Color Changes in Radiation Pasteurized Beef

Color Changes In Radiation Pasteurized Beef .T. F. Richards and B. O. Morrison Department of Food Science The University of British Columbia Vancouver 8, B.C.

Abstract The effect of doses of gamma radiation varying from 0.1 to 1.5 Mrad applied to beef at O·C on meat color was assessed by tristimulus colorimetry. Marked differences in redness and yellowness occurred among samples with the surface myoglobin in the reduced (Mb), oxygenated (Mb02) or oxidized (Mh+) state. Irradiation of samples packaged in oxygen-permeable film (Vitafilm) resulted in a greater decrease in redness than irradiation of comparable samples packaged in oxygen-impermeable film (Saran). Samples packaged in Vitafilm and overwrapped in Saran prior to irradiation with O.S. Mrad retained the ability to reoxygenate after as long as 8 days post-irradiation storage at 4.4·C before removal of the outer wrap. No significant differences (P>0.05) in redness were noted among the unirradiated days and samples from which the outer control samples at wrap was removed after 0, 2, 4, 6 or 8 days storage. The decrease in redness after removal of the outer wrap was not affected by time of storage.

°

Resume L'effet de doses d'irradiation gamma entre 0.1 et 1.5 Mrad sur la couleur de la vian(le de boeuf a ete evaJue par colorimetrie tristumulus. Des differences importantes dans les couleurs rouge et jaune ont ete observees parmi les echantillons a la myoglobine superficielle dans l'etat reduit (Mb), oxygene (Mb02) ou oxyde (Mb+). L'irradiat;on a cause une diminution plus considerable de la couJeur rouge lorsque les echantillons etaient embaJJes dans un film permeable it l'oxygene (Vitafilm) que dans un film imperm 6 ahle a l'oxygene (Saran). Les echantillons doublement emhaJJes dans Ie Vitafilm et Ie Saran avant I'irradiation it 0.8 Mrad ont retenu leur aptitude it la reoxygenation apres 8 jours de stockage post-irradiation a 4.4·C avant l'enlevement du Saran. Aucune difference significative (P>0.05) dans la couleur rouge n'a ete observee parmi les echantillons temoin non irradies a jour et les echantillons dont Ie Saran a ete enleve apres 0, 2, 4, 6 ou 8 jours de stockage. La diminution de la couleur rouge apres l'enlevement du Saran n'a pas ete influencee par la duree du stockage.

a o·C

°

Introduction The bright red surface color of fresh beef is important in determining consumer acceptance of the product. The factors affecting fresh meat color have been reviewed by Solberg (1968) and include preslaughter, postslaugrter, processing and post-processing treatments. The development of the bright red color of oxymyoglobin and oxyhemoglobin at the surface of cut meat is known to be a function of many factors including partial pressure of oxygen, tempera ture, pH, and oxidation-reduction potential of the tissue (Solberg, 1970) Attempts to maintain the desirable bright red color of the oxygenated form of the meat pigments seldom provide more than a 3 day shelflife under commercial conditions, far short of that required for centralized prepackaging (Naumann, 1968). Marriot et al. (1967) found that meat with low initial microbial loads stored at -1 °0 in darkness for 10 days changed only slightly in color. Pirko and Ayres (1957) have shown that the myoglobin of beef 1

packaged in gas impermeable films readily reoxyge ated after storage for 14: days at 4:.4:°0. Ordal (196 concluded that anaerobic packaging of beef usi oxygen impermeable films or materials having 10 oxygen transmission rates provides a means for t control of psychrophilic microorganisms that are co monly associated with fresh meat spoilage. Becan microbial population can determine shelf-life eith directly or by affecting color stability, the use of g ma radiation to control microbial load has been s gested. Urbain et al. (1968) studied the effect of 10 doses of gamma radiation on the microbial growth a color of fresh beef. They concluded (1) that 50 to l' Krad delayed microbial spoilage for more than days at 3.3°0 and (2) that based on visual col appraisal, vacuum-packaged fresh beef subjected 100 Krad would "bloom" to the normal red color exposed to oxygen after as long as 10 days storage 3.3°0. Limited data from reflectance spectropho~ metry of similarly treated samples suggested storagll periods of as long as 18 to 21 days might be POSSib~ without destroying the blooming potential of the mea The study reported herein was undertaken evaluate the effect of varying doses of gamma radi~ tion on the color of fresh beef assessed by tristimuI~' colorimetry with particular emphasis on the effect . oxidation state of the surface pigment at the time irradiation.

