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Quality characteristics of Chinese sausages made from PSE pork
Meat Science 64 (2003) 441–449 www.elsevier.com/locate/meatsci
Quality characteristics of Chinese sausages made from PSE pork C.C. Kuo*, C.Y. Chu Department of Food Science, Tunghai University, 407 Taichung, Taiwan Received 29 April 2002; received in revised form 5 August 2002; accepted 5 August 2002
Abstract Chinese sausages made from normal and different levels of PSE pork (100% Normal, 50%Normal+50% PSE and 100% PSE) were vacuum-packaged and stored at 4 C for 45 days. The composition, processing yield, pH value, thiobarbituric acid (TBA) value, water activity, lactic acid bacteria counts and sensory properties of the meat products were evaluated. PSE pork loins had lower pH value, water holding capacity, moisture, fat and myofibrillar proteins content, but higher L* value, drip loss and protein content than normal pork. Sausages made from 100% PSE pork had lower pH value, processing yield, moisture and fat content, but higher protein content than those of the 100% Normal and the 50% Normal+50% PSE treatments. Water activity was higher in the 100% PSE treatment than in other treatments. No differences in lactic acid bacterial counts among these treatments were observed. The pH values and water activity of the meat samples decreased, while lactic acid bacterial counts increased with storage time. TBA values among these treatments were not significantly different; however, the increase% of TBA values was higher for the 100% PSE treatment. TBA values of all treatments remained relatively low during storage. Chinese sausages made with 50–100% PSE pork had lower sensory texture, flavor and overall acceptability scores than the control samples, but were of acceptable quality. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Lipid oxidation; Water activity; pH; Lactic acid bacteria; PSE pork; Chinese sausages; Storage time
1. Introduction Pigs have been subjected to intense genetic selection for rapid lean muscle growth. The selection traits are most often associated with economic importance rather than biophysical significance, which often results in stress syndrome and pale, soft, exudative (PSE) muscle condition (Solomon, van Laack, & Eastridge, 1998). Both the rate and the extent of the acidification of pork muscles after slaughter have a profound effect upon meat paleness, softness and exudation. The paleness of pork is inversely proportional to pH (Bendall & Swatland, 1988). The drip losses, muscle softness and pale musculature are linked to the denaturation of myosin and sarcoplasmic proteins (Bendall & Wismer-Pederson, 1962; Offer & Knight, 1988). Water holding capacity and color of pork are affected by rate of pH decline and ultimate pH (Bendall & Swatland, 1988; Offer & Knight, 1988). Red, soft, exudative (RSE) pork * Corresponding author. Tel.: +886-4-23590307; fax: +886-423596647. E-mail address: [email protected] (C.C. Kuo).
is a mild form of PSE; RSE samples would have become PSE if the pH would have decreased further (van Laack & Kauffman, 1999). PSE pork could be a consequence of rapid post-mortem glycolysis leading to a muscle pH value of about 5.5 while the carcass temperature is still high (Varnam & Sutherland, 1995). It was proposed that a pH 45 of approximately 6.2 could be used to discriminate between normal and PSE pork. The majority of white muscles on the carcass have ultimate pH values in the range 5.4–5.8 (Bendall & Swatland, 1988). The PSE condition is usually restricted to the muscles of ham and loin and is associated with lower processing yields, increased cooking losses, and reduced juiciness (Hedrick, Aberle, Forrest, Judge, & Merkel, 1994). PSE pork become internationally recognized as major economic factors in the consumption of fresh pork and in the manufacture of processed pork. Camou and Sebranek (1991) proposed that the possibility and feasibility of using PSE pork in processed meat products. They indicated that the PSE muscle protein gels exhibited decreased functionality, but enough proteins were present to facilitate protein-protein interactions and gel formation. Redden and Chen
0309-1740/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. PII: S0309-1740(02)00213-9
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(1995) used PSE pork for the manufacture of Chinese meatballs and dried meat floss (shredded meat), and found that PSE pork was not suitable for meatball production, even with the inclusion of potato or corn starch as a binding agent. However, the pale color of PSE pork used for manufacturing dried meat floss was highly favored by the tasting panel. Huang, Mikel, and Jones (1997) studied the effect of carrageenan on the quality of restructured PSE hams and found that carrageenan increased the texture and overall acceptability scores in PSE hams. Motzer, Carpenter, Reynolds, and Lyon (1998) also studied restructured hams made with PSE pork and binders, and reported that modified food starch could enhance the water retention of PSE pork in restructured ham. Li and Wick (2001) indicated that the addition of mechanically deboned turkey meat to processed meat made with PSE pork has the potential to enhance the economic value to both of these low value raw materials. Lipid oxidation in meat and meat products is a major cause of spoilage resulting in development of off flavor. Yasosky, Aberle, Peng, Mills, and Judge (1984) studied lipid oxidation (TBA value) and ultimate pH of ground pork, and found the TBA values of pork decreased as the pH values increased. They conclued that inhibition of oxidation occurred at high pH. McDonald and Hultin (1987) reported that lipid oxidation is affected by pH, lipid composition, ionic strength, temperature, redox potential, light exposure and iron content. Petrovic, Okanovic, and Rede (1995) studied the properties of normal and PSE pork and found the chemical composition of these two meat types similar; however, the pH value of PSE pork was lower than that of normal muscle. Arnau, Guerrero, Casademont, and Gou (1995) reported that the pH value between the PSE and normal dry cured hams was not different. Most of the previous studies were associated with the quality of meat products made from PSE pork hams; there is little information available regarding lipid oxidation, microbial growth and water activity of meat products made with PSE pork loin muscles. The objectives of this study were to compare the chemical and physical properties of PSE and normal pork loins, and to evaluate Chinese sausages made with different levels of PSE pork loins for pH value, lipid oxidation, water activity, lactic acid bacterial growth, and sensory properties during storage at 4 C.
2. Materials and methods 2.1. Raw materials Pigs (YorkshireLandraceDuroc) with a live weight of approximately 95–124 kg at the time of slaughter were used in this experiment. In order to obtain sufficient meat samples for three replications, 10 animals (five PSE; five
normal) were used. Twenty pork loins (Longissimus dorsi) were selected at a local commercial plant at 24-h postmortem. These were subjectively evaluated for color, texture and the amount of drip. Paler, watery and softer loins were classified as PSE muscle and separated from the normal loins, which were darker, drier and firmer in color or texture. Pork loins primal cuts were then deboned and trimmed of visible fat and connective tissue in the commercial plant. Boneless loins were wrapped with polyvinyl chloride (PVC) film and stored in boxes, and were placed in freezers (30 C) for about 24 h. Subsequently, the loins were transported to the university and stored at 18 C for about 2 weeks. All frozen meat samples were thawed at 4 C for about 24 h, and the drip loss was determined from weights recorded prior to thawing and immediately after thawing. Thawed pork loins were determined in the university laboratory for pH, and the pH of meat samples was measured with a portable pH meter (PHM 201, Meter Lab., Radiometer, Copenhagen, France). PSE and normal pork loins were assigned to each of three treatment groups: 100% Normal, 50% Normal+50% PSE and 100% PSE treatments. This experiment was replicated three times with triplicate samples in each treatment. 2.2. Chinese sausage preparation and processing yield Lean meat from the loins was ground through a 1.6-cm grinder kidney plate. The pork fat was cut manually into cubes (0.5 cm3). The meat block was composed of seven parts of coarse ground lean meat and three parts of cubed fat by weight. Lean meat and fat were thoroughly blended in a mixer. The curing ingredients added to each treatment (100% Normal, 50% Normal+50% PSE and 100% PSE treatments) were the same and consisted of sugar (10%), isolated soy protein (2%), sodium chloride (1.8%), sodium tripolyphosphate (0.3%), white pepper powder (0.1%), five spices powder (0.1%), erythorbic acid (0.02%), and sodium nitrite (0.012%). Percentage of all ingredients was based on the weight of the meat block. Phosphate and nitrite were dissolved in approximately 20 ml of distilled water prior to addition. All curing ingredients and the meat block were mixed thoroughly and cured at 4 C for 12 h and then stuffed into natural hog casings and linked into 10-cm units. The sausages were then dried in a forced air oven at 50 C for about 7 h. Finished sausages from each treatment were vacuum packaged (Nylon/Cast polypropylene=15/75 mil; 1925 cm) by using a Multivac (Gastrovac A 300/42, Germany) packaging machine. The sausages from each treatment were randomly assigned to storage for 0, 15, 30 and 45 days at 4 C. Processing yield was determined from weights recorded prior to drying and after removal from the forced air oven.
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Both raw pork meat and Chinese sausage samples were analyzed for percent moisture, fat and protein (AOAC, 1995). Prior to analyses, raw pork loins or two Chinese sausages from each treatment were finely ground using a food processor. The pH value of meat samples was determined according to Ockerman (1989). Of the meat samples, 10 g were blended with 100 ml of distilled water for 1 min using a blender (IKA-Labortecknic T-25, Germany) and the pH values were read with a portable pH meter (PHM 201, Meter Lab, Radiometer, Copenhagen, France).
and passed through a polyethylene strainer to remove connective tissue and debris. Five more volumes, resulting in 10 vol. (v/w) total of the original isolating medium, were used to further facilitate passage of myofibrils through the strainer. Again, the supernatant was sedimented at 1000 g for 15 min and the supernatants decanted. The sediments were washed three more times by suspending in 5 vol. (v/w) of the original isolating medium, and were sedimented at 1000 g for 15 min. Finally, the sedimented myofibrils were resuspended in 5 vol. (v/w) of the original isolating medium. The protein concentration determined by the biuret procedure described by Clark and Switzer (1977).
2.4. Color measurement
2.7. Catalase activity
Instrumental color values (L*, a *, b* values) of raw pork chops (1.0 cm thick) and Chinese sausages (0.5 cm) were evaluated using a Nippon Denshoku Industries Company ZE 2000 Color Difference Meter (Tokyo, Japan) standardized with a white plate (X=93.90, Y=91.89, Z=110.26). Measurements were averaged over six non-overlapped zones of each chop.
The hydrogen peroxide decomposition test procedure described by Ang, Liu, Townsend, and Fung (1994) was used. Hydrogen peroxide (4 ml, 3%) was added to a tube containing 2 g of meat sample and incubated at room temperature for up to 120 min. Observations of the reaction were made after incubation. Floating or separation of the solid phase indicated a positive enzyme reaction. Precipitation of all solids at the bottom of the tube indicated a negative reaction. The incubation time required to obtain a positive reaction was recorded. The quantitative analysis of the enzymatic activity was expressed as an inverse of incubation time (1/s).
