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Animal Science Journal (2014) 85, 595–601
doi: 10.1111/asj.12170
ORIGINAL ARTICLE IMP improves water-holding capacity, physical and sensory properties of heat-induced gels from porcine meat Yukinobu NAKAMURA,1 Koshiro MIGITA,2 Akihiro OKITANI2 and Masanori MATSUISHI2 1
Japan Meat Science and Technology Institute and 2Department of Food Science and Technology, Nippon Veterinary and Life Science University, Tokyo, Japan
ABSTRACT Water-holding capacity (WHC) of heat-induced pork gels was examined. The heat-induced gels were obtained from meat homogenates prepared by adding nine volumes of 0.3–0.5 mol/L NaCl solutions containing 9–36 mmol/L disodium inosine-5′-monophosphate (IMP) or 9 mmol/L tetrapotassium pyrophosphate (KPP) to minced pork. IMP at 36 mmol/L enhanced the WHC to the same level as attained by KPP. Physical and sensory properties of heat-induced gels were also examined. The heat-induced gels were prepared from porcine meat homogenates containing 0.3 mol/L NaCl and 9–36 mmol/L IMP or 9 mmol/L KPP. IMP at 36 mmol/L enhanced the values of hardness, cohesiveness, gumminess and springiness, measured with a Tensipresser, and several organoleptic scores to the same level as the score attained by KPP. Thus, it is concluded that IMP is expected to be a practical substitute for pyrophosphates to improve the quality of sausages.
Key words: heat-induced gels, inosine-5′-monophosphate, physical property, pyrophosphate, water-holding capacity.
INTRODUCTION Sausages are heat-induced gels produced from the salted emulsion of comminuted meats. The gels have an ability to bind comminuted meats and hold added water and fat, that is, they possess a binding property. It has been shown that the high level of binding in sausages can be ascribed to salt-solubilized myosin or actomyosin (Fukazawa et al. 1961a; Yasui et al. 1979, 1980; Samejima et al. 1981; Ishioroshi et al. 1982, 1983; Hermansson et al. 1986; Yamamoto et al. 1988; Yamamoto 1990), which are the major myofibrillar proteins. When salt-solubilized myosin or actomyosin is heated, a three-dimensional network of proteins that encloses water is formed (Xiong 2004). In meats used as the raw materials of sausages, myosin and actin exist in the form of actomyosin because of the post-mortem disappearance of adenosine triphosphate (ATP). Actomyosin is a salt-soluble protein. In order to generate a high level of binding in sausages, actomyosin is extracted from myofibrils using a NaCl concentration as high as 0.5 mol/L (3%) (Offer & Trinick 1983). A NaCl concentration of about 0.3 mol/L (2%) is used in the majority of sausages produced in Japan, since Japanese consumers do not find salty sausages (0.5 mol/L NaCl) palatable and are mindful of the risk © 2014 Japanese Society of Animal Science
of developing hypertension. However, 0.3 mol/L NaCl is not sufficient to extract actomyosin from myofibrils (Offer & Trinick 1983). Since pyrophosphates dissociate actomyosin to actin and myosin and enhance the extractability of myosin (Yasui et al. 1964; Ishiwata 1981), pyrophosphates have been used as an additive to enhance the binding property of sausages (Fukazawa et al. 1961b). However, pyrophosphateadded sausages are unacceptable to some consumers because pyrophosphates, which are exogenous inorganic polyphosphate chelating agents, inhibit small intestinal Ca ion absorption and exhibit an astringent taste. Previously, we showed that the umami seasoning disodium inosine-5′-monophosphate (IMP), which is an endogenous substance in meat, dissociates actomyosin into actin and myosin (Okitani et al. 2008), and enhances the extractability of actin and myosin from porcine meats in the presence of ca. 0.3-0.5 mol/L NaCl (Nakamura et al. 2012). Moreover,
Correspondence: Yukinobu Nakamura, Japan Meat Science and Technology Institute, Shibuya, Tokyo 150-0013, Japan. (Email: [email protected]) Received 24 July 2013; accepted for publication 15 October 2013.
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we showed that the IMP-induced extraction of both proteins is increased by increasing the extraction time from 0 to 12 h at 4°C, while pyrophosphate-induced extraction is not (Nakamura et al. 2013). Thus, there is a similarity between IMP and pyrophosphate in enhancing the extractability of actin and myosin. However, the effect of IMP on the binding property of sausage has not been examined. In the present study, we prepared heat-induced gels in the presence of 0.3-0.5 mol/L NaCl and IMP or tetrapotassium pyrophosphate (KPP) and determined whether IMP improves the quality of heat-induced gels, by investigating the effect of incubation time and NaCl concentration on the water-holding capacity (WHC) and physical and sensory properties of the obtained heat-induced gels. On the basis of the results obtained, we discuss the suitability of IMP as a substitute of pyrophosphates for the sausage industry.
