Effects of low-level gamma irradiation on the characteristics of fermented pork sausage during storage

Radiation Physics and Chemistry 81 (2012) 466–472

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Effects of low-level gamma irradiation on the characteristics of fermented pork sausage during storage I.S. Kim a, C. Jo b, K.H. Lee c, E.J. Lee d, D.U. Ahn d, S.N. Kang a,n a

Department of Animal Resources Technology, Gyeongnam National University of Science and Technology, Gyeongnam 660-758, Republic of Korea Department of Animal Science and Biotechnology, Chungnam National University, Daejeon 305-764, Republic of Korea c Department of Food Science and Nutrition, Chungju National University, 368-701 Chungj, Republic of Korea d Department of Animal Science, Iowa State University, Ames, IA 50011-3150, USA b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 31 March 2011 Accepted 23 December 2011 Available online 5 January 2012

The effect of gamma irradiation (0.5, 1, 2, and 4 kGy) on the quality of vacuum-packaged dry fermented sausages during refrigerated storage was evaluated. At Day 0 of irradiation, the pH, redness (CIE an), yellowness (CIE bn), 2-thiobarbituric acid-reactive substances (TBARS) and volatile basic nitrogen (VBN) values of samples irradiated at 2 and 4 kGy were higher (p o 0.05), but the CIE Ln values (lightness) were lower than those of the non-irradiated control (po 0.05). Ato 1 kGy irradiation, however, the pH, CIE Ln, CIE an and CIE bn-value of samples were not significantly influenced by irradiation. The CIE an, and CIE bn-values of samples irradiated at 2 and 4 kGy decreased with the increase of storage time. The VBN, TBARS, and CIE Ln-values of samples irradiated at 4 kGy were not changed significantly during refrigerated storage for 90 days (p4 0.05). The total plate counts (TPC) and lactic acid bacteria (LAB) in the samples irradiated at 4 kGy were significantly lower (p o 0.01) than those with lower irradiation doses. At the end of storage, the TPC, coliform, and LAB in the samples were not increased after irradiation at 1, 0.5 and 1 kGy, respectively. TPC and LAB were not detected in samples irradiated at 4 kGy at Day 90. In addition, no coliform bacteria were found in samples irradiated at 1 kGy during refrigerated storage. Sensory evaluation indicated that the rancid flavor of samples irradiated at 4 kGy was significantly higher, but aroma and taste scores were lower than those of the control at Day 3 of storage. Irradiation of dry fermented sausages at 2 kGy was the best conditions to prolong the shelf-life and decrease the rancid flavor without significant quality deterioration. & 2011 Elsevier Ltd. All rights reserved.

Keywords: Fermented sausage Gamma irradiation Storage Lactic acid bacteria Lipid oxidation

1. Introduction Several methods, which include cooking, freezing, fermenting, salting, drying, and pickling (Choi et al., 2009; Jin et al., in press; Kang et al., 2002; Kim et al., 2009) have been used to reduce the number of microorganisms and increase the shelf-life and safety of meat (Farkas, 1998). One of the most promising approaches to improve microbial safety of meat, however, would be the use of low or medium-dose irradiation (1–10 kGy) (WHO, 1999). A number of investigators have shown that irradiation is very effective in controlling the growth of pathogenic and spoilage bacteria in meat (Grant and Patterson, 1991; Huhtanen et al., 1989; Patterson et al., 1993; Sommers et al., 2003; Thayer and Boyd, 1993; Thayer et al., 1990; Zhu et al., 2005). However, meat is generally susceptible to oxidative deterioration due to the oxidation of polyunsaturated fatty acids in phospholipids.

n

Corresponding author. Tel.: þ82 55 751 3288; fax: þ 82 55 751 3689. E-mail address: [email protected] (S.N. Kang).