2.3. Chemical analysis and ultimate pH
2.5. Water holding capacity Water holding capacity (WHC) of the meat samples was measured by the press method described by Ockerman (1989) and expressed as a percentage of bound water. The meat sample (0.5 g) was placed on a filter paper and pressed between two plexglass sheets with a Casver Lab press at 500 psi for 1 min. The inner and outer surface of pressed meat and juice were measured (in2) with a polar planimeter (Tamaya, Model Planix 7, Japan). % Free water ¼ ðtotal surface area meat film areaÞ 61:1=total moisture ðmgÞ of meat sample ð0:5 gÞ 100%
2.8. TBA value 2-Thiobarbituric acid (TBA) values were determined by the distillation method described by Ockerman (1989). Absorbances at 538 nm were read with an UVVIS spectrophotometer (Spectronic Genesys 5, Milton Roy, USA). TBA values were expressed as mg malonaldehyde/kg meat. 2.9. Water activity
% Bound water=100% % free water 2.6. Myofibrillar proteins The procedure used to determine myofibrillar proteins was similar to that of Olson, Parrish, and Stromer (1976). Myofibrils were isolated from normal and PSE muscles by homogenizing 4 g of minced muscle in a waring blendor for 30 s in 10 vol. (v/w) of a 2 C isolating medium containing 100 mM KCl, 20 mM potassium phosphate (pH 7.0), 1 mM EDTA and 1mM sodium azide. The homogenate was sedimented at 1000g for 15 min and the supernatant decanted. The sediment was resuspended at 1000g for 15 min and the supernatant decanted. The sediment was again resuspended in 5 vol. (v/w) of the original isolating medium
Water activity of the meat products was determined at room temperature using a water activity analyzer (Aqua Lab, Model CX-2, Washington, USA). 2.10. Microbiological evaluation After each storage interval, a package of sausage samples from each treatment was ground and mixed through a blender, which had been cleaned and sterilized. A 10-g ground meat sample was then aseptically removed and placed into stomacher bags containing 90 ml of a sterile peptone water (0.1%) solution. Meat samples were placed into a stomacher apparatus (Stomacher Lab-Blender 400, Tekmar Company, Cincinnati, OH) and homogenized for 2 min. Appropriate
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serial dilutions were made in sterile peptone water and 0.1 ml of each dilution were spread onto Lactobacilli MRS agar (Difco Laboratories, Detroit, MI). Plates were incubated at 37 C for 48 h, and the lactic acid bacterial colonies were counted and reported as CFU/g meat. 2.11. Sensory evaluation Sausage samples were heated on a frying pan to an internal temperature of 75 C monitored by a pocket thermocouple. A portion of sausage (about 0.5 cm) from each treatment was used for presentation to the panelists at ambient temperature. The panelists (n=10) consisted of graduate students, faculty and staff of the Tunghai University. Each panelist had previous sensory evaluation experience. Panelists were instructed to rinse their pallet with water between samples. At each evaluation three samples were coded with random numbers and evaluated for texture, flavor and overall acceptability on a 9-point hedonic scale (9=like extremely; 5=neither like nor dislike; 1=dislike extremely). Sensory scores of above 5.0 were assumed to be acceptable. Effect of storage time on sensory quality of Chinese sausages was not determined in this experiment. Only at day 15, a sensory acceptance panel test was conducted. 2.12. Statistical analysis This experiment was replicated three times with triplicate samples in each replication (n=9). Bacterial numbers of CFU/g were transformed to log10 for statistical analysis. Data were evaluated using SAS General Linear Models Procedures (SAS Institute, Inc., 1993). Treatment means were separated using Duncan’s new multiple range tests (SAS Institute, Inc., 1993). Statistical models included treatments (3: 100% Normal, 50% Normal+50% PSE, 100% PSE) and storage time (4: 0, 15, 30 and 45) as independent variables. Significance was established at P < 0.05.
3. Results and discussion 3.1. Physical and chemical properties of raw normal and PSE pork loins As would be expected, the ultimate pH values (Table 1) were higher (P < 0.05) for normal pork loin (5.96) than for PSE pork (5.60). van Laack et al. (1999) found the pH of PSE and normal pork loins was 5.32 and 5.64, respectively. Lien et al. (2002) also indicated that the pork chops from chilled PSE and normal loins were 5.2 and 5.6, respectively. Nam, Ahn, and Jo (2002) found that pH for PSE pork loins (5.47) was higher than that of normal pork (5.69). This result indicated
Table 1 The physical and chemical properties of raw normal and PSE pork loinsa Properties
Normal meat
PSE meat
PH L* a* b* Drip loss (%) Water holding capacity (% bound water ) Moisture (%) Crude fat (%) Crude protein (%) Myofibrillar proteins (mg/ml) Catalase activity (1/s)
5.96 a 44.8 b 17.5 a 9.9 b 4.51 b 70.5 a 73.6 a 3.8 a 21.2 b 12.07 a 0.22 a
5.60 b 51.5 a 16.3 a 11.7 a 8.34 a 66.5 b 72.1 b 2.3 b 22.8 a 6.34 b 0.28 a
a Values are means of three replicates (n=9). Means in the same row with different letters are significantly different (P<0.05).
that the pH values of PSE and normal pork were lower than that in our findings. This may be due to differences in experimental variables and conditions, including animal breed, postmortem muscle removal time, anatomical location of muscle or tissue site, animal diet, sample handling method, procedure or equipment used to determine pH value. Bendall and Swatland (1988) reported that the majority of white muscles on the carcass had ultimate pH in the range 5.4–5.8. Warner, Kauffman, and Greaser (1997) classified PSE hams as pH < 5.8, while normal muscles had pH values between 5.8 and 6.1. PSE pork had higher (P < 0.05) L* values (51.5) and b* values (11.7), but lower (P > 0.05) a* values (16.3) than those of the normal pork loins (44.8, 9.9 and 17.5, respectively). This was probably due to the denaturation of muscle proteins, resulting in pale (less redness), soft and exudative (more whiteness) condition in pork. Lien et al. (2002) found a L* value of 55.5 for normal pork and 59.2 for pork loins; PSE pork had a higher b* value (19.9) than normal pork (18.3). However, they indicated that the differences in a* value were not significantly different between normal and PSE pork. van Laack and Kauffman (1999) also found PSE pork loins had a higher L* value (55.9) than normal pork (45.1). Bendall and Swatland (1988) reported that the paleness of pork is inversely proportional to pH. Myosin denaturation is the main factor causing the unacceptable exudation in PSE pork (Offer et al., 1988). The differences in percentage drip loss between the normal (4.51) and PSE (8.34) were significant (P < 0.05). This result agreed with Lien et al. (2002) who found that PSE pork had a higher drip loss (3.3%) than normal pork (1.6%). van Laack and Kauffman (1999) also indicated that PSE pork had a higher drip loss (11.2%) than normal pork loins (4.2%). They used drip loss and L* values to classify PSE (drip loss > 6%; L* value > 50) and normal pork (drip loss < 6%; L* value < 50).
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As expected, water holding capacity, expressed as% bound water, of normal pork (70.5) was higher (P < 0.05) than that of PSE pork (66.5). The rate of pH declining and ultimate pH values are the two main determinations of water holding capacity (exudation) and color (Bendall & Swatland, 1988; Offer et al., 1988). The PSE pork loins had lower (P < 0.05) percent moisture (72.1) and fat (2.3), but higher (P < 0.05) percent protein (22.8) than the normal pork loins (73.6, 3.8 and 21.2, respectively). Okanovic, Petrovic, and Beara (1992) reported that the composition of normal and PSE hams were similar, but color, structure and technological properties of the two meat types were significantly different. Concentration of myofibrillar proteins or protein solubility was used as a measure of denaturation, as can be seen in Table 1. PSE pork had lower (P < 0.05) concentration of myofibrillar proteins (12.07 mg/ml) than the normal pork (6.34 mg/ml). These results indicated that proteins in PSE meat were denatured considerably. Researchers reported that PSE pork muscles tend to exhibit decreased protein extraction and solubility (Schimidt & Trout, 1982; Vadehra & Baker, 1970). Lawrie (1979) indicated that pork muscle with a fast rate of pH fall post mortem, resulting in an unusually low ultimate pH, which would tend to denature muscle proteins and lower their capacity to hold water. The lower the pH of animal muscles, the lower the water holding capacity and the extractability of the myofibrillar proteins. Petrovic et al. (1995) found that the composition of normal and PSE pork hams was similar, but PSE hams had lower salt soluble proteins and total pigment concentration. Activity of catalase, expressed as an inverse of incubation time (1/s), of normal (0.22) and PSE pork (0.28) was similar. Rhee (1988) reported that catalase activity may be important in decreasing the amount of H 2O2 remaining in the muscle tissue, was higher in pork longissimus dorsi (LD) muscle than in beef LD or chicken thigh or breast muscles; however, during storage at 20 C, the catalase activity would be limited. 3.2. Processing yield and composition of Chinese sausages The 100% Normal treatment (Table 2) had a higher (P < 0.05) processing yield (81.4%) than the 100% PSE treatment (79.6%) due to its higher water holding capacity or higher fat content (Table 1). The PSE meat groups had more myofibrillar proteins become partially denatured and lost their water holding capacity, resulting in lower processing yields. Also Arnau et al. (1995) suggested that the lower processing loss (higher processing yield) of meat product could be due to the barrier effect of fat on water diffusion and evaporation during processing. Candek-Potakar, Monin, and Ziender (2002) indicated that a lower dry-cured ham processing
Table 2 The processing yield and composition of Chinese sausages made from normal and/or PSE porka Meat type
Processing yield (%) Moisture (%) Crude protein (%) Crude fat (%)
100% Normal
50% Normal+ 50% PSE
100% PSE
81.4 a 45.1 a 20.0 b 22.1 a
80.7 a, b 43.5 b 21.0 a, b 21.4 a, b
79.6 b 42.7 b 21.6 a 20.8 b
a Values are means of three replicates (n=9). Means in the same row with different letters are significantly different (P<0.05).