MATERIALS AND METHODS Materials The cuts of fresh meat (mainly Musculus semimembranosus, M. adductor and M. gracilis) of Large White × Landrace × Duroc crossbred pigs (n = 3) were obtained from retail stores and immediately minced in a meat chopper after removing fat and connective tissues. Minced meat was vacuum-packed and stored at −20°C until use. KPP was purchased from Wako Pure Chemical Industries (Osaka, Japan) and IMP was obtained from Tokyo Chemical Industries (Tokyo, Japan). All other chemicals used were of analytical grade.
Preparation of heat-induced gels for the determination of WHC Meat homogenates for heat-induced gels were prepared by the same methods as in the previous studies determining the effect of IMP on actin and myosin extraction (Nakamura et al. 2012, 2013). Minced meat (3 g) was mixed with nine volumes (27 mL) of each of the extraction solutions containing 0.3, 0.4 or 0.5 mol/L NaCl and 0, 9, 18 or 36 mmol/L IMP or 9 mmol/L KPP and homogenized twice at 12 000 rpm for 30 sec with a homogenizer (Excel Auto, Nippon Seiki, Nagaoka, Japan). We chose 9 mmol/L KPP for comparison with the effect of IMP, since this KPP concentration is currently used in the sausage industry. After the addition of the extraction solutions containing 0.3, 0.4 and 0.5 mol/L NaCl, the total salt (KCl plus NaCl) concentrations in the homogenates were 0.29, 0.38 and 0.47 mol/L, respectively, assuming that the salt concentration in minced meat is 0.2 mol/L, and supported by the finding that the ionic strength in muscle cells was found to be 0.2 (Offer & Knight 1988). The addition of IMP and KPP diluted the concentrations in the homogenate to 0.9-fold of initial concentrations. One portion of the homogenate was immediately packed in a flat-bottomed 2.0 mL polypropylene (PP) tube and was heated at 63°C in an oven for 35 min immediately after homogenization. The core temperature of the homogenate reached 60°C after 23 min and 62.3°C after 35 min. The obtained heat-induced gels were designated as 0-h gels. The other portion of the homogenate was incubated at 4°C for © 2014 Japanese Society of Animal Science
12 h before being heated. The obtained heat-induced gels were designated as 12-h gels. The 0-h and 12-h gels were subjected to the determination of WHC.
Determination of WHC Heat-induced gels (9 mm diameter) in the PP tubes were centrifuged at 1000 × g for 30 sec and the weight of the released water from the gels was then determined. WHC was calculated by using the following formula:
WHC (%) = {1 − ( Ww Wg )} × 100
where Ww is the weight of the water released from the heat-induced gels by centrifugation and Wg is the weight of the heat-induced gels.
Preparation of heat-induced gels for the determination of physical properties and sensory evaluation We prepared the heat-induced gels for the determination of physical properties and sensory evaluation, essentially following the method of sausage making. Minced meat (30 g) was mixed with 0.5 volumes (15 mL) of salt (NaCl) solutions containing IMP or KPP and homogenized thrice at 12 000 rpm for 30 sec with a homogenizer (Excel Auto, Nippon Seiki). The total salt (NaCl plus KCl) concentration of the obtained meat homogenate was 0.3 mol/L, assuming that the salt concentration of minced meat was 0.2 mol/L (Offer & Knight 1988). IMP was added to the meat homogenate at a final concentration of 9, 18 and 36 mmol/L. KPP was added to the meat homogenate at a final concentration of 9 mmol/L, the concentration currently applied in the sausage industry. For the determination of physical properties, the meat homogenate (1.5 g) was immediately packed in a flatbottomed 2.0 mL PP tube and centrifuged at 100 × g for 10 sec to degas the homogenate. Then, the homogenate was heated at 63°C in an oven for 35 min. The core temperature of the homogenate reached 60°C after 26 min and 63.8°C after 35 min. The gels were placed on ice until used in the examination. For the sensory test, the homogenate (40 g) was packed in a 50 mL PP tube immediately after homogenization, centrifuged at 100 × g for 10 sec, and then heated at 65°C in a water bath for 40 min. The core temperature of the homogenate reached 65°C after 6 min and was maintained at 65°C for 34 min. The obtained heat-induced gels were placed on ice until used in the examination.
Determination of physical properties Physical properties of the heat-induced gels were measured by the two-bite method using a texture analyzer, Tensipresser TTP-50BX (Taketomo Electric Inc., Tokyo, Japan). The 5 mm diameter hollow plunger penetrated the heat-induced gels (9 mm diameter, 20 mm thickness) in PP tubes at a speed of 6 mm/sec. The clearance was 14.0 mm. Figure 1 shows the H1, A1, A2, P1 and P2 given by the Tensipresser. H is the compression force (N) of the plunger, P is the moving distance (mm) of the plunger, and A is the area (mm2) surrounded by the stress profile and abscissa (workload). Hardness, H1, cohesiveness, A1/A2, gumminess, H1×A1/A2, and springiness, P2/P1×100, were determined from the texture profile by using the software provided with the Tensipresser. Animal Science Journal (2014) 85, 595–601
IMP IMPROVES HEAT-INDUCED MEAT GEL
Figure 1 Texture profile of heat-induced gels generated by the two-bite method using a Tensipresser. Physical properties of heat-induced gels were measured using the two-bite method with a Tensipresser TTP-50BX. H, compression force of the plunger; P, moving distance of the plunger; B, breaking point.
