Effect of the dietary supplementation with vitamin E on colour stability and lipid oxidation in packaged, minced pork

PII:

so309-1740(97)00103-4

Meat Science, Vol. 48, No. 314, 2655213, 1998 0 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0309-1740/98 $19.00+0.00

ELSEVIER

Effect of the Dietary Supplementation with Vitamin E on Colour Stability and Lipid Oxidation in Packaged, Minced Pork J. H. Houben,a G. Eikelenboomb & A. H. Hoving-Bolinkb aDepartment

of the Science of Food of Animal Origin, Faculty of Veterinary Medicine, Utrecht University, PO Box 80.175, 3508 TD Utrecht, The Netherlands bDepartment of Food Science, Institute of Animal Science and Health (ID-DLO), PO Box 65,820O AB Lelystad, The Netherlands (Received 25 May 1997; revised version received 3 September 1997; accepted 9 September 1997) ABSTRACT The effect of supplementation of vitamin E (200 IU kg-’ feed) in the diet of pigs on colour stability and lipid oxidation in minced pork was studied. Control and enriched diets were provided for the last 12 weeks before slaughter. Half of the samples of minced shoulder meat from control and supplemented pigs were packaged on trays with oxygen-permeable overwraps and harf in modtfted atmosphere packs (initial gas mixture: O,jCO,/hr, = 661 2717). Meats were storedfor 10 days at 7°C in an illuminated retail display cabinet. The meat from vitamin E-supplemented pigs was more resistant to lipid oxidation than was the control meat. Gaspackagingappeared to increase lipidoxidation in control meat, whereas lipid oxidation was stable in meat from vitamin E-supplemented pigs. Colour stability for gaspacked meat was comparable for both dietary groups. However, oxygen-permeable overwraps had a negative eflect on colour stability in vitamin E-enriched meat. The reason for this is not known. The shelf-hfe of enriched and control meat was similar. Thus supplementation of pig feeds with vitamin E is recommended tf an improved stability against lipid oxidation of (minced) pork is required. 0 1998 Elsevier Science Ltd. AN rights reserved

INTRODUCTION

There are several reports in the literature on the benefits of supplementing the diets of fattening pigs with vitamin E (recently articles appeared from Cannon et al., 1995; Cheah et al., 1995; Lanari et al., 1995; Pfalzgraf et al., 1995a,b; Cannon et al., 1996; Dirinck et al., 1996; Leonhardt et al., 1996). In their recent review, Buckley et al. (1995) focused on the antioxidant function of vitamin E and how vitamin E supplementation influences the rate of lipid peroxidation, colour, water-holding capacity, and cholesterol oxidation in meat. However, little or no attention has been paid to the effects of dietary enrichment with vitamin E on the quality of (cured) meat products. Moreover, the effects of illumination during retail display and the effects of newer modified atmosphere packaging techniques on the quality of dietary supplemented meat have scarcely been studied. 265

J. H. Houben et al.

266

Because the conditions that prevail during the fattening of animals (breed, diet, climate, etc.) in The Netherlands have not yet been thoroughly studied, a joint project between IDDLO and Utrecht University was started on the fattening of pigs and steers. In the beginning the project concentrated on feeding experiments with pigs, and results on the effect of vitamin E supplementation on pork quality, in particular colour stability, have been reported by Hoving-Bolink et al. (1998). The current paper describes the results for minced pork and another will deal with the results obtained for cured meats. Dietary enriched and control freshly deboned shoulder meat was minced and packaged in two ways: on trays with an oxygen-permeable overwrap and in modified atmosphere packs (enrichment with oxygen and carbon dioxide). The meat was exposed for 10 days in a permanently illuminated retail display cabinet at 7°C. At regular intervals samples were taken for physical, chemical, and microbiological analyses.