0969-806X/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2011.12.037

Irradiation accelerates free radical reactions resulting in the possibility of color changes, lipid oxidation and odor generation, which may generate negative consumer responses (Ahn et al., 1997; Du et al., 2000; Jo and Ahn, 2000; Luchsinger et al., 1996; Patterson and Stevenson, 1995; Thayer and Boyd, 1993). Fermented sausages have a long tradition and have been originated from Mediterranean countries with a dry climate ¨ (Spain, Italy, France, Portugal and Turkey) (Lucke, 1985; PerezAlvarez et al., 1999). A mixture of comminuted lean meat (pork and/or beef), pork back fat, salt, curing agent (nitrate and/or nitrite), and spices with lactic acid starter culture is used to produce fermented sausages (Caplice and Fitzgerald, 1999). During fermentation, a slow but substantial heating takes place, which is very important for encouraging the growth of lactic acid bacteria (LAB) (Acton and Dick, 1977). These LAB, together with the lipolytic and protelytic enzymes (Olesen and Stahnke, 2000), determine the characteristics of the final product. At the end of the ripening process, fermented sausages are characterized with accentuated acidity, slight sourness, elastic, and semi-hard consistency (Comi et al., 2005; Houben and van’t Hooft, 2005).

I.S. Kim et al. / Radiation Physics and Chemistry 81 (2012) 466–472

Dry fermented sausages being relatively high fat foodstuffs and long period of manufacturing steps and post-fermentation storage, lipid oxidation can damage their sensorial properties, which are associated to rancid taste and odor (Ansorena and Astiasara´n, 2004). Numerous studies have been conducted to determine the impact of irradiation on meat quality (Badr, 1998; Brewer, 2009; Brewer, 2004; Hampson et al., 1996; Zhou et al., 2010), but little information on the quality changes of irradiated dry fermented meat products is available (Cava et al., 2009). The quality characteristics of irradiated fermented sausages would be very important for the acceptance of irradiation technology. Smith and Palumbo (1983) suggested that fermented sausages treated with irradiation induced the dominance of lactic acid bacteria (LAB) in the microflora to produce desirable flavor. However, consumer awareness of food irradiation, in general, is very low, as majority of consumers are uncertain about the safety of irradiated foods. Therefore, establishing optimum process conditions to minimize the negative effects of irradiation on lipid oxidation and LAB survival is critical to increase consumer acceptance of irradiated dry fermented sausage. The objective of this study was to investigate the effect of lowlevel gamma-irradiation (0.5, 1, 2 and 4 kGy) on the color, lipid oxidation, microbial counts, and sensory characteristics of vacuum-packaged dry fermented sausages during storage.

2. Materials and methods 2.1. Preparation of dry, fermented sausages Fresh boneless pork loin and backfat were ground separately in a mincer (Model 5K5SS, USA) equipped with an adjustable plate set with a hole diameter of 5 mm, and used to make sausages. Seasonings, additives, and a starter culture were added according to the following formula: (a) raw material (%, w/w): pork meat (86), pork backfat (9), NaCl (2.5), NaNO3 (0.012), NaNO2 (0.008), sodium ascorbate (0.25), glucose (0.3), sucrose (0.4), powdered black pepper (0.2), red pepper (0.2), garlic (0.5) and commercial seasoning (0.58), and mixed in a silent cutter (K15, Roman, Spain) for 3 min at 10 1C. Seasonings and additives were obtained from MSC Co., Ltd. (Seongnam, Korea). A commercially available frozen meat starter (Abiasa, Canada) (0.05%) consisting of Lactobacillus pentosus and Staphylococcus carnosus (C-P-77S Bactoferm TM, Chr. Inc., Hansen, Denmark) was added at a concentration of ca. 9 log CFU/g, according to the manufacturer’s instructions. All the sausages were manufactured at the same day, using the same technology, ingredients and formulation. The final mixture was stuffed into synthetic casings (4.5 mm diameter). The sausages were fermented in a ripening cabinet at 25 1C and 90% relative humidity (RH) for 24 h. Then, the temperature and RH were slowly reduced to reach 10 1C and 70% RH, respectively and ripened for 30 days. At the end of the ripening process, the final products were vacuum-packaged (0.5 cm3/m2/atm/24 h, Danisco Flexible Lyngby, Denmark) and stored at 4 1C for 3 days. The experiment was triplicated with 2 observations per replications. 2.2. Irradiation and storage conditions The vacuum-packaged sausages were irradiated at 0 (control), 0.5, 1, 2, and 4 kGy using a Co-60 gamma irradiator (point source, AECL, IR-79, MDS Nordion International Co., Ltd., Ottawa, Ontario, Canada) with the source strength of 100 kCi. The dosimetry was performed using 5 mm-diameter alanine dosimeters (Bruker Instruments, Rheinstetten, Germany), and the free radical signal