Sensory evaluation Sensory evaluation of three types of heat-induced gels with 9 mmol/L KPP or 36 mmol/L IMP and without KPP and IMP, designated as KPP gels, IMP gels and control gels, respectively, was conducted twice by trained panelists. The panelists were one female and six males (age 30 s, two; age 40 s, three; age 60 s, two) affiliated with Japan Meat Science and Technology Institute, Tokyo. The heat-induced gels were 28 mm in diameter and 3 mm thick. Gels were kept at room temperature (25°C) for 1 h before the test. The texture evaluation parameters were hardness, springiness, binding property and juiciness. The flavor evaluation parameters were umami, saltiness, astringency, odor and overall preference. Differences were expressed within a seven-point scale (−3 to +3), setting the value for the KPP-added gels as zero.
Statistical analysis The values of WHC and physical properties are expressed as mean ± standard error of triplicate determinations. In the sensory test, the scores between the KPP-added gels and the other gels were analyzed using Student’s t-test.
RESULTS AND DISCUSSION Effects of IMP on WHC of heat-induced gels from porcine meat Figure 2A, B and C show the WHC of 0-h and 12-h gels prepared with extraction solutions containing various concentrations of NaCl and 0–36 mmol/L IMP or 9 mmol/L KPP. KPP was used for comparison with the effect of IMP. In the case of the 0.3 mol/L NaCl extraction solution (Fig. 2A), the WHC of 0-h gels was 32% in the absence of IMP and KPP. The addition of 9 and 18 mmol/L IMP into the extraction solution slightly increased the WHC. The addition of 36 mmol/L IMP resulted in a fairly high WHC of 80%. The WHC of 12-h gels was 35% in the absence of IMP and KPP. The addition of 9, 18 and 36 mmol/L IMP increased WHC to 39, 70 and 96%, respectively. These values are higher than the corresponding values of the 0-h gels, indicating that Animal Science Journal (2014) 85, 595–601
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the WHC of the IMP-added gels is enhanced in a time-dependent manner. On the other hand, the addition of 9 mmol/L KPP into the 0.3 mol/L NaCl extraction solution increased the WHC of the 0-h and the 12-h gels to 87 and 97%, respectively. Thus, it was found that IMP enhanced the WHC of heat-induced gels and that the enhancing effect of 36 mmol/L IMP for the 0-h and 12-h gels was comparable to that of 9 mmol/L KPP. In the case of the 0.4 mol/L NaCl extraction solution (Fig. 2B), the WHC of the 0-h gels was 35% in the absence of IMP and KPP. The addition of 9, 18 and 36 mmol/L IMP into the NaCl solutions resulted in fairly high values: 61, 77 and 91%, respectively. These values are higher than the corresponding values of the IMP-added gels at 0.3 mol/L NaCl. This showed that the increase in the NaCl concentration from 0.3 to 0.4 mol/L enhances the WHC of the IMP-added gels. The WHC of the 12-h gels was 37% in the absence of IMP and KPP. The addition of 9, 18 and 36 mmol/L IMP increased the WHC to 71, 97 and 100%, respectively. These values are higher than the corresponding values of the 0-h gels, indicating that the WHC of the IMP-added gels is enhanced in a time-dependent manner. On the other hand, the addition of 9 mmol/L KPP into the extraction solution increased the WHC of the 0-h and 12-h gels to 89 and 96%, respectively. These values were comparable to those obtained for 18 and 36 mmol/L IMP. In the case of the 0.5 mol/L NaCl extraction solution (Fig. 2C), the WHC of the 0-h gels was 48% in the absence of IMP and KPP. The addition of 9, 18 and 36 mmol/L IMP into the extraction solutions increased the WHC to 78, 81 and 94%, respectively, which were almost equal to the corresponding values of the IMPadded gels at 0.4 mol/L NaCl. The WHC of the 12-h gel was 40% in the absence of IMP and KPP. The addition of 9, 18 and 36 mmol/L IMP increased the WHC to 95, 98 and 99%, respectively. These values are higher than the corresponding values of the 0-h gels, indicating that the WHC of the IMP-added gels is enhanced in a time-dependent manner. On the other hand, the addition of 9 mmol/L KPP into the extraction solutions increased the WHC of the 0-h and 12-h gels to 82 and 98%, respectively. These values were comparable to those obtained for 9, 18 and 36 mmol/L IMP. From the results described above, it was found that IMP has the ability to enhance the WHC of the heatinduced gels, and that this ability is enhanced by three factors: the increased concentrations of IMP and NaCl, and the increased incubation time of the meat homogenates at 4°C. We showed previously that the extractability of actin and myosin from porcine meat is enhanced by the three above-mentioned factors (Nakamura et al. 2012, 2013). Thus, because there is a similarity in the effectiveness of the three above-mentioned factors © 2014 Japanese Society of Animal Science
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Figure 2 Effects of disodium inosine-5′-monophosphate (IMP) and tetrapotassium pyrophosphate (KPP) on the water-holding capacity (WHC) of heat-induced gels. Meat homogenates were prepared by mixing minced meat with nine volumes of 0.3 mol/L (A), 0.4 mol/L (B) and 0.5 mol/L (C) NaCl solution containing 0–36 mmol/L IMP incubated for 0 (○) and 12 h (•) or containing 9 mmol/L KPP incubated for 0 (□) and 12 h (■). Homogenates were then subjected to heating. The WHC of the obtained heat-induced gels was determined. Each result is presented as the mean ± SE of three independent measurements. Other conditions are described in the ‘Materials and Methods’ section.