loss could be attributed to its higher intramuscular fat content. Partially due to its higher fat content, the 100% Normal treatment had higher processing yield than the other two treatments. The processing yield decreased as the proportion of PSE pork increased. Motzer et al. (1998) studied the restructured hams made with different levels of PSE pork and found a similar result. Honkavaara (1990) also reported that cooked hams made from PSE pork had a lower cooking yield than the normal cooked hams, due to decreased water holding capacity. Hedrick et al. (1994) indicated that PSE condition was associated with lower processing yields, increased cooking losses, and reduced juiciness The 100% Normal treatment had higher (P < 0.05) moisture (45.1) and fat content (22.1), but lower protein content (20.0) than the 100% PSE treatment (42.7, 20.8 and 21.6, respectively). The 100% PSE treatment contained a slightly lower percentage of moisture and fat, but a higher percentage of protein than the 50% Normal+50% PSE treatment; however, the differences were not significant (P > 0.05). Honkavaara (1990) studied the chemical composition of cooked PSE pork hams and found a similar result. 3.3. Changes in pH value The pH values of Chinese sausages made from different levels of PSE meat were significantly different (P < 0.05) at day 0 (Fig. 1). As expected, sausages made from PSE pork (the 100% PSE and the 50% Normal+50% PSE treatments) had lower (P < 0.05) pH values (6.08 and 6.16, respectively) than the 100% Normal treatment (6.21). This was probably due to the lower pH values of the raw PSE muscle (5.60), compared to the normal muscle (5.96; Table 1). The pH value of the 100% PSE treatment was lower than that of the 50% Normal+50% PSE treatment; however, the differences between these two treatments were not significant. Petrovic et al. (1995) reported that the pH values of PSE cooked hams was lower than that of of normal pork. Motzer et al. (1998) manufactured hams with PSE pork and also found the 100% PSE meat
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C.C. Kuo, C.Y. Chu / Meat Science 64 (2003) 441–449 Table 3 Lactic acid bacterial growth (log CFU/g) of Chinese sausages made from normal and/or PSE pork as affected by storage timea Days
Meat type
0 15 30 45
100% Normal
50% Normal+ 50% PSE
100% PSE
4.34 5.48 6.43 7.42
4.28 5.46 6.38 7.40
4.20 5.36 6.32 7.36
a, a, a, a,
w x y z
a, a, a, a,
w x y z
a, a, a, a,
w x y z
a Values are means of three replicates (n=9). Means in the same row with the same letter are not significantly different (P <0.05). Means in the same column with different letters (w–z) are significantly different (P<0.05).
Fig. 1. The pH value of Chinese sausages made from normal and/or PSE pork as affected by storage time (n=9). Values on the display day with different superscript letters (a, b, c) are significantly different (P<0.05).
treatment had lower pH values than the 50% Normal+50% PSE blend and the 100% Normal treatments. At each storage time (15, 30 or 45 days), the 100% PSE treatment consistently had the lowest pH value, followed by the 50% Normal+50% PSE and the 100% Normal treatments. The pH value of all sausage samples decreased as the storage time increased. This was probably due to the accumulation of lactic acid produced by the growth of lactic acid bacteria in vacuum-packed sausages. Ockerman and Kuo (2001) reported that the pH value of drycured hams decreased during storage. This decrease was probably due to lactic acid producing bacteria fermenting sucrose to lactic acid. Banwart (1979) indicated that cured meat became sour (low pH) because of the fermentation of carbohydrates by lactic acid bacteria. Chinese sausages contained 10% of sugar, which probably could be used by lactic acid bacteria to produce lactic acid, resulting in lower pH value during storage. At days 0, 15, 30 and 45, the 100% PSE treatment consistently had lower pH values than the 50% Normal+50% PSE treatment or the 100% Normal treatment even though their lactic acid bacterial counts were not different (Table 3). Perhaps because of the 100% PSE treatment had lower water holding capacity and higher drip loss among these treatments; therefore, more phosphate and other basic compounds were probably lost during storage, resulting in lower pH value. Guerrero, Gou, Alonso, and Arnau (1996) indicated that the pH value diminished during the salting period in ham muscles was due to the loss of phosphate or some other basic compounds, and the salt uptake. Arnau et al. (1995) reported that PSE and normal drycured hams differed only in pH45, but not during the processing.
3.4. TBA value Lipid oxidation, expressed as the TBA value, is shown in Table 4. During storage, the differences in TBA values among these three treatments were not significantly. However, the 100% Normal treatment had slightly higher (P > 0.05) TBA values than the 100% PSE or the 50% Normal+50% PSE treatments due to its higher lipid content (Table 1) Ockerman et al. (2001) reported that TBA values were positively correlated with fat content in dry-cured hams. Since fat is more apt to produce oxidative rancidity. Rhee, Anderson, and Sams (1996) indicated that TBA values of frozen raw samples for beef and pork were higher due to their higher heme iron content. However, in a previous study, we found that PSE pork had lower heme iron content than normal pork (data not shown). As would be expected, mean TBA values of all meat products increased as the storage time increased, indicating that lipid oxidation had occurred in the vacuumpackaged Chinese sausages. However, TBA values of all products throughout storage time were in the range of 0.09–0.32, which were relatively low and well below the
Table 4 TBA value of Chinese sausages made from normal and/or PSE pork as affected by storage timea Days
0 15 30 45
Meat type 100% Normal
50% Normal+ 50% PSE
100% PSE
0.17 0.22 0.27 0.32
0.13 0.20 0.23 0.28
0.09 0.15 0.20 0.23
a, a, a, a,
w (100) w, x (129) x, y (159) y (188)
a, a, a, a,
w (100) w, x (154) x, y (177) b, y (215)
a, a, a, a,
w (100) w, x (167) x, y (222) y (256)
a Values are means of three replicates (n=9). Means in the same row with the same letter are not significantly different (P <0.05). Means in the same column with different letters (w–y) are significantly different (P <0.05). Value in brackets is the % of initial TBA value within each meat type.
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threshhold value (1.0 mg malonaldehyde/kg) for detection of warmed-over flavor (Boles & Parrish, 1990). Gray and Pearson (1987) indicated that rancid flavor was initially detected between TBA values of 0.5 and 2.0. From our result, it suggested that vacuum-packaged Chinese sausages could be stored at 4 C up to 45 days without causing any serious rancid problem. The relatively low extent of lipid oxidation could be attributed to the vacuum packaging and low storage temperature. Kuo, Yuan, Lee, and Shin (1986) studied the effect of packaging on quality of Chinese sausages and found that the use of vacuum packaging could be a means of reducing lipid oxidation in meat products. Although TBA values among these treatments were not different (P > 0.05), the increase% of TBA values within each treatment was different due to its different lipid oxidation rate. On day 15, 30 and 45, TBA values of the 100% Normal, 50% Normal+50% PSE, and 100% PSE treatments were 29–88, 54–115 and 67–156% higher than those at zero time, respectively (Table 4). These results demonstrated that the lipid oxidation rate was much faster in the Chinese sausages made from 100% PSE meat even though their initial and final TBA values were lower. The higher increase% of TBA values in the 100% PSE treatment was probably due to its lower pH value. This result agreed with Yasosky, Aberle, Peng, Mills, and Judge (1984) who studied lipid oxidation and pH value (5.4–6.8) of ground pork after 12 days of storage, and concluded that inhibition of oxidation occurred at high pH. Nam et al. (2001) also reported that PSE pork was more susceptible to lipid oxidation than the normal and dark, firm, dry (DFD) pork when irradiated and stored under aerobic conditions. Shin, Abugroun, Forrest, Okos, and Judge (1993) found that pre-rigor cooked roasts (higher pH) are better in oxidative stability than post-rigor cooked meats. Chen, Forrest, Peng, Pratt and Judge (1993) reported an inverse relationship between pH and TBA values. McDonald and Hultin (1987) indicated that lipid oxidation was not only affected by pH, but also lipid composition, ionic strength, temperature, redox potential, light exposure, and iron content. 3.5. Water activity At zero time, the 100% Normal treatment had lower (P < 0.05) water activity (0.946) in comparison with the 100% PSE (0.956) and the 50% Normal+50% PSE (0.953) treatments (Table 5). The difference in water activity between the 100% Normal and the 100% PSE treatments was significant (P < 0.05), but small. Water activity for all sausages was below 0.96. Leistner, Rodel, and Krispien (1981) reported that the main hurdles for microbiologically stability of meat products are water activity, pH and temperature. Banwart (1979) indicated that at a water activity of 0.96 or less, most of the usual
Table 5 Water activity of Chinese sausages made from normal and/or PSE pork as affected by storage timea Days
0 15 30 45
Meat type 100% Normal
50% Normal+ 50% PSE
100% PSE
0.946 0.943 0.935 0.930
0.953 0.945 0.938 0.934
0.956 0.949 0.945 0.939
b, w a, w b, x b, x
a, a, a, a,
w x b, y b, y
a, a, a, a,
w x x, y y
a Values are means of three replicates (n=9). Means in the same row with different letters (a–c) are significantly different (P <0.05). Means in the same column with different letters (w–y) are significantly different (P<0.05).
microorganisms causing spoilage of fresh meat are inhibited. After 15, 30 and 45 days of storage, the 100% PSE treatment consistently retained a higher water activity, followed by the 50% Normal+50% PSE and 100% Normal treatments even though its moisture content was lower (Table 2). Changes in water activity of all meat products at each storage time followed essentially the same pattern as those at zero time. These results indicate that the higher the proportion of PSE pork used for manufacturing of Chinese sausages, the higher their water activity (Table 2). This could be best explained by its fat content of the meat product. Leistner et al. (1981) reported that water activity of the lean and the fat portion do not come to equilibrium either in short- or long-ripened meat products. In general, water activity of meat products increased as their fat content decreased. Since the 100% PSE treatment had lower fat percent (20.8), compared to the 100% Normal (22.1) and the 50% Normal+50% PSE (21.4) treatments (Table 2); therefore, water activity of the 100% PSE treatment was higher than the other two treatments. During storage, there was a decrease in water activity in all meat treatments. Kuo et al. (1986) studied the effect of fat and nitrite levels on quality of Chinese sausages and also found a similar result. Arnau et al. (1995) indicated that a decrease in water activity is the main factor responsible for the preservation of the dry-cured hams, which might be achieved essentially by the penetration of salt and removal of water from the meat. They found that PSE hams contained more salt than normal hams. 3.6. Lactic acid bacteria No differences (P > 0.05) in lactic acid bacterial counts were observed among these treatments at any given storage time; but during the storage period, counts increased logarithmically (Table 3). Due to high levels of initial contamination, the numbers of lactic acid bacteria of all treatments increased to 5.2–5.5, 6.2–6.4
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Table 6 Sensory property scores of Chinese sausages made from normal and/ or PSE pork Sensory propertya
Texture Flavor Overall acceptability
Meat type 100% Normal
50% Normal+ 50% PSE
100% PSE
7.4 b 7.1 b 7.2 b
6.8 c 6.6 c 6.6 c
5.4 d 5.8 d 5.5 d
a Hedonic scale: 1=extremely, dislike in texture, flavor or overall acceptability; 5=neither like nor dislike; 9=extremely like in texture, flavor or overall acceptability. Values are means of three replicates (n=9). Means in the same row with different letters (b–d) are significantly different (P <0.05).
content than normal pork. The processing yield and chemical properties of Chinese sausages were affected by meat type; and pH, TBA values and lactic acid bacteria were affected by storage time. As the storage time increased while the pH values decreased, TBA values and lactic acid bacteria increased. TBA values as observed throughout storage time were below 0.4, suggesting that the vacuum-packaged Chinese sausages could be stored up to 45 days at 4 C. Sensory properties of Chinese sausages made from PSE meat (100 or 50%) were inferior to those of the control, but were of acceptable quality.