467

was measured using a Bruker EMS 104 EPR Analyzer. To confirm the target dose, alanine dosimeters attached to the top and bottom surfaces of the sample packs were read. The actual dose was within 72% of the target dose. The non-irradiated control was placed outside of the irradiation chamber to maintain the temperatures conditions as the irradiating ones. The control and irradiated samples were transferred to a 4 1C refrigerator and stored at 4 1C for 90 days. The quality (pH, color, lipid oxidation, volatile basic nitrogen, microbial) and sensory characteristics of the dry fermented sausages were determined after 1, 3, 30, 60, and 90 day of storage at 4 1C. 2.3. Quality evaluation The pH values were determined by homogenizing (T25B, IKA Sdn. Bhd., Malaysia) 10 g of a ground sample with 90 mL distilled water, and then measured with a pH meter (Model 8603, Metrohm, Swiss). For color measurements, sausages were cut into slices of 3 cmthickness and the surface color of the slices was measured three times for each sample using a spectrocolorimeter (CR 400, Minolta Co., Japan) (l ¼400–700 nm, Dl ¼10 nm, D65, 101) calibrated with a white plate and light trap supplied by the manufacturer. Color was expressed using the CIE Ln, an, bn color system (CIE, 1976). TBARS method (Tarladgis et al., 1960) was used to determine the degree of lipid oxidation in fermented sausages. A 5 g sample was homogenized in a 50 mL centrifuge tube with 50 mL of BHA (7.2% in ethanol) and 15 mL of distilled water using a homogenizer (IKA model T-25 Basic, Malaysia). 2 mL of the homogenate was mixed with 4 mL of thiobarbituric acid (TBA)/trichloroacetic acid (TCA) solution (20 mM TBA in 15% TCA), heated at 90 1C in water bath, cooled in ice and centrifuged for 15 min at 2,000 rpm (UNION 5KR; Hanil Science Industrial, Co. Ltd., Incheon, Korea). The absorbance of the supernatant was measured at 532 nm using a spectrophotometer (Spectronic model Genesys 5, USA). The concentration (mg malonaldehyde/kg sample on the basis of wet weight) was calculated using a standard curve prepared with 1,1,3,3 tetraethoxypropane (0–1.0 mM). Measurement of VBN in the sample was done according to the Conway micropipette diffusion method (Pearson, 1968). Each meat sample (3 g) was homogenized (T25B, IKA Sdn. Bhd., Malaysia) for 1 min with 25 mL distilled water, and then centrifuged (Hanil) at 13,000 rpm for 15 min. The supernatant was filtered using a filter paper (no. 1, Whatman), and the filtrate was placed in a test tube and made up to a final volume of 30 mL with distilled water. A volume of 0.01 N boric acid as a VBN absorber was placed in the inner section of a Conway micro-diffusion cell (Sibata Ltd. Tokyo, Japan). 1 mL sample solution and 1 mL saturated K2CO3 were also placed in the outer section of the same cell and the lid was immediately closed. Distilled water was used as blank. The cell was incubated at 37 1C for 120 min, and then titrated against 0.02 N sulfuric acid. The concentration of VBN was calculated as ammonia equivalent using the following equation: VBN value ðmg=100 g meatÞ ¼ ½0:28ðtitration volume of sample solution2titration volume of blankÞ10=100: For microbial analyses, duplicated samples (25 g for each) were taken aseptically from each treatment, transferred to sterile plastic pouches and homogenized for 2 min at room temperature with 225 mL sterile 0.88% (w/v) NaCl solution using a stomacher Lab-Blender 78860 (ST-Nom, Interscience, France). Appropriate dilutions of samples were prepared in sterile 0.88% (w/v) NaCl solution, plated in duplicate onto plate count agar (PCA; Difco Laboratory, Detroit, MI, USA) for total bacteria and incubated at