between WHC and extractability, the improvement of the WHC appears to be a result of the increased extractability. We showed in our previous paper (Nakamura et al. 2012) that the IMP-induced enhancement of the extractability of actin and myosin is ascribable to the dissociation of actomyosin to actin and myosin. Therefore, the dissociation of actomyosin appears to be the trigger for the improvement of WHC. The KPPinduced improvement of WHC also seems to be attributable to the increased extractability of actin and myosin, caused by the dissociation of actomyosin to actin and myosin. However, in the correlation between WHC and extractability, there is a noticeable difference between IMP and KPP in the case of the 0.3 mol/L NaCl extraction solution. As mentioned above, with respect to the WHC of 12-h gels, 36 mmol/L IMP (96%) has an enhancing effect equal to 9 mmol/L KPP (97%). On the other hand, as described previously (Nakamura et al. 2013), with respect to actin and myosin extractability with a 12-h extraction, 36 mmol/L IMP showed an extraction of 32% for actin and 30% for myosin, while 9 mmol/L KPP showed an extraction of 55% for actin and 93% for myosin, although 36 mmol/L IMP and 9 mmol/L KPP were assumed to almost completely eliminate the interaction between thin and thick filaments. As the reason for the discrepancy between IMP- and KPP-induced extraction of actin and myosin, we proposed the following scheme. The thin filaments containing actin and the thick filaments containing myosin are connected with scaffolds of myofibrils. Thus, it is necessary for actin and myosin to be © 2014 Japanese Society of Animal Science
extracted so that both filaments are released from the scaffolds, as well as to eliminate interaction between these filaments. Hence, we assumed that the scaffoldreleasing activity of 36 mmol/L IMP was lower than that of 9 mmol/L KPP, resulting in the low extractabilities of actin and myosin induced by IMP. It is possible that the scaffold connected to the thin filaments is comprised of Z-disks, because the α-actinin of Z-disks interacts with F-actin of the thin filaments (Goll et al. 1972). On the other hand, the scaffold connected with thick filaments is possibly connectin and/or Z-disk, because Funatsu et al. (1993) observed the interaction of connectin filaments along with thick filaments and the interaction of both ends of connectin filaments with Z-disks. On the basis of the above scheme, the present results that 36 mmol/L IMP exhibited the same high level of WHC as 9 mmol/L KPP in spite of its low actin and myosin extractabilities, suggests that WHC is enhanced by the elimination of interactions between thin and thick filaments and is not influenced by the connection of both filaments with the scaffold of myofibrils. When the interaction between both filaments is weakened, the thin filaments are freed from myosin and thick filaments are freed from actin. Thus, the heat-induced gels from these free filaments may construct a fine, three-dimensional network to hold large amounts of water.
Effects of IMP on physical properties of heat-induced gels from porcine meat Figure 3 shows the physical properties of gels containing 0.3 mol/L total salt and 9, 18 and 36 mmol/L IMP or 9 mmol/L KPP. Animal Science Journal (2014) 85, 595–601
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Figure 3 Effects of disodium inosine-5′-monophosphate (IMP) and tetrapotassium pyrophosphate (KPP) on physical properties of heat-induced gels. Meat homogenates were prepared by mixing minced meat with 0.5 volumes of NaCl solutions containing 0–36 mmol/L IMP (○) or 9 mmol/L KPP (□) and then heated. The hardness (A), cohesiveness (B), gumminess (C) and springiness (D) of the obtained heat-induced gels were determined. The salt (NaCl plus KCl) concentration of the heat-induced gels was 0.3 mol/L. Each result is presented as the mean ± SE of three independent measurements. Other conditions are described in the ‘Materials and Methods’ section.