MATERIALS

AND METHODS

Feeding experiments

Piglets [GY x (FL x NL)] breeds-32 barrows and 40 gilts-were allotted, in closely related pairs, at random to two feeding groups and fattened at the experimental farm belonging to ID-DLO. From 12 weeks before slaughter one group received a dietary supplement of vitamin E (Rovimix E-50 SD); 200 IU vitamin E kg-’ feed in addition to the 8 IU vitamin E kg-’ feed already present. The control group did not receive the supplement. Feeding of the extra vitamin was started at an average weight of 44.3 kg and was continued to a mean slaughter weight of 110.8 kg. Further details of the feeding experiments are given in Hoving-Bolink et al. (1998). Selection of raw materials After slaughter a number of carcasses had to be excluded from the experiments because of signs of PSE (Pale Soft Exudative) meat or a high ultimate pH ( > 630). Shoulders were used from 12 animals per feeding regimen (6 barrows and 6 gilts); closely related pairs that had been randomized over the two feeding regimens were selected. Meat samples from the control animals were coded ‘C’ and those from the animals receiving the vitamin E-enriched diet were coded ‘E’. Manufacturing,

packaging and display of the minced meat

Minced meat was prepared two days after the animals had been slaughtered from freshly deboned shoulders from which fatty tissue and rind were removed. Meat was minced with a Svenska type Cl06 (equipped with a 3 mm plate) and weighed in portions of 500 g. The portions were packaged in two ways: (a) on trays wrapped in oxygen-permeable foil and (b) in plastic boxes (PS/EVOH/PE) which, after gassing with a mixture of 66% 02/27% C02/7% N2, were closed by heat-sealing with VPA/PE-AF foil (Oz-permeability: 1.5 cm3 m-*.d-i.bar-’ CO2 permeability: 2.5cm3 m-*.d-l.bar-l, both measured at 20°C and 75% relative humidity). The meat volume gas ratio was about 2:l. Packaging was performed at a commercial meat plant. Twenty-four packages per dietary group and type of packaging were stored in a refrigerated display cabinet at 7°C. This relatively high display temperature was selected to speed up microbiological and (bio)chemical processes occurring in the meat. Moreover, 7°C is the maximum temperature at which minced meat can be displayed for sale in The

Effect of the dietary supplementation

on colour stability and lipid oxidation in minced pork

267

Netherlands (Anon., 1987). During storage, the temperature in two packages was continuously recorded with a Honeywell 15 instrument, using copper-constantan thermocouples. During storage, the position of the experimental packages in the cabinet was changed regularly, to even out location effects. The display cabinet was equipped with fluorescent Philips TLD36W79 ‘meat’ lamps (colour temperature 3800 K) which were continuously illuminated, simulating critical retail conditions. The illumination intensity on the surface of the packages was measured with a BBC Goertz Metrawatt MX4 instrument and was on average 812 lx (standard deviation 97.8 lx). Measurements

during storage

The colour of the meat was measured through the packaging every three days. Three packages per group were selected at random and colour was assessed at three sites. Because it was not possible to measure the colour of meat through the packaging of the gas-packaged items, the meat was removed from the packages and wrapped in the oxygen-permeable foil. The colour of the meat was immediately measured trough the packaging. These samples were then withdrawn from the experiments. Colour (CIELAB L’, a* and b’ values) was measured with a Minolta chromameter II. The effective diameter of the measuring head, equipped with a C-light source, was 53 mm. Before each measuring session the instrument was calibrated against a white tile tightly covered with the oxygen-permeable foil. Three randomly selected packages per group were used for microbiological analyses and measurement of thiobarbituric acid (TBA) values and pH. These packages were then discarded. pH was measured at three sites per package with an Electrofact Digital pH meter equipped with an Ingold-electrode. The gas composition of the packages was measured in the modified atmosphere packages, which had to be opened for analytical purposes, with a Servomex UK Ltd. Analyser (series 1400). Methods of analysis

Moisture content was determined according to ISO/ guidelines (1973); protein content was measured as described by Grtindig (1994); fat content was measured by the Fosslet method (AOAC method 24.007/24.008) and the ash content was measured according to IS/R936 guidelines (1969). TBA-values were measured as described by Raharjo et al. (1992). The total number of aerobic bacteria was counted on Plate Count Agar (APHA; pour plates and incubated for three days at 30°C). The number of Enterobacteriaceae was determined after plating of samples on Violet Red Bile Glucose Agar (pour plates with cover layer of the same medium and incubated for 24 f 2 hr at 37°C).