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32 1C for 48 h under anaerobic conditions. Lactic acid bacteria were incubated anaerobically on Lactobacilli MRS Agar (Difco) at 32 1C for 2 days. Coliforms were incubated on E. coli/coliform count plate petrifilm (3M Health care, Minnesota, USA) at 30 1C for 2 days under the same aerobic conditions. The sensory characteristics of the dry fermented sausages were assessed by 12 trained panelists. To acquaint panelists with product attributes and intensities, six 1 h training sessions were carried out over a week period prior to sample testing. During this phase, dry, fermented sausages from a variety of manufacturers corresponding to maximum and minimum intensities that might be found for each attribute (1, very low, to 6, very high) were presented to panelists. To test the panel reproducibility, one additional dry-fermented sausage was presented at each session. It was the replicate of the second sample of the set and was served as the last of the session. The panel sessions were held at mid-morning, about 3 h after breakfast. Slices (1.5 mm-thick) of the samples were prepared with a slicing machine (manufacturer, spec) and served to panelists on plates with random codes. The color, aroma, taste (1¼extremely undesirable, 6¼extremely desirable) and rancid flavor (1¼extremely low intensity, 6¼extremely high intensity) of the samples were evaluated using 6-point descriptive scale. Panelists were required to clean their palate between samples with water. Five samples were successively evaluated in each session at day 3, 60 and 90 of storage and the sample order was randomized within sessions. 2.4. Statistical analysis Whole experiment was conducted 3 times with 2 observations per each replication and the results were presented as a mean 7standard deviation. An analysis of variance were performed on all variables measured using the general linear model procedure of the SAS software (SAS, 2002). Duncan’s multiple range test was used to determine differences among treatment means (p o0.05).

sugars (dextrose and lactose) added in the meat to lactic acid ˆ 1985). Irradiation had no effects on the (Flores and Alvarruo~ Az, pH of the fermented sausages. 3.2. Color evaluation The color changes of the irradiated dry fermented sausages during storage are presented in Table 2. Color changes of dry fermented sausages were dose-dependent after irradiation (day 1). Lightness (Ln-value) decreased while redness (an-value) and yellowness (bn-values) increased with irradiation. These results are in agreement with previous findings in dry-cured ham (Cava et al., 2005, 2009) as well as uncured raw and cooked meat (Luchsinger et al., 1996; Millar et al., 2000; Nam and Ahn, 2002). Nam and Ahn (2002) attributed the red color 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 et al., 1999). After 90 day of refrigerated storage, irradiated dry fermented sausages had significantly lower (po0.01) CIE an- and CIE bnvalues than those of the non-irradiated ones, while this trend was not found in Ln-values. Storage tended to decrease the lightness of non-irradiated dry fermented sausages while redness and yellowness tended to increase. The effects of irradiation on the color changes in fermented sausages are not well established, but the fading of redness in the irradiated dry fermented sausages during storage could be related to the destruction of nitrosoheme pigment by irradiation process. The results suggested that the increase in redness and yellowness immediately after irradiation are a reversible phenomenon, and the cured meat pigment can also be oxidized during storage. Previous studies have reported that nitrite inhibited the changes in color by irradiation (Fan et al., 2004), but Cava et al. (2009) observed that the CIE an-values declined markedly upon extended storage of dry-cured ham.

3. Results and discussion

3.3. TBARS values

3.1. pH value

Irradiation increased the TBARS of dry fermented sausages in a dose-dependent manner at Days 1 and 30. The samples irradiated at 4 kGy had higher TBARS values than those irradiated at 0, 0.5, 1, or 2 kGy at Days 1 and 30 (0.52 and 0.45 mg MA/kg, respectively) (Table 3). These results are in agreement with previous findings in meat and meat products (Ahn et al., 1998, 1999; Hampson et al., 1996; Luchsinger et al., 1996). However, irradiation had no significant effects on the TBARS values of dry fermented sausages at Days 60 and 90 of storage. The initial TBARS values (day 1) of samples irradiated at 0, 0.5, and 1 kGy did not changed until Day 30, but increased at day 60 (p o0.01), indicating a slow development of lipid oxidation under refrigerated storage conditions. No significant changes in the TBARS values of dry fermented sausages irradiated at 2 and 4 kGy during refrigerated storage were observed after rapid increase of TBARS values at Day 1. In general, irradiation induces lipid oxidation and accelerates oxidative process during storage (Kanatt et al., 1998). However, Choi et al. (2009) observed the decrease of TBARS values in dry cured loin meat treated with electron beam irradiation (5 and 10 kGy) during refrigerated storage.