References and 7.3–7.4 log CFU/g at 15, 30 and 45 days of storage, respectively. Lactic acid bacteria have been found to be one of the natural microbial flora of Chinese sausages (Kuo & Lin, 1993). Gill (1982) reported that the flora of vacuum packaged meat is usually dominated by species of Lactobacillus. The normal spoilage of cured meat products is one of a souring nature due to the growth of Lactobacilliace, but other organisms may also be found. During storage, the growth of lactic acid bacteria probably caused the accumulation of lactic acid, resulting in decrease of pH values of all meat samples (Fig. 1). 3.7. Sensory properties Sensory properties of Chinese sausages made from different levels of PSE meat were compared (Table 6). Effect of storage time on sensory quality of these meat products was not determined in this experiment. Only the meat products stored at 4 C for 15 days were evaluated. Due to their lower moisture and fat contents, and slightly higher acid flavor (lower pH value), the 100% PSE and the 50% Normal+50% PSE treatments had lower (P < 0.05) texture, flavor and overall acceptability scores than the 100% Normal treatment, but were of acceptable quality. A 9-point hedonic scale was used to evaluate the sensory quality of Chinese sausages in this study. The sensory scores of above 5.0 (neither like nor dislike) were assumed to be acceptable. (Table 6). The differences in texture, flavor or overall acceptability scored between the 100% PSE and the 50% Normal+50% PSE treatments were also significant (P < 0.05).
4. Conclusions PSE pork loins had lower pH value, water holding capacity, moisture, fat and myofibrillar proteins contents, but higher L* values, drip loss and protein
Ang, C. Y. W., Liu, F., Townsend, W. E., & Fung, D. Y. C. (1994). Sensitive catalase test for end-point temperature of heated chicken meat. Journal of Food Science, 59, 494–497. AOAC. (1995). Official Methods of Analysis (16th ed.). Virginia, USA: Association of Official Analytical Chemists International. Arnau, J., Guerrero, L., Casademont, G., & Gou, P. (1995). Physical and chemical changes in different zones of normal and PSE dry cured ham during processing. Food Chemistry, 52, 63–69. Banwart, G. J. (1979). Basic Food Microbiology. Connecticut: AVI Publishing Company. Bendall, J. R., & Swatland, H. J. (1988). A review of the relationships of pH with physical aspects of pork quality. Meat Science, 24, 85– 126. Bendall, J. R., & Wismer-Pedersen, J. (1962). Some properties of the myofibrillar proteins of normal and watery pork muscle. Journal of Food Science, 27, 144–159. Boles, J. A., & Parrish, F. C. Jr. (1990). Sensory and chemical characteristics of precooked microwave-reheatable pork roasts. Journal of Food Science, 55, 618–620. Candek-Potokar, M., Monin, G., & Zlender, B. (2002). Pork quality, processing, and sensory characteristics of dry-cured hams as influenced by Duroc crossing and sex. Journal of Animal Science, 80, 988–996. Camou, J. P., & Sebranek, J. G. (1991). Gelation characteristics of muscle protein from pale, soft, exudative (PSE) pork. Meat Science, 30, 207–220. Chen, W., Forrest, J. C., Peng, I. C., Pratt, D. E., & Judge, M. D. (1993). Palatability of prerigor cooked boar meat. Journal of Animal Science, 71, 645–650. Clark, J. M. Jr., & Switzer, R. L. (1977). Experimental biochemistry. San Francisco: W. H. Freeman & Company. Gill, C. O. (1982). Microbial interaction with meats. In M. H. Brown (Ed.), Meat microbiology (pp. 246). London/New York: Applied Science Publishers. Gray, J. I., & Pearson, A. M. (1987). Rancidity and warmed-over flavor. Advanced Meat Research, 3, 221–269. Guerrero, L., Gou, P., Alonso, P., & Arnau, J. (1996). Study of the physicochemical and sensorial characteristics of dry-cured hams in three pig genetic types. Journal of Science and Food Agriculture, 70, 526–530. Hedrick, H. B., Aberle, E. D., Forrest, J. C., Judge, M. D., & Merkel, R. A. (1994). Principles of Meat Science. Iowa: Kendall/Hunt Publishing Company. Honkavaara, M. T. (1990). Effect of porcine stress on the development of PSE meat, its characteristic and influence on the economics of meat product manufacture. Dissertation Abstracts International, C51, 28, ISBN 952–90118–7-3.
C.C. Kuo, C.Y. Chu / Meat Science 64 (2003) 441–449 Huang, C. Y., Mikel, W. B., & Jones, W. R. (1997). Carrageenan influences on the characteristic of restructured normal and pale, soft and exudative hams. Journal of Muscle Foods, 8, 85–93. Kuo, C. C., & Lin, Y. H. (1993). Effects of sodium lactate and sodium acetate on microbial counts, pH and water activity of Chinese sausages. Tunghai Journal, 34, 1069–1088. Kuo, J. C., Yuan, C. K. R., Lee, F. L., & Shin, C. H. (1986). Vacuum packaged Chinese sausage as influenced by different fat and nitrite levels. Chinese Food Science, 13, 21–31. Lawrie, R. A. (1979). Meat science. New York: Pergamon Press. Leistner, W., Rodel, W., & Krispien, K. (1981). Microbiology of meat and meat products in high- and intermediate- moisture ranges. In L. B. Rockland, & G. F. Stewart (Eds.), Water activity: influences on food quality (pp. 855–916). New York/London/Toronto/Sydney/San Francisco: Academic Press. Li, C. T., & Wick, M. (2001). Improvement of the physicochemical properties of pale soft and exudative (PSE) pork meat products with an extract from mechanically deboned turkey meat (MDTM). Meat Science, 58, 189–195. Lien, R., Hunt, M. C., Anderson, S., Kropf, D. H., Loughin, T. M., Dikeman, M. E., & Velazco, J. (2002). Journal of Food Science, 67, 1007–1010. McDonald, R. E., & Hultin, H. O. (1987). Some characteristics of the enzymic peroxidation system in the microsomal fraction of flounder skeletal muscle. Journal of Food Science, 52, 15–21 27. Motzer, E. A., Carpenter, J. A., Reynolds, A. E., & Lyon, C. E. (1998). Quality of restructured hams manufactured with PSE pork as affected by water binders. Journal of Food Science, 63, 1007–1011. Nam, K. C., Ahn, D. U., & Jo, C. (2001). Lipid oxidation, color, volatiles, and sensory characteristics of aerobically packaged and irradiated pork with different ultimate pH. Journal of Food Science, 66, 1225–1229. Ockerman, H. W. (1989). Quality control of postmortem muscle tissue. Ohio: The Ohio State University. Ockerman, H. W., & Kuo, J. C. (2001). Effects of nitrate and storage on the properties of tumbled dry-cured hams. In M. L. Eastrige (Ed.), Research and Reviews: Meat 2001 (pp. 67–72). Ohio: Ohio Agricultural Research and Development Center / Ohio State University / College of Food, Agricultural, and Enviromental Sciences. Offer, G., & Knight, P. (1988). The structural basis of water-holding in meat part II: Drip losses. In R. Lawrie (Ed.), Development in meat science (pp. 173–243). New York: Elsevier Applied Science.
449
Okanovic, D., Petrovic, L., & Beara, M. (1992). Incidence of the PSE defect in hams at the Mitros meat factory and some characteristics of the affected muscles. Tehnologija Mesa, 33, 211–216. Olson, D. G., Parrish, F. C. Jr., & Stromer, M. H. (1976). Myofibril fragmentation and shear resistance of three bovine muscles during postmortem storage. Journal of Food Science, 41, 1036–1041. Redden, V. R., & Chen, T. (1995). The potential of Chinese meatballs and dried meat as value added PSE pork products. Food Australia, 47, 323–326. Petrovic, L., Okanovic, D., & Rede, R. (1995). Film-packed cooked hams from PSE meat. Fleischwirtschaft, 75, 480–481. Rhee, K. S. (1988). Enzyme and nonenzyme catalysis of lipid oxidation in muscle foods. Food Technology, 42, 127–132. Rhee, K. S., Anderson, L. M., & Sams, A. R. (1996). Lipid oxidation potential of beef, chicken, and pork. Journal of Food Science, 61, 8– 12. SAS Institute, Inc.. (1993). SAS user’s guide: statistics, 1993 Edition. Cary, NC: SAS Institute, Inc. Schmidt, G. R., & Trout, G. R., (1982). Chemistry of meat binding. In Proceedings of Meat Science Technology International Symposium, 1–4 November 1982. Lincoln: NB. Shin, H. K., Abugroun, H. A., Forrest, J. C., Okos, M. R., & Judge, M. D. (1993). Effect of heating rate on palatability and associated properties of pre- and post-rigor muscle. Journal of Animal Science, 71, 939–945. Solomon, M. B., van Laack, R. L. J. M., & Eastrige, J. S. (1998). Biophysical basis of pale, soft, exudative (PSE) pork and poutry muscle: a review. Journal of Muscle Foods, 9, 1–12. Vadehra, D. V., & Baker, R. C. (1970). The mechanisms of heat initiated binding of poultry meat. Food Technology, 24, 766–775,778– 779. van Laack, R. L. J. M., & Kauffman, R. G. (1999). Glycolytic potential of red, soft, exudative pork longissimus muscle. Journal of Animal Science, 77, 2971–2973. Varnam, A. H., & Sutherland, J. P. (1995). Meat and meat products: technology, chemistry and microbiology. London: Chapman & Hall. Warner, R. D., Kauffman, R. G., & Greaser, M. L. (1997). Muscle protein changes postmortem in relation to pork quality traits. Meat Science, 45, 339–352. Yasosky, J. J., Aberle, E. D., Peng, I. C., Mills, E. W., & Judge, M. D. (1984). Effects of pH and time of grinding on lipid oxidation of fresh ground pork. Journal of Food Science, 49, 1510–1512.
