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Decolouration and lipid oxidation changes of vacuum-packed Iberian dry-cured loin treated with E-beam irradiation (5 kGy and 10 kGy) during refrigerated storage
Innovative Food Science and Emerging Technologies 10 (2009) 495–499
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Innovative Food Science and Emerging Technologies j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i f s e t
Decolouration and lipid oxidation changes of vacuum-packed Iberian dry-cured loin treated with E-beam irradiation (5 kGy and 10 kGy) during refrigerated storage Ramón Cava a,⁎, Ruth Tárrega b, Rosario Ramírez c, Juan Atanasio Carrasco b a b c
Tecnología de los Alimentos, Facultad de Veterinaria, Campus Universitario, Universidad de Extremadura, 10071 Cáceres, Spain Departamento de Ingeniería, Instituto del Frío, Consejo Superior de Investigaciones Científicas, Ciudad Universitaria, 28040 Madrid, Spain Instituto Tecnológico Agroalimentario de Extremadura (INTAEX), Carretera de San Vicente sn. 06071 Badajoz, Spain
a r t i c l e
i n f o
Article history: Received 26 November 2008 Accepted 20 April 2009 Editor Proof Receive Date 1 May 2009 Keywords: Iberian dry-cured loin Feeding regime Irradiation Refrigerated storage Colour TBA-RS Hexanal
a b s t r a c t The effect of irradiation (0, 5 and 10 kGy) on the oxidative and colour stability of vacuum-packed Iberian drycured loin slices from pigs fed on concentrate feed (CON) or free-range reared (FRG) stored under refrigerated storage was studied. Irradiation treatment increased lipid oxidation, measured as TBA-RS values and hexanal content of dry-cured loins. It also increased redness (CIE a⁎) and lightness (CIE L⁎) of dry-cured loins. Refrigerated storage reduced the differences due to irradiation treatment of instrumental colour values like lightness. However, the decrease of redness during storage was more marked in irradiated than in nonirradiated dry-cured loin. Storage increased differences in TBA-RS values between irradiated and nonirradiated FRG dry-cured loin, while the opposite trend was found for CON dry-cured loins. In addition, no differences in the hexanal content were found after 30 days of refrigerated storage. Therefore, the storage of Iberian dry-cured loin in absence of oxygen by using a vacuum packaging could be an adequate method to reduce changes associated to irradiation treatment in Iberian dry-cured loin. Industrial relevance: Iberian dry-cured loin is a high sensory quality meat product with increasing projection in external markets Irradiation has shown to be an effective method to control pathogen and spoilage microorganisms in meat and meat products. However, e-beam irradiation can promote colour and oxidation changes that could modify their sensory characteristics. The study aimed the evaluation of e-beam irradiation at two levels (5 and 10 kGy) — higher doses than those that could be necessary to control pathogen microorganisms in this kind of product — on colour changes and lipid oxidation at vacuum-packed slices of Iberian dry-cured loin during subsequent extended chilled storage. E-beam treatment induced changes in colour and lipid oxidation in sliced Iberian dry-cured loin immediately after treatment and subsequent refrigerated storage. © 2009 Elsevier Ltd. All rights reserved.
1. Introduction Irradiation is the most effective technology in reducing pathogens in meat and meat based products. In addition, irradiation can be performed at ambient or lower temperatures which guarantee better preservation of nutritive values and physical–chemical properties of foods. Such advantages make irradiation treatment a viable technology for preservation of food products (O'Bryan, Crandall, Ricke, Olson et al., 2008). However, consumer awareness of food irradiation, in general, is very low, as majority of consumers are uncertain about the safety of irradiated foods.
⁎ Corresponding author. Tecnología de los Alimentos, Facultad de Veterinaria, Universidad de Extremadura, Cáceres 10071, Spain. Tel.: +34 927 257 169; fax: +34 927 257 110. E-mail address: [email protected] (R. Cava). 1466-8564/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.ifset.2009.04.006
Several papers have pointed out that doses lower than 10 kGy control the growth of pathogenic and spoilage bacteria on meat and meat products, such as Listeria monocytogenes, Salmonella typhimurium, Escherichia coli O157:H7 and Yersinia enterocolitica (Fu, Sebranek, & Murano, 1995; Shenoy, Murano, & Olson, 1998; Olson, 1998). However, meats are generally susceptible to oxidative deterioration principally due to the oxidation of polyunsaturated fatty acids present in phospholipids. Irradiation enhances free radical reactions resulting in the possibility of colour changes, lipid oxidation and odour generation, which can generate negative consumer responses to this quality deterioration (Patterson & Stevenson, 1995; Ahn, Jo, & Olson, 2000; Jo & Ahn, 2000; Du, Hur, & Ahn, 2002). In addition, storage could increase irradiation effect, as it can promote lipid oxidation, particularly during post-irradiation storage. Free radicals generated from radiolysis of water, such as hydroxyl radicals (OH), hydrated electrons and H+ (Merrit, Angelini, & Grahm, 1978) attack food components (proteins, amino acids, lipids etc.), leading to an increased rate of lipid oxidation. These free radicals appear in aqueous systems (Thakur & Singh, 1994) and also
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in meat, because over the 75% of muscle cells are composed of water and are surrounded by lipid bilayers. These are very prone to free-radical attack as a result of their high content of phospholipids rich in polyunsaturated fatty acids highly susceptible to lipid peroxidation (Pikul, Leszczynski, & Kummerow, 1984; Buckley et al., 1989). Irradiation has been reported to increase 2-thiobarbituric acid-reactive substances (TBA-RS) in different meat species, packaging and storage conditions (Hampson, Fox, Lakritz, & Thayer, 1996; Ahn et al., 1997; Du, Ahn, Nam, & Sell, 2000). In addition, previous studies have shown that irradiation can induce oxidative deterioration of fatty acids and consequently generate offflavours that comprise consumer's acceptability. Unsaturated lipidderived aldehydes, and especially hexanal, are the major volatile compounds related to oxidative changes in meat and meat products. However, irradiation can induce the development of off-odours at high doses for certain products. Previous studies (Carrasco, Tárrega, Ramírez, Mingoarranz, & Cava, 2005) in dry-cured loin showed that irradiation increased hexanal content, the main lipid oxidation derived aroma volatile compound which level could increase during storage and as a consequence reduce consumer's acceptability of these products. On the other hand, discoloration processes and lipid oxidation phenomena are close related due to the fact that the oxidation processes of muscle pigments can catalyze the oxidation of lipids (Akamittath, Brekke, & Schanus, 1990). Free radicals generated by irradiation can also react with myoglobin or haemoglobin and modify colour of irradiated samples (Kamarei, Karel, & Weirbicki, 1979; Jo, Jin, & Ahn, 2000). Meat and meat products colour is an important quality attribute that influences consumer acceptance of the meat, as they prefer bright-red fresh meats, brown-grey cooked meats, and pink cured meats (Cornforht, 1994). The mechanisms of lipid oxidation in irradiated meat are not fully understood, but they are likely to proceed via traditional pathways. Therefore, the susceptibility of irradiated muscle tissues to lipid oxidation and the intensity of the changes depends on i. endogenous characteristics of the tissue including the fat content, the fatty acid profile, the composition of phospholipids in cell membrane, antioxidant concentrations in muscle as well as ii. exogenous characteristics such as the irradiation dose level, packaging and storage conditions (Gray, Gomaa, & Buckley, 1996; Ahn et al., 1997; Morrissey, Brandon, Buckley, Sheehy, & Frigg, 1997; Ahn, Olson, Jo, Love, & Jin, 1999; Nanke, Sebranek, & Olson, 1998). Iberian dry-cured loin is a meat product with a high consumer acceptance due to its particular sensory characteristics derived both from raw meat composition (high intramuscular fat and oleic acid contents) and the physical, chemical and biochemical changes that take place during ripening period. The main factors affecting sensory quality of Iberian dry-cured meat products are the characteristics of the pigs fattening phase, either rising in free-range rearing and fed on acorns and pasture or reared in confinement with concentrate feeds. These factors modify the intramuscular fat content, fatty acid profiles of intramuscular lipid fractions and muscle antioxidant contents (Cava et al., 1997; Cava, Ruiz, Ventanas, & Antequera, 1999a). Although irradiation could have great importance for meat industry, only there are a few studies about the impact of irradiation on the quality of dry-cured meat products (Carrasco et al., 2005; Cava, Tárrega, Ramírez, Mingoarranz, & Carrasco, 2005) whereas no information about quality changes of irradiated dry-cured meat products under storage is available. However, nowadays it is important for industry to offer drycured meat products microbiologically safe and with longer shelf-life, which could favour the commercialization of these products. Therefore, the objective of the present study was to investigate the effect of different ionization doses (5 kGy and 10 kGy) on instrumental colour, lipid oxidation and hexanal changes of vacuum-packaged slices of Iberian dry-cured loins from free-range reared pigs and intensively reared pigs under refrigerated storage.
