The relation of blood glucose level to muscle fiber characteristics and pork quality traits

Meat Science 83 (2009) 62–67

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The relation of blood glucose level to muscle fiber characteristics and pork quality traits J.H. Choe a, Y.M. Choi a, S.H. Lee a, Y.J. Nam a, Y.C. Jung b, H.C. Park c, Y.Y. Kim d, B.C. Kim a,* a

Division of Food Bioscience and Technology, College of Life Sciences and Biotechnology, Korea University, 5-1 Anam-dong, Sungbuk-gu, Seoul 136-713, South Korea Jung P & C Institute, 272-5 Veterinary Science Center, Seohyeon-dong, Bundang-gu, Seongnam-si, Gyeonggi-do 463-050, South Korea c Dasan-jong don, Gasan-ri, Unbong-eup, Namwon-si, Jeonbuk 590-831, South Korea d Department of Food and Animal Biotechnology, College of Agriculture and Life Sciences, Seoul National University, 599 Gwanak-ro Gwanak-gu, Seoul 151-742, South Korea b

a r t i c l e

i n f o

Article history: Received 15 July 2008 Received in revised form 4 March 2009 Accepted 30 March 2009

Keywords: Blood glucose Muscle fiber characteristics Glycolytic rate Protein solubility Pork quality

a b s t r a c t The purpose of this study was to examine the relationships between blood glucose level, muscle fiber characteristics, and pork quality. Muscle samples were classified into three groups based on blood glucose level measured at slaughter. Pigs with higher area percentages of fiber type IIB showed higher blood glucose levels compared to pigs with lower area percentages of fiber type IIB. The high blood glucose level group presented lower pH values at 45 min and 24 h postmortem, and also had higher L* values and reduced water holding capacity. In addition, blood glucose level had a negative relationship with pH45 min and the solubility of sarcoplasmic and myofibrillar proteins, whereas it had a positive relationship with drip loss and filter-paper fluid uptake. In conclusion, blood glucose level was related to muscle fiber area composition and could partially indicate ultimate pork quality. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction Meat comes from skeletal muscle which is composed of different muscle fibers, which can be categorized as type I, IIA, and IIB based on their contractile and metabolic properties (Brook & Kaiser, 1970a; Larzul et al., 1997; Peter, Barnard, Edgerton, Gillespie, & Stempel, 1972). These contractile and metabolic properties strongly affect the pattern of energy metabolism within live animals (Hocquette, Ortigues-Marty, Pethick, Herpin, & Fernandez, 1998), as well as during the postmortem conversion of muscle to meat (Monin & Ouali, 1992). Moreover, insulin sensitivity and glycogen level are different among muscle fiber types (Fernandez, Meunier-Salaün, & Mormedem, 1994; He, Watkins, & Kelley, 2001; Karlsson, Klont, & Fernandez, 1999). In pigs, the main sources of glucose for glycolysis are blood glucose and glucose stored as glycogen within muscle. After exsanguination, when oxygen is not available to the muscle, glycolysis results in lactate formation (i.e., lactate formation is a prerequisite for anaerobic energy production) (Pösö & Puolanne, 2005). The lactate formed cannot be removed and accumulates in the muscle, causing a decline in muscle pH (Pösö & Puolanne, 2005; Scheffler & Gerrard, 2007). This decline in pH strongly affects muscle protein denaturation and subsequently meat quality (Honikel & Kim, 1986; * Corresponding author. Tel.: +82 2 3290 3052; fax: +82 2 925 1970. E-mail address: [email protected] (B.C. Kim). 0309-1740/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2009.03.011