Quality characteristics of Chinese sausages made from PSE pork C.C. Kuo*, C.Y. Chu Department of Food Science, Tunghai University, 407 Taichung, Taiwan Received 29 April 2002; received in revised form 5 August 2002; accepted 5 August 2002
Abstract Chinese sausages made from normal and different levels of PSE pork (100% Normal, 50%Normal+50% PSE and 100% PSE) were vacuum-packaged and stored at 4 C for 45 days. The composition, processing yield, pH value, thiobarbituric acid (TBA) value, water activity, lactic acid bacteria counts and sensory properties of the meat products were evaluated. PSE pork loins had lower pH value, water holding capacity, moisture, fat and myofibrillar proteins content, but higher L* value, drip loss and protein content than normal pork. Sausages made from 100% PSE pork had lower pH value, processing yield, moisture and fat content, but higher protein content than those of the 100% Normal and the 50% Normal+50% PSE treatments. Water activity was higher in the 100% PSE treatment than in other treatments. No differences in lactic acid bacterial counts among these treatments were observed. The pH values and water activity of the meat samples decreased, while lactic acid bacterial counts increased with storage time. TBA values among these treatments were not significantly different; however, the increase% of TBA values was higher for the 100% PSE treatment. TBA values of all treatments remained relatively low during storage. Chinese sausages made with 50–100% PSE pork had lower sensory texture, flavor and overall acceptability scores than the control samples, but were of acceptable quality. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Lipid oxidation; Water activity; pH; Lactic acid bacteria; PSE pork; Chinese sausages; Storage time
1. Introduction Pigs have been subjected to intense genetic selection for rapid lean muscle growth. The selection traits are most often associated with economic importance rather than biophysical significance, which often results in stress syndrome and pale, soft, exudative (PSE) muscle condition (Solomon, van Laack, & Eastridge, 1998). Both the rate and the extent of the acidification of pork muscles after slaughter have a profound effect upon meat paleness, softness and exudation. The paleness of pork is inversely proportional to pH (Bendall & Swatland, 1988). The drip losses, muscle softness and pale musculature are linked to the denaturation of myosin and sarcoplasmic proteins (Bendall & Wismer-Pederson, 1962; Offer & Knight, 1988). Water holding capacity and color of pork are affected by rate of pH decline and ultimate pH (Bendall & Swatland, 1988; Offer & Knight, 1988). Red, soft, exudative (RSE) pork * Corresponding author. Tel.: +886-4-23590307; fax: +886-423596647. E-mail address: [email protected] (C.C. Kuo).
is a mild form of PSE; RSE samples would have become PSE if the pH would have decreased further (van Laack & Kauffman, 1999). PSE pork could be a consequence of rapid post-mortem glycolysis leading to a muscle pH value of about 5.5 while the carcass temperature is still high (Varnam & Sutherland, 1995). It was proposed that a pH 45 of approximately 6.2 could be used to discriminate between normal and PSE pork. The majority of white muscles on the carcass have ultimate pH values in the range 5.4–5.8 (Bendall & Swatland, 1988). The PSE condition is usually restricted to the muscles of ham and loin and is associated with lower processing yields, increased cooking losses, and reduced juiciness (Hedrick, Aberle, Forrest, Judge, & Merkel, 1994). PSE pork become internationally recognized as major economic factors in the consumption of fresh pork and in the manufacture of processed pork. Camou and Sebranek (1991) proposed that the possibility and feasibility of using PSE pork in processed meat products. They indicated that the PSE muscle protein gels exhibited decreased functionality, but enough proteins were present to facilitate protein-protein interactions and gel formation. Redden and Chen
0309-1740/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. PII: S0309-1740(02)00213-9
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(1995) used PSE pork for the manufacture of Chinese meatballs and dried meat floss (shredded meat), and found that PSE pork was not suitable for meatball production, even with the inclusion of potato or corn starch as a binding agent. However, the pale color of PSE pork used for manufacturing dried meat floss was highly favored by the tasting panel. Huang, Mikel, and Jones (1997) studied the effect of carrageenan on the quality of restructured PSE hams and found that carrageenan increased the texture and overall acceptability scores in PSE hams. Motzer, Carpenter, Reynolds, and Lyon (1998) also studied restructured hams made with PSE pork and binders, and reported that modified food starch could enhance the water retention of PSE pork in restructured ham. Li and Wick (2001) indicated that the addition of mechanically deboned turkey meat to processed meat made with PSE pork has the potential to enhance the economic value to both of these low value raw materials. Lipid oxidation in meat and meat products is a major cause of spoilage resulting in development of off flavor. Yasosky, Aberle, Peng, Mills, and Judge (1984) studied lipid oxidation (TBA value) and ultimate pH of ground pork, and found the TBA values of pork decreased as the pH values increased. They conclued that inhibition of oxidation occurred at high pH. McDonald and Hultin (1987) reported that lipid oxidation is affected by pH, lipid composition, ionic strength, temperature, redox potential, light exposure and iron content. Petrovic, Okanovic, and Rede (1995) studied the properties of normal and PSE pork and found the chemical composition of these two meat types similar; however, the pH value of PSE pork was lower than that of normal muscle. Arnau, Guerrero, Casademont, and Gou (1995) reported that the pH value between the PSE and normal dry cured hams was not different. Most of the previous studies were associated with the quality of meat products made from PSE pork hams; there is little information available regarding lipid oxidation, microbial growth and water activity of meat products made with PSE pork loin muscles. The objectives of this study were to compare the chemical and physical properties of PSE and normal pork loins, and to evaluate Chinese sausages made with different levels of PSE pork loins for pH value, lipid oxidation, water activity, lactic acid bacterial growth, and sensory properties during storage at 4 C.
2. Materials and methods 2.1. Raw materials Pigs (YorkshireLandraceDuroc) with a live weight of approximately 95–124 kg at the time of slaughter were used in this experiment. In order to obtain sufficient meat samples for three replications, 10 animals (five PSE; five
normal) were used. Twenty pork loins (Longissimus dorsi) were selected at a local commercial plant at 24-h postmortem. These were subjectively evaluated for color, texture and the amount of drip. Paler, watery and softer loins were classified as PSE muscle and separated from the normal loins, which were darker, drier and firmer in color or texture. Pork loins primal cuts were then deboned and trimmed of visible fat and connective tissue in the commercial plant. Boneless loins were wrapped with polyvinyl chloride (PVC) film and stored in boxes, and were placed in freezers (30 C) for about 24 h. Subsequently, the loins were transported to the university and stored at 18 C for about 2 weeks. All frozen meat samples were thawed at 4 C for about 24 h, and the drip loss was determined from weights recorded prior to thawing and immediately after thawing. Thawed pork loins were determined in the university laboratory for pH, and the pH of meat samples was measured with a portable pH meter (PHM 201, Meter Lab., Radiometer, Copenhagen, France). PSE and normal pork loins were assigned to each of three treatment groups: 100% Normal, 50% Normal+50% PSE and 100% PSE treatments. This experiment was replicated three times with triplicate samples in each treatment. 2.2. Chinese sausage preparation and processing yield Lean meat from the loins was ground through a 1.6-cm grinder kidney plate. The pork fat was cut manually into cubes (0.5 cm3). The meat block was composed of seven parts of coarse ground lean meat and three parts of cubed fat by weight. Lean meat and fat were thoroughly blended in a mixer. The curing ingredients added to each treatment (100% Normal, 50% Normal+50% PSE and 100% PSE treatments) were the same and consisted of sugar (10%), isolated soy protein (2%), sodium chloride (1.8%), sodium tripolyphosphate (0.3%), white pepper powder (0.1%), five spices powder (0.1%), erythorbic acid (0.02%), and sodium nitrite (0.012%). Percentage of all ingredients was based on the weight of the meat block. Phosphate and nitrite were dissolved in approximately 20 ml of distilled water prior to addition. All curing ingredients and the meat block were mixed thoroughly and cured at 4 C for 12 h and then stuffed into natural hog casings and linked into 10-cm units. The sausages were then dried in a forced air oven at 50 C for about 7 h. Finished sausages from each treatment were vacuum packaged (Nylon/Cast polypropylene=15/75 mil; 1925 cm) by using a Multivac (Gastrovac A 300/42, Germany) packaging machine. The sausages from each treatment were randomly assigned to storage for 0, 15, 30 and 45 days at 4 C. Processing yield was determined from weights recorded prior to drying and after removal from the forced air oven.
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Both raw pork meat and Chinese sausage samples were analyzed for percent moisture, fat and protein (AOAC, 1995). Prior to analyses, raw pork loins or two Chinese sausages from each treatment were finely ground using a food processor. The pH value of meat samples was determined according to Ockerman (1989). Of the meat samples, 10 g were blended with 100 ml of distilled water for 1 min using a blender (IKA-Labortecknic T-25, Germany) and the pH values were read with a portable pH meter (PHM 201, Meter Lab, Radiometer, Copenhagen, France).
and passed through a polyethylene strainer to remove connective tissue and debris. Five more volumes, resulting in 10 vol. (v/w) total of the original isolating medium, were used to further facilitate passage of myofibrils through the strainer. Again, the supernatant was sedimented at 1000 g for 15 min and the supernatants decanted. The sediments were washed three more times by suspending in 5 vol. (v/w) of the original isolating medium, and were sedimented at 1000 g for 15 min. Finally, the sedimented myofibrils were resuspended in 5 vol. (v/w) of the original isolating medium. The protein concentration determined by the biuret procedure described by Clark and Switzer (1977).
2.4. Color measurement
2.7. Catalase activity
Instrumental color values (L*, a *, b* values) of raw pork chops (1.0 cm thick) and Chinese sausages (0.5 cm) were evaluated using a Nippon Denshoku Industries Company ZE 2000 Color Difference Meter (Tokyo, Japan) standardized with a white plate (X=93.90, Y=91.89, Z=110.26). Measurements were averaged over six non-overlapped zones of each chop.
The hydrogen peroxide decomposition test procedure described by Ang, Liu, Townsend, and Fung (1994) was used. Hydrogen peroxide (4 ml, 3%) was added to a tube containing 2 g of meat sample and incubated at room temperature for up to 120 min. Observations of the reaction were made after incubation. Floating or separation of the solid phase indicated a positive enzyme reaction. Precipitation of all solids at the bottom of the tube indicated a negative reaction. The incubation time required to obtain a positive reaction was recorded. The quantitative analysis of the enzymatic activity was expressed as an inverse of incubation time (1/s).