2. Material and methods 2.1. Dry-cured loin samples Iberian dry-cured loins from pigs fed on concentrate (CON) and free-range reared (FRG) were used for the experiment. FRG pigs were reared outdoors and exclusively fed on available acorns and pasture. Regarding loins manufacture, they were seasoned by rubbing a mixture of salt, nitrite, olive oil and spices such as Spanish paprika (Capsicum annuum, L.), oregano (Origanum vulgare L.) and garlic (Altium sativum, L.). Loins were kept at 4 °C for some days to allow the seasoning mixture to penetrate. Then, loins were stuffed into collagen casings and held at low temperature and high relative humidity which was increased at the end of the ripening. Before packaging, dry-cured loins were liberated of casings and sliced using a slicing machine to give 3 mm thick slices. 2.2. Vacuum-packaging, irradiation treatment and refrigerated storage Dry-cured loin slices were vacuum-packaged in nylon/polyethylene bags (9.3 ml O2/m2/24 h a 0 °C) containing 5 slices/pack. Dry-cured loin slices were irradiated at 0, 5 and 10 kGy dose (IONMED Esterilización, S. A. Cuenca, Spain) using an Electron Beam irradiator (Rhodotron TT200, IBA, Louvain La Neuve, Belgium) with a 10 MeV energy level, a 10 kW power level, and an average 98 kGy/min dose rate after storage overnight in a 4 °C cooler. The irradiation process was conducted at room temperature (~20 °C) with single layer display and single-sided dosage. The samples were returned to the refrigerator immediately after irradiation. To confirm the target dose, 2 alanine dosimeters per cart were attached to the top and bottom surfaces of the sample. The alanine dosimeter was read using a 104 Electron Paramagnetic Resonance instrument (Bruker Instruments Inc., Billerica, MA). The final doses were 5.21 ± 0.32 kGy for 5 kGy and 10.47 ± 0.65 for 10 kGy treatments. Irradiated samples were stored at 4 °C in darkness before colour measurement and stored at −80 °C until TBA-RS and hexanal content determinations. After irradiation treatment, packages with samples were stored under refrigeration at +4 °C in the darkness for 0, 30, 60 and 90 days. 2.3. Physical–chemical analysis 2.3.1. Instrumental colour Colour measurements were taken immediately after opening the package (in order to prevent colour degradation as a result of light and oxygen) in accordance with the recommendations on colour determination of the American Meat Science Association (Hunt et al., 1991). The following colour coordinates were measured: lightness (L⁎), redness (a⁎, red ± green) and yellowness (b⁎, yellow ± blue). Colour parameters were determined using a Minolta CR-300 colorimeter (Minolta Camera, Osaka, Japan) with illuminant D65, a 0° standard observer and a 2.5 cm port/viewing area. The colorimeter was standardized before use with a white tile. The measurement was repeated on eight randomly selected locations on each loin slice and averaged for statistical analysis. 2.3.2. Lipid oxidation Lipid oxidation was measured using a complete dry-cured loin slice and homogenised using a kitchen blender. The extent of lipid oxidation was estimated as TBA-RS using a modified version of Salih, Smith, Price, & Dawson (1987) method. TBA-RS were measured on two slices from each pack and were expressed as mg malondialdehyde (MDA)/kg meat. 2.3.3. Hexanal content Hexanal content was assessed according to Carrasco et al. (2005). A Solid Phase Micro Extraction, SPME (Supelco Co., Bellefonte, PA) fibre
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(10 mm length) coated with DVB/Carboxen/PDMS (50/30 µm thickness) was used for the determination of hexanal content of the samples. Prior to analysis the SPME fibre was preconditioned at 280 °C for 1 h in the GC injection port. For HS-SPME extraction, loin slices were grounded with a commercial grinder. 0.5 g were weighed into a 10 ml screwcapped vial containing 3 ml of distilled water and 2 g of sodium chloride, the mixture was homogenized at 3000 rpm for 2 min. The fibre was inserted into the sample vial through the septum and then exposed to headspace. The extractions were carried out in an oven to ensure a homogeneous temperature for sample and headspace. The extraction was performed at 50 °C for 30 min. Before extraction, samples were equilibrated for 15 min at the same temperature used for extraction. Analyses were performed in an Agilent Technologies series 6890, mod. G1530A gas chromatograph coupled to a mass selective detector (Agilent 5973N MSD, mod. G2577A). Volatiles were separated using a 5% phenyl–methyl silicone (HP-5) bonded-phase fused silica capillary column (Hewlett-Packard, 50 m × 0.32 mm i.d., film thickness 1.05 µm), operating at 5 psi of column head pressure, resulting in a flow of 1.3 ml min− 1 at 40 °C. The injection port was in a splitless mode. The temperature program was isothermal for 10 min at 40 °C, raised to 200 °C at a rate of 5 °C min− 1, and then raised to 250 °C at a rate of 20 °C min− 1, and held for 5 min. The transfer line to the mass spectrometer (MS) was maintained at 280 °C. The mass spectra were obtained using a mass selective detector (Hewlett-Packard HP-5971 A) by electronic impact at 70 eV, a multiplier voltage of 1753 V, and collecting data at a rate of 2.83 scan s− 1 over the m/z range of 30 to 550. Hexanal was tentatively identified by comparing its mass spectra with the contained in the NIST/EPA/NIH and Wiley libraries and by comparison of Kovats index with that reported in the literature. The quantification of the hexanal content was performed using an external standard. 2.4. Statistical analysis Samples from the two types of loins, free-range reared and concentrate fed pigs, were randomly assigned to the treatments. There were five replicates per dose and day of storage. The effect of dose and day of storage and the interaction between irradiation and day of storage of each type of dry-cured loin was analyzed using the General Linear Model procedure of SPSS (ANOVA), version 10.0 (SPSS, 1999). Means were used to compare differences between treatments. Tukey's test was used to compare the mean values of the treatments and storage time. Mean values and standard errors of the means (SEM) were reported. Pearson's correlation coefficients were also calculated. 3. Results and discussion 3.1. Lipid oxidation Irradiation significantly increased lipid oxidation, measured as TBA-RS values in both sets of vacuum-packed Iberian dry-cured loin slices (Table 1) immediately after irradiation (day 0). Irradiation increased TBA-RS in a dose-dependent fashion, so samples irradiated at 10 kGy had higher TBA-RS values than those irradiated at 5 kGy or the non-irradiated control. TBA-RS increased linearly with irradiation dose (r = + 0.64, p b 0.001). The prooxidant effect of irradiation and the dose dependent effect on lipid oxidation have been widely reported in different meat and meat products (Hampson et al., 1996; Luchsinger et al., 1996; Ahn et al., 1998; Ahn et al., 1999). TBA-RS values showed small changes during refrigerated storage. The evolution of TBA-RS values in CON and FRG samples showed great differences, while in CON samples TBA-RS decreased in irradiated and non-irradiated samples in FRG samples irradiation at 10 kGy increased TBA-RS values. FRG irradiated samples showed higher TBA-RS values (p b 0.05) at day 30 than those non irradiated and at the end of refrigerated storage FRG samples treated at 10 kGy had the highest
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Table 1 Thiobarbituric acid-reactive substances (TBA-RS, measured as mg MDA/kg meat) of vacuum-packed Iberian dry-cured loin slices stored for 90 days after irradiating. SEMa Concentrate (CON)
Type of loin
Free-range (FRG)
Dose
Control
5 kGy 10 kGy
0.44 b x 0.34 b y 0.38 xy 0.40 b xy 0.01
0.50 a 0.48 a 0.52 0.67 b 0.04
SEMa
Control
5 kGy
10 kGy
0.33 c x 0.35 b x 0.19 c z 0.26 c y 0.02
0.39 0.29 0.25 0.32 0.01
0.52 a w 0.44 a x 0.32 a z 0.39 a y 0.02
Days of storage 0 30 60 90 SEMb
0.52 a y 0.49 a y 0.52 y 1.00 a x 0.08
0.01 0.03 0.03 0.10
bx cy bz by
0.02 0.02 0.02 0.01
Means with a different letter (a,b,c) within a row of the same type of loin and the same day of storage are different (p b 0.05). Means with a different letter (x,y,z) within a column of the same irradiation dose are different (p b 0.05). a SEM: Standard error of the means among the same irradiation dose (n = 15). b SEM: Standard error of the means among the same storage day (n = 20).
TBA-RS values (p b 0.05). These results indicate a prooxidant effect of irradiation at 10 kGy on the oxidative stability of FRG dry-cured loins during refrigerated storage. In contrast, in CON samples TBA-RS values decreased significantly during storage (p b 0.05) although differences among treated and non-treated samples immediately after irradiation maintained during storage. Non-irradiated samples showed significantly (p b 0.05) lower TBA-RS values than those irradiated at 5 kGy and 10 kGy and TBA-RS in irradiated samples were dose-dependent and increase with the dose of irradiation. In general, it is known that irradiation induces lipid oxidation and oxidation progresses during storage (Kanatt, Paul, D'Souza, & Thomas, 1998), which is in contrast with our findings in dry-cured Iberian loin. Regarding differences in the pattern of formation of TBA-RS in FRG and CON samples during storage, these could be attributable to distinct characteristics of the raw material for the manufacture of dry-cured loins such as intramuscular fat content, fatty acid profiles, haem pigments, initial lipid oxidation levels and muscle antioxidant contents (Cava, Ruiz, Tejeda, Ventanas, & Antequera, 2000; Cava, Estévez, Morcuende, & Antequera, 2003). 3.2. Hexanal content Changes in hexanal content of both sets of vacuum-packed Iberian dry-cured loin slices during refrigerated storage are shown in Table 2. Hexanal contents of vacuum-packed dry-cured loin slices increased in a dose-dependent fashion immediately after irradiation (day 0). Irradiation doses at 5 and 10 kGy promoted production of hexanal in a different extent in CON and FRG dry-cured loin, being the rate of formation of hexanal much higher in FRG samples than in CON samples. We presume that the possible higher intramuscular fat content of FRG samples (data not shown) could have been a contributing factor for its high hexanal formation immediately after irradiation. Findings regarding hexanal content agree with results previously reported for TBA-RS, as evidenced the positive Pearson's correlation coefficient found between TBA-RS and hexanal contents (r = +0.40, p b 0.01). This close relationship between these two lipid oxidation indicators has been previously described in meat and meat products (Ang & Lyon, 1990; Ahn et al., 1999). In contrast to reported for TBA-RS, the changes occurring during storage were different from those occurring immediately after irradiation. Hexanal contents decreased or remained unchanged during refrigerated storage in the two sets of dry-cured loins. At the end of refrigerated storage, hexanal content reductions were more marked in FRG samples than in CON ones. In FRG samples, no significant differences (p N 0.05) were found as a result of irradiation treatment or dose of
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Table 2 Hexanal contents (µg hexanal/g sample) of vacuum-packaged Iberian dry-cured loin slices stored for different periods of time after irradiating. SEMa Concentrate (CON)
Type of loin
Free-range (FRG)
Dose
Control 5 kGy
10 kGy
2.6 b x 0.9 y 2.3 xy 1.8 xy 0.3
12.0 a x 1.6 y 1.7 y 3.4 y 1.1
Control 5 kGy
10 kGy
3.9 b 5.0 ab 1.2 b 2.1 0.7
8.5 a x 2.8 b y 2.1 a y 2.9 y 0.7
SEMb
Days of storage 0 30 60 90 SEMb
10.0 a x 1.9 y 3.4 y 3.1 y 0.8
1.3 0.3 0.3 0.4
4.0 b y 8.6 a x 2.1 a y 3.4 y 0.6
0.7 1.0 0.2 0.3
Means with a different letter (a,b,c) within a row of the same type of loin and the same day of storage are different (p b 0.05). Means with a different letter (x,y,z) within a column of the same irradiation dose are different (p b 0.05). a SEM: Standard error of the means among the same irradiation dose (n = 15). b SEM: Standard error of the means among the same storage day (n = 20).