Irving, Swatland, & Millman, 1989; Joo, Kauffman, Kim, & Park, 1999; Offer et al., 1989; Scheffler & Gerrard, 2007). Thus, the contents of glucose and glycogen in muscle can determine the rate and extent of postmortem glycolysis. There are many studies that have examined the effects of glucose and glycogen contents on postmortem changes and meat quality (Choe et al., 2008; Choi, Ryu, & Kim, 2007; Fernandez & Tornberg, 1991; Ryu, Choi, & Kim, 2005). Living organisms regulate their blood glucose levels for homeostasis, and thus blood glucose is maintained within a reference range. Blood glucose levels are primarily regulated by the balance between anabolic (insulin) and catabolic (glucagon, catecholamine, growth hormone) hormones (Maughan, 2005; Tappy, 2008). When blood glucose levels are high, insulin is secreted to promote glucose uptake from the blood into the muscles and liver. In contrast, when blood glucose levels are low, catabolic hormones enhance hepatic glucose production and decrease glucose utilization in skeletal muscle and adipose tissue (Tappy, 2008). However, individuals who have the metabolic disorder remain in a state of high or low blood glucose (World Health Organization, 1999). Thus, the blood glucose level is used for the diagnosis and management of the disease because blood glucose measurements are rapid and easy. In addition, some studies have looked at blood metabolite concentrations in cattle, suggesting that such concentrations may be useful indicators for evaluating metabolic changes (Arai et al., 2003, 2006; Mori et al., 2007; Sako et al., 2007). Also, a close relationship has been shown between free glucose in exudates and

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meat quality traits (Hamilton, Miller, Ellis, McKeith, & Wilson, 2003). These previous studies, however, focused on cattle and free glucose in exudates, and were not centered on pork quality. Therefore, the purpose of this study was to examine the relationships between blood glucose level at slaughter, muscle fiber characteristics, and pork quality measurements.

2. Materials and methods 2.1. Animals and muscle samples A total of 160 crossbred (Landrace  Yorkshire  Duroc) pigs were evaluated. The treatment conditions for all pigs were similar both before and after slaughter, and all treatment conditions and experimental procedures were approved by the Ministry for Food, Agriculture, Forestry, and Fisheries. The pigs were fed the same commercial diet and were raised in different pens at the same farm under similar conditions. The pigs were transported to a commercial abattoir under the same conditions and handling, and were slaughtered at a similar live weight (110 ± 5 kg). During the winter period, the pigs were slaughtered in three batches (50, 50, and 60 pigs per each slaughter batch) at the slaughter plant by standard procedures under the supervision of the Korean grading service for animal products. The slaughter plant used electrical stunning and a traditional scalding–singeing process. Following electrical stunning, while the pigs were exsanguinated, blood samples were collected to measure blood glucose levels. After evisceration, the carcasses were weighed and the loin eye area was measured at the level of the last rib. At 45 min postmortem, muscle samples were taken for histochemical analysis from the longissimus dorsi muscles at the 8th thoracic vertebra. After 24 h of chilling in 4 °C cold room, samples from the pork loins (the 10th–13th thoracic vertebra) were taken to measure meat quality traits and protein solubility. 2.2. Blood glucose level Blood samples were collected at the slaughter plant during exsanguination using 10.0 ml tubes treated with heparin (BD VacutainerÒ sodium heparin tube, Becton Dickinson). The blood glucose levels of the samples were measured immediately using a human blood glucose checking device (OneTouch UltraÒ, LifeScan, Inc.). This process involved the addition of over 1 ll of sample to a test strip that was then fed into a glucose analyzer. All measurements were done within 10 min after exsanguination. 2.3. Histochemical analysis At 45 min postmortem, the muscle samples were cut into 0.5  0.5  1.0 cm pieces, promptly frozen in isopentane cooled by liquid nitrogen, and stored at 80 °C until subsequent analyses. Using a cryostat (CM1850, Leica, Germany) at 20 °C, serial transverse muscle sections (10 lm) were obtained from each sample and then mounted on glass slides. For classifying muscle fiber types of samples, staining method for the myofibrillar adenosine triphosphatase (mATPase) activity was used (Brook & Kaiser, 1970b; Lind & Kernell, 1991). Staining procedure is as follows. (1) Unfixed sections were pre-incubated at room temperature for 10 min in a buffer consisting of 100 mM potassium chloride in 100 mM sodium acetate, adjusted to pH 4.7 with acetic acid. (2) Sections washed for 30 s in a 20 mM glycine buffer (pH 9.4) containing 20 mM CaCl2. (3) Sections were incubated at room temperature for 25 min in 40 mM glycine buffer (pH 9.4) containing 20 mM CaCl2 and 2.5 mM ATP disodium salt. (4) Sections washed in three 30 s changes of 1% CaCl2. (5) Sections kept in 2% CoCl2