RESULTS

AND DISCUSSION

Composition of the minced meat

The gross chemical composition of duplicate samples of freshly minced meat are presented in Table 1. The composition of the meat from the two groups of pigs was similar. Vitamin E concentrations in minced pork were not assessed in this study, but in a parallel study the vitamin E content of the m. hgissimus dorsi and m. psoas majur was 6-7

J. H. Houben et al.

268

Gross Chemical

Composition

TABLE 1 (in % m m-l)

of the Minced

Meat

C” Moisture Protein Fat Ash nControl. bVitamin

Eb

680 187 13.4 0.94

68.3 18.7 12.9 0.96

E supplemented.

and 7.6 mg kg-’ muscle for vitamin E-supplemented for control pigs (Hoving-Bolink et al., 1998). Microbiological

pigs and 1e3 and 1.4 mg kg-’ muscle

analyses and meat pH

The results of the microbiological analyses are presented in Tables 2 and 3. Mesophilic aerobic organisms and Enterobacteriaceae had similar growth patterns in minced meat from animals in the two groups. This is in agreement with published data for vitamin E dietary enriched (minced) beef (Smith et al., 1994; Chan et al., 1995). We did not find comparable microbiological studies for pork in the literature. The gas packaging appeared to improve the shelf-life and to slow down the growth of Enterobacteriaceae in comparison to foil overwrapping. Although the pH of different meat samples was sometimes significantly different, overall the differences were small and were not important in the context of this investigation (data not presented). Lipid oxidation

Table 4 presents the TBA-values measured during storage of the samples, Lipid oxidation was significantly higher in gas-packed control meat samples than in control meat packaged on foil overwrapped trays. Gas-packaging did not influence the oxidation of vitamin E-enriched meat. After storage lipid oxidation was significantly lower in vitamin E-enriched meat than in control meat, demonstrating the powerful anti-oxidant effect of vitamin E. Irrespective of the type of packaging used, TBA-values in vitamin E-enriched stored

Aerobic

Plate Counts

(average log N g-r

Period of display (days)

TABLE 2 f standard deviation) at 7°C

Foil

0

4.06 * 0.053

3

4.97& 1.317

6 10

’

Gas

during Display of the Minced Meat

Foil

E

Gas

3.991tO.128 3.97 f 0.247

8.85”J’+O.505 7.42qZt 0.792 9.6W*O.O91 7.98qkO.563

5.17J” f 0.098 4.31qIt0.340 7.72bJ’&0.571 ~ 8.9Y JoO-480 -

6.224 ZIZ 0.092 7.66q* 0.428

*Per horizontal line (possible diet effect) and diagonal (possible packaging effect) Student’s t-tests or (two sided; p
Effect of the dietary supplementation

Numbers

of Enterobacteriaceae

on colour stability and lipid oxidation in mincedpork

TABLE 3 (average log N g- * f standard Minced Meat at 7°C

deviation)

during Display of

c Period of display (days)

Foil

3

3.06 &-***

6

7.26 zt 0.254

E Gas

Foil

Gas

3.54 f 0.035 2.72*--

2.00*6.74pztO.718 6.06 i 1.461

10

8.32p * 0.392

4.774 f 0.030 7.72P* 1.046

6.3Y+ 1.069

5.28q+ 0.643

See first footnote Table 2. ***Counts below limit of detection. For the calculation of the corresponding levels were arbitrarily set at 2.00. TABLE 4 TBA-values (averages f standard deviations; expressed in mg malonaldehyde Display of Minced Meat at 7°C

averages, undetectable

kg-’ product) during

c Period of display (days) 0

Foil

E Gas

0.02 * 0.000

3

0.06q’O.OlO

9

0.134 f 0.073

11

0.24q+o.110

269

Foil

Gas

0.07 It 0.022 0.05 f 0.015b 0.18n”: * 0.025 0.6O”J’*O.l2Ci 1.2o”,p*o.137

0.07 f 0.007 0.018* 0.005

0.076 f 0.006 0.015+ 0.046 0.17ztO.085

0.096 f 0.010 0.10~f0.021

See first footnote Table 2. meat were lower than 0.2 mg malonaldehyde kg-’ meat, a concentration at which the first signs of rancidity become apparent (Frigg, 1992). Lanari et al. (1995) also reported decreased lipid oxidation in chops from pigs fed supplemental vitamin E when the chops were packaged in an atmosphere enriched with oxygen and carbon dioxide. Other investigators have also reported on the protective effect of dietary vitamin E against lipid oxidation in pork tissues (Tsai et al., 1978; Buckley et al., 1989; Ashgar et al., 1991; Monahan et al,, 1992, 1994; Cannon et al., 1995, 1996; Dirinck et al., 1995, 1996; Pfalzgraf et al., 1995aJ). The O2 content of the gas packages gradually decreased to 63.5 f 3.44% after 11 days and the CO2 content increased, to 25.3 *2.70% after 11 days. These changes can be attributed to the metabolism of aerobic micro-organisms and to the catabolism of the meat. No differences in gas composition were observed between the packages of meat from the two groups of pigs (data not shown). Meat colour The changes in meat colour over the first three days of storage are given in Table 5. More than lo6 micro-organisms per gram may influence the colour of the meat (Satterlee and Hansmeyer, 1974), which could influence the data for meat colour measured after six days of display (and longer). Figure 1 presents average a*-values measured for the foil-overwrapped minced meat over the entire storage period. The stability of the red colour of the gas-packed minced