The pH changes of the irradiated dry, fermented sausages during refrigerated storage are presented in Table 1. Fermented sausages are characterized by low acidity and the final pH is in the range of 4.8–6.2 (Aymerich et al., 2003; Dirinck et al., 1997; Johansson et al., 1994; Sanchez-Molinero and Arnau, 2008). Regardless of irradiation treatments, the pH values of the dry, fermented sausages were in the range of 4.88 to 4.93 during the refrigerated storage. The observed low pH values of sausages were due to the activity of starter culture which metabolized

Table 1 pH values of vacuum-packaged dry fermented sausages stored for 90 days at 4 1C after irradiation. Dose (kGy)

0 0.5 1.0 2.0 4.0 n¼ 3.

Storage (day) 1

30

60

90

4.917 0.04 4.927 0.02 4.937 0.05 4.937 0.05 4.947 0.04

4.91 70.04 4.90 70.06 4.89 70.08 4.91 70.06 4.88 70.04

4.89 7 0.06 4.91 7 0.05 4.90 7 0.06 4.92 7 0.07 4.91 7 0.05

4.89 7 0.06 4.90 7 0.04 4.92 7 0.03 4.91 7 0.04 4.91 7 0.08

3.4. VBN values The VBN values of dry fermented sausages irradiated at 41 kGy were significantly higher than those of the 0.5 kGy and non-irradiated samples at Day 1 (p o0.01). The VBN values of

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Table 2 Effect of gamma irradiation on the CIE Ln, an, and bn-values of dry-fermented sausages during storage. Dose (kGy)

CIE Ln

0 0.5 1.0 2.0 4.0

Storage (day)

Sig.

1

30

60

90

44.607 0.36Aa 43.807 0.79ABa 43.707 0.56ABa 42.707 0.17BCab 41.67 70.85C

43.607 1.68ab 42.83 70.51ab 43.13 70.64a 43.23 70.64a 42.33 70.29

43.13 70.31ab 42.27 70.40bc 41.14 70.32b 41.907 0.95b 41.57 71.46

42.63 70.67b 41.607 0.35c 41.83 70.72b 41.63 70.35b 41.407 1.15

12.17 70.59ab 12.707 0.36 12.107 0.61 11.93 70.57b 11.037 0.50b

12.607 0.66Aa 12.107 0.79AB 12.107 0.66AB 10.937 0.51BCc 9.977 0.47Cc

13.077 0.67Aa 12.67 70.57A 12.57 70.38A 11.077 0.57Bc 9.607 1.06Cc

nn

nnn

6.207 0.44a 5.907 0.70 5.607 0.20 5.907 0.20a 5.807 0.36a

6.43 70.32Aa 6.007 0.32AB 5.67 70.26BC 5.077 0.32CDb 4.96 70.40Db

n nnn n

nn

Sig. n

CIE a

11.207 0.66Cb 12.41 70.22B 12.307 0.26B 13.37 70.21Aa 12.83 70.15Aa

0 0.5 1.0 2.0 4.0

nnn

Sig. CIE bn

5.407 0.10Cb 5.507 0.10C 5.777 0.35BC 5.937 0.15Ba 6.437 0.25Aa

0 0.5 1.0 2.0 4.0

5.637 0.21b 6.107 0.26 5.907 0.20 6.177 0.25a 6.107 0.26a

nnn

Sig.

n

nnn nnn

nn

nn nnn

nnn

n¼ 3. Sig. means Significance. a–d means with different letters within a row of the same irradiation dose are different (npo 0.05, nnp o0.01, nnnp o0.001). A–D means with different letters within a column of the same day of storage are different (nnp o 0.01, nnnp o 0.001).

