Effects of Dietary Inosinic Acid on Carcass Characteristics, Meat Quality, and Deposition of Inosinic Acid in Broilers1

METABOLISM AND NUTRITION Effects of Dietary Inosinic Acid on Carcass Characteristics, Meat Quality, and Deposition of Inosinic Acid in Broilers1 G. Q. Zhang, Q. G. Ma, and C. Ji2 National Laboratory of Animal Nutrition, College of Animal Science and Technology, China Agricultural University, Beijing, 100094, P. R. China values of thigh muscle. Hunter b* values in thigh muscle were lower (P < 0.05) in the 0.75% IMP supplementation group than in the control group. Both breast and thigh muscle of birds fed with 0.25% IMP diet resulted in a lower (P < 0.05) shear force value compared with those fed with the other diets. All of the test groups had greater (P < 0.05) deposition of IMP in breast and thigh muscle than that of the control group with the exception of the 0.75% IMP supplementation group for thigh muscle. Greater (P < 0.05) corrected IMP value in breast muscle was detected for the test groups compared with the control group. These results suggest that extraneous IMP addition may contribute to the improvement of growth, meat quality, and deposition of IMP in broilers.

Key words: dietary inosinic acid, carcass characteristic, meat quality, deposition of inosinic acid, broiler 2008 Poultry Science 87:1364–1369 doi:10.3382/ps.2007-00193

INTRODUCTION Inosinic acid (inosine 5′-monophosphate, IMP) is a dietary nucleotide that has been associated with immunity and intestinal health. Infants that were fed milk fortified with nucleotides had an increased humoral antibody response (Fanslow et al., 1988; Pickering et al., 1998). Dietary nucleotides enhance the intestinal absorption of iron, have trophic effects on the liver and intestinal mucosa, and reduce the rate of diarrhea (Cosgrove, 1998; Schlimme et al., 2000). Nucleotide supplementation increases the amount of mucosal protein, the amount of DNA, and the length of small intestinal villi, which indicates that nucleotides may promote the growth and maturation of intestinal epithelial cells (Carver, 1994). Hans and Christopher (2004) reported that the requirement for nucleotides increases during periods of rapid growth, periods of stress, and in immunocompromised animals.

©2008 Poultry Science Association Inc. Received May 14, 2007. Accepted March 26, 2008. 1 Financially supported by National Basic Research Program of China (Project No: 2004CB117500). 2 Corresponding author: [email protected]

Inosine 5′-monophosphate is the main umami compound in the meat of poultry, livestock, and fish, and plays an important role in meat flavor formation. Many studies have confirmed the close relationship between IMP, meat flavor, and acceptability of fish meat (Kodama, 1913; Bremner et al., 1988; Greene and BernatByrne, 1990). Umami, which was discovered in 1908, is a primary element of taste, complementary to sweet, sour, salty, and bitter. The characteristic compounds of umami taste can be classified into 2 groups: monosodium glutamate, which results from protein hydrolyzation and the 5′-ribonucleotide typified by IMP (Kawamura and Kare, 1986), which is degraded by adenosine triphosphate (ATP) in the process of muscle curing. The studies above focused mostly on the effects of nucleotides supplementation in the diets of humans and rats, and showed that dietary nucleotides did promote growth and health. The effect of dietary IMP on birds has not been reported yet. Furthermore, the contribution of dietary IMP to umami taste and meat quality has not yet been described. In this study, we aim to evaluate the effects of IMP supplementation in diets on carcass characteristics, meat quality, and deposition of IMP in Arbor Acres broilers, and to establish the relationship between dietary IMP and meat quality.

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ABSTRACT An experiment was conducted to evaluate the effects of dietary inosinic acid (inosine 5′-monophosphate, IMP) on carcass characteristics, meat quality, and deposition of IMP in Arbor Acres broilers. A total of two hundred forty 1-d-old male Arbor Acres broilers were allocated to 4 inosinic acid treatments (0, 0.25, 0.50, and 0.75% dietary IMP supplementation). Birds were slaughtered at 42 d old. Dietary IMP did not significantly affect the carcass characteristics of broilers. No significant difference among treatments was observed in muscle pH within 1 h or at 24 h postmortem (PM), or in the decrease of muscle pH within 24 h PM. Inosinic acid had no marked effect on the color of breast muscle or Hunter L* and a*

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DEPOSITION OF INOSINIC ACID AND MEAT QUALITY

MATERIALS AND METHODS

Table 1. Ingredients and nutrient composition of basal diets in different growing phases