As for hardness (Fig. 3A), in the absence of IMP and KPP, the gel exhibited a value of 4.2 N. In the presence of 9, 18 and 36 mmol/L IMP, the gels exhibited increased values of 5.4, 6.3 and 7.9 N, respectively. On the other hand, in the presence of 9 mmol/L KPP, the gels exhibited a value of 8.1 N. As for cohesiveness (Fig. 3B), in the absence of IMP and KPP, the gels exhibited a value of 0.28. In the presence of 9, 18 and 36 mmol/L IMP, the gels exhibited increased values of 0.32, 0.39 and 0.46, respectively. On the other hand, in the presence of 9 mmol/L KPP, the gels exhibited a value of 0.43. As for gumminess (Fig. 3C), in the absence of IMP and KPP, the gels exhibited a value of 1.2 N. In the Animal Science Journal (2014) 85, 595–601
presence of 9, 18 and 36 mmol/L IMP, the gels exhibited increased values of 1.7, 2.5 and 3.6 N, respectively. On the other hand, in the presence of 9 mmol/L KPP, the gels exhibited a value of 3.5 N. As for springiness (Fig. 3D), in the absence of IMP and KPP, the gels exhibited a value of 57%. In the presence of 9, 18 and 36 mmol/L IMP, the gels exhibited increased values of 64, 71 and 73%, respectively. On the other hand, in the presence of 9 mmol/L KPP, the gels exhibited a value of 74%. The results described above indicated that 36 mmol/L IMP enhances physical properties, such as hardness, cohesiveness, gumminess and springiness, of heat-induced gels from porcine meat to the same level © 2014 Japanese Society of Animal Science
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Figure 4 shows the results of the sensory evaluation of texture. As compared with KPP gels, IMP gels
exhibited a slightly low score in hardness and no differences in springiness, binding property and juiciness, whereas control gels exhibited very low scores in all evaluation items except juiciness. The texture of IMP gels was evaluated as comparable to that of KPP gels. This result is consistent with the results of the WHC and physical properties obtained in the previous section. A low score in hardness might be ascribable to a lower extractability of actin and myosin obtained by IMP, in comparison with KPP, as described above. Figure 5 shows the results of the sensory evaluation of flavor. As compared with KPP gels, IMP gels exhibited high scores in umami and overall preference and no differences in saltiness, astringency and odor, whereas control gels exhibited no differences in umami, saltiness and astringency and low scores in odor and overall preference. This is reasonable since IMP is an umami agent. It was noticeable that the control gels exhibited a rancid odor resulting from lipid oxidation, whereas IMP gels did not. Inorganic polyphosphates, including pyrophosphate, are able to prevent the generation of rancid odors (Matlock et al. 1984a, b; Sofos 1986). Thus, IMP, an organic polyphosphate, appears to possess the same ability. On the basis of the results described above, it was found that IMP improves the sensory properties of heat-induced gels and that the increased sensory scores of IMP gels are higher or at the same level as those of KPP gels.
Figure 4 Sensory evaluation of heat-induced gel texture. Sensory evaluation of the heat-induced gels was conducted using three heat-induced gels with 9 mmol/L tetrapotassium pyrophosphate (KPP) (KPP gels, a standard expressed as dotted line) or 36 mmol/L disodium inosine-5′monophosphate (IMP) (IMP gels, ○) and without KPP and IMP (control gels, é). Differences were expressed within a seven-point scale (−3 to +3), setting the value of the KPP gels as zero. Other conditions are described in the ‘Materials and Methods’ section. *P < 0.05 (vs. KPP gels); **P < 0.01 (vs. KPP gels).
Figure 5 Sensory evaluation of heat-induced gel flavor. Sensory evaluation of heat-induced gels was conducted using three heat-induced gels with 9 mmol/L tetrapotassium pyrophosphate (KPP) (KPP gels, a standard expressed as dotted line) or 36 mmol/L disodium inosine-5′monophosphate (IMP) (IMP gels, ○) and without KPP and IMP (control gels, é). Differences are expressed within a seven-point scale (−3 to +3), setting the value of the KPP gels as zero. Other conditions are described in the ‘Materials and Methods’ section. *P < 0.05 (vs. KPP gels); **P < 0.01 (vs. KPP gels).
as obtained by 9 mmol/L KPP. Protein extractability of beef myofibrils is positively correlated with the strength of the gel prepared with beef myofibrils (Samejima et al. 1985). Thus, we suggest that the IMPinduced enhancement of physical properties of the gels is ascribable to the increased extractability of actin and myosin obtained by IMP. In the previous section, we proposed a possible reason why 36 mmol/L IMP exhibited the same high level of WHC as 9 mmol/L KPP in 0.3 mol/L NaCl in spite of its low extractability of actin and myosin. As for the heat-induced gels used here for determination of physical properties, we assumed that 36 mmol/L IMP exhibited the same level of WHC as 9 mmol/L KPP. Thus, the high level of the physical properties induced by 36 mmol/L IMP might be related to the 36 mmol/L IMP-induced high level of WHC and not to the low extractability of actin and myosin induced by 36 mmol/L IMP. As observed with WHC, the IMPinduced elimination of the interaction between thin and thick filaments renders the thin filaments free from myosin and the thick filaments free from actin. Thus, the heat-induced gels from those free filaments may construct fine, three-dimensional networks to account for the favorable physical properties.