2.3. Chemical analysis and ultimate pH
2.5. Water holding capacity Water holding capacity (WHC) of the meat samples was measured by the press method described by Ockerman (1989) and expressed as a percentage of bound water. The meat sample (0.5 g) was placed on a filter paper and pressed between two plexglass sheets with a Casver Lab press at 500 psi for 1 min. The inner and outer surface of pressed meat and juice were measured (in2) with a polar planimeter (Tamaya, Model Planix 7, Japan). % Free water ¼ ðtotal surface area meat film areaÞ 61:1=total moisture ðmgÞ of meat sample ð0:5 gÞ 100%
2.8. TBA value 2-Thiobarbituric acid (TBA) values were determined by the distillation method described by Ockerman (1989). Absorbances at 538 nm were read with an UVVIS spectrophotometer (Spectronic Genesys 5, Milton Roy, USA). TBA values were expressed as mg malonaldehyde/kg meat. 2.9. Water activity
% Bound water=100% % free water 2.6. Myofibrillar proteins The procedure used to determine myofibrillar proteins was similar to that of Olson, Parrish, and Stromer (1976). Myofibrils were isolated from normal and PSE muscles by homogenizing 4 g of minced muscle in a waring blendor for 30 s in 10 vol. (v/w) of a 2 C isolating medium containing 100 mM KCl, 20 mM potassium phosphate (pH 7.0), 1 mM EDTA and 1mM sodium azide. The homogenate was sedimented at 1000g for 15 min and the supernatant decanted. The sediment was resuspended at 1000g for 15 min and the supernatant decanted. The sediment was again resuspended in 5 vol. (v/w) of the original isolating medium
Water activity of the meat products was determined at room temperature using a water activity analyzer (Aqua Lab, Model CX-2, Washington, USA). 2.10. Microbiological evaluation After each storage interval, a package of sausage samples from each treatment was ground and mixed through a blender, which had been cleaned and sterilized. A 10-g ground meat sample was then aseptically removed and placed into stomacher bags containing 90 ml of a sterile peptone water (0.1%) solution. Meat samples were placed into a stomacher apparatus (Stomacher Lab-Blender 400, Tekmar Company, Cincinnati, OH) and homogenized for 2 min. Appropriate
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serial dilutions were made in sterile peptone water and 0.1 ml of each dilution were spread onto Lactobacilli MRS agar (Difco Laboratories, Detroit, MI). Plates were incubated at 37 C for 48 h, and the lactic acid bacterial colonies were counted and reported as CFU/g meat. 2.11. Sensory evaluation Sausage samples were heated on a frying pan to an internal temperature of 75 C monitored by a pocket thermocouple. A portion of sausage (about 0.5 cm) from each treatment was used for presentation to the panelists at ambient temperature. The panelists (n=10) consisted of graduate students, faculty and staff of the Tunghai University. Each panelist had previous sensory evaluation experience. Panelists were instructed to rinse their pallet with water between samples. At each evaluation three samples were coded with random numbers and evaluated for texture, flavor and overall acceptability on a 9-point hedonic scale (9=like extremely; 5=neither like nor dislike; 1=dislike extremely). Sensory scores of above 5.0 were assumed to be acceptable. Effect of storage time on sensory quality of Chinese sausages was not determined in this experiment. Only at day 15, a sensory acceptance panel test was conducted. 2.12. Statistical analysis This experiment was replicated three times with triplicate samples in each replication (n=9). Bacterial numbers of CFU/g were transformed to log10 for statistical analysis. Data were evaluated using SAS General Linear Models Procedures (SAS Institute, Inc., 1993). Treatment means were separated using Duncan’s new multiple range tests (SAS Institute, Inc., 1993). Statistical models included treatments (3: 100% Normal, 50% Normal+50% PSE, 100% PSE) and storage time (4: 0, 15, 30 and 45) as independent variables. Significance was established at P < 0.05.
3. Results and discussion 3.1. Physical and chemical properties of raw normal and PSE pork loins As would be expected, the ultimate pH values (Table 1) were higher (P < 0.05) for normal pork loin (5.96) than for PSE pork (5.60). van Laack et al. (1999) found the pH of PSE and normal pork loins was 5.32 and 5.64, respectively. Lien et al. (2002) also indicated that the pork chops from chilled PSE and normal loins were 5.2 and 5.6, respectively. Nam, Ahn, and Jo (2002) found that pH for PSE pork loins (5.47) was higher than that of normal pork (5.69). This result indicated
Table 1 The physical and chemical properties of raw normal and PSE pork loinsa Properties
Normal meat
PSE meat
PH L* a* b* Drip loss (%) Water holding capacity (% bound water ) Moisture (%) Crude fat (%) Crude protein (%) Myofibrillar proteins (mg/ml) Catalase activity (1/s)
5.96 a 44.8 b 17.5 a 9.9 b 4.51 b 70.5 a 73.6 a 3.8 a 21.2 b 12.07 a 0.22 a
5.60 b 51.5 a 16.3 a 11.7 a 8.34 a 66.5 b 72.1 b 2.3 b 22.8 a 6.34 b 0.28 a
a Values are means of three replicates (n=9). Means in the same row with different letters are significantly different (P<0.05).
that the pH values of PSE and normal pork were lower than that in our findings. This may be due to differences in experimental variables and conditions, including animal breed, postmortem muscle removal time, anatomical location of muscle or tissue site, animal diet, sample handling method, procedure or equipment used to determine pH value. Bendall and Swatland (1988) reported that the majority of white muscles on the carcass had ultimate pH in the range 5.4–5.8. Warner, Kauffman, and Greaser (1997) classified PSE hams as pH < 5.8, while normal muscles had pH values between 5.8 and 6.1. PSE pork had higher (P < 0.05) L* values (51.5) and b* values (11.7), but lower (P > 0.05) a* values (16.3) than those of the normal pork loins (44.8, 9.9 and 17.5, respectively). This was probably due to the denaturation of muscle proteins, resulting in pale (less redness), soft and exudative (more whiteness) condition in pork. Lien et al. (2002) found a L* value of 55.5 for normal pork and 59.2 for pork loins; PSE pork had a higher b* value (19.9) than normal pork (18.3). However, they indicated that the differences in a* value were not significantly different between normal and PSE pork. van Laack and Kauffman (1999) also found PSE pork loins had a higher L* value (55.9) than normal pork (45.1). Bendall and Swatland (1988) reported that the paleness of pork is inversely proportional to pH. Myosin denaturation is the main factor causing the unacceptable exudation in PSE pork (Offer et al., 1988). The differences in percentage drip loss between the normal (4.51) and PSE (8.34) were significant (P < 0.05). This result agreed with Lien et al. (2002) who found that PSE pork had a higher drip loss (3.3%) than normal pork (1.6%). van Laack and Kauffman (1999) also indicated that PSE pork had a higher drip loss (11.2%) than normal pork loins (4.2%). They used drip loss and L* values to classify PSE (drip loss > 6%; L* value > 50) and normal pork (drip loss < 6%; L* value < 50).
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As expected, water holding capacity, expressed as% bound water, of normal pork (70.5) was higher (P < 0.05) than that of PSE pork (66.5). The rate of pH declining and ultimate pH values are the two main determinations of water holding capacity (exudation) and color (Bendall & Swatland, 1988; Offer et al., 1988). The PSE pork loins had lower (P < 0.05) percent moisture (72.1) and fat (2.3), but higher (P < 0.05) percent protein (22.8) than the normal pork loins (73.6, 3.8 and 21.2, respectively). Okanovic, Petrovic, and Beara (1992) reported that the composition of normal and PSE hams were similar, but color, structure and technological properties of the two meat types were significantly different. Concentration of myofibrillar proteins or protein solubility was used as a measure of denaturation, as can be seen in Table 1. PSE pork had lower (P < 0.05) concentration of myofibrillar proteins (12.07 mg/ml) than the normal pork (6.34 mg/ml). These results indicated that proteins in PSE meat were denatured considerably. Researchers reported that PSE pork muscles tend to exhibit decreased protein extraction and solubility (Schimidt & Trout, 1982; Vadehra & Baker, 1970). Lawrie (1979) indicated that pork muscle with a fast rate of pH fall post mortem, resulting in an unusually low ultimate pH, which would tend to denature muscle proteins and lower their capacity to hold water. The lower the pH of animal muscles, the lower the water holding capacity and the extractability of the myofibrillar proteins. Petrovic et al. (1995) found that the composition of normal and PSE pork hams was similar, but PSE hams had lower salt soluble proteins and total pigment concentration. Activity of catalase, expressed as an inverse of incubation time (1/s), of normal (0.22) and PSE pork (0.28) was similar. Rhee (1988) reported that catalase activity may be important in decreasing the amount of H 2O2 remaining in the muscle tissue, was higher in pork longissimus dorsi (LD) muscle than in beef LD or chicken thigh or breast muscles; however, during storage at 20 C, the catalase activity would be limited. 3.2. Processing yield and composition of Chinese sausages The 100% Normal treatment (Table 2) had a higher (P < 0.05) processing yield (81.4%) than the 100% PSE treatment (79.6%) due to its higher water holding capacity or higher fat content (Table 1). The PSE meat groups had more myofibrillar proteins become partially denatured and lost their water holding capacity, resulting in lower processing yields. Also Arnau et al. (1995) suggested that the lower processing loss (higher processing yield) of meat product could be due to the barrier effect of fat on water diffusion and evaporation during processing. Candek-Potakar, Monin, and Ziender (2002) indicated that a lower dry-cured ham processing
Table 2 The processing yield and composition of Chinese sausages made from normal and/or PSE porka Meat type
Processing yield (%) Moisture (%) Crude protein (%) Crude fat (%)
100% Normal
50% Normal+ 50% PSE
100% PSE
81.4 a 45.1 a 20.0 b 22.1 a
80.7 a, b 43.5 b 21.0 a, b 21.4 a, b
79.6 b 42.7 b 21.6 a 20.8 b
a Values are means of three replicates (n=9). Means in the same row with different letters are significantly different (P<0.05).