Birds and Housing

Diets Inosine 5′-monophosphate is a nucleotide that is mainly found in feeds rich in protein (Carver and Walker, 1995). Generally, feed ingredients containing cellular structure are potential dietary sources of nucleotides in the form of nucleoproteins, and feeds from animal sources mostly have a relatively high concentration of nucleoproteins, such as fish meal, organ meats, and meat and bone meal (Kojima, 1974; Barness, 1994). Therefore, to avoid the effect of interior nucleotides in the feedstuff, corn and soybean meal basal diets that contained no animal by-products were formulated in the present study. All nutrient contents met or exceeded the NRC recommendations (NRC, 1994). The supplements of IMP for the 4 groups were 0, 0.25, 0.50, and 0.75%. The composition and nutrient content of basal diets formulated for broilers in different growing phases are shown in Table 1.

Sample Collection Procedures such as electrical stunning and scalding that may produce potential effects on different-sized birds were not used. At the end of the experiment, 2 birds with BW close to the mean were selected from each pen. Feed and water were withdrawn 12 h before slaughter. Birds were slaughtered by bleeding the left jugular vein. Breast and thigh muscle from the right sides of each carcass was skinned and deboned to determine carcass traits, muscle color (Hunter L*, a*, and b* values), pH, and shear force values; the other sides were used to analyze IMP deposition. Fillets taken from the left sides were immediately frozen in liquid nitrogen and stored at −76°C until analysis.

Measurements Carcass Characteristics and Muscle pH. Carcasses were weighed before deboning; breast and thigh muscle

Item Ingredients, % Corn Soybean meal Dicalcium phosphate Limestone Salt Zeolite powder L-Lysine DL-Methionine Corn oil Vitamin-trace mineral premix1 Nutrients ME, Mcal/kg CP, % Ca, % Available P, % Lys, % Met, % Met + cystine, %

d 1 to d 21

d 22 to d 42

58.15 32.85 1.60 1.35 0.30 0.75 0.04 0.26 4.00 0.70

61.35 28.15 1.60 1.35 0.30 0.75 0.06 0.14 5.50 0.80

3.02 20.00 1.00 0.40 1.10 0.56 0.89

3.15 18.00 0.99 0.40 0.99 0.42 0.72

1 Vitamin and mineral premix supplied the following per kilogram of diet: vitamin A, 15,000 IU; cholecalciferol, 3,000 IU; vitamin E (DLα-tocopheryl acetate), 20 IU; vitamin K3, 2.16 mg; thiamine, 2.16 mg; riboflavin, 8.00 mg; pyridoxine, 4.41 mg; vitamin B12, 0.02 mg; calcium pantothenate, 25.58 mg; nicotinic acid, 65.95 mg; folic acid, 0.98 mg; biotin, 0.20 mg; Fe, 109.58 mg; Cu, 8.14 mg; Zn, 78.04 mg; Mn, 105.00 mg; I, 0.34 mg; Se, 0.14 mg; choline chloride, 1,500 mg.

was removed from each carcass within 30 min postmortem (PM), trimmed, weighed, and chilled on ice. Muscle pH was measured within 1 h and at 24 h after slaughter using a model PHB-10B pH meter (Shanghai Kang-Yi Instrument Co. LTD., Shanghai, China). The pH meter was standardized by a 2-point method against standard buffers of pH 4.0 and pH 7.0. Three measurements were recorded and averaged for each breast and thigh muscle. Muscle Color. Hunter L* (lightness), a* (redness), and b* (yellowness) values were obtained from breast and thigh muscle at the time of deboning using a hand-held color-difference meter (SC-80C, Kangguang Apparatus Co. Ltd., Beijing, China), with an illuminant D65 and 10° standard observer. An average of 3 readings from the medial surface of the muscle free from color defects, bruising, and hemorrhages was taken for color evaluation (Fletcher, 1999). Shear Analysis. Fillets (12.7 mm diameter) were removed from the anterior end of each fillet with attached sampler. Thereafter, they were cooked in an 80°C water bath for several minutes until the internal temperature reached 75°C. Fillets were then cooled to room temperature (20°C) and prepared to measure shear force. Each sample was sheared perpendicular to the grain of the muscle fiber using a 25-kg load cell and crosshead speed of 200 mm/min with a Digital Meat Tenderness Meter (Model C-LM3, Northeast Agricultural University, Harbin, China). Shear force was expressed in Newtons (N) and used as a criterion for tenderness of the chicken meat. Deposition of IMP. Five grams of meat was weighed into a 50-mL homogenizer cup and 15 mL of 5% aqueous perchloride acid was added; the mixture was homoge-