Effects of IMP on sensory properties of heat-induced gels from porcine meat
© 2014 Japanese Society of Animal Science
Animal Science Journal (2014) 85, 595–601
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In conclusion, IMP is expected to be a practical substitute for pyrophosphates to improve the quality of sausages. Furthermore, we expect that IMP has the ability to improve the quality of other meat products, such as ham and bacon. Thus, we are examining the effect of IMP on the quality of ham and bacon. Further studies are needed to clarify this subject.
REFERENCES Fukazawa T, Hashimoto Y, Yasui T. 1961a. Effect of some proteins on the binding quality of an experimental sausage. Journal of Food Science 26, 541–549. Fukazawa T, Hashimoto Y, Yasui T. 1961b. The relationship between the components of myofibrillar protein and the effect of various phosphates that influence the binding quality of sausage. Journal of Food Science 26, 550–555. Funatsu T, Kono E, Higuchi H, Kimura S, Ishiwata S, Yoshioka T, Maruyama K, Tsukita S. 1993. Elastic filaments in situ in cardiac muscle: deep-etch replica analysis in combination with selective removal of actin and myosin filaments. The Journal of Cell Biology 120, 711–724. Goll DE, Suzuki A, Temple J, Holmes GR. 1972. Studies on purified α-actinin: I. Effect of temperature and tropomyosin on the α-actinin/F-actin interaction. Journal of Molecular Biology 67, 469–472. Hermansson A, Harbitz O, Langton M. 1986. Formation of two types of gels from bovine myosin. Journal of the Science and Food Agriculture 37, 69–84. Ishioroshi M, Samejima K, Yasui T. 1982. Further studies on the roles of the head and tall regions of the myosin molecule in heat-induced gelation. Journal of Food Science 47, 114–120. Ishioroshi M, Samejima K, Yasui T. 1983. Heat-induced gelation of myosin filaments at a low salt concentration. Agricultural and Biological Chemistry 47, 2809–2816. Ishiwata S. 1981. Melting from both ends of an A-band in a myofibril. Observation with a phase-contrast microscope. Journal of Biochemistry 89, 1647–1650. Matlock RG, Terrell RN, Savell JW, Rhee KS, Dutson TR. 1984a. Factors affecting properties of raw-frozen pork sausage patties made with various NaCl/phosphate combinations. Journal of Food Science 49, 1363–1366, 1371. Matlock RG, Terrell RN, Savell JW, Rhee KS, Dutson TR. 1984b. Factors affecting properties of precooked-frozen pork sausage patties made with various NaCl/phosphate combinations. Journal of Food Science 49, 1372–1375.
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Nakamura Y, Migita K, Okitani A, Matsuishi M. 2012. Enhancing effect of IMP on myosin and actin extraction from porcine meat. Bioscience Biotechnology, and Biochemistry 76, 1611–1615. Nakamura Y, Migita K, Okitani A, Matsuishi M. 2013. Mode of IMP and pyrophosphate enhancement of myosin and actin extraction from porcine meat. Bioscience, Biotechnology, and Biochemistry 77, 1214–1218. Offer G, Knight P. 1988. The structural basis of water-holding in meat. In: Lawrie R (ed.), Developments in Meat Science, Vol. 4, pp. 63–171. Elsevier Science Publishers, Barking, Essex. Offer G, Trinick J. 1983. On the mechanism of water holding in meat: the swelling and shrinking of myofibrils. Meat Science 8, 245–281. Okitani A, Ichinose N, Koza M, Yamanaka K, Migita K, Matsuishi M. 2008. AMP and IMP Dissociate Actomyosin into Actin and Myosin. Bioscience Biotechnology, and Biochemistry 72, 2005–2011. Samejima K, Ishioroshi M, Yasui T. 1981. Relative roles of the head and tail portions of the molecule in heat-induced gelation of myosin. Journal of Food Science 46, 1412–1418. Samejima K, Egelandsdal B, Fretheim K. 1985. Heat gelation properties and protein extractability of beef myofibrils. Journal of Food Science 50, 1540–1543, 1555. Sofos JN. 1986. Use of phosphates in low-sodium meat products. Food Technology 40, 53–63. Xiong YL. 2004. Chemical and physical characteristics of meat. Protein functionality. In: Jensen WK, Devine C, Dikeman M (eds), Encyclopedia of Meat Science, Vol. 1, pp. 218–225. Elsevier Academic Press, Kidlington, Oxford. Yamamoto K. 1990. Electron microscopy of thermal aggregation of myosin. Journal of Biochemistry 108, 896– 898. Yamamoto K, Samejima K, Yasui T. 1988. Heat-induced gelation of myosin filaments. Agricultural and Biological Chemistry 52, 1803–1811. Yasui T, Fukazawa T, Sakanishi M, Hashimoto Y. 1964. Phosphate effects on meat, effect of inorganic polyphosphates on solubility and extractability of myosin B. Journal of Agricultural and Food Chemistry 12, 392–399. Yasui T, Ishioroshi M, Nakano H, Samejima K. 1979. Changes in shear modulus, ultrastructure and spin-spin relaxation times of water associated with heat-induced gelation of myosin. Journal of Food Science 44, 1201–1204, 1211. Yasui T, Ishioroshi M, Samejima K. 1980. Heat-induced gelation of myosin in the presence of actin. Journal of Food Biochemistry 4, 61–78.