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for 3 min and washed in three 30 s changes of distilled water. (6) Sections immersed in 1% yellow ammonium sulfide solution for 30 s and washed in distilled water. Thereafter, sections embedded in glycerol jelly. All histochemical samples were examined by an image analysis system. The operational system consisted of an optical microscope equipped with a CCD color camera (IK-642 K, Toshiba, Japan) and a standard workstation computer that controlled the entire image analysis system (Image-Pro Plus, Media Cybernetics, L.P., USA). All portions of the analyzed sections were free from tissue disruption and freeze-damage; approximately 600 fibers per sample were evaluated. Using the nomenclature of Brook and Kaiser (1970a, 1970b), the muscle fibers were divided into type I, IIA, and IIB. The fiber cross-sectional area was the ratio of the total fiber area measured to the total number of fibers counted. Fiber density (fiber number/mm2) was calculated from the mean number of fibers per mm2. The fiber area percentage was the ratio of the total cross-sectional area of each fiber type to the total measured fiber area, and fiber number percentage was obtained from the ratio of the number of each fiber type to the total number of fibers counted. 2.4. Meat quality traits and protein solubility In cold room, muscle pH at 45 min postmortem (pH45 min) and 24 h postmortem (pH24 h) were measured directly on the carcasses at the 7th/8th thoracic vertebra using a spear-type electrode (PH 27-SS, IQ Scientific Instruments Inc., USA) with portable pH meter (IQ-150, IQ Scientific Instruments Inc., USA). In order to evaluate water holding capacity (WHC), measurements for drip loss, cooking loss (Honikel, 1998), and filter-paper fluid uptake (FFU) (Kauffman, Eikelenboom, van der Wal, Merkus, & Zaar, 1986) were performed. For drip loss, meat samples were cut from carcasses at 24 h postmortem in 4 °C cold room and immediately weighed (initial weight for drip loss). Samples were placed in the netting and suspended in an inflated bag, ensuring that the sample does not contact with the bag. After 48 h storage period at 4 °C, samples were taken from the bag, gently blotted dry and weighed. Drip loss was expressed as percentages of the initial sample weight (Honikel, 1998). For cooking loss, different samples were freshly cut from carcasses at 24 h postmortem in 4 °C cold room and weighed (initial weight for cooking loss). The samples were put in thin-walled polyethylene bags and these were placed in a continuously boiling water bath. Samples were cooked to 75 °C internal temperature. When the end point temperature was attained, samples were removed from the water bath. Thereafter, samples were cooled in ice slurry and held in 4 °C cold room until equilibrated. Samples were taken from the bag, blotted dry and weighed. Cooking loss is expressed as a percentage of the initial sample weight (Honikel, 1998). For FFU, different samples were cut from carcasses at 24 h postmortem in 4 °C cold room and filterpaper (Whatman #2, 42.5 mm in diameter) was pre-weighed. Then we put the filter-paper on surface of sample, absorbed fluids (<2 s), and weighed the filter-paper again. FFU was expressed as milligrams of exudate absorbed into the filter-paper. Meat color was measured with a Minolta chromameter (CR300, Minolta Camera Co., Japan). Samples were cut from carcasses at 24 h postmortem in 4 °C cold room and placed on the table for 30 min in 4 °C cold room to expose the surface of the samples to air without any packaging (for bloom) prior to measuring meat color. The CR-300 contains a pulsed xenon lamp in the measuring head as a light source, and was calibrated against the calibration plate supplied by the manufacturer. The illuminant used was C, and the standard observer position was 2°. Only the light reflected perpendicular to the specimen surface is collected by the optical fiber cable for color analysis. The average of triplicate measurements was recorded and the results were expressed as Commission