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A total of two hundred forty 1-d-old male Arbor Acres broilers were obtained from Beijing Huadu Poultry Breeding Co. Ltd. (Beijing, China) and allocated to 4 treatments with 6 replicates of 10 birds per replicate pen for each treatment. There were no significant differences in initial BW (42.39 ± 0.38 g) across treatment groups. Broilers were vaccinated for Newcastle disease and infectious bronchitis disease at hatching, d 7, and d 21. A 24-h lighting regimen was carried out during the first 3 d, and 23 h of lighting with 1 h of darkness started on d 4. Mean air temperature of the animal chamber was approximately 35°C during the first week and then decreased gradually to a constant temperature of 25°C, which was held until the end of the trial. Feed and water were freely available to all birds. The entire experiment period lasted 42 d.

Growing phase

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ZHANG ET AL. Table 2. Effects of dietary inosinic acid (IMP) on carcass characteristics of broilers Supplementation of IMP in diets Parameter Breast muscle weight, g Thigh muscle weight, g Carcass weight, g Eviscerated yield, g Dressing percentage, % Breast muscle percentage, % Thigh muscle percentage, % Percentage of eviscerated yield, %

0

0.25%

0.50%

0.75%

Pooled SEM

327.45 324.77 1,961.82 1,565.21 91.37 20.95 20.74 72.47

340.43 331.72 1,996.42 1,577.25 91.50 21.56 21.03 72.29

339.33 334.38 2,042.50 1,627.27 91.68 20.92 20.58 73.02

339.78 324.28 2,031.00 1,616.24 91.63 21.07 20.30 72.05

4.39 5.27 14.64 13.80 0.06 0.25 0.29 0.31

Statistical Analyses Data were analyzed using a randomized complete block design. All analyses were performed using the GLM ANOVA procedure of SAS (SAS Institute, 2001). Significant effects (P < 0.05) were further explored using Duncan’s multiple range test to ascertain differences among treatment means.

RESULTS AND DISCUSSION Table 2 describes the effects of dietary IMP on carcass traits. There was no significant difference in the examined parameters of carcass characteristics between the control and the experimental groups. Inosine 5′-monophosphate, which is an important component of monosodium glutamate (and thus its supplementation in diets may ameliorate the feed palatability and increase the feed intake), did not cause obvious effects on the carcass traits that were checked. Data for muscle pH within 1 h and at 24 h PM of birds are presented in Table 3. Muscle pH decreases during the progression of rigor mortis because of ATP hydrolyzation and accumulation of lactic acid (Calkins et al., 1982; Lawrie, 1991). The changes in muscle pH affected meat color, tenderness, and water-holding capacity. No significant

difference among treatments was observed in muscle pH within 1 h and at 24 h PM, and in the decrease of muscle pH within 24 h PM. Le Bihan-Duval et al. (2001) reported a strong negative correlation between ultimate pH and drip loss. Generally, a slight difference of decrease of muscle pH within 24 h PM may be caused by differences in glycolytic potential in bird muscle. Color of meat is a determinant factor on deciding the consumer’s acceptance of the product. Strain, sex, age, stress, moisture, rigor development, and other processing factors all influence the color of meat (Mugler and Cunningham, 1972; Owens et al., 2000; Woelfel et al., 2002). There were no significant differences among treatments with regards to breast muscle color and to Hunter L* and a* values of thigh muscle (Table 4). Only the 0.75% IMP supplementation group presented significantly lower Hunter b* values compared with the control group. This result is in agreement with previous research that found an association between paler meat and higher lightness, lower redness, and higher yellowness values (Boulianne and King, 1995; Qiao et al., 2001). Other investigations reported that yellowness value was mainly affected by the types of myoglobin (Lindahl et al., 2001), but whether it gave rise to the difference of Hunter b* value in thigh muscle was unclear, because the types of myoglobin were not measured in this study. El Rammouz et al. (2004) reported that ultimate pH (24 h PM) was significantly correlated with lightness (r = −0.37) and yellowness (r = −0.36). The above studies were consistent with the findings that both reduction of lightness and yellowness valTable 3. Effects of dietary inosinic acid (IMP) on muscle pH within 1 h and at 24 h postmortem (PM) and the decrease of muscle pH within 24 h PM of broilers Supplementation of IMP in diets Parameter