loss could be attributed to its higher intramuscular fat content. Partially due to its higher fat content, the 100% Normal treatment had higher processing yield than the other two treatments. The processing yield decreased as the proportion of PSE pork increased. Motzer et al. (1998) studied the restructured hams made with different levels of PSE pork and found a similar result. Honkavaara (1990) also reported that cooked hams made from PSE pork had a lower cooking yield than the normal cooked hams, due to decreased water holding capacity. Hedrick et al. (1994) indicated that PSE condition was associated with lower processing yields, increased cooking losses, and reduced juiciness The 100% Normal treatment had higher (P < 0.05) moisture (45.1) and fat content (22.1), but lower protein content (20.0) than the 100% PSE treatment (42.7, 20.8 and 21.6, respectively). The 100% PSE treatment contained a slightly lower percentage of moisture and fat, but a higher percentage of protein than the 50% Normal+50% PSE treatment; however, the differences were not significant (P > 0.05). Honkavaara (1990) studied the chemical composition of cooked PSE pork hams and found a similar result. 3.3. Changes in pH value The pH values of Chinese sausages made from different levels of PSE meat were significantly different (P < 0.05) at day 0 (Fig. 1). As expected, sausages made from PSE pork (the 100% PSE and the 50% Normal+50% PSE treatments) had lower (P < 0.05) pH values (6.08 and 6.16, respectively) than the 100% Normal treatment (6.21). This was probably due to the lower pH values of the raw PSE muscle (5.60), compared to the normal muscle (5.96; Table 1). The pH value of the 100% PSE treatment was lower than that of the 50% Normal+50% PSE treatment; however, the differences between these two treatments were not significant. Petrovic et al. (1995) reported that the pH values of PSE cooked hams was lower than that of of normal pork. Motzer et al. (1998) manufactured hams with PSE pork and also found the 100% PSE meat
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C.C. Kuo, C.Y. Chu / Meat Science 64 (2003) 441–449 Table 3 Lactic acid bacterial growth (log CFU/g) of Chinese sausages made from normal and/or PSE pork as affected by storage timea Days
Meat type
0 15 30 45
100% Normal
50% Normal+ 50% PSE
100% PSE
4.34 5.48 6.43 7.42
4.28 5.46 6.38 7.40
4.20 5.36 6.32 7.36
a, a, a, a,
w x y z
a, a, a, a,
w x y z
a, a, a, a,
w x y z
a Values are means of three replicates (n=9). Means in the same row with the same letter are not significantly different (P <0.05). Means in the same column with different letters (w–z) are significantly different (P<0.05).
Fig. 1. The pH value of Chinese sausages made from normal and/or PSE pork as affected by storage time (n=9). Values on the display day with different superscript letters (a, b, c) are significantly different (P<0.05).
treatment had lower pH values than the 50% Normal+50% PSE blend and the 100% Normal treatments. At each storage time (15, 30 or 45 days), the 100% PSE treatment consistently had the lowest pH value, followed by the 50% Normal+50% PSE and the 100% Normal treatments. The pH value of all sausage samples decreased as the storage time increased. This was probably due to the accumulation of lactic acid produced by the growth of lactic acid bacteria in vacuum-packed sausages. Ockerman and Kuo (2001) reported that the pH value of drycured hams decreased during storage. This decrease was probably due to lactic acid producing bacteria fermenting sucrose to lactic acid. Banwart (1979) indicated that cured meat became sour (low pH) because of the fermentation of carbohydrates by lactic acid bacteria. Chinese sausages contained 10% of sugar, which probably could be used by lactic acid bacteria to produce lactic acid, resulting in lower pH value during storage. At days 0, 15, 30 and 45, the 100% PSE treatment consistently had lower pH values than the 50% Normal+50% PSE treatment or the 100% Normal treatment even though their lactic acid bacterial counts were not different (Table 3). Perhaps because of the 100% PSE treatment had lower water holding capacity and higher drip loss among these treatments; therefore, more phosphate and other basic compounds were probably lost during storage, resulting in lower pH value. Guerrero, Gou, Alonso, and Arnau (1996) indicated that the pH value diminished during the salting period in ham muscles was due to the loss of phosphate or some other basic compounds, and the salt uptake. Arnau et al. (1995) reported that PSE and normal drycured hams differed only in pH45, but not during the processing.
3.4. TBA value Lipid oxidation, expressed as the TBA value, is shown in Table 4. During storage, the differences in TBA values among these three treatments were not significantly. However, the 100% Normal treatment had slightly higher (P > 0.05) TBA values than the 100% PSE or the 50% Normal+50% PSE treatments due to its higher lipid content (Table 1) Ockerman et al. (2001) reported that TBA values were positively correlated with fat content in dry-cured hams. Since fat is more apt to produce oxidative rancidity. Rhee, Anderson, and Sams (1996) indicated that TBA values of frozen raw samples for beef and pork were higher due to their higher heme iron content. However, in a previous study, we found that PSE pork had lower heme iron content than normal pork (data not shown). As would be expected, mean TBA values of all meat products increased as the storage time increased, indicating that lipid oxidation had occurred in the vacuumpackaged Chinese sausages. However, TBA values of all products throughout storage time were in the range of 0.09–0.32, which were relatively low and well below the
Table 4 TBA value of Chinese sausages made from normal and/or PSE pork as affected by storage timea Days
0 15 30 45
Meat type 100% Normal
50% Normal+ 50% PSE
100% PSE
0.17 0.22 0.27 0.32
0.13 0.20 0.23 0.28
0.09 0.15 0.20 0.23
a, a, a, a,
w (100) w, x (129) x, y (159) y (188)
a, a, a, a,
w (100) w, x (154) x, y (177) b, y (215)
a, a, a, a,
w (100) w, x (167) x, y (222) y (256)
a Values are means of three replicates (n=9). Means in the same row with the same letter are not significantly different (P <0.05). Means in the same column with different letters (w–y) are significantly different (P <0.05). Value in brackets is the % of initial TBA value within each meat type.
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threshhold value (1.0 mg malonaldehyde/kg) for detection of warmed-over flavor (Boles & Parrish, 1990). Gray and Pearson (1987) indicated that rancid flavor was initially detected between TBA values of 0.5 and 2.0. From our result, it suggested that vacuum-packaged Chinese sausages could be stored at 4 C up to 45 days without causing any serious rancid problem. The relatively low extent of lipid oxidation could be attributed to the vacuum packaging and low storage temperature. Kuo, Yuan, Lee, and Shin (1986) studied the effect of packaging on quality of Chinese sausages and found that the use of vacuum packaging could be a means of reducing lipid oxidation in meat products. Although TBA values among these treatments were not different (P > 0.05), the increase% of TBA values within each treatment was different due to its different lipid oxidation rate. On day 15, 30 and 45, TBA values of the 100% Normal, 50% Normal+50% PSE, and 100% PSE treatments were 29–88, 54–115 and 67–156% higher than those at zero time, respectively (Table 4). These results demonstrated that the lipid oxidation rate was much faster in the Chinese sausages made from 100% PSE meat even though their initial and final TBA values were lower. The higher increase% of TBA values in the 100% PSE treatment was probably due to its lower pH value. This result agreed with Yasosky, Aberle, Peng, Mills, and Judge (1984) who studied lipid oxidation and pH value (5.4–6.8) of ground pork after 12 days of storage, and concluded that inhibition of oxidation occurred at high pH. Nam et al. (2001) also reported that PSE pork was more susceptible to lipid oxidation than the normal and dark, firm, dry (DFD) pork when irradiated and stored under aerobic conditions. Shin, Abugroun, Forrest, Okos, and Judge (1993) found that pre-rigor cooked roasts (higher pH) are better in oxidative stability than post-rigor cooked meats. Chen, Forrest, Peng, Pratt and Judge (1993) reported an inverse relationship between pH and TBA values. McDonald and Hultin (1987) indicated that lipid oxidation was not only affected by pH, but also lipid composition, ionic strength, temperature, redox potential, light exposure, and iron content. 3.5. Water activity At zero time, the 100% Normal treatment had lower (P < 0.05) water activity (0.946) in comparison with the 100% PSE (0.956) and the 50% Normal+50% PSE (0.953) treatments (Table 5). The difference in water activity between the 100% Normal and the 100% PSE treatments was significant (P < 0.05), but small. Water activity for all sausages was below 0.96. Leistner, Rodel, and Krispien (1981) reported that the main hurdles for microbiologically stability of meat products are water activity, pH and temperature. Banwart (1979) indicated that at a water activity of 0.96 or less, most of the usual
Table 5 Water activity of Chinese sausages made from normal and/or PSE pork as affected by storage timea Days
0 15 30 45
Meat type 100% Normal
50% Normal+ 50% PSE
100% PSE
0.946 0.943 0.935 0.930
0.953 0.945 0.938 0.934
0.956 0.949 0.945 0.939
b, w a, w b, x b, x
a, a, a, a,
w x b, y b, y
a, a, a, a,
w x x, y y
a Values are means of three replicates (n=9). Means in the same row with different letters (a–c) are significantly different (P <0.05). Means in the same column with different letters (w–y) are significantly different (P<0.05).
microorganisms causing spoilage of fresh meat are inhibited. After 15, 30 and 45 days of storage, the 100% PSE treatment consistently retained a higher water activity, followed by the 50% Normal+50% PSE and 100% Normal treatments even though its moisture content was lower (Table 2). Changes in water activity of all meat products at each storage time followed essentially the same pattern as those at zero time. These results indicate that the higher the proportion of PSE pork used for manufacturing of Chinese sausages, the higher their water activity (Table 2). This could be best explained by its fat content of the meat product. Leistner et al. (1981) reported that water activity of the lean and the fat portion do not come to equilibrium either in short- or long-ripened meat products. In general, water activity of meat products increased as their fat content decreased. Since the 100% PSE treatment had lower fat percent (20.8), compared to the 100% Normal (22.1) and the 50% Normal+50% PSE (21.4) treatments (Table 2); therefore, water activity of the 100% PSE treatment was higher than the other two treatments. During storage, there was a decrease in water activity in all meat treatments. Kuo et al. (1986) studied the effect of fat and nitrite levels on quality of Chinese sausages and also found a similar result. Arnau et al. (1995) indicated that a decrease in water activity is the main factor responsible for the preservation of the dry-cured hams, which might be achieved essentially by the penetration of salt and removal of water from the meat. They found that PSE hams contained more salt than normal hams. 3.6. Lactic acid bacteria No differences (P > 0.05) in lactic acid bacterial counts were observed among these treatments at any given storage time; but during the storage period, counts increased logarithmically (Table 3). Due to high levels of initial contamination, the numbers of lactic acid bacteria of all treatments increased to 5.2–5.5, 6.2–6.4
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Table 6 Sensory property scores of Chinese sausages made from normal and/ or PSE pork Sensory propertya
Texture Flavor Overall acceptability
Meat type 100% Normal
50% Normal+ 50% PSE
100% PSE
7.4 b 7.1 b 7.2 b
6.8 c 6.6 c 6.6 c
5.4 d 5.8 d 5.5 d
a Hedonic scale: 1=extremely, dislike in texture, flavor or overall acceptability; 5=neither like nor dislike; 9=extremely like in texture, flavor or overall acceptability. Values are means of three replicates (n=9). Means in the same row with different letters (b–d) are significantly different (P <0.05).
content than normal pork. The processing yield and chemical properties of Chinese sausages were affected by meat type; and pH, TBA values and lactic acid bacteria were affected by storage time. As the storage time increased while the pH values decreased, TBA values and lactic acid bacteria increased. TBA values as observed throughout storage time were below 0.4, suggesting that the vacuum-packaged Chinese sausages could be stored up to 45 days at 4 C. Sensory properties of Chinese sausages made from PSE meat (100 or 50%) were inferior to those of the control, but were of acceptable quality.