irradiation at days 30, 60 and 90 of refrigerated storage, although hexanal contents tended to be higher in irradiated samples. A similar trend as that reported for FRG samples was found in CON samples. Hexanal contents in refrigerated samples decreased in comparison with hexanal contents found immediately after irradiation. No differences were found in refrigerated samples as a result of irradiation dose, and only at day 60 irradiated samples showed significantly higher (p b 0.05) hexanal contents than control ones. Scientific literature concerning changes in volatile compounds of sliced Iberian dry-cured loin during storage is not available and no information about the effect of raw material on the evolution of lipid-derived aldehydes in sliced vacuum packaged can be found. However, the different trend of hexanal content observed in the two sets of samples during storage could be related to the chemical characteristics of both types of loins such as: i. intramuscular fat content (Cava et al., 1999a), ii. fatty acids composition of total lipids and lipid fractions (Cava, Ruiz, Ventanas, & Antequera, 1999b) and/or iii. endogenous antioxidant contents and prooxidant/ antioxidant balance (Cava et al., 2000). Similar results were found by Shahidi, Pegg, and Shamsuzzaman (1991), who observed that the hexanal contents declined markedly upon extended storage of meat. They indicated that the reactions of hexanal with meat components or its further oxidation to hexanoic acid were responsible for the reduction of hexanal in meat during storage. Jo, Ahn, and Byun (2002) found that the hexanal content decreased during storage in irradiated vacuum-packed sausages while it increased in the non-vacuum packed. Therefore, agreeing with that previously reported for TBA-RS values, maybe the presence of oxygen affects the formation of hexanal in irradiated meat products. It is probable that the vacuumpacked storage of irradiated dry-cured meat products could be effective to stop degradation processes related to lipid oxidation. The mechanisms of volatile production in irradiated meats are not fully understood, but several previous researches suggested that the radiolytic products of proteins as well as the lipid oxidation by-products as a result of oxidation processes are responsible for the off-odour in irradiated meats (Ang & Lyon,1990; Lefebvren, Thibault, Charbonneau, & Piette,1994; Patterson & Stevenson, 1995; Hashim, Resurreccion, & MacWatters, 1995; Hampson et al.,1996; Ahn et al.,1997,1998; Ahn, Jo, Du, Olson, & Nam, 2000). In this respect, in dry-cured meat products high levels of hexanal are generally associated with rancid and undesirable flavours (Cava et al., 1999a). Instead, further knowledge of hexanal changes in irradiated dry-cured loin is necessary to elucidate the effect of irradiation on its flavour.
3.3. Surface instrumental colour Changes in instrumental colour parameters (CIE L⁎, a⁎, b⁎) of both sets of Iberian dry-cured loin slices during refrigerated storage are shown in Table 3.
Colour changes of vacuum-packed Iberian dry-cured loin slices were dose-dependent immediately after irradiation (day 0). Lightness (L⁎value) decreased with irradiation dose while redness (a⁎-value) increased in irradiated samples compared to control samples in both sets of dry-cured loins. Results are in agreement with previous findings in dry-cured ham (Cava et al., 2005) as well as in uncured raw and cooked meats (Luchsinger et al., 1996; Millar, Moss, & Stevenson, 2000; Nam & Ahn, 2002). Nam and Ahn (2002) attributed the red colour increase in irradiated turkey meat to the formation of carbon monoxide– myoglobin (CO–Mb) complexes. Compared with oxymyoglobin, CO–Mb complex is not easily oxidized to brown metmyoglobin, because of the strong binding of CO to the iron-porphyrin in myoglobin molecule (Sorheim, Nessen, & Nesbakken, 1999). However, the effects of irradiation and the causes of colour changes in dry-cured products are not well established. Other factors could be implicated in the reported changes in redness of dry-cured meat products, in which nitrosylmyoglobin is the predominant haem pigment. In this sense, previous studies have reported that nitrite inhibited the changes in colour due to irradiation (Fan, Sommers, Kimberly, & Sokorai, 2004). Storage tended to decrease the lightness and the redness of Iberian dry-cured loin slices while the yellowness tended to increase, especially in CON samples. After 90 days of refrigerated storage, irradiated drycured loins of both sets of sliced loins had significantly lower (p b 0.05) L⁎-values and a⁎-values than those non-irradiated. Additionally, at day 90 irradiated FRG dry-cured loin had significantly lower (p b 0.05) CIE b⁎-values, while this trend was not found for CON loins. So, the increase in CIE a⁎ in Iberian dry-cured loin slices as a consequence of irradiation was lessened during storage, so at the end of the refrigeration period the redness of the irradiated dry-cured loins was lower than the control ones. Results suggest that the increase in redness immediately after irradiation seems to be reversible phenomena, at least in cured meat that makes the pigment formed more easily oxidized during storage. By contrast, Nam and Ahn (2002) found an increase of redness
Table 3 Colour surface of vacuum-packaged Iberian dry-cured loin slices stored for different periods of time after irradiating. SEMa Concentrate (CON)
Type of Free-range (FRG) loin Dose
Control
5 kGy
10 kGy
40.0 a x 38.8 b y 35.6 b yz 34.9 b z 0.61
34.6 b 34.1 c 33.7 c 33.4 c 0.22
a⁎-value 0 24.3 b 30 23.8 b 60 24.8 90 26.3 a SEM 0.41
28.7 a x 26.7 a x 23.6 y 23.1 b y 0.58
b⁎-value 0 14.0 y 30 14.7 a xy 60 15.5 a x 90 15.1 a xy SEMb 0.21
14.9 x 14.3 a xy 13.3 b xy 11.7 b y 0.43
SEMa
Control
5 kGy
10 kGy
0.73 0.79 0.79 0.62
43.3 b y 46.0 a x 44.6 a xy 44.8 a xy 0.29
46.9 a x 44.9 a xy 43.3 a yz 42.1 b z 0.47
42.3 b 42.2 b 42.1 b 43.0 b 0.19
0.60 0.51 0.34 0.35
30.5 a x 26.9 a y 24.2 z 23.1 b z 0.69
0.77 0.54 0.27 0.52
24.4 b y 25.7 a x 24.2 a y 23.5 a y 0.22
24.0 b xy 24.9 ab x 22.5 b y 20.3 b z 0.45
26.6 a x 23.3 b y 20.8 c xy 18.3 c z 0.78
0.39 0.40 0.47 0.64
12.2 11.9 b 11.4 b 13.1 b 0.25
0.36 0.45 0.56 0.46
14.8 b y 19.8 a x 17.3 xy 19.8 x 0.61
17.1 a z 18.2 b y 19.1 xy 19.6 x 0.25
16.3 a y 17.0 b y 17.7 y 19.6 x 0.33
0.30 0.37 0.49 0.25
Days of storage L⁎-value 0 40.7 30 40.8 60 40.2 90 38.5 SEMb 0.26
ax ax ax ay
Means with a different letter (a,b,c) within a row of the same type of loin and the same day of storage are different (p b 0.05). Means with a different letter (x,y,z) within a column of the same irradiation dose are different (p b 0.05). a SEM: Standard error of the means among the same irradiation dose (n = 15). b SEM: Standard error of the means among the same storage day (n = 20).