Materials and Methods Experiment 1a. Reference color values were detel\ mined for meat samples with surface pigment pr~

dominantly in the myoglobin, oxymyoglobin or met: myoglobin form. The 3 pigment forms were created b~ using the methods outlined by Snyder (1964:). Mea! from the round of a 14: day-aged Hereford carcass (3~ months at slaughter) was defatted and eight slices a~ proximately 1.5 cm thick were cut and fitted into thi bottom of 6-inch (ca. 15 cm) diameter Petri dishes' The samples were then wrapped in Saran 1 and stored at room temperatures until myoglobin (Mb) predoIll inated (ca. 4: hours) at which time color evaluatioD was conducted by determining color coordinates oD both the Land R d scale of a Hunter color and color difference meter (HODM)2. The samples were theD unwrapped and rewrapped in an oxygen-permeablE film (Vitafilm-Top 35)3 and stored at 1.1°0 for 21 hours to allow development of oxymyoglobin (MbOz) Hunter color coordinates were again measured o~ both scales. To oxidize the pigment at the sample sur face to metmyoglobin (Mb+) the meat was painted with a 0.2% potassium ferricyanide solution at hour 1 W. R. Grace and Co. 2 Model D-25L with 45· circumferential lighting, O· viewing and! inch specimen area standardized against a red disc with L :::: 35.1, a = 25.5, b = 11.9. 3 Goodyear Rubber Co. Can. Inst. Food Techno!. J. Vo!. 4, No. I, 1!f11

. tervals for 3 hours and then stored for an addilr ln l 4 hours before color readings were taken. tIOna E eriment lb. The effect of doses of 0.1, 0.5, 1.0 and 1 Mrad of gamma radiation on the color of Vitafilm . Saran-wrapped samples of beef was investigated. ~r mples were prepared as above and allowed to equilib:ate at 4.4 0 0 for 16 hours after wrapping and before irradiation. One sample from each treatment served as control and was stored at 4.4 0 0 throughout the :xperiment. The other samples were irradiated with Cobalt-60 in a Gammacell 220 4 at 0 0 0. The dose ~ate was approximately 1.0 Mrad per hour. 00101' readmgs were taken 3 hours after irradiation and at intervals to 14 days.

o

~

~rMbo,~

10

:P

0

C<

6

1';

~ Z 5

T.

-fMb

• 0.1 0.5

li

::> J:

°d

.

0- Oooys. vitafilm wrQP, (befOfe i"odiolionJ .-above Klmples at 14 doys

'-5

0-0

O~5 ~

doy~.

saran wrap

.-above samples at 14 days

01 13

HUNTER

Figure 1.

EllJperiment 2. Only limited changes were observed in the color values in Experiment 1 when samples were irradiated with the surface pigment in the reduced (Mb) state (Saran-wrapped). Therefore, this exp~ri­ ment was designed to assess the effect of applymg gamma radiation to meat samples with surface pigment predominantly in the Mb state on the subsequent "blooming" potential of the meat after storage for up to 8 days at 4.4 0 0. A dose of 0.5 Mrad was selected as an upper pasteurization limit to place maximum stress on the myoglobin pigment system. Fresh meat samples were prepared as described previously and placed in Petri dishes. The seven treatments and two replications were arranged in a randomized complete-block design. The treatments were as follows: Vitafilm-wrapped. and unirradiated; Vitafilm-wrapped and irradiated; Vitafilm-wrapped and overwrapped in Saran with the overwrap removed 0, 2, 4, 6 or 8 days after irradiation. 00101' measurements were read on the L-scale of the HODM before and after irradiation. Samples from which the overwrap was removed were allowed to bloom for 16 hours at 4.4 0 0 before the first color readings were taken. SUbsequent readings for all samples were obtained at 2 day intervals up to 8 days post-irradiation. A final reading was obtained 11 days after irradiation.