270

J. H. Houben et al.

EflPct of the dietary supplementation

on colour stability and lipid oxidation in minced pork

18

271

0 = Control A = Vitamin E enriched

101

,

0

50

I 100

1 150

I 200

25

Period of display at 7°C (h) Fig. 1. Redness of the foil-overwrapped

minced meats.

meat was similar for both dietary groups. Colour differences (AE = overall colour change

during display) were calculated with the formula:

+ (b; JUG - G>*+ (a; - CT;)*

-

b;)*}

A colour difference corresponding to a calculated value of 1.0 is just discernible by the average human observer (Yudd and Wyszecki, 1975). Calculated values are presented in Table 6. As expected, redness values (Fig. 1 and Table 5) decreased with increasing time in illuminated storage. Gas packaging had a pronounced positive effect on the stability of the red colour component, which can be attributed to the (initially) thicker layer with a higher concentration of oxymyoglobin in gas-packaged meat as compared with foil-over-wrapped meat. Minced meat from the vitamin E-supplemented pigs did not show any better stability of the colour overall, nor was the red component more stable. In the foil-overwrapped packages, the redness values for vitamin E-enriched meat decreased more steeply than did those for control meat. Because the rate of discoloration is thought to be related to the effectiveness of oxidation processes and reducing enzyme systems in controlling metmyoglobin concentrations (Cassens et al., 1993), we have no explanation for this observation. Asghar ef al. (1991) and Monahan et al. (1994) improved the colour stability of pork chops by supplementing the pigs’ diets with vitamin E. However, Cannon et al. (1996) did

Calculated

Colour

Differences

TABLE 6 During Display

of Minced

Meat at 7°C

C Period of display (days) 3

Foil

E Gas

Foil 5.10

3.90

2.91

1.62 6

5.99*

9

5.95*

3.17 4.62 *Underlining means that average log mesophilic aerobic would probably no longer be acceptable for retail purposes.

counts

Gas

surpassed

8.70 ~ 6.25 __

3.68 4.60

7.70; these products

272

J. H. Ho&en

et al.

not find vitamin E supplementation to affect meat colour. Also Hoving-Bolink et al. (1998), who examined chops derived from the same animals as the minced meat used in this study, did not find any colour differences in meat from the two dietary groups until six days after cutting (meat stored at 7°C). Overall colour changes during storage were smallest for the gas- packaged meat (Table 6). This was mainly due to an increased stability of the redness component of the meat (higher oxymyoglobin levels) and a decreased growth rate of aerobic (spoilage) organisms. CONCLUSIONS Minced pork prepared from animals fed on a vitamin E-enriched diet was considerably more resistant to lipid oxidation than was minced meat prepared from control pigs. The meat from vitamin E-supplemented animals was relatively resistant to oxidation, even at the increased 02 concentrations prevailing in the gas packages, oxygen concentrations which clearly induced lipid oxidation in the control meat. The colour of meat from vitamin E-supplemented pigs deteriorated rapidly when the meat was foil-overwrapped. Meat colour stability was comparable for gas-packaged control and vitamin E-enriched meat. The shelf-life of the minced pork was similar for both groups.

ACKNOWLEDGEMENTS The authors gratefully acknowledge the enthusiastic interest and skilled assistance of C. V. M. Gerris, G. Keizer, J. L. M. Tjeerdsma-van Bokhoven, A. A. M. Spanjer and D. Keuzenkamp. This study was partly financed by the Dutch Product Boards for Livestock, Meat, Poultry and Eggs (grant no. 94.1.20) and was supported by Roche Nederland B.V. (Mjidrecht), Hanskamp B.V. (Deventer) and Philips Lighting (Roosendaal).

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