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after 10 days of storage in irradiated vacuum packaged raw turkey breast. No explanation has been found in the literature for CIE a⁎-value decrease in irradiated meat during refrigerated storage. It is possible that nitrite could have played an important role in the colour evolution and its effect needs to be elucidated in future researches In addition, intrinsic characteristics of dry-cured loins (pH, moisture, fat, NaCl content, Aw, fatty acid profiles etc.) are important factors that could influence the intensity of the changes due to irradiation. Therefore, future studies are necessary to elucidate their effects since few papers in the literature deal with irradiation consequences in cured meat products quality. 4. Conclusions Irradiation at doses of 5 kGy and 10 kGy induced changes in colour and lipid oxidation of dry-cured Iberian loin slices immediately after irradiation and affected the evolution of instrumental colour, TBA-RS values and hexanal contents during refrigerated storage. These changes could induce undesirable effects that compromise the quality of the irradiated products. In the case that irradiation doses necessary to eliminate the risk of pathogens in sliced dry-cured loin were lower than those used in this study, changes in colour and lipid oxidation after irradiation could be less marked than those described in the present paper as changes are directly related to the dose of irradiation. Acknowledgements Authors want to thank Inmaculada Linares and José Navarro for their technical assistance. References Ahn, D. U., Jo, C., Du, M., Olson, D. G., & Nam, K. C. (2000). Quality characteristics of pork patties irradiated and stored in different packaging and storage conditions. Meat Science, 56, 203−209. Ahn, D. U., Jo, C., & Olson, D. G. (2000). Analysis of volatile components and the sensory characteristics of irradiated raw pork. Meat Science, 54, 209−215. Ahn, D. U., Olson, D. G., Jo, C., Chen, X., Wu, C., & Lee, J. I. (1998). Effect of muscle type, packaging, and irradiation on lipid oxidation, volatile production and colour in raw pork patties. Meat Science, 49, 37−39. Ahn, D. U., Olson, D. G., Jo, C., Love, J., & Jin, S. K. (1999). Volatiles production and lipid oxidation on irradiated cooked sausage as related to packaging and storage. Journal of Food Science, 64, 226−229. Ahn, D. U., Sell, J. L., Jeffery, M., Jo, C., Chen, X., Wu, C., et al. (1997). Dietary vitamin E affects lipid oxidation and total volatiles of irradiated raw turkey meat. Journal of Food Science, 62, 954−958. Akamittath, J. G., Brekke, C. J., & Schanus, E. G. (1990). Lipid oxidation and colour stability in restructured meat systems during frozen storage. Journal of Food Science, 55, 1513−1517. Ang, C. Y. W., & Lyon, B. G. (1990). Evaluation of warmed-over flavour during chill storage of cooked broiler breast, thigh and skin by chemical, instrumental and sensory methods.Journal of Food Science, 55, 644−648 673. Buckley, D. J., Gray, J. I., Ashgar, A., Price, J. F., Crackle, R. L., Booren, A. M., et al. (1989). Effects of dietary antioxidants and oxidized oil on membranal lipid stability and pork product quality. Journal of Food Science, 54, 1193−1197. Carrasco, A., Tárrega, R., Ramírez, M. R., Mingoarranz, F. J., & Cava, R. (2005). Colour and lipid oxidation changes in dry-cured loins from free-range reared and intensively reared pigs as affected by ionizing radiation dose level. Meat Science, 69, 609−615. Cava, R., Estévez, M., Morcuende, D., & Antequera, T. (2003). Evolution of fatty acids from intramuscular lipid fractions during ripening of Iberian hams as affected by αtocopheryl acetate supplementation in diet. Food Chemistry, 81, 199−207. Cava, R., Ruiz, J., López-Bote, C., Martín, García, C., Ventanas, J., et al. (1997). Influence of finishing diet on fatty acid profiles of intramuscular lipids, tryglicerides and phospholipids in muscles of the Iberian pig. Meat Science, 45, 263−270. Cava, R., Ruiz, J., Tejeda, J. F., Ventanas, J., & Antequera, T. (2000). Effect of free-range rearing and α-tocopherol and copper suplementation on fatty acid profiles and susceptibility to lipid oxidation of fresh meat from Iberian pigs. Food Chemistry, 68, 51−59. Cava, R., Ruiz, J., Ventanas, J., & Antequera, T. (1999). Oxidative and lipolytic changes during ripening of Iberian hams as affected by feeding regime: Extensive feeding and alpha-tocopheryl acetate supplementation. Meat Science, 52, 165−172. Cava, R., Ruiz, J., Ventanas, J., & Antequera, T. (1999). Effect of alpha-tocopheryl acetate supplementation and extensive feeding of the pigs on the evolution of volatile aldehydes during the processing of Iberian ham. Food Science and Technology International, 5, 235−241.
499
Cava, R., Tárrega, R., Ramirez, M. R., Mingoarranz, F. J., & Carrasco, A. (2005). Effect of irradiation on colour and lipid oxidation of dry-cured hams from free-range reared and intensively reared pigs. Innovative Food Science and Emerging Technologies, 6, 135−141. Cornforht, D. (1994). Colour — Its basis and importance. In A. M. Pearson & T. R. Dutson (Eds.), Quality attributes and their measurement in meat, poultry and fish productsAdvances in Meat Research Series, vol. 9. (pp. 34−78). Du, M., Ahn, D. U., Nam, K. C., & Sell, J. L. (2000). Influence of dietary conjugated linolenic acid on volatile profiles, colour and lipid oxidation of irradiated raw chicken meat. Meat Science, 56, 387−395. Du, M., Hur, S. J., & Ahn, D. U. (2002). Raw-meat packaging and storage affect the colour and odor of irradiated broiler breast fillets after cooking. Meat Science, 61, 49−54. Fan, X., Sommers, C. H., Kimberly, J. B., & Sokorai, B. J. (2004). Ionizing radiation and antioxidants affect volatile sulfur compounds, lipid oxidation, and color of readyto-eat turkey bologna. Journal of Agricultural and Food Chemistry, 52, 3509−3515. Fu, A. H., Sebranek, J. G., & Murano, E. A. (1995). Survival of Listeria monocytogenes, Yersinia enterocolitica and Escherichia coli O157:H7 and quality changes after irradiation of beef steaks and ground beef. Journal of Food Science, 60, 972−977. Gray, J. I., Gomaa, E. A., & Buckley, D. J. (1996). Oxidative quality and shelf life of meats. Meat Science, 43, S111−S123. Hampson, J. W., Fox, J. B., Lakritz, L., & Thayer, D. W. (1996). Effect of low dose gamma radiation on lipids in five different meats. Meat Science, 42, 271−276. Hashim, I. B., Resurreccion, A. V. A., & MacWatters, K. H. (1995). Disruptive sensory analysis of irradiated frozen or refrigerated chicken. Journal of Food Science, 60, 664−666. Hunt, M. C., Acton, J. C., Benedict, R. C., Calkins, C. R., Cornforth, D. P., Jeremiah, L. E., et al. (1991). AMSA guidelines for meat colour evaluation. Proceedings 44th Annual Reciprocal Meat Conference Chicago: National Livestock and Meat Board. Jo, C., & Ahn, D. U. (2000). Volatiles and oxidative changes in irradiated pork sausage with different fatty acid composition and tocopherol content. Journal of Food Science, 65, 270−275. Jo, C., Ahn, D. U., & Byun, M. W. (2002). Irradiation-induced oxidative changes and production of volatile compounds in sausages prepared with vitamin E-enriched commercial soybean oil. Food Chemistry, 76(3), 299−305. Jo, C., Jin, S. K., & Ahn, D. U. (2000). Color changes in irradiated cooked pork sausage with different fat sources and packaging during storage. Meat Science, 55, 107−113. Kamarei, A. R., Karel, M., & Weirbicki, E. (1979). Spectral studies on the role of ionising radiation in colour changes in radappertised beef. Journal of Food Science, 44, 25−32. Kanatt, S. R., Paul, P., D'Souza, S. F., & Thomas, P. (1998). Lipid peroxidation in chicken meat during chilled storage as affected by antioxidants combined with low-dose gamma irradiation. Journal of Food Science, 63, 386−389. Lefebvren, N., Thibault, C., Charbonneau, R., & Piette, J. P. (1994). Improvement of shelflife and wholesomeness of ground beef by irradiation. 2. Chemical analysis and sensory evaluation. Meat Science, 36, 371−380. Luchsinger, S. E., Kropf, D. H., García Zepeda, C. M., Hunt, M. C., Marsden, J. L., Rubio Canas, E. J., et al. (1996). Color and oxidative rancidity of gamma and electron beanirradiated boneless pork chops. Journal of Food Science, 61, 1000−1005. Merrit, C., Jr, Angelini, P., & Grahm, R. A. (1978). Effect of radiation parameters on the formation of radiolysis products in meat and meat substances. Journal of Agricultural and Food Chemistry, 26, 29−35. Millar, S. J., Moss, B. W., & Stevenson, M. H. (2000). The effect of ionising radiation on the colour of leg and breast of poultry meat. Meat Science, 55, 361−370. Morrissey, P. A., Brandon, S., Buckley, D. J., Sheehy, P. J. A., & Frigg, M. (1997). Tissue content of alpha-tocopherol and oxidative stability of broilers receiving dietary-tocopheryl acetate supplementation for various periods pre-slaughter. British Poultry Science, 38, 84−88. Nam, K. C., & Ahn, D. U. (2002). Carbon monoxide-heme pigment is responsible for the pink colour in irradiated raw turkey breast meat. Meat Science, 30, 25−33. Nanke, K. E., Sebranek, J. G., & Olson, D. G. (1998). Color characteristics of irradiated vacuum-packaged pork, beef and turkey. Journal of Food Science, 63, 1001−1006. O'Bryan, C. A., Crandall, P. G., Ricke, S. C., & Olson, D. G. (2008). Impact of irradiation on the safety and quality of poultry and meat products: A review. Critical Reviews in Food Science and Nutrition, 48, 442−457. Olson, D. G. (1998). Irradiation of food. Food Technology, 52, 56−62. Patterson, R. L. S., & Stevenson, M. H. (1995). Irradiation-induced off-odor in chicken and its possible control. British Poultry Science, 36, 425−441. Pikul, J., Leszczynski, D. E., & Kummerow, F. A. (1984). Relative role of phospholipids, triacylglycerols and cholesterol esters on malonaldehyde formation in fat extracted from chicken meat. Journal of Food Science, 49, 704−708. Salih, A. M., Smith, D. M., Price, J. F., & Dawson, L. E. (1987). Modified extraction 2-thiobarbituric acid method for measuring lipid oxidation in poultry. Poultry Science, 66, 1483−1489. Shahidi, F., Pegg, R. B., & Shamsuzzaman, K. (1991). Color and oxidative stability of nitritefree cured meat after gamma irradiation. Journal of Food Science, 56, 1450−1452. Shenoy, K., Murano, E. A., & Olson, D. G. (1998). Survival of heat-shocked Yersinia enterocolitica after irradiation in ground pork. International Journal Of Food Microbiology, 39, 133−137. Sorheim, O., Nessen, H., & Nesbakken, T. (1999). The storage life of beef and pork packaged in an atmosphere with low carbon monoxide and high carbon dioxide. Meat Science, 52, 157−164. SPSS (1999). SPSS Base 10.0. User manual: Application guide. Republic of Ireland. Thakur, B. R., & Singh, R. K. (1994). Food irradiation. Chemistry and applications. Food Review International, 10, 437−473.