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Internationale de l’Eclairage (Commission Internationale de l’Eclairage, 1978) lightness (L*), redness (a*), and yellowness (b*). Samples were taken from carcasses at 24 h postmortem in 4 °C cold room, promptly frozen by liquid nitrogen and stored at 80 °C until protein solubility analysis. To determine sarcoplasmic protein solubility, muscle samples were made into muscle powder using Waring blender (7010/51BL30, Waring CommercialÒ, USA) adding liquid nitrogen and sarcoplasmic protein was extracted immediately from 1 g of the muscle powder using 10 ml of ice-cold 0.025 M potassium phosphate buffer (pH 7.2) (Joo et al., 1999). To determine total (sarcoplasmic + myofibrillar) protein solubility, muscle samples were also made into muscle powder using Waring blender adding liquid nitrogen and the total protein was extracted immediately from 1 g of the muscle powder using 20 ml of ice-cold 1.1 M potassium iodide in a 0.1 M phosphate buffer (pH 7.2) (Joo et al., 1999). The samples were homogenized on ice with a polytron at the lowest setting, and then left on a shaker at 4 °C overnight. Next, the samples were centrifuged at 1500g for 20 min, and the protein concentrations of the supernatants were determined via the Biuret method (Gornall, Bardawill, & David, 1949). Myofibrillar protein solubility was obtained by the difference between the total and sarcoplasmic protein solubilities (Joo et al., 1999). 2.5. Statistical analysis The blood glucose levels were classified using cluster analysis with the FASTCLUS program from SAS Institute (2001). The observations were allocated to the groups based on the smallest Euclidean distance from the initial seeds in the cluster. The data were classified into three clusters according to blood glucose level (high, n = 42; intermediate, n = 72; low, n = 46). A General Linear Model was used to evaluate the significant differences among the high, intermediate, and low blood glucose level groups; the model was: yijk = l + BGi + Sj + Bk + eijk, where yijk is the observation; l is the general mean; BGi is the fixed effect of the blood glucose level

i; Sj is the fixed effect of sex j; Bk is the fixed effect of batch k; and eijk is the random error. When significant differences (P < 0.05) were detected, the mean values were separated by the probability difference (PDIFF) option at a predetermined probability rate of 5%. The results for the groups were presented as least-square means (LSM) together with the standard errors of LSM. Finally, Pearson partial correlation coefficients were evaluated to characterize the relationship between the blood glucose level and meat quality measurements. 3. Results and discussion 3.1. Blood glucose level and muscle fiber characteristics To examine the relationships between blood glucose levels and muscle fiber characteristics, samples were classified into three groups according to blood glucose level, and muscle fiber characteristics were determined by histochemical analysis using myofibrillar ATPase activity (Table 1). Blood glucose levels were significantly different between the high group and the intermediate, low groups (231 vs. 135 vs. 88 mg/dl, P < 0.001). There were no significant differences in live weight and carcass weight among groups, but the loin eye area of the high group was significantly smaller than those of the intermediate and low groups (54.45 vs. 62.88 vs. 61.91 cm2, P < 0.001). The high group also showed significantly smaller fiber cross-sectional area than the intermediate and low groups (3285 vs. 4358 vs. 4360 lm2, P < 0.001). However, higher fiber density values were observed in the high group comparing to the intermediate and low groups (313 vs. 242 vs. 236 fiber number/mm2, P < 0.001). According to the results of Miller, Ellis, Bidner, McKeith, and Wilson (2000), a high glycolytic potential group showed high levels of free glucose in exudates and also showed larger loin eye areas. Moreover, Ryu and Kim (2004) reported that loin eye area presented a positive relationship

Table 1 Blood glucose level, live weight, carcass traits, and muscle fiber characteristics of porcine longissimus muscle in groups categorized by blood glucose level measured at slaughter. Blood glucose level

High (N = 42)

Intermediate (N = 72)

Low (N = 46)

Blood glucose level (mg/dl)

231a (3.72)A 114.5 (1.27) 85.8 (1.10) 54.45b (1.65) 3285b (149) 313a (8.89)

135b (2.84) 112.6 (1.05) 84.1 (0.84) 62.88a (1.57) 4358a (123) 242b (7.76)

88b (3.56) 114.9 (1.55) 83.7 (1.05) 61.91a (1.26) 4360a (149) 236b (8.89)

6.44b (0.73) 7.83 (0.63) 85.68a (1.04)

8.77a (0.55) 9.14 (0.47) 82.09b (0.76)

8.56a (0.68) 9.20 (0.58) 82.24b (0.95)

9.61 (1.07) 12.62 (0.96) 77.80 (1.49)

12.10 (0.81) 14.51 (0.70) 73.39 (1.09)

11.78 (1.00) 13.99 (0.87) 74.23 (1.36)

Live weight (kg) Carcass weight (kg) Loin eye area (cm2) Fiber cross-sectional area (lm2) Fiber density (fiber number/mm2) Muscle fiber area composition (%) Type I Type IIA Type IIB Muscle fiber number composition (%) Type I Type IIA Type IIB

Level of significance: NS = not significance; *P < 0.05, ***P < 0.001. A Standard error of least-square means. a–b Least-square means with different superscripts in the same row significantly differ (P < 0.05).