'0'

15

17

19

21

2J

VALUES

The effect of dose rate (control 0.1, 0.5, 1.0 and 1.5 Mrad) and wrap (Saran and Vitafilm) on the color of beef at 0 and 14 days.

form occurred in the a-value and to a lesser extent in b-value. Lightness (L or R d ) differed only slightly among samples. Similarly the alb ratios for l\fb and MbO z did not differ markedly especially for the L-scale measurements. Haas and Bratzler (1965) also found only minor differences in the aL!b L ratios between Mb and MbO z compared to the change in aL alone or in total color difference (~E). Snyder (1964) concluded that the usefulness of the alb ratio per se is limited to denoting differences between the oxidized (Mb+) and reduced (Mb or MbO z) forms of myoglobin. Although our results support this conclusion, a plot of aL vs. bL values (Fig. 1) proved to be a more valuable method of assessment than simply following changes in aL and bL individually. The results of experiment 1b summarized in Figs. 1 and 2 indicate clearly that both irradiated and unirradiated Vitafilm-wrapped samples decreased in redness (a-value) more rapidly and to a greater extent than comparable Saran-wrapped samples which fluctuated in redness during storage. A marked decrease in redness was evident immediately after irradiation of Vitafilm samples, the magnitude of the decrease increasing with dose. There was a decline in yellowness (Hunter bvalue) of both Vitafilm and Saran-wrapped samples with time. At the higher dose levels the initial decline was more severe for Vitafilm than Saran-wrapped samples although the latter had consistently lower Hunter b-values.

Results and Discussion EllJperiment 1. The results in Table 1 indicate that for both the Land R d scale the major differences among reference samples differing in predominant pigment 4 Atomic Energy of Canada Ltd.

Table 1

0

0.5

'-5

Average HCDM color coordinates and ratios for beef treated so that myoglobin (Mb), oxymyoglobin (Mb02 ) or metmyoglogin (Mb+) predominated. L-Scale

Mb0 2 Mb Mb+

32.6 30.5 31.6

± + +

0.44 0.70 0.53

21.1 12.0 4.7

± ± ±

alb

b

a

L

1.90 0.83 0.41

10.3 5.8 7.5

± ± ±

0.55 0.46 0.41

2.05 2.07 0.62

Rd Scale Rd Mb0 2 Mb Mb+

9.4 8.6 9.8

+ + +

0.17 0.51 0.33

J. lnst. Can. Techno!. Aliment. Vo!. 4, No 1, 1971

23.9 10.8 6.3

+ + ±

alb

b

a

2.45 1.10 0.63

13.5 7.2 11.2

± ± ±

0.90 0.42 0.38

1.77 1.47 0.56

2

l'he changes in redness and yellowness of Vitafilm and Saran-wrapped samples in relation to the reference values established in Experiment 1a indicate that tile ultimate color of Vitafilm-wrapped samples approached that of the Mb+ reference. The Saran-wrappel] samples approximated the redness of the Mb refel'cnce color but had much lower yellowness values. 'rhe color of Vitafilm-wrapped samples was visu:illy assessed immediately after irradiation and all lINe considered to be commercially unacceptable. \·itafilm control silll1ples became unacceptable after i~ to 4 days of storage. Both control and irradiated Saran-wrapped samples were considered unacceptable in color before irradiation and throughout the storage period. 'rhe results of this experiment generally agree with the findings of Ginger et al. (1955) for comminuted beef irradiated in Visking or Saran casings witIt doses ranging from 4.85 X 104 to 2.3 X 106 reps. Experiment 2. Samples with the surface pigment predominantly in the Mb form at the time of irradiation retained the ability to reoxygenate (bloom) when the Saran overwrap was removed after as long as 8 days post-irradiation storage (Table 2). Urbain et al. (1968) reported similar findings for vacuum-packaged beef irradiated with doses of 50-150 Krad and stored for as long as 18 days at 3.3°C. The color of the Vitafilmwrapped controls changed according to the pattern for comparable samples in Experiment lb. Statistical comparison of the means (Table 3) indicated that, with one exception, samples which had been Saran overwrapped during irradiaton had significantly (P<0.05) higher aL and b L values than the Vitafilmwrapped samples 8 days after irradiation. Generally redness and yellowness values at 8 days increased with increasing length of time prior to removal of tIte overwrap. No significant differences (P=.47 in Lvalue was found among treatments 8 days after irradiation. The highest aL value obtained for each treatment occurred immediately after unwrapping and was not significantly affected by length of storage before removal of the overwrap (Table 4). In addition, all Saran-wrapped samples were considered acceptable at the time of the first HCDM reading after unwrapping. 'With one exception the overwrapped and irradiated samples had higher peak aL-values than the unirradiated control with which they were compared. The rate of decline in aL value after unwrapping was approximately the same for all treatments. The Vitafilm wrapped and irradiated samples had significantly (P<0.05) lower peak aL values than all other silll1ples. Differences among treatments in bL-value were minor and irregular in pattern. Differences in L-value among treatments were not significant (P = .33). It should be noted that the fresh unirradiated Vitafilm-wrapped samples were not equivalent in redness to the oxymyoglobin reference established in Experiment 1b although the treatment was similar. Also, the Saran-overwrapped samples had lower HCDM redness values than comparably treated samples in Experiment 1. These differences may be 3