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Innovative Food Science and Emerging Technologies j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i f s e t
Decolouration and lipid oxidation changes of vacuum-packed Iberian dry-cured loin treated with E-beam irradiation (5 kGy and 10 kGy) during refrigerated storage Ramón Cava a,⁎, Ruth Tárrega b, Rosario Ramírez c, Juan Atanasio Carrasco b a b c
Tecnología de los Alimentos, Facultad de Veterinaria, Campus Universitario, Universidad de Extremadura, 10071 Cáceres, Spain Departamento de Ingeniería, Instituto del Frío, Consejo Superior de Investigaciones Científicas, Ciudad Universitaria, 28040 Madrid, Spain Instituto Tecnológico Agroalimentario de Extremadura (INTAEX), Carretera de San Vicente sn. 06071 Badajoz, Spain
a r t i c l e
i n f o
Article history: Received 26 November 2008 Accepted 20 April 2009 Editor Proof Receive Date 1 May 2009 Keywords: Iberian dry-cured loin Feeding regime Irradiation Refrigerated storage Colour TBA-RS Hexanal
a b s t r a c t The effect of irradiation (0, 5 and 10 kGy) on the oxidative and colour stability of vacuum-packed Iberian drycured loin slices from pigs fed on concentrate feed (CON) or free-range reared (FRG) stored under refrigerated storage was studied. Irradiation treatment increased lipid oxidation, measured as TBA-RS values and hexanal content of dry-cured loins. It also increased redness (CIE a⁎) and lightness (CIE L⁎) of dry-cured loins. Refrigerated storage reduced the differences due to irradiation treatment of instrumental colour values like lightness. However, the decrease of redness during storage was more marked in irradiated than in nonirradiated dry-cured loin. Storage increased differences in TBA-RS values between irradiated and nonirradiated FRG dry-cured loin, while the opposite trend was found for CON dry-cured loins. In addition, no differences in the hexanal content were found after 30 days of refrigerated storage. Therefore, the storage of Iberian dry-cured loin in absence of oxygen by using a vacuum packaging could be an adequate method to reduce changes associated to irradiation treatment in Iberian dry-cured loin. Industrial relevance: Iberian dry-cured loin is a high sensory quality meat product with increasing projection in external markets Irradiation has shown to be an effective method to control pathogen and spoilage microorganisms in meat and meat products. However, e-beam irradiation can promote colour and oxidation changes that could modify their sensory characteristics. The study aimed the evaluation of e-beam irradiation at two levels (5 and 10 kGy) — higher doses than those that could be necessary to control pathogen microorganisms in this kind of product — on colour changes and lipid oxidation at vacuum-packed slices of Iberian dry-cured loin during subsequent extended chilled storage. E-beam treatment induced changes in colour and lipid oxidation in sliced Iberian dry-cured loin immediately after treatment and subsequent refrigerated storage. © 2009 Elsevier Ltd. All rights reserved.
1. Introduction Irradiation is the most effective technology in reducing pathogens in meat and meat based products. In addition, irradiation can be performed at ambient or lower temperatures which guarantee better preservation of nutritive values and physical–chemical properties of foods. Such advantages make irradiation treatment a viable technology for preservation of food products (O'Bryan, Crandall, Ricke, Olson et al., 2008). However, consumer awareness of food irradiation, in general, is very low, as majority of consumers are uncertain about the safety of irradiated foods.
⁎ Corresponding author. Tecnología de los Alimentos, Facultad de Veterinaria, Universidad de Extremadura, Cáceres 10071, Spain. Tel.: +34 927 257 169; fax: +34 927 257 110. E-mail address: [email protected] (R. Cava). 1466-8564/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.ifset.2009.04.006
Several papers have pointed out that doses lower than 10 kGy control the growth of pathogenic and spoilage bacteria on meat and meat products, such as Listeria monocytogenes, Salmonella typhimurium, Escherichia coli O157:H7 and Yersinia enterocolitica (Fu, Sebranek, & Murano, 1995; Shenoy, Murano, & Olson, 1998; Olson, 1998). However, meats are generally susceptible to oxidative deterioration principally due to the oxidation of polyunsaturated fatty acids present in phospholipids. Irradiation enhances free radical reactions resulting in the possibility of colour changes, lipid oxidation and odour generation, which can generate negative consumer responses to this quality deterioration (Patterson & Stevenson, 1995; Ahn, Jo, & Olson, 2000; Jo & Ahn, 2000; Du, Hur, & Ahn, 2002). In addition, storage could increase irradiation effect, as it can promote lipid oxidation, particularly during post-irradiation storage. Free radicals generated from radiolysis of water, such as hydroxyl radicals (OH), hydrated electrons and H+ (Merrit, Angelini, & Grahm, 1978) attack food components (proteins, amino acids, lipids etc.), leading to an increased rate of lipid oxidation. These free radicals appear in aqueous systems (Thakur & Singh, 1994) and also
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in meat, because over the 75% of muscle cells are composed of water and are surrounded by lipid bilayers. These are very prone to free-radical attack as a result of their high content of phospholipids rich in polyunsaturated fatty acids highly susceptible to lipid peroxidation (Pikul, Leszczynski, & Kummerow, 1984; Buckley et al., 1989). Irradiation has been reported to increase 2-thiobarbituric acid-reactive substances (TBA-RS) in different meat species, packaging and storage conditions (Hampson, Fox, Lakritz, & Thayer, 1996; Ahn et al., 1997; Du, Ahn, Nam, & Sell, 2000). In addition, previous studies have shown that irradiation can induce oxidative deterioration of fatty acids and consequently generate offflavours that comprise consumer's acceptability. Unsaturated lipidderived aldehydes, and especially hexanal, are the major volatile compounds related to oxidative changes in meat and meat products. However, irradiation can induce the development of off-odours at high doses for certain products. Previous studies (Carrasco, Tárrega, Ramírez, Mingoarranz, & Cava, 2005) in dry-cured loin showed that irradiation increased hexanal content, the main lipid oxidation derived aroma volatile compound which level could increase during storage and as a consequence reduce consumer's acceptability of these products. On the other hand, discoloration processes and lipid oxidation phenomena are close related due to the fact that the oxidation processes of muscle pigments can catalyze the oxidation of lipids (Akamittath, Brekke, & Schanus, 1990). Free radicals generated by irradiation can also react with myoglobin or haemoglobin and modify colour of irradiated samples (Kamarei, Karel, & Weirbicki, 1979; Jo, Jin, & Ahn, 2000). Meat and meat products colour is an important quality attribute that influences consumer acceptance of the meat, as they prefer bright-red fresh meats, brown-grey cooked meats, and pink cured meats (Cornforht, 1994). The mechanisms of lipid oxidation in irradiated meat are not fully understood, but they are likely to proceed via traditional pathways. Therefore, the susceptibility of irradiated muscle tissues to lipid oxidation and the intensity of the changes depends on i. endogenous characteristics of the tissue including the fat content, the fatty acid profile, the composition of phospholipids in cell membrane, antioxidant concentrations in muscle as well as ii. exogenous characteristics such as the irradiation dose level, packaging and storage conditions (Gray, Gomaa, & Buckley, 1996; Ahn et al., 1997; Morrissey, Brandon, Buckley, Sheehy, & Frigg, 1997; Ahn, Olson, Jo, Love, & Jin, 1999; Nanke, Sebranek, & Olson, 1998). Iberian dry-cured loin is a meat product with a high consumer acceptance due to its particular sensory characteristics derived both from raw meat composition (high intramuscular fat and oleic acid contents) and the physical, chemical and biochemical changes that take place during ripening period. The main factors affecting sensory quality of Iberian dry-cured meat products are the characteristics of the pigs fattening phase, either rising in free-range rearing and fed on acorns and pasture or reared in confinement with concentrate feeds. These factors modify the intramuscular fat content, fatty acid profiles of intramuscular lipid fractions and muscle antioxidant contents (Cava et al., 1997; Cava, Ruiz, Ventanas, & Antequera, 1999a). Although irradiation could have great importance for meat industry, only there are a few studies about the impact of irradiation on the quality of dry-cured meat products (Carrasco et al., 2005; Cava, Tárrega, Ramírez, Mingoarranz, & Carrasco, 2005) whereas no information about quality changes of irradiated dry-cured meat products under storage is available. However, nowadays it is important for industry to offer drycured meat products microbiologically safe and with longer shelf-life, which could favour the commercialization of these products. Therefore, the objective of the present study was to investigate the effect of different ionization doses (5 kGy and 10 kGy) on instrumental colour, lipid oxidation and hexanal changes of vacuum-packaged slices of Iberian dry-cured loins from free-range reared pigs and intensively reared pigs under refrigerated storage.