Level of significance *** NS NS *** *** ***

* NS *

NS NS NS

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with fiber cross-sectional area and a negative relationship with fiber density. However, studies by Larzul et al. (1997) and Ryu and Kim (2005) indicated that fiber cross-sectional area and fiber density were not closely related to pork quality compared to the relationship between muscle fiber type composition and pork quality. In muscle fiber area composition, muscles of the high group were composed of less fiber type I area (6.44 vs. 8.77 vs. 8.56%, P < 0.05) and more fiber type IIB area (85.68 vs. 82.09 vs. 82.24%, P < 0.05) than those of the intermediate and low groups. However, there was no difference in type IIA area percentage among groups. Number percentages of all muscle fiber types were not significantly different among groups. By using conventional myofibrillar ATPase staining procedures, three types of muscle fibers, having different characteristics, are shown to exist in adult porcine muscle (Aberle et al., 2001; De Bock, Derave, Ramaekers, Richter, & Hespel, 2007; Eggert, Depreux, Schinckel, Grant, & Gerrard, 2002). Thus, the difference in muscle fiber type composition is a key factor in determining the predominant metabolic capacity of muscle. In addition, there are differences in substrate content with different types of metabolism. In general, muscle fiber type IIB contains more glycogen, whereas fiber type I contains more lipid (Aberle et al., 2001; Fernandez & Tornberg, 1991; Karlsson et al., 1999). Therefore, muscles with a higher proportion of fiber type IIB, which has a higher glycolytic capacity, can have higher glucose and glycogen concentrations than muscles with a lower proportion of fiber type IIB (Fernandez & Tornberg, 1991; Karlsson et al., 1999). In the current study, pigs with higher area percentages of fiber type IIB showed higher blood glucose levels compared to pigs with lower area percentages of fiber type IIB. 3.2. Meat quality traits and protein solubility Table 2 presents the differences in meat quality measurements among the high, intermediate, and low blood glucose level groups. The high group had significantly lower muscle pH45 min values compared to the other groups (5.95 vs. 6.27 vs. 6.23, P < 0.001).

Muscle pH24 h of the high group was significantly lower than that of the intermediate group (5.74 vs. 5.82, P < 0.05). Moreover, the high group showed reduced WHC, with significantly higher drip loss (5.17 vs. 3.07 vs. 2.46%, P < 0.001) and FFU (33.89 vs. 23.72 vs. 20.69 mg, P < 0.001) values than the intermediate and low groups. Cooking loss of the high group was significantly higher than that of the low group (29.95 vs. 27.61%, P < 0.05), but not significantly different compared to the intermediate group. In terms of meat color, the high group had significantly different values for both lightness (49.13 vs. 46.62, P < 0.001) and redness (7.02 vs. 7.60, P < 0.1) comparing to the intermediate and low groups. Finally, there were significant differences in sarcoplasmic and myofibrillar protein solubilities among the groups. The high group had significantly lower values for sarcoplasmic (P < 0.01) and myofibrillar protein solubility (P < 0.001) than the other groups. Moreover, there was a significant difference in total protein solubility between the high and the intermediate, low groups (178.1 vs. 202.3 vs. 207.4 mg/g, P < 0.001). The development of fresh meat quality is significantly impacted by the rate and extent of pH decline during the postmortem period (Scheffler & Gerrard, 2007). Rapid postmortem glycolysis produces large amounts of lactate, protons, and heat during the first hour after slaughter, causing a rapid decline of muscle pH, and subsequently, severe denaturation of sarcoplasmic and myofibrillar proteins (Honikel & Kim, 1986; Scheffler & Gerrard, 2007). In terms of meat color, a higher lightness value can be attributed to a higher level of sarcoplasmic protein denaturation. Furthermore, reduced WHC may be explained by myofibrillar protein denaturation (Irving et al., 1989; Joo et al., 1999; Offer et al., 1989; Scheffler & Gerrard, 2007). The results of Miller et al. (2000) showed that a high glycolytic potential group with high levels of free glucose in exudates had lower muscle pH24 h and higher values of lightness and drip loss. The current study showed that the high blood glucose level group with lower muscle pH45 min and pH24 h values presented severe denaturation of muscle protein and inferior pork quality compared to the intermediate and low blood glucose level groups.