Table 3 2-thiobarbituric acid-reactive substances (TBARS) of vacuum-packaged dry-fermented sausages stored for 90 days at 4 1C after gamma-irradiation (mg malondialdehyde/kg meat). Dose (kGy)

0 0.5 1.0 2.0 4.0 Sig.

Storage (day)

Sig.

1

30

60

90

0.337 0.05Db 0.417 0.03CBb 0.367 0.03Cc 0.457 0.01B 0.527 0.03A

0.367 0.01Bb 0.397 0.01Bb 0.367 0.03Bc 0.387 0.05B 0.457 0.04A

0.427 0.02a 0.477 0.03a 0.457 0.01b 0.437 0.04 0.467 0.03b

0.447 0.03a 0.497 0.01a 0.527 0.02a 0.457 0.01 0.497 0.04

nn

n

nn nn nn

n¼ 3. Sig. means Significance. a–c means with different letters within a rows of the same irradiation dose are different (nnp o 0.01). A–D means with different letters within a column of the same day of storage are different (np o 0.05, nnpo 0.01).

Table 4 Volatile basic nitrogen (VBN) of vacuum-packaged dry-fermented sausages stored for 90 days at 4 1C after gamma-irradiation (mg VBN/100 g meat). Dose (kGy)

0 0.5 1.0 2.0 4.0 Sig.

Storage (day)

Sig.

1

30

60

90

14.93 7 0.43Bd 14.93 7 0.43Bc 16.24 7 0.56Ac 17.08 7 0.28Ab 17.08 7 0.56A

16.05 70.43Bc 16.05 70.70Bbc 16.99 70.65ABc 16.80 70.56ABb 17.45 70.43A

19.60 7 0.28Ab 17.17 7 0.86Bb 16.15 7 0.70Bb 17.27 7 0.58Bb 16.80 7 0.48B

20.35 70.43Aa 19.41 7 0.43Aa 19.69 7 0.58Aa 19.79 7 0.43Aa 18.20 71.01B

nn

n

nn

n

nn nn nn n

n¼3. Sig. means Significance. a–c means with different letters within a row of the same irradiation dose are different (np o0.05, nnp o 0.01). A–D means with different letters within a column of the same day of storage are different (np o0.05, nnp o 0.01).

3.5. Microbiological properties

samples irradiated at 4 kGy were significantly higher than those of non-irradiated samples at Day 30, while those of samples irradiated at o4 kGy were significantly lower than that of the non-irradiated control at Days 60 and 90. Storage significantly increased the VBN of dry fermented sausages irradiated at 0, 0.5, 1, and 2 kGy while no significant changes in VBN values were observed for the sample irradiated at 4 kGy (Table 4). The decrease of VBN formation in dry fermented sausages irradiated at 4 kGy during storage was caused by the reduction of the initial levels of common spoilage bacteria. The VBN is related to bacterial activities (Banwart, 1981) and protein breakdown (Eagan et al., 1981). The S-containing volatiles were highly dependent upon irradiation dose in pork (Ahn et al., 2000) and in ground beef (Ahn and Nam, 2004). In this study higher VBN values were associated with a increase in protein breakdown caused by the increase in applied radiation (Table 4). These results agree with previous observations (Badr, 1998; Javanmard et al., 2006).

The most common microorganisms in dry fermented sausages are lactic acid bacteria and members of Micrococcaceae family ˜ ez et al., 1999). at levels higher than 6–7 log CFU/g (Ordo´n The changes of total plate counts (TPC) (log CFU/g) in the irradiated dry fermented sausages during refrigerated storage are presented in Table 5. Significant differences were observed between nonirradiated and irradiated samples at Days 1, 30, 60, and 90 (po0.01). The initial TPC (Day 1) of non-irradiated samples were 6.34 log CFU/g, while those irradiated at 1, 2, and 4 kGy were 5.23, 5.36, and 2.46 log CFU/g, respectively. Significant changes in TPC were not found in samples irradiated at 0 and 1.0 kGy during refrigerated storage. However, TPC of 2 and 4 kGy-irradiated samples decreased significantly during refrigerated storage. In addition, samples irradiated at 4 kGy initially had detectable TPC numbers but undetectable after 90 days of storage. There was no recovery of radiation-damaged cells and no growth in samples irradiated at 2 kGy. Chung et al. (2000) also reported that TPC decreased with storage time for 4 kGy-irradiated meat products. Grant and Patterson (1992) reported that sublethal damage to cells

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Table 5 Changes of total plate count, coliform and lactic acid bacteria of vacuum-packaged dry-fermented sausages stored for 90 days at 4 1C after gamma-irradiation. Dose (kGy) Storage (day)

Sig.