© 2014 Japanese Society of Animal Science
Animal Science Journal (2014) 85, 595–601
doi: 10.1111/asj.12170
ORIGINAL ARTICLE IMP improves water-holding capacity, physical and sensory properties of heat-induced gels from porcine meat Yukinobu NAKAMURA,1 Koshiro MIGITA,2 Akihiro OKITANI2 and Masanori MATSUISHI2 1
Japan Meat Science and Technology Institute and 2Department of Food Science and Technology, Nippon Veterinary and Life Science University, Tokyo, Japan
ABSTRACT Water-holding capacity (WHC) of heat-induced pork gels was examined. The heat-induced gels were obtained from meat homogenates prepared by adding nine volumes of 0.3–0.5 mol/L NaCl solutions containing 9–36 mmol/L disodium inosine-5′-monophosphate (IMP) or 9 mmol/L tetrapotassium pyrophosphate (KPP) to minced pork. IMP at 36 mmol/L enhanced the WHC to the same level as attained by KPP. Physical and sensory properties of heat-induced gels were also examined. The heat-induced gels were prepared from porcine meat homogenates containing 0.3 mol/L NaCl and 9–36 mmol/L IMP or 9 mmol/L KPP. IMP at 36 mmol/L enhanced the values of hardness, cohesiveness, gumminess and springiness, measured with a Tensipresser, and several organoleptic scores to the same level as the score attained by KPP. Thus, it is concluded that IMP is expected to be a practical substitute for pyrophosphates to improve the quality of sausages.
Key words: heat-induced gels, inosine-5′-monophosphate, physical property, pyrophosphate, water-holding capacity.
INTRODUCTION Sausages are heat-induced gels produced from the salted emulsion of comminuted meats. The gels have an ability to bind comminuted meats and hold added water and fat, that is, they possess a binding property. It has been shown that the high level of binding in sausages can be ascribed to salt-solubilized myosin or actomyosin (Fukazawa et al. 1961a; Yasui et al. 1979, 1980; Samejima et al. 1981; Ishioroshi et al. 1982, 1983; Hermansson et al. 1986; Yamamoto et al. 1988; Yamamoto 1990), which are the major myofibrillar proteins. When salt-solubilized myosin or actomyosin is heated, a three-dimensional network of proteins that encloses water is formed (Xiong 2004). In meats used as the raw materials of sausages, myosin and actin exist in the form of actomyosin because of the post-mortem disappearance of adenosine triphosphate (ATP). Actomyosin is a salt-soluble protein. In order to generate a high level of binding in sausages, actomyosin is extracted from myofibrils using a NaCl concentration as high as 0.5 mol/L (3%) (Offer & Trinick 1983). A NaCl concentration of about 0.3 mol/L (2%) is used in the majority of sausages produced in Japan, since Japanese consumers do not find salty sausages (0.5 mol/L NaCl) palatable and are mindful of the risk © 2014 Japanese Society of Animal Science
of developing hypertension. However, 0.3 mol/L NaCl is not sufficient to extract actomyosin from myofibrils (Offer & Trinick 1983). Since pyrophosphates dissociate actomyosin to actin and myosin and enhance the extractability of myosin (Yasui et al. 1964; Ishiwata 1981), pyrophosphates have been used as an additive to enhance the binding property of sausages (Fukazawa et al. 1961b). However, pyrophosphateadded sausages are unacceptable to some consumers because pyrophosphates, which are exogenous inorganic polyphosphate chelating agents, inhibit small intestinal Ca ion absorption and exhibit an astringent taste. Previously, we showed that the umami seasoning disodium inosine-5′-monophosphate (IMP), which is an endogenous substance in meat, dissociates actomyosin into actin and myosin (Okitani et al. 2008), and enhances the extractability of actin and myosin from porcine meats in the presence of ca. 0.3-0.5 mol/L NaCl (Nakamura et al. 2012). Moreover,
Correspondence: Yukinobu Nakamura, Japan Meat Science and Technology Institute, Shibuya, Tokyo 150-0013, Japan. (Email: [email protected]) Received 24 July 2013; accepted for publication 15 October 2013.