1

Breast muscle pH1 pH24 pHd Thigh muscle pH1 pH24 pHd

0

0.25%

0.50%

0.75%

Pooled SEM

6.69 5.82 0.86

6.65 5.83 0.77

6.51 5.78 0.71

6.61 5.81 0.80

0.03 0.02 0.03

6.50 5.84 0.69

6.47 5.99 0.53

6.46 5.91 0.58

6.40 5.86 0.53

0.03 0.03 0.03

1 pH1 = means of muscle pH within 1 h PM; pH24 = means of muscle pH at 24 h PM; pHd = means of the decrease of muscle pH within 24 h PM.

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nized in an ice bath at 15,000 rpm using a T-25 UltraTurrax homogenizer (IKA, Staufen, Germany) for 3 min with three 30-s intervals to avoid heat production. The homogenate was transferred to a 50-mL centrifuge tube, the homogenizer cutter and cup were washed with 10 mL of 5% perchloride acid, and the total homogenate was centrifuged at 18,000 × g with a high-speed refrigerated centrifuge CR 3i (Nous, Jouan S. A., Saint-Herblain, France) at 4°C for 10 min, and then filtered into a 100mL beaker. After adding 15 mL of 5% perchloride acid to the precipitate and shaking for 5 min, the mixture was centrifuged and filtered as described above. The filtrate was pooled with the first filtrate in a beaker. The pH of the filtrate was adjusted to 6.5 with 5 N and 0.5 N NaOH and diluted to calibration tails with double-distilled water. The solution was filtered through a 0.45-␮m membrane filter before being used for HPLC (Shimadzu Corporation, Kyoto, Japan) with a modification of the method of Kitada et al. (1983).

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DEPOSITION OF INOSINIC ACID AND MEAT QUALITY Table 4. Effects of dietary inosinic acid (IMP) on meat color (L*, a*, b*) and shear force value (SFV) of broilers Supplementation of IMP in diets Parameter Breast muscle L* value a* value b* value SFV, N Thigh muscle L* value a* value b* value SFV, N

0

0.25%

0.50%

0.75%

Pooled SEM

52.70 5.89 13.95 21.74a

54.60 6.77 14.07 18.01b

51.78 6.76 12.83 18.43b

50.66 6.91 12.31 21.50a

1.22 0.34 0.37 0.47

58.39 6.56 16.39a 18.22a

56.51 6.89 15.61ab 14.61b

55.86 6.92 14.61ab 16.10ab

54.10 7.23 13.90b 17.40a

1.49 0.30 0.33 0.48

Means within a row that do not share a common superscript differ significantly (P < 0.05).

a,b

Calkins and Seideman, 1988; Wheeler and Koohmaraie, 1994). The calpain system is activated by accumulation of Ca2+ during rigor development, which causes hydrolyzation of the myofibrillar protein and thus improves meat tenderness (Bamoy et al., 1996; Hopkins and Thompson, 2001; Ilian et al., 2001). Therefore, the shear force values that were found in our study may have been caused by the dose effect of dietary IMP on collagen fibril and on calpain enzymatic activity. The variation of deposition of IMP in Arbor Acres broilers’ muscle was the main object of research in this experiment. Results are listed in Table 5. The data indicate that breast muscle from birds in the test groups had a significantly greater concentration of IMP than that of the control group, and the 0.25 and 0.50% IMP supplementation groups had a significantly greater IMP value than the control group in thigh muscle. There was a significantly greater corrected IMP value of all experimental groups compared with control group in breast muscle, but no obvious difference of corrected IMP value was found in thigh muscle. Corrected IMP value is the result of dividing ATP metabolism contents by respective molecular weight and multiplying by the molecular weight of IMP. It can better represent the generating potential of IMP in muscle. Although dietary IMP consistently increased the deposition of IMP in broiler muscle, the results illustrated that IMP deposition decreased with the increase of dietary IMP, and more IMP was deposited in muscle when 0.25% IMP was supplemented in diets. The trend simultaneously indicated that more is not always better.