References and 7.3–7.4 log CFU/g at 15, 30 and 45 days of storage, respectively. Lactic acid bacteria have been found to be one of the natural microbial flora of Chinese sausages (Kuo & Lin, 1993). Gill (1982) reported that the flora of vacuum packaged meat is usually dominated by species of Lactobacillus. The normal spoilage of cured meat products is one of a souring nature due to the growth of Lactobacilliace, but other organisms may also be found. During storage, the growth of lactic acid bacteria probably caused the accumulation of lactic acid, resulting in decrease of pH values of all meat samples (Fig. 1). 3.7. Sensory properties Sensory properties of Chinese sausages made from different levels of PSE meat were compared (Table 6). Effect of storage time on sensory quality of these meat products was not determined in this experiment. Only the meat products stored at 4 C for 15 days were evaluated. Due to their lower moisture and fat contents, and slightly higher acid flavor (lower pH value), the 100% PSE and the 50% Normal+50% PSE treatments had lower (P < 0.05) texture, flavor and overall acceptability scores than the 100% Normal treatment, but were of acceptable quality. A 9-point hedonic scale was used to evaluate the sensory quality of Chinese sausages in this study. The sensory scores of above 5.0 (neither like nor dislike) were assumed to be acceptable. (Table 6). The differences in texture, flavor or overall acceptability scored between the 100% PSE and the 50% Normal+50% PSE treatments were also significant (P < 0.05).
4. Conclusions PSE pork loins had lower pH value, water holding capacity, moisture, fat and myofibrillar proteins contents, but higher L* values, drip loss and protein
Ang, C. Y. W., Liu, F., Townsend, W. E., & Fung, D. Y. C. (1994). Sensitive catalase test for end-point temperature of heated chicken meat. Journal of Food Science, 59, 494–497. AOAC. (1995). Official Methods of Analysis (16th ed.). Virginia, USA: Association of Official Analytical Chemists International. Arnau, J., Guerrero, L., Casademont, G., & Gou, P. (1995). Physical and chemical changes in different zones of normal and PSE dry cured ham during processing. Food Chemistry, 52, 63–69. Banwart, G. J. (1979). Basic Food Microbiology. Connecticut: AVI Publishing Company. Bendall, J. R., & Swatland, H. J. (1988). A review of the relationships of pH with physical aspects of pork quality. Meat Science, 24, 85– 126. Bendall, J. R., & Wismer-Pedersen, J. (1962). Some properties of the myofibrillar proteins of normal and watery pork muscle. Journal of Food Science, 27, 144–159. Boles, J. A., & Parrish, F. C. Jr. (1990). Sensory and chemical characteristics of precooked microwave-reheatable pork roasts. Journal of Food Science, 55, 618–620. Candek-Potokar, M., Monin, G., & Zlender, B. (2002). Pork quality, processing, and sensory characteristics of dry-cured hams as influenced by Duroc crossing and sex. Journal of Animal Science, 80, 988–996. Camou, J. P., & Sebranek, J. G. (1991). Gelation characteristics of muscle protein from pale, soft, exudative (PSE) pork. Meat Science, 30, 207–220. Chen, W., Forrest, J. C., Peng, I. C., Pratt, D. E., & Judge, M. D. (1993). Palatability of prerigor cooked boar meat. Journal of Animal Science, 71, 645–650. Clark, J. M. Jr., & Switzer, R. L. (1977). Experimental biochemistry. San Francisco: W. H. Freeman & Company. Gill, C. O. (1982). Microbial interaction with meats. In M. H. Brown (Ed.), Meat microbiology (pp. 246). London/New York: Applied Science Publishers. Gray, J. I., & Pearson, A. M. (1987). Rancidity and warmed-over flavor. Advanced Meat Research, 3, 221–269. Guerrero, L., Gou, P., Alonso, P., & Arnau, J. (1996). Study of the physicochemical and sensorial characteristics of dry-cured hams in three pig genetic types. Journal of Science and Food Agriculture, 70, 526–530. Hedrick, H. B., Aberle, E. D., Forrest, J. C., Judge, M. D., & Merkel, R. A. (1994). Principles of Meat Science. Iowa: Kendall/Hunt Publishing Company. Honkavaara, M. T. (1990). Effect of porcine stress on the development of PSE meat, its characteristic and influence on the economics of meat product manufacture. Dissertation Abstracts International, C51, 28, ISBN 952–90118–7-3.
C.C. Kuo, C.Y. Chu / Meat Science 64 (2003) 441–449 Huang, C. Y., Mikel, W. B., & Jones, W. R. (1997). Carrageenan influences on the characteristic of restructured normal and pale, soft and exudative hams. Journal of Muscle Foods, 8, 85–93. Kuo, C. C., & Lin, Y. H. (1993). Effects of sodium lactate and sodium acetate on microbial counts, pH and water activity of Chinese sausages. Tunghai Journal, 34, 1069–1088. Kuo, J. C., Yuan, C. K. R., Lee, F. L., & Shin, C. H. (1986). Vacuum packaged Chinese sausage as influenced by different fat and nitrite levels. Chinese Food Science, 13, 21–31. Lawrie, R. A. (1979). Meat science. New York: Pergamon Press. Leistner, W., Rodel, W., & Krispien, K. (1981). Microbiology of meat and meat products in high- and intermediate- moisture ranges. In L. B. Rockland, & G. F. Stewart (Eds.), Water activity: influences on food quality (pp. 855–916). New York/London/Toronto/Sydney/San Francisco: Academic Press. Li, C. T., & Wick, M. (2001). Improvement of the physicochemical properties of pale soft and exudative (PSE) pork meat products with an extract from mechanically deboned turkey meat (MDTM). Meat Science, 58, 189–195. Lien, R., Hunt, M. C., Anderson, S., Kropf, D. H., Loughin, T. M., Dikeman, M. E., & Velazco, J. (2002). Journal of Food Science, 67, 1007–1010. McDonald, R. E., & Hultin, H. O. (1987). Some characteristics of the enzymic peroxidation system in the microsomal fraction of flounder skeletal muscle. Journal of Food Science, 52, 15–21 27. Motzer, E. A., Carpenter, J. A., Reynolds, A. E., & Lyon, C. E. (1998). Quality of restructured hams manufactured with PSE pork as affected by water binders. Journal of Food Science, 63, 1007–1011. Nam, K. C., Ahn, D. U., & Jo, C. (2001). Lipid oxidation, color, volatiles, and sensory characteristics of aerobically packaged and irradiated pork with different ultimate pH. Journal of Food Science, 66, 1225–1229. Ockerman, H. W. (1989). Quality control of postmortem muscle tissue. Ohio: The Ohio State University. Ockerman, H. W., & Kuo, J. C. (2001). Effects of nitrate and storage on the properties of tumbled dry-cured hams. In M. L. Eastrige (Ed.), Research and Reviews: Meat 2001 (pp. 67–72). Ohio: Ohio Agricultural Research and Development Center / Ohio State University / College of Food, Agricultural, and Enviromental Sciences. Offer, G., & Knight, P. (1988). The structural basis of water-holding in meat part II: Drip losses. In R. Lawrie (Ed.), Development in meat science (pp. 173–243). New York: Elsevier Applied Science.
449
Okanovic, D., Petrovic, L., & Beara, M. (1992). Incidence of the PSE defect in hams at the Mitros meat factory and some characteristics of the affected muscles. Tehnologija Mesa, 33, 211–216. Olson, D. G., Parrish, F. C. Jr., & Stromer, M. H. (1976). Myofibril fragmentation and shear resistance of three bovine muscles during postmortem storage. Journal of Food Science, 41, 1036–1041. Redden, V. R., & Chen, T. (1995). The potential of Chinese meatballs and dried meat as value added PSE pork products. Food Australia, 47, 323–326. Petrovic, L., Okanovic, D., & Rede, R. (1995). Film-packed cooked hams from PSE meat. Fleischwirtschaft, 75, 480–481. Rhee, K. S. (1988). Enzyme and nonenzyme catalysis of lipid oxidation in muscle foods. Food Technology, 42, 127–132. Rhee, K. S., Anderson, L. M., & Sams, A. R. (1996). Lipid oxidation potential of beef, chicken, and pork. Journal of Food Science, 61, 8– 12. SAS Institute, Inc.. (1993). SAS user’s guide: statistics, 1993 Edition. Cary, NC: SAS Institute, Inc. Schmidt, G. R., & Trout, G. R., (1982). Chemistry of meat binding. In Proceedings of Meat Science Technology International Symposium, 1–4 November 1982. Lincoln: NB. Shin, H. K., Abugroun, H. A., Forrest, J. C., Okos, M. R., & Judge, M. D. (1993). Effect of heating rate on palatability and associated properties of pre- and post-rigor muscle. Journal of Animal Science, 71, 939–945. Solomon, M. B., van Laack, R. L. J. M., & Eastrige, J. S. (1998). Biophysical basis of pale, soft, exudative (PSE) pork and poutry muscle: a review. Journal of Muscle Foods, 9, 1–12. Vadehra, D. V., & Baker, R. C. (1970). The mechanisms of heat initiated binding of poultry meat. Food Technology, 24, 766–775,778– 779. van Laack, R. L. J. M., & Kauffman, R. G. (1999). Glycolytic potential of red, soft, exudative pork longissimus muscle. Journal of Animal Science, 77, 2971–2973. Varnam, A. H., & Sutherland, J. P. (1995). Meat and meat products: technology, chemistry and microbiology. London: Chapman & Hall. Warner, R. D., Kauffman, R. G., & Greaser, M. L. (1997). Muscle protein changes postmortem in relation to pork quality traits. Meat Science, 45, 339–352. Yasosky, J. J., Aberle, E. D., Peng, I. C., Mills, E. W., & Judge, M. D. (1984). Effects of pH and time of grinding on lipid oxidation of fresh ground pork. Journal of Food Science, 49, 1510–1512.