Table 2 Meat quality measurements of porcine longissimus muscle in groups categorized by blood glucose level measured at slaughter. Blood glucose level Meat quality traits Muscle pH45 min Muscle pH24

h

Drip loss (%) Filter-paper fluid uptake (mg) Cooking loss (%) Lightness Redness Yellowness Protein solubility (mg/g) Sarcoplasmic protein Myofibrillar protein Total protein  

*

High

Intermediate

Low

5.95b (0.05)A 5.74b (0.03) 5.17a (0.33) 33.89a (2.10) 29.95a (0.55) 49.13a (0.49) 7.02b (0.18) 2.86 (0.13)

6.27a (0.04) 5.82a (0.02) 3.07b (0.26) 23.72b (1.60) 29.24a (0.43) 46.87b (0.37) 7.16ab (0.14) 2.66 (0.10)

6.23a (0.04) 5.79ab (0.02) 2.46b (0.32) 20.69b (2.01) 27.61b (0.53) 46.62b (0.47) 7.60a (0.17) 2.66 (0.12)

69.05b (1.54) 109.0b (3.34) 178.1b (3.60)

74.91a (1.18) 127.4a (2.57) 202.3a (2.77)

75.97a (1.47) 131.4a (3.19) 207.4a (3.44)

**

***

Level of significance: NS = not significance; P < 0.1, P < 0.05, P < 0.01, P < 0.001. A Standard error of least-square means. a–b Least-square means with different superscripts in the same row significantly differ (P < 0.05).

Level of significance

*** * *** *** * ***   NS

** *** ***

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Pearson correlation coefficients were estimated to examine the relationships between blood glucose level and meat quality measurements (Fig. 1). The blood glucose level had a negative relationship with muscle pH45 min (r2 = 0.317, P < 0.001), and a positive relationship with lightness (r2 = 0.119, P < 0.001), drip loss (r2 = 0.383, P < 0.001), and FFU (r2 = 0.188, P < 0.001). Furthermore, blood glucose level was correlated to sarcoplasmic (r2 = 0.193, P < 0.01) and myofibrillar protein solubilities (r2 = 0.342, P < 0.001). Hamilton et al. (2003) reported that free glucose in exudates was significantly correlated with live animal- and postmortem glycolytic potential and meat quality traits. Significantly higher glyco-

lytic potential can be found in pale, soft, exudative pork (van Laack & Kauffman, 1999). According to the results of Ryu and Kim (2005), muscle pH45 min was negatively correlated to lightness at 45 min and 24 h postmortem as well as drip loss and FFU. And Joo et al. (1999) showed that ultimate pH was positively correlated with sarcoplasmic protein solubility, and sarcoplasmic protein solubility was negatively correlated with lightness and drip loss. In our results, blood glucose level was significantly correlated with pork quality traits and sarcoplasmic and myofibrillar protein solubilities. Therefore, we conclude that blood glucose level is associated with muscle fiber area composition, and could partially indicate

7.5

14

y = -0.003x + 6.6343 ( r 2 = 0.317)

y = 0.0232x + 0.2305 ( r 2 = 0.383) 12

7.0

Drip loss (%)

Muscle pH 45 min

10

6.5

6.0

8

6

4

5.5 2

5.0

0

0

100

200

300

400

0

60

y = 0.0518x + 45.085 ( r 2 = 0.119)

300

400

300

400

300

400

80

Filter-paper fluid uptake (mg)

Lightness ( L *)

200

y = 0.0742x + 11.605 (r 2 = 0.188)

55

50

45

40

35

60

40

20

0 0

100

200

300

400

0

120

100

200

200

y = -0.0602x + 81.913 ( r 2 = 0.193)

y = -0.2024x + 153.44 ( r 2 = 0.342) 180

Myofibrillar protein solubility (mg/g)

Sarcoplasmic protein solubility (mg/g)

100

100

100

80

60

40

160

140 120

100

80

60 20 0

100

200

Blood glucose level (mg/dl)

300

400

0

100

200

Blood glucose level (mg/dl)

Fig. 1. Relationships between blood glucose level and meat quality measurements. The regression lines were drawn from the equations.

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