Table 5. Effects of dietary inosinic acid (IMP) on deposition of IMP and corrected IMP (IMPc) in broilers’ muscle Supplementation of IMP in diets Parameter, mg/g Breast muscle IMP IMPc1 Thigh muscle IMP IMPc

0

0.25%

0.50%

0.75%

Pooled SEM

2.51b 3.76b

2.80a 4.27a

2.79a 4.32a

2.76a 4.38a

0.04 0.09

1.83b 3.51

2.22a 4.09

2.21a 4.25

2.06ab 3.65

0.06 0.15

Means within a row that do not share a common superscript differ significantly (P < 0.05). IMPc = (ATP/507.19 + ADP/427.2 + AMP/347.22 + IMP/346.19 + Hx/136.11 + I/268.23) × 346.19, where ATP = adenosine 5′-triphosphate; ADP = adenosine 5′-diphosphate; AMP = adenosine 5′-monophosphate; HX = hypoxanthine; I = inosine. a,b 1

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ues and increase of redness value contribute to the amelioration of meat color. Therefore, our results show that dietary IMP improves the acceptability of meat to a certain extent. Table 4 shows the effect of dietary IMP on shear force value. Both breast muscle and thigh muscle of birds fed with 0.25% IMP diets had significantly lower shear force values compared with those of birds in the other treatments. Shear force value is indicative of meat tenderness, which has been noted as the most important factor in consumer perception of palatability or quality of meat products (Savell et al., 1989). In addition to sex and muscle size, tenderness alterations of muscle are affected by the histological properties of myofibers. A difference in the physiological maturity of the birds at the time of harvest may result in a difference in collagen cross-linking, which increases with age and is often associated with increased toughness (Fletcher, 2002). Because all birds in the present trial were harvested at the same chronological ages, it was unlikely that increased collagen content was the factor responsible for the observed difference in shear force. Liu et al. (1996) showed that the diameter of collagen fibrils and the thickness of the perimysium of chicken muscles were significantly correlated with shear force value, so that the 3-dimensional architecture of collagen fibers in the perimysium may well be a second factor determining meat toughness. Moreover, the histochemical changes of muscle caused by calpain-induced proteolysis during rigor mortis directly affect tenderness (Goll et al., 1964;

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ACKNOWLEDGMENTS We appreciate the kind assistance of Daniel Hojman. This research was supported by the National Basic Research Program of China (No, 2004CB117500) from Ministry of Science and Technology of the People’s Republic of China.

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Dietary nucleic acids and nucleotides should be enzymatically hydrolyzed before absorption and they were absorbed mainly in the form of nucleosides and small molecular nucleotides (Bronk and Hastewell, 1987). Nucleotides with highly negatively charged phosphate groups hinder absorption. Thus, nucleotides enter enterocytes mainly in the form of nucleosides and the effective process is carried out mainly by facilitated diffusion and by special sodium ion-dependent carrier mediated mechanisms (Bronk and Hastewell, 1987). Nucleosides, endogenous nucleotides, and partial dietary metabolic products are transported into muscle tissue through the circulation system. While one portion of the products were decomposed into uric acid or β-alanine and excreted, the others were resynthesized for nucleotides and participated in metabolism again (Carver and Walker, 1995; Thorell et al., 1996). Therefore, as a type of small molecular nucleotide, partial dietary IMP is likely to be absorbed directly. However, little IMP exists in muscle of live animals, and the deposition of IMP in muscle basically occurs during the progression of rigor mortis. Without considering the influence of strain, sex, and size, enzymes associated with ATP metabolism could be the important factor that affected the amount of IMP in broilers’ muscle. The enzymes involved include ATPase, 5′-nucleotidase, and phosphatase. Inosine 5′-monophosphate is the intermediate product in ATP metabolism, so there should be a positive correlation between the concentration of IMP in muscle and ATP hydrolase activity as well as a negative correlation between the concentration of IMP in muscle and IMP degrading enzyme activity. The possible reason for the improvement of IMP amount in broilers’ muscle is that the dietary IMP influenced ATP hydrolase and IMP degrading enzyme. Further studies may help to clarify the mechanism. In conclusion, the results presented in this study show that dietary IMP did not significantly affect all the examined carcass traits of broilers, but caused a significant increase of IMP deposition in broiler muscle PM. The IMP supplementation in diets did not obviously contribute to muscle pH and meat color of broilers, but reduced the shear force value of breast and thigh muscle in birds fed with 0.25% IMP diets, and thus improved meat tenderness. Therefore, dietary IMP partly ameliorated meat quality and increased IMP deposition in broilers.

DEPOSITION OF INOSINIC ACID AND MEAT QUALITY

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