11

24

Control

5

v 4 b 0

4

8

1 b 0

12

0.1 Mrad

5

w

w

v 4 bO

4

8

12

-'

-'

«

12

r:~s 1b 0

4

8

12

1 b 0

4

8

12

1b 0

4

8

12

.«

24 0.5 Mrod

>

8

Il f"~~v

24

V)

4

>

:0

:a 5

v

.... Z

4 b 0

4

8

w

....

12

Z

24

::>

::>

J:

J:

5

v 4 b 0

4

8

12

11

.24

v

5

5

v 1 b 0

4

8

12

DAY 5

Figure 2.

Changes in redness (Hunter 'a' value) and yellowness (Hunter 'b' value) of irradiated beef samples wrapped in Saran (S) or Vitafilm (V) over time. (b = immediately before irradiation; 0 = immediately after irradiation). Can. Inst. Food Techno!. J. Vo!. 4, No.1. 1971

Table 2

Experiment 2 1,2

Mean HCDM redness (a) and yellowness (b) values -

Vitafilm and Saran-wrapped Vitafilm-wrapped only Not irradiated 16.23 9.6 3

Before irradiation After irrad. 0 days 2 days

14.7 8.8 13.4 8.4 12.2 7.9 6.8 6.5 6.8 6.1 8.2 5.1

4 days 6 days

8 days 11 days

Days of post-irradiation storage before removal of Saran overwrap

Irradiated

0

19.0 9.0 9.2 7.2 8.2 5.8 6.9 6.8 4.1 6.2 4.9 6.6 3.6 6.5

9.1 8.5 15.6 9.4 13.8 8.7 11.7 8.8 10.4 7.8 10.4 8.5 8.0 8.0

2

4

6

8.0 8.4

5.7 8.8

9.6 8.1

17.5 10.4 16.7 11.1 11.7 8.8 11.5 9.0 10.2 8.4

15.7 11.0 13.6 8.6 120 9.4 9.5 9.3

13.6 9.2 11.9 9,1 9.8 8.5

8 11.2 7.2

15.6 9.9 11.7 8.9

Each value is the mean of duplicate readinlZs on each of two replicate samples. Irradiation dosp- was 0.5 Mrad at 32°F (DoC). 3 The first number of each pair is HCDM redness (a). The second number is HCDM yellowness (b). 1

2

Table 3

Mean HCDM redness (a) and yellowness (b) values and results of Duncan's multiple range test for samples 8 days atter irradiation with 0.5 Mrad. - Experiment 2. 8 days

a-value 1

b-value 1

1 2

Means 2 days 4 days 6 days 8 days VNR VR

15.6

12.0

8 days

4 days

9.9

underscored = Vitafilm = Vitafilm = Vita£ilm = Vitafilm Vita£ilm = Vitafilm

4 days

9.4

Treatment2 6 days 2 days 11.9

11.5

Treatment2 6 days 2 days 9.1

by the same line are not significantly and Saran wrapped - Saran overwrap and Saran wrapped - Saran overwrap and Saran wrapped - Saran overwrap and Saran wrapped - Saran overwrap wrapped samples - not irradiated. wrapped samples - irradiated.