1

30

60

90

TPC 0 0.5 1.0 2.0 4.0

6.34 7 0.13A 5.49 7 0.10Bb 5.23 7 0.82B 5.36 7 0.05Ba 2.46 7 0.17Ca

5.77 7 0.05A 5.13 7 0.23Bb 5.19 7 0.48B 3.68 7 0.10Cb 1.28 7 0.17Db

5.777 0.49A 5.607 0.53Ab 5.437 0.10A 3.817 0.28Bb 0.867 0.41Cb

6.367 0.33A 6.097 0.37Aa 5.117 0.12B 3.127 0.10Cc NDDc

Coliform 0 0.5 1.0 2.0 4.0

2.87 7 0.23A 1.70 7 0.16B NDC NDC NDC

2.22 7 0.42A 1.45 7 0.08B NDC NDC NDC

2.237 0.62A 1.427 0.21B NDC NDC NDC

2.137 0.52A 1.317 0.12B NDC NDC NDC

LAB 0 0.5 1.0 2.0 4.0

Ab

4.93 7 0.31 4.25 7 0.42Ab 4.93 7 0.20Aab 4.85 7 0.38Aab 2.38 7 0.51Ba

Ab

5.17 7 0.12 4.19 7 0.08Bb 4.20 7 0.09Bbc 4.27 7 0.25Bb 2.44 7 0.38Ca

Ab

4.777 0.13 3.957 0.31ABb 3.687 0.85Bc 3.447 0.43Bc 1.487 0.01Cb

Aa

6.817 0.54 5.817 0.23Ba 5.567 0.23Ba 4.927 0.14Ca NDDc

n

nn nn

Table 6 Effect of gamma irradiation on the sensory characteristics of dry fermented sausages during storage at 4 1C. Dose (kGy)

Color 0 0.5 1.0 2.0 4.0 Aroma 0 0.5 1.0 2.0 4.0 Sig.

nn nn nn nn nn

n¼ 3. Sig. means Significance. a–c means with different letters within a row of the same irradiation dose are different (*p o 0.05, **p o0.01). A–D means with different letters within a column of the same day of storage are different (p o 0.05).

by irradiation is likely to increase their sensitivity to environmental stress factor. Kim et al. (2000) reported that the decrease of microbial population in irradiated meat during storage was due to post-irradiation effect where survived cells that had been damaged by gamma irradiation could not adapt to the surrounding environment during storage and gradually died. The initial coliform count (Day 1) of non-irradiated samples was 1.87 log CFU/g, while that of the sample irradiated at 0.5 kGy was 1.70 log CFU/g. No coliforms were detected in the samples irradiated at 1.0 kGy or above. Significant differences in the number of LAB were observed between non-irradiated and irradiated samples at day 1, 30, 60 and 90 (p o0.01). The initial LAB count (Day 1) of non-irradiated sample was 4.93 log CFU/g, while those of irradiated samples at 0.5, 1, 2, and 4 kGy were 4.25, 4.93, 4.85, and 2.38 log CFU/g, respectively. There were no significant differences in LAB counts between non-irradiated and irradiated samples up to 2 kGy at Day 1. However, the LAB counts of samples irradiated at 4 kGy was reduced to 2.55 log CFU/g at Day 1 (p o0.01). No growth in LAB was observed in samples irradiated at 4 kGy during refrigerated storage. The increased population of LAB during the fermentation process caused pH drop, which resulted in reduced TPC and coliforms (Gonzalez and Diez, 2002; Lizaso et al., 1999). The TPC and coliforms could be significantly reduced by 2 kGy-irradiation, but the number of LAB can be increased slowly during storage (Dickson and Maxcy, 1985). 3.6. Sensory analysis The rancid flavor and taste scores of 4 kGy-irradiated samples were significantly lower than those of the control at Day 3 of storage. However, no differences in color and aroma among the tested samples at Day 3 of storage were observed (Table 6). Previous studies showed that irradiation initiated the auto-oxidation of fats and increased lipid oxidation and rancid