2. Material and methods 2.1. Dry-cured loin samples Iberian dry-cured loins from pigs fed on concentrate (CON) and free-range reared (FRG) were used for the experiment. FRG pigs were reared outdoors and exclusively fed on available acorns and pasture. Regarding loins manufacture, they were seasoned by rubbing a mixture of salt, nitrite, olive oil and spices such as Spanish paprika (Capsicum annuum, L.), oregano (Origanum vulgare L.) and garlic (Altium sativum, L.). Loins were kept at 4 °C for some days to allow the seasoning mixture to penetrate. Then, loins were stuffed into collagen casings and held at low temperature and high relative humidity which was increased at the end of the ripening. Before packaging, dry-cured loins were liberated of casings and sliced using a slicing machine to give 3 mm thick slices. 2.2. Vacuum-packaging, irradiation treatment and refrigerated storage Dry-cured loin slices were vacuum-packaged in nylon/polyethylene bags (9.3 ml O2/m2/24 h a 0 °C) containing 5 slices/pack. Dry-cured loin slices were irradiated at 0, 5 and 10 kGy dose (IONMED Esterilización, S. A. Cuenca, Spain) using an Electron Beam irradiator (Rhodotron TT200, IBA, Louvain La Neuve, Belgium) with a 10 MeV energy level, a 10 kW power level, and an average 98 kGy/min dose rate after storage overnight in a 4 °C cooler. The irradiation process was conducted at room temperature (~20 °C) with single layer display and single-sided dosage. The samples were returned to the refrigerator immediately after irradiation. To confirm the target dose, 2 alanine dosimeters per cart were attached to the top and bottom surfaces of the sample. The alanine dosimeter was read using a 104 Electron Paramagnetic Resonance instrument (Bruker Instruments Inc., Billerica, MA). The final doses were 5.21 ± 0.32 kGy for 5 kGy and 10.47 ± 0.65 for 10 kGy treatments. Irradiated samples were stored at 4 °C in darkness before colour measurement and stored at −80 °C until TBA-RS and hexanal content determinations. After irradiation treatment, packages with samples were stored under refrigeration at +4 °C in the darkness for 0, 30, 60 and 90 days. 2.3. Physical–chemical analysis 2.3.1. Instrumental colour Colour measurements were taken immediately after opening the package (in order to prevent colour degradation as a result of light and oxygen) in accordance with the recommendations on colour determination of the American Meat Science Association (Hunt et al., 1991). The following colour coordinates were measured: lightness (L⁎), redness (a⁎, red ± green) and yellowness (b⁎, yellow ± blue). Colour parameters were determined using a Minolta CR-300 colorimeter (Minolta Camera, Osaka, Japan) with illuminant D65, a 0° standard observer and a 2.5 cm port/viewing area. The colorimeter was standardized before use with a white tile. The measurement was repeated on eight randomly selected locations on each loin slice and averaged for statistical analysis. 2.3.2. Lipid oxidation Lipid oxidation was measured using a complete dry-cured loin slice and homogenised using a kitchen blender. The extent of lipid oxidation was estimated as TBA-RS using a modified version of Salih, Smith, Price, & Dawson (1987) method. TBA-RS were measured on two slices from each pack and were expressed as mg malondialdehyde (MDA)/kg meat. 2.3.3. Hexanal content Hexanal content was assessed according to Carrasco et al. (2005). A Solid Phase Micro Extraction, SPME (Supelco Co., Bellefonte, PA) fibre
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(10 mm length) coated with DVB/Carboxen/PDMS (50/30 µm thickness) was used for the determination of hexanal content of the samples. Prior to analysis the SPME fibre was preconditioned at 280 °C for 1 h in the GC injection port. For HS-SPME extraction, loin slices were grounded with a commercial grinder. 0.5 g were weighed into a 10 ml screwcapped vial containing 3 ml of distilled water and 2 g of sodium chloride, the mixture was homogenized at 3000 rpm for 2 min. The fibre was inserted into the sample vial through the septum and then exposed to headspace. The extractions were carried out in an oven to ensure a homogeneous temperature for sample and headspace. The extraction was performed at 50 °C for 30 min. Before extraction, samples were equilibrated for 15 min at the same temperature used for extraction. Analyses were performed in an Agilent Technologies series 6890, mod. G1530A gas chromatograph coupled to a mass selective detector (Agilent 5973N MSD, mod. G2577A). Volatiles were separated using a 5% phenyl–methyl silicone (HP-5) bonded-phase fused silica capillary column (Hewlett-Packard, 50 m × 0.32 mm i.d., film thickness 1.05 µm), operating at 5 psi of column head pressure, resulting in a flow of 1.3 ml min− 1 at 40 °C. The injection port was in a splitless mode. The temperature program was isothermal for 10 min at 40 °C, raised to 200 °C at a rate of 5 °C min− 1, and then raised to 250 °C at a rate of 20 °C min− 1, and held for 5 min. The transfer line to the mass spectrometer (MS) was maintained at 280 °C. The mass spectra were obtained using a mass selective detector (Hewlett-Packard HP-5971 A) by electronic impact at 70 eV, a multiplier voltage of 1753 V, and collecting data at a rate of 2.83 scan s− 1 over the m/z range of 30 to 550. Hexanal was tentatively identified by comparing its mass spectra with the contained in the NIST/EPA/NIH and Wiley libraries and by comparison of Kovats index with that reported in the literature. The quantification of the hexanal content was performed using an external standard. 2.4. Statistical analysis Samples from the two types of loins, free-range reared and concentrate fed pigs, were randomly assigned to the treatments. There were five replicates per dose and day of storage. The effect of dose and day of storage and the interaction between irradiation and day of storage of each type of dry-cured loin was analyzed using the General Linear Model procedure of SPSS (ANOVA), version 10.0 (SPSS, 1999). Means were used to compare differences between treatments. Tukey's test was used to compare the mean values of the treatments and storage time. Mean values and standard errors of the means (SEM) were reported. Pearson's correlation coefficients were also calculated. 3. Results and discussion 3.1. Lipid oxidation Irradiation significantly increased lipid oxidation, measured as TBA-RS values in both sets of vacuum-packed Iberian dry-cured loin slices (Table 1) immediately after irradiation (day 0). Irradiation increased TBA-RS in a dose-dependent fashion, so samples irradiated at 10 kGy had higher TBA-RS values than those irradiated at 5 kGy or the non-irradiated control. TBA-RS increased linearly with irradiation dose (r = + 0.64, p b 0.001). The prooxidant effect of irradiation and the dose dependent effect on lipid oxidation have been widely reported in different meat and meat products (Hampson et al., 1996; Luchsinger et al., 1996; Ahn et al., 1998; Ahn et al., 1999). TBA-RS values showed small changes during refrigerated storage. The evolution of TBA-RS values in CON and FRG samples showed great differences, while in CON samples TBA-RS decreased in irradiated and non-irradiated samples in FRG samples irradiation at 10 kGy increased TBA-RS values. FRG irradiated samples showed higher TBA-RS values (p b 0.05) at day 30 than those non irradiated and at the end of refrigerated storage FRG samples treated at 10 kGy had the highest
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Table 1 Thiobarbituric acid-reactive substances (TBA-RS, measured as mg MDA/kg meat) of vacuum-packed Iberian dry-cured loin slices stored for 90 days after irradiating. SEMa Concentrate (CON)
Type of loin
Free-range (FRG)
Dose
Control
5 kGy 10 kGy
0.44 b x 0.34 b y 0.38 xy 0.40 b xy 0.01
0.50 a 0.48 a 0.52 0.67 b 0.04
SEMa
Control
5 kGy
10 kGy
0.33 c x 0.35 b x 0.19 c z 0.26 c y 0.02
0.39 0.29 0.25 0.32 0.01
0.52 a w 0.44 a x 0.32 a z 0.39 a y 0.02
Days of storage 0 30 60 90 SEMb
0.52 a y 0.49 a y 0.52 y 1.00 a x 0.08
0.01 0.03 0.03 0.10
bx cy bz by
0.02 0.02 0.02 0.01
Means with a different letter (a,b,c) within a row of the same type of loin and the same day of storage are different (p b 0.05). Means with a different letter (x,y,z) within a column of the same irradiation dose are different (p b 0.05). a SEM: Standard error of the means among the same irradiation dose (n = 15). b SEM: Standard error of the means among the same storage day (n = 20).
TBA-RS values (p b 0.05). These results indicate a prooxidant effect of irradiation at 10 kGy on the oxidative stability of FRG dry-cured loins during refrigerated storage. In contrast, in CON samples TBA-RS values decreased significantly during storage (p b 0.05) although differences among treated and non-treated samples immediately after irradiation maintained during storage. Non-irradiated samples showed significantly (p b 0.05) lower TBA-RS values than those irradiated at 5 kGy and 10 kGy and TBA-RS in irradiated samples were dose-dependent and increase with the dose of irradiation. In general, it is known that irradiation induces lipid oxidation and oxidation progresses during storage (Kanatt, Paul, D'Souza, & Thomas, 1998), which is in contrast with our findings in dry-cured Iberian loin. Regarding differences in the pattern of formation of TBA-RS in FRG and CON samples during storage, these could be attributable to distinct characteristics of the raw material for the manufacture of dry-cured loins such as intramuscular fat content, fatty acid profiles, haem pigments, initial lipid oxidation levels and muscle antioxidant contents (Cava, Ruiz, Tejeda, Ventanas, & Antequera, 2000; Cava, Estévez, Morcuende, & Antequera, 2003). 3.2. Hexanal content Changes in hexanal content of both sets of vacuum-packed Iberian dry-cured loin slices during refrigerated storage are shown in Table 2. Hexanal contents of vacuum-packed dry-cured loin slices increased in a dose-dependent fashion immediately after irradiation (day 0). Irradiation doses at 5 and 10 kGy promoted production of hexanal in a different extent in CON and FRG dry-cured loin, being the rate of formation of hexanal much higher in FRG samples than in CON samples. We presume that the possible higher intramuscular fat content of FRG samples (data not shown) could have been a contributing factor for its high hexanal formation immediately after irradiation. Findings regarding hexanal content agree with results previously reported for TBA-RS, as evidenced the positive Pearson's correlation coefficient found between TBA-RS and hexanal contents (r = +0.40, p b 0.01). This close relationship between these two lipid oxidation indicators has been previously described in meat and meat products (Ang & Lyon, 1990; Ahn et al., 1999). In contrast to reported for TBA-RS, the changes occurring during storage were different from those occurring immediately after irradiation. Hexanal contents decreased or remained unchanged during refrigerated storage in the two sets of dry-cured loins. At the end of refrigerated storage, hexanal content reductions were more marked in FRG samples than in CON ones. In FRG samples, no significant differences (p N 0.05) were found as a result of irradiation treatment or dose of
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Table 2 Hexanal contents (µg hexanal/g sample) of vacuum-packaged Iberian dry-cured loin slices stored for different periods of time after irradiating. SEMa Concentrate (CON)
Type of loin
Free-range (FRG)
Dose
Control 5 kGy
10 kGy
2.6 b x 0.9 y 2.3 xy 1.8 xy 0.3
12.0 a x 1.6 y 1.7 y 3.4 y 1.1
Control 5 kGy
10 kGy
3.9 b 5.0 ab 1.2 b 2.1 0.7
8.5 a x 2.8 b y 2.1 a y 2.9 y 0.7
SEMb
Days of storage 0 30 60 90 SEMb
10.0 a x 1.9 y 3.4 y 3.1 y 0.8
1.3 0.3 0.3 0.4
4.0 b y 8.6 a x 2.1 a y 3.4 y 0.6
0.7 1.0 0.2 0.3
Means with a different letter (a,b,c) within a row of the same type of loin and the same day of storage are different (p b 0.05). Means with a different letter (x,y,z) within a column of the same irradiation dose are different (p b 0.05). a SEM: Standard error of the means among the same irradiation dose (n = 15). b SEM: Standard error of the means among the same storage day (n = 20).