9.0

different removed removed removed removed

attributable to inherent differences in reducing sub· stances, myoglobin, concentrations or pH between the tissues used in the two experiments and does not detract from the validity of the treatment comparison. 1I0wever, it does indicate a need for further study of the variability in blooming potential among tissues and carcasses.

SUmmary The effect of gamma irradiation on the color of fresh beef was studied using the reflectance measurements, L, aL and bL, obtained from a Hunter color and color difference meter. The overwrapping of Vitafilmwrapped samples in an oxygen impermeable film prior to irradiation (0.1 to 1.5 IMrad) resulted in only limited changes in meat color during post-irradiation J. lnst. Can. Techno!. Aliment. Vo!. 4. No 1, 1971

o days

VNR

VR

10.4

6.8

4.9

o days

VR

VNR

8.5

6.6

6.1

at P < 0.05. 2 day;-after irradiation. 4 days after irradiation. 6 days after irradiation. 8 days after irradiation.

storage and preserved the blooming potential of samples subjected to 0.5 Mrad for as long as 8 days storage at 4.4°C.

Acknowledgement This research was financially supported by A.tomic Energy of Canada Ltd. under Contract No. 8032-524.

References Ginger, I. D., Lewis, U. J. and Schweigert, B. S. 1955. Changes associated with Irradiating meat and meat extracts with gamma rays. J. Agric. Food Chem. 3:156. Haas, M. C. and Bratzler, L. J. 1965. Determination of myoglobin , oxygenation rates In pork, beef and lamb by Munsell and reflectance colorimetry. J. Food Sc. 30:64. Marrlot, N. G .. Naumann, H. D., Stringer, W. C. and Hedrick. H. B. 1967. Color stability of prepackaged fresh beef as influenced by pre-display environments. Food Techno!. 21:1518.

4

Table 4

a-value l

b-value l

1

2

Mean HCDM redness (a) and yellowness (b) values and results of Duncan's multiple range test for samples 16 hours after removal of outer Saran-wrap. 2 days

4 days

17.5

15.7

4 days

2 days

11.0

10.4

Treatment2 8 days 0 days 15.6

15.6

Treatment2 8 days 0 days 9.9

6 days

VR

14.7

13.6

9.2

6 days

VNR

VR

9.2

8.8

7.2

9.4

Means underscored by the same line are not significantly dif ferent at 2 days Vitafilm and Saran wrapped - Saran overwrap removed 2 4 days Vitafilm and Saran wrapped - Saran overwrap removed 4 6 days Vitafilm and Saran wrapped - Saran overwrap re moved 6 8 days Vitafilm and Saran wrapped - Saran overwrap removed 8 VNR Vitafilm wrapped samples - not irradiated. VR Vitafilm wrapped samples - irradiated.

Naumann, H. D. 1968. Cutting and packaging of fresh meats. Proc. Meat Ind. Res. Conf. p. 157. Drdal, Z. J. 1962. Anaerobic packaging of fresh meat. Prec. Meat Ind. Res. Conf. p. 39. Pirko. P. C. and J. C. Ayres, 1957. Pigment changes in packaged beef during storage. Food Techno!. 9:46l. Snyder, H. E. 1964. Measurement of discoloration in fresh beef. J. Food Sc. 29:535.

VNR

P < day7 days days days

0.05. after irradiation. after irradiation. after irradiation. after irradiation.

Solberg, M. 1968. Factors affecting fresh meat color. Proc. Meat Ind. Res. Conf. p. 32. Solberg, M. 1970. The chemistry of color stability in meat - A review. Can. Inst. Food Techno!. J. 3:55. Urbain. W. M., Giddings, G. G., Belo, P. S. and Ballantyne, W. W. Feb. 1967 - Feb. 1968. Radiation Pasteurization of Fresh Meat and Poultry. Annual Report. United States Atomic Energy Commission. Division of Technical Information. Received July 2, 1970.

Can. Inst. Food Techno!. J. Vo!. 4, No. I, 1971