Storage (days) 3

30

60

90

5.23 7 0.78a 5.11 7 0.57a 4.85 7 0.53 4.72 7 0.81 4.63 7 0.49

5.177 0.76a 4.567 0.50a 4.487 0.58 4.817 0.17 4.857 0.50

4.33 7 0.58b 4.17 7 0.76ab 4.50 70.87 5.02 71.04 4.92 7 1.04

3.627 0.76c 3.787 1.32b 4.237 1.44 4.927 1.32 4.837 0.76

n

3.70 7 0.70a 3.50 7 0.26a 3.30 7 0.26a 2.37 7 0.98 3.30 7 1.04

3.877 0.32Aa 3.337 0.58ABa 3.007 0.20ABab 2.677 0.58B 2.707 0.52B

3.50 70.50Aa 3.37 7 0.55ABa 2.60 70.17ABCbc 2.30 70.26BC 1.83 7 1.04C

2.307 0.75b 1.937 0.55b 2.137 0.40c 1.907 0.55 1.637 0.32

n

n

n

3.527 0.55 3.557 0.37 3.587 0.35 3.777 0.45 3.987 0.42

3.65 7 0.58 3.50 70.50 3.67 7 0.39 3.78 7 0.52 4.05 70.36

3.657 0.50 3.707 0.55 3.777 0.42 3.757 0.89 4.027 0.48

3.47 7 0.06A 3.03 7 0.45AB 3.30 7 0.36A 2.37 7 0.32B 2.33 7 0.49B

3.177 0.35A 2.977 0.35AB 2.937 0.21AB 2.337 0.58BC 2.107 0.36C

3.07 70.12A 3.07 70.12A 2.80 70.61AB 2.10 70.66BC 1.73 7 0.47C

3.137 0.55A 3.007 0.26A 2.807 0.50A 1.977 0.26B 1.837 0.32B

nn

n

nn

n

Rancid flavor 0 3.37 7 0.32B 0.5 3.32 7 0.45B 1.0 3.36 7 0.24B 2.0 3.88 7 0.45A 4.0 3.98 7 0.38A Taste 0 0.5 1.0 2.0 4.0 Sig.

Sig.

n

nn nn

n¼3. Sig. means Significance. a–c means with different letters within a row of the same irradiation dose are different (*p o0.05, **po 0.01). A–D means with different letters within a column of the same day of storage are different (*p o0.05, **po 0.01). Color, aroma, taste (1 ¼extremely undesirable, 6¼ extremely desirable), rancid flavor (1 ¼extremely low intensity, 6¼ extremely high intensity).

off-flavors in vacuum-packaged meat products (Dempsters et al., 1985; Formanek et al., 2003). The color, aroma and taste scores of all dry fermented sausages gradually decreased with storage. In samples irradiated at 0 and 0.5 kGy, color and aroma scores at Day 90 of storage were significantly lower than those at Day 3 (p o0.05); however, no significant changes in the color, aroma, rancid flavor and taste score for samples irradiated at 2 and 4 kGy were observed.

4. Conclusion The application of irradiation to vacuum-packaged dry fermented sausages induced significant changes in color, VBN, lipid oxidation and microbial counts (TPC, coliform and LAB) in a dose dependent manner. These modifications could have an important impact on meat quality. In the case that irradiation doses necessary to control the pathogens in dry fermented sausages are lower than those used in this study, less changes in color and lipid oxidation after irradiation than those described in the present results can be expected. When refrigerated storage is applied, irradiation of dry fermented sausages at 2 kGy was the most effective on the survival of LAB with significant reduction in total plate counts and coliforms at the initial stage of fermentation. At this dose, sensory quality was maintained with minimal rancid flavor and off-taste.

I.S. Kim et al. / Radiation Physics and Chemistry 81 (2012) 466–472

Acknowledgments This work was supported by Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (20090093813) and the grant of Gyeongnam National University of Science and Technology.

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