irradiation at days 30, 60 and 90 of refrigerated storage, although hexanal contents tended to be higher in irradiated samples. A similar trend as that reported for FRG samples was found in CON samples. Hexanal contents in refrigerated samples decreased in comparison with hexanal contents found immediately after irradiation. No differences were found in refrigerated samples as a result of irradiation dose, and only at day 60 irradiated samples showed significantly higher (p b 0.05) hexanal contents than control ones. Scientific literature concerning changes in volatile compounds of sliced Iberian dry-cured loin during storage is not available and no information about the effect of raw material on the evolution of lipid-derived aldehydes in sliced vacuum packaged can be found. However, the different trend of hexanal content observed in the two sets of samples during storage could be related to the chemical characteristics of both types of loins such as: i. intramuscular fat content (Cava et al., 1999a), ii. fatty acids composition of total lipids and lipid fractions (Cava, Ruiz, Ventanas, & Antequera, 1999b) and/or iii. endogenous antioxidant contents and prooxidant/ antioxidant balance (Cava et al., 2000). Similar results were found by Shahidi, Pegg, and Shamsuzzaman (1991), who observed that the hexanal contents declined markedly upon extended storage of meat. They indicated that the reactions of hexanal with meat components or its further oxidation to hexanoic acid were responsible for the reduction of hexanal in meat during storage. Jo, Ahn, and Byun (2002) found that the hexanal content decreased during storage in irradiated vacuum-packed sausages while it increased in the non-vacuum packed. Therefore, agreeing with that previously reported for TBA-RS values, maybe the presence of oxygen affects the formation of hexanal in irradiated meat products. It is probable that the vacuumpacked storage of irradiated dry-cured meat products could be effective to stop degradation processes related to lipid oxidation. The mechanisms of volatile production in irradiated meats are not fully understood, but several previous researches suggested that the radiolytic products of proteins as well as the lipid oxidation by-products as a result of oxidation processes are responsible for the off-odour in irradiated meats (Ang & Lyon,1990; Lefebvren, Thibault, Charbonneau, & Piette,1994; Patterson & Stevenson, 1995; Hashim, Resurreccion, & MacWatters, 1995; Hampson et al.,1996; Ahn et al.,1997,1998; Ahn, Jo, Du, Olson, & Nam, 2000). In this respect, in dry-cured meat products high levels of hexanal are generally associated with rancid and undesirable flavours (Cava et al., 1999a). Instead, further knowledge of hexanal changes in irradiated dry-cured loin is necessary to elucidate the effect of irradiation on its flavour.
3.3. Surface instrumental colour Changes in instrumental colour parameters (CIE L⁎, a⁎, b⁎) of both sets of Iberian dry-cured loin slices during refrigerated storage are shown in Table 3.
Colour changes of vacuum-packed Iberian dry-cured loin slices were dose-dependent immediately after irradiation (day 0). Lightness (L⁎value) decreased with irradiation dose while redness (a⁎-value) increased in irradiated samples compared to control samples in both sets of dry-cured loins. Results are in agreement with previous findings in dry-cured ham (Cava et al., 2005) as well as in uncured raw and cooked meats (Luchsinger et al., 1996; Millar, Moss, & Stevenson, 2000; Nam & Ahn, 2002). Nam and Ahn (2002) attributed the red colour increase in irradiated turkey meat to the formation of carbon monoxide– myoglobin (CO–Mb) complexes. Compared with oxymyoglobin, CO–Mb complex is not easily oxidized to brown metmyoglobin, because of the strong binding of CO to the iron-porphyrin in myoglobin molecule (Sorheim, Nessen, & Nesbakken, 1999). However, the effects of irradiation and the causes of colour changes in dry-cured products are not well established. Other factors could be implicated in the reported changes in redness of dry-cured meat products, in which nitrosylmyoglobin is the predominant haem pigment. In this sense, previous studies have reported that nitrite inhibited the changes in colour due to irradiation (Fan, Sommers, Kimberly, & Sokorai, 2004). Storage tended to decrease the lightness and the redness of Iberian dry-cured loin slices while the yellowness tended to increase, especially in CON samples. After 90 days of refrigerated storage, irradiated drycured loins of both sets of sliced loins had significantly lower (p b 0.05) L⁎-values and a⁎-values than those non-irradiated. Additionally, at day 90 irradiated FRG dry-cured loin had significantly lower (p b 0.05) CIE b⁎-values, while this trend was not found for CON loins. So, the increase in CIE a⁎ in Iberian dry-cured loin slices as a consequence of irradiation was lessened during storage, so at the end of the refrigeration period the redness of the irradiated dry-cured loins was lower than the control ones. Results suggest that the increase in redness immediately after irradiation seems to be reversible phenomena, at least in cured meat that makes the pigment formed more easily oxidized during storage. By contrast, Nam and Ahn (2002) found an increase of redness
Table 3 Colour surface of vacuum-packaged Iberian dry-cured loin slices stored for different periods of time after irradiating. SEMa Concentrate (CON)
Type of Free-range (FRG) loin Dose
Control
5 kGy
10 kGy
40.0 a x 38.8 b y 35.6 b yz 34.9 b z 0.61
34.6 b 34.1 c 33.7 c 33.4 c 0.22
a⁎-value 0 24.3 b 30 23.8 b 60 24.8 90 26.3 a SEM 0.41
28.7 a x 26.7 a x 23.6 y 23.1 b y 0.58
b⁎-value 0 14.0 y 30 14.7 a xy 60 15.5 a x 90 15.1 a xy SEMb 0.21
14.9 x 14.3 a xy 13.3 b xy 11.7 b y 0.43
SEMa
Control
5 kGy
10 kGy
0.73 0.79 0.79 0.62
43.3 b y 46.0 a x 44.6 a xy 44.8 a xy 0.29
46.9 a x 44.9 a xy 43.3 a yz 42.1 b z 0.47
42.3 b 42.2 b 42.1 b 43.0 b 0.19
0.60 0.51 0.34 0.35
30.5 a x 26.9 a y 24.2 z 23.1 b z 0.69
0.77 0.54 0.27 0.52
24.4 b y 25.7 a x 24.2 a y 23.5 a y 0.22
24.0 b xy 24.9 ab x 22.5 b y 20.3 b z 0.45
26.6 a x 23.3 b y 20.8 c xy 18.3 c z 0.78
0.39 0.40 0.47 0.64
12.2 11.9 b 11.4 b 13.1 b 0.25
0.36 0.45 0.56 0.46
14.8 b y 19.8 a x 17.3 xy 19.8 x 0.61
17.1 a z 18.2 b y 19.1 xy 19.6 x 0.25
16.3 a y 17.0 b y 17.7 y 19.6 x 0.33
0.30 0.37 0.49 0.25
Days of storage L⁎-value 0 40.7 30 40.8 60 40.2 90 38.5 SEMb 0.26
ax ax ax ay
Means with a different letter (a,b,c) within a row of the same type of loin and the same day of storage are different (p b 0.05). Means with a different letter (x,y,z) within a column of the same irradiation dose are different (p b 0.05). a SEM: Standard error of the means among the same irradiation dose (n = 15). b SEM: Standard error of the means among the same storage day (n = 20).
