 sd = 0.0619 t = 3.056 t = 4.203 P < 0.05 P < 0.01

5 ii = -0.1109 b = -0.1456 Sd = 0.1753 Sd = 0.0641 t = 1.55 t = 5.565

P < 0.01

8 ii = -0.0865 b = -0.1176 Sd = 0.1760 Sd = 0.1278 t = 1.204 t = 2.254

P < 0.10

a Fig. 1 %Average differences, fresh meat fractional

value minus reheated meat fractional value. sd = Standard deviation t = t-test value

Volume 43 (1978)--JOURNAL OF FOOD SCIENCE-1 199

Table 4-Mass spectral data of significant peak compared with standard compounds

Heptanal (Peak 4)a.d n-Nona-3,6dienalb (Peak 5)a 1 -Nonene (Peak 81a

We Standard Isolate m/e Standard Isolate m/e Standard=

27 35.7 42.9 27 32.5 13.7 27 46.4 29 50.0 53.6 29 14.8 11.5 29 48.3 41 69.0 69.6 39 27 .O 10.0 39 36.8 42 54.8 42.9 41 42.4 16.1 41 81.8 43 83.3 77.7 43 11.5 5.2 42 38.7 44 100.0 100.0 53 11.8 15.0 43 100.0 55 55.6 44.6 54 10.7 2.8 55 65.4 57 50.8 42.0 67 16.9 4.3 56 77.8 70 90.5 59.8 81 100.0 100.0 69 34.4 71 27.0 24.1 82 10.7 23.5 70 36.3

55 9.1 138 14.1

a Fig. 1 b Literature values for n-nona-2,4dienal obtained from Complication of M&s Spectra/ Data, Supplement II, A. Cornu and R. Massot c Literature values obtained from the American Petroleium Institute Research Project 44, Serial Number 240. d Compound cochromatographed with standard.

Isolate

39.6 48.1 24.5 69.8 46.2

100.0 61.3 93.4 27.4 ,

7.5

due to the formation of additional volatile material rather than a reduction in the “fresh turkey” flavor components.

Two of the three significant peaks were identified, peak 4 as heptaldehyde and peak 5 as n-nona-3,6-dienal (see Table 4). Flavors attributed to heptaldehyde are characterized as “very strong, fatty, harsh, pungent odor, and unpleasant fatty taste” (Furia and Bellanca, 1975). Nonconjugated dienals (Cs - Cr e) have a “trainy-fishy” odor (Badings, 1960). Both of these compounds are typical products of lipid oxidation. This fur- ther supports the contention that WOF is the result of lipid oxidation.

REFERENCES

Badings, H.T. 1960. Principles of autoxidation process in lipids with special regard to the development of autoxidation off-flavors. Neth. Milk & Dairy J. 14: 215.

Furia, T.E. and Bellanca. N. 1975. “Fenaroli’s Handbook of Flavor Ingredients.” 2nd ed. CRC Press. Inc.. Cleveland. OH.

Hiran;. Y. and Olcott, H.S. 1971. Effect of heme compounds on lipid oxidation. J. Am. Oil Chem. Sot. 48: 523.

Kendrick. J. and Watts. B.M. 1969. Acceleration and inhibition of lipid oxidation by heme compounds. Lipids 4: 454.

Love. J.P. and Pearson. A.M. 1974. MetmvoeIobin and nonheme iron as pioxidants in cookdd meat. J. Agric. Fbod Chem. 22: 1032.

‘Murray. E.C. and Keller, R.N. 1969. Purification of hydrocarbon sol- vents with a silver nitrate column. J. Org. Chem. 34: 2234.

Sato. K. and Hegarty. G.R. 1971. Warmed-over flavor in cooked meats. J. Food Sci. 36: 1098.

Wilson. B.R.. Pearson. A.M. and Shorland. F.B. 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.

Younathan. M.T. and Watts, B.M. 1960. Relationship of meat pigments to lipid oxidation. Food Res. 25: 538.

MS received 8117177: revised 1114178: accepted 1118178.

Scientific Journal Series Paper No. 9980. Minnesota Agricultural Experiment Station, St. Paul, MN 55108.

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