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after 10 days of storage in irradiated vacuum packaged raw turkey breast. No explanation has been found in the literature for CIE a⁎-value decrease in irradiated meat during refrigerated storage. It is possible that nitrite could have played an important role in the colour evolution and its effect needs to be elucidated in future researches In addition, intrinsic characteristics of dry-cured loins (pH, moisture, fat, NaCl content, Aw, fatty acid profiles etc.) are important factors that could influence the intensity of the changes due to irradiation. Therefore, future studies are necessary to elucidate their effects since few papers in the literature deal with irradiation consequences in cured meat products quality. 4. Conclusions Irradiation at doses of 5 kGy and 10 kGy induced changes in colour and lipid oxidation of dry-cured Iberian loin slices immediately after irradiation and affected the evolution of instrumental colour, TBA-RS values and hexanal contents during refrigerated storage. These changes could induce undesirable effects that compromise the quality of the irradiated products. In the case that irradiation doses necessary to eliminate the risk of pathogens in sliced dry-cured loin were lower than those used in this study, changes in colour and lipid oxidation after irradiation could be less marked than those described in the present paper as changes are directly related to the dose of irradiation. Acknowledgements Authors want to thank Inmaculada Linares and José Navarro for their technical assistance. References Ahn, D. U., Jo, C., Du, M., Olson, D. G., & Nam, K. C. (2000). Quality characteristics of pork patties irradiated and stored in different packaging and storage conditions. Meat Science, 56, 203−209. Ahn, D. U., Jo, C., & Olson, D. G. (2000). Analysis of volatile components and the sensory characteristics of irradiated raw pork. Meat Science, 54, 209−215. Ahn, D. U., Olson, D. G., Jo, C., Chen, X., Wu, C., & Lee, J. I. (1998). Effect of muscle type, packaging, and irradiation on lipid oxidation, volatile production and colour in raw pork patties. Meat Science, 49, 37−39. Ahn, D. U., Olson, D. G., Jo, C., Love, J., & Jin, S. K. (1999). Volatiles production and lipid oxidation on irradiated cooked sausage as related to packaging and storage. Journal of Food Science, 64, 226−229. Ahn, D. U., Sell, J. L., Jeffery, M., Jo, C., Chen, X., Wu, C., et al. (1997). Dietary vitamin E affects lipid oxidation and total volatiles of irradiated raw turkey meat. Journal of Food Science, 62, 954−958. Akamittath, J. G., Brekke, C. J., & Schanus, E. G. (1990). Lipid oxidation and colour stability in restructured meat systems during frozen storage. Journal of Food Science, 55, 1513−1517. Ang, C. Y. W., & Lyon, B. G. (1990). Evaluation of warmed-over flavour during chill storage of cooked broiler breast, thigh and skin by chemical, instrumental and sensory methods.Journal of Food Science, 55, 644−648 673. Buckley, D. J., Gray, J. I., Ashgar, A., Price, J. F., Crackle, R. L., Booren, A. M., et al. (1989). Effects of dietary antioxidants and oxidized oil on membranal lipid stability and pork product quality. Journal of Food Science, 54, 1193−1197. Carrasco, A., Tárrega, R., Ramírez, M. R., Mingoarranz, F. J., & Cava, R. (2005). Colour and lipid oxidation changes in dry-cured loins from free-range reared and intensively reared pigs as affected by ionizing radiation dose level. Meat Science, 69, 609−615. Cava, R., Estévez, M., Morcuende, D., & Antequera, T. (2003). Evolution of fatty acids from intramuscular lipid fractions during ripening of Iberian hams as affected by αtocopheryl acetate supplementation in diet. Food Chemistry, 81, 199−207. Cava, R., Ruiz, J., López-Bote, C., Martín, García, C., Ventanas, J., et al. (1997). Influence of finishing diet on fatty acid profiles of intramuscular lipids, tryglicerides and phospholipids in muscles of the Iberian pig. Meat Science, 45, 263−270. Cava, R., Ruiz, J., Tejeda, J. F., Ventanas, J., & Antequera, T. (2000). Effect of free-range rearing and α-tocopherol and copper suplementation on fatty acid profiles and susceptibility to lipid oxidation of fresh meat from Iberian pigs. Food Chemistry, 68, 51−59. Cava, R., Ruiz, J., Ventanas, J., & Antequera, T. (1999). Oxidative and lipolytic changes during ripening of Iberian hams as affected by feeding regime: Extensive feeding and alpha-tocopheryl acetate supplementation. Meat Science, 52, 165−172. Cava, R., Ruiz, J., Ventanas, J., & Antequera, T. (1999). Effect of alpha-tocopheryl acetate supplementation and extensive feeding of the pigs on the evolution of volatile aldehydes during the processing of Iberian ham. Food Science and Technology International, 5, 235−241.
499
Cava, R., Tárrega, R., Ramirez, M. R., Mingoarranz, F. J., & Carrasco, A. (2005). Effect of irradiation on colour and lipid oxidation of dry-cured hams from free-range reared and intensively reared pigs. Innovative Food Science and Emerging Technologies, 6, 135−141. Cornforht, D. (1994). Colour — Its basis and importance. In A. M. Pearson & T. R. Dutson (Eds.), Quality attributes and their measurement in meat, poultry and fish productsAdvances in Meat Research Series, vol. 9. (pp. 34−78). Du, M., Ahn, D. U., Nam, K. C., & Sell, J. L. (2000). Influence of dietary conjugated linolenic acid on volatile profiles, colour and lipid oxidation of irradiated raw chicken meat. Meat Science, 56, 387−395. Du, M., Hur, S. J., & Ahn, D. U. (2002). Raw-meat packaging and storage affect the colour and odor of irradiated broiler breast fillets after cooking. Meat Science, 61, 49−54. Fan, X., Sommers, C. H., Kimberly, J. B., & Sokorai, B. J. (2004). Ionizing radiation and antioxidants affect volatile sulfur compounds, lipid oxidation, and color of readyto-eat turkey bologna. Journal of Agricultural and Food Chemistry, 52, 3509−3515. Fu, A. H., Sebranek, J. G., & Murano, E. A. (1995). Survival of Listeria monocytogenes, Yersinia enterocolitica and Escherichia coli O157:H7 and quality changes after irradiation of beef steaks and ground beef. Journal of Food Science, 60, 972−977. Gray, J. I., Gomaa, E. A., & Buckley, D. J. (1996). Oxidative quality and shelf life of meats. Meat Science, 43, S111−S123. Hampson, J. W., Fox, J. B., Lakritz, L., & Thayer, D. W. (1996). Effect of low dose gamma radiation on lipids in five different meats. Meat Science, 42, 271−276. Hashim, I. B., Resurreccion, A. V. A., & MacWatters, K. H. (1995). Disruptive sensory analysis of irradiated frozen or refrigerated chicken. Journal of Food Science, 60, 664−666. Hunt, M. C., Acton, J. C., Benedict, R. C., Calkins, C. R., Cornforth, D. P., Jeremiah, L. E., et al. (1991). AMSA guidelines for meat colour evaluation. Proceedings 44th Annual Reciprocal Meat Conference Chicago: National Livestock and Meat Board. Jo, C., & Ahn, D. U. (2000). Volatiles and oxidative changes in irradiated pork sausage with different fatty acid composition and tocopherol content. Journal of Food Science, 65, 270−275. Jo, C., Ahn, D. U., & Byun, M. W. (2002). Irradiation-induced oxidative changes and production of volatile compounds in sausages prepared with vitamin E-enriched commercial soybean oil. Food Chemistry, 76(3), 299−305. Jo, C., Jin, S. K., & Ahn, D. U. (2000). Color changes in irradiated cooked pork sausage with different fat sources and packaging during storage. Meat Science, 55, 107−113. Kamarei, A. R., Karel, M., & Weirbicki, E. (1979). Spectral studies on the role of ionising radiation in colour changes in radappertised beef. Journal of Food Science, 44, 25−32. Kanatt, S. R., Paul, P., D'Souza, S. F., & Thomas, P. (1998). Lipid peroxidation in chicken meat during chilled storage as affected by antioxidants combined with low-dose gamma irradiation. Journal of Food Science, 63, 386−389. Lefebvren, N., Thibault, C., Charbonneau, R., & Piette, J. P. (1994). Improvement of shelflife and wholesomeness of ground beef by irradiation. 2. Chemical analysis and sensory evaluation. Meat Science, 36, 371−380. Luchsinger, S. E., Kropf, D. H., García Zepeda, C. M., Hunt, M. C., Marsden, J. L., Rubio Canas, E. J., et al. (1996). Color and oxidative rancidity of gamma and electron beanirradiated boneless pork chops. Journal of Food Science, 61, 1000−1005. Merrit, C., Jr, Angelini, P., & Grahm, R. A. (1978). Effect of radiation parameters on the formation of radiolysis products in meat and meat substances. Journal of Agricultural and Food Chemistry, 26, 29−35. Millar, S. J., Moss, B. W., & Stevenson, M. H. (2000). The effect of ionising radiation on the colour of leg and breast of poultry meat. Meat Science, 55, 361−370. Morrissey, P. A., Brandon, S., Buckley, D. J., Sheehy, P. J. A., & Frigg, M. (1997). Tissue content of alpha-tocopherol and oxidative stability of broilers receiving dietary-tocopheryl acetate supplementation for various periods pre-slaughter. British Poultry Science, 38, 84−88. Nam, K. C., & Ahn, D. U. (2002). Carbon monoxide-heme pigment is responsible for the pink colour in irradiated raw turkey breast meat. Meat Science, 30, 25−33. Nanke, K. E., Sebranek, J. G., & Olson, D. G. (1998). Color characteristics of irradiated vacuum-packaged pork, beef and turkey. Journal of Food Science, 63, 1001−1006. O'Bryan, C. A., Crandall, P. G., Ricke, S. C., & Olson, D. G. (2008). Impact of irradiation on the safety and quality of poultry and meat products: A review. Critical Reviews in Food Science and Nutrition, 48, 442−457. Olson, D. G. (1998). Irradiation of food. Food Technology, 52, 56−62. Patterson, R. L. S., & Stevenson, M. H. (1995). Irradiation-induced off-odor in chicken and its possible control. British Poultry Science, 36, 425−441. Pikul, J., Leszczynski, D. E., & Kummerow, F. A. (1984). Relative role of phospholipids, triacylglycerols and cholesterol esters on malonaldehyde formation in fat extracted from chicken meat. Journal of Food Science, 49, 704−708. Salih, A. M., Smith, D. M., Price, J. F., & Dawson, L. E. (1987). Modified extraction 2-thiobarbituric acid method for measuring lipid oxidation in poultry. Poultry Science, 66, 1483−1489. Shahidi, F., Pegg, R. B., & Shamsuzzaman, K. (1991). Color and oxidative stability of nitritefree cured meat after gamma irradiation. Journal of Food Science, 56, 1450−1452. Shenoy, K., Murano, E. A., & Olson, D. G. (1998). Survival of heat-shocked Yersinia enterocolitica after irradiation in ground pork. International Journal Of Food Microbiology, 39, 133−137. Sorheim, O., Nessen, H., & Nesbakken, T. (1999). The storage life of beef and pork packaged in an atmosphere with low carbon monoxide and high carbon dioxide. Meat Science, 52, 157−164. SPSS (1999). SPSS Base 10.0. User manual: Application guide. Republic of Ireland. Thakur, B. R., & Singh, R. K. (1994). Food irradiation. Chemistry and applications. Food Review International, 10, 437−473.