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we showed that the IMP-induced extraction of both proteins is increased by increasing the extraction time from 0 to 12 h at 4°C, while pyrophosphate-induced extraction is not (Nakamura et al. 2013). Thus, there is a similarity between IMP and pyrophosphate in enhancing the extractability of actin and myosin. However, the effect of IMP on the binding property of sausage has not been examined. In the present study, we prepared heat-induced gels in the presence of 0.3-0.5 mol/L NaCl and IMP or tetrapotassium pyrophosphate (KPP) and determined whether IMP improves the quality of heat-induced gels, by investigating the effect of incubation time and NaCl concentration on the water-holding capacity (WHC) and physical and sensory properties of the obtained heat-induced gels. On the basis of the results obtained, we discuss the suitability of IMP as a substitute of pyrophosphates for the sausage industry.
MATERIALS AND METHODS Materials The cuts of fresh meat (mainly Musculus semimembranosus, M. adductor and M. gracilis) of Large White × Landrace × Duroc crossbred pigs (n = 3) were obtained from retail stores and immediately minced in a meat chopper after removing fat and connective tissues. Minced meat was vacuum-packed and stored at −20°C until use. KPP was purchased from Wako Pure Chemical Industries (Osaka, Japan) and IMP was obtained from Tokyo Chemical Industries (Tokyo, Japan). All other chemicals used were of analytical grade.
Preparation of heat-induced gels for the determination of WHC Meat homogenates for heat-induced gels were prepared by the same methods as in the previous studies determining the effect of IMP on actin and myosin extraction (Nakamura et al. 2012, 2013). Minced meat (3 g) was mixed with nine volumes (27 mL) of each of the extraction solutions containing 0.3, 0.4 or 0.5 mol/L NaCl and 0, 9, 18 or 36 mmol/L IMP or 9 mmol/L KPP and homogenized twice at 12 000 rpm for 30 sec with a homogenizer (Excel Auto, Nippon Seiki, Nagaoka, Japan). We chose 9 mmol/L KPP for comparison with the effect of IMP, since this KPP concentration is currently used in the sausage industry. After the addition of the extraction solutions containing 0.3, 0.4 and 0.5 mol/L NaCl, the total salt (KCl plus NaCl) concentrations in the homogenates were 0.29, 0.38 and 0.47 mol/L, respectively, assuming that the salt concentration in minced meat is 0.2 mol/L, and supported by the finding that the ionic strength in muscle cells was found to be 0.2 (Offer & Knight 1988). The addition of IMP and KPP diluted the concentrations in the homogenate to 0.9-fold of initial concentrations. One portion of the homogenate was immediately packed in a flat-bottomed 2.0 mL polypropylene (PP) tube and was heated at 63°C in an oven for 35 min immediately after homogenization. The core temperature of the homogenate reached 60°C after 23 min and 62.3°C after 35 min. The obtained heat-induced gels were designated as 0-h gels. The other portion of the homogenate was incubated at 4°C for © 2014 Japanese Society of Animal Science
12 h before being heated. The obtained heat-induced gels were designated as 12-h gels. The 0-h and 12-h gels were subjected to the determination of WHC.
Determination of WHC Heat-induced gels (9 mm diameter) in the PP tubes were centrifuged at 1000 × g for 30 sec and the weight of the released water from the gels was then determined. WHC was calculated by using the following formula:
WHC (%) = {1 − ( Ww Wg )} × 100
where Ww is the weight of the water released from the heat-induced gels by centrifugation and Wg is the weight of the heat-induced gels.
Preparation of heat-induced gels for the determination of physical properties and sensory evaluation We prepared the heat-induced gels for the determination of physical properties and sensory evaluation, essentially following the method of sausage making. Minced meat (30 g) was mixed with 0.5 volumes (15 mL) of salt (NaCl) solutions containing IMP or KPP and homogenized thrice at 12 000 rpm for 30 sec with a homogenizer (Excel Auto, Nippon Seiki). The total salt (NaCl plus KCl) concentration of the obtained meat homogenate was 0.3 mol/L, assuming that the salt concentration of minced meat was 0.2 mol/L (Offer & Knight 1988). IMP was added to the meat homogenate at a final concentration of 9, 18 and 36 mmol/L. KPP was added to the meat homogenate at a final concentration of 9 mmol/L, the concentration currently applied in the sausage industry. For the determination of physical properties, the meat homogenate (1.5 g) was immediately packed in a flatbottomed 2.0 mL PP tube and centrifuged at 100 × g for 10 sec to degas the homogenate. Then, the homogenate was heated at 63°C in an oven for 35 min. The core temperature of the homogenate reached 60°C after 26 min and 63.8°C after 35 min. The gels were placed on ice until used in the examination. For the sensory test, the homogenate (40 g) was packed in a 50 mL PP tube immediately after homogenization, centrifuged at 100 × g for 10 sec, and then heated at 65°C in a water bath for 40 min. The core temperature of the homogenate reached 65°C after 6 min and was maintained at 65°C for 34 min. The obtained heat-induced gels were placed on ice until used in the examination.
Determination of physical properties Physical properties of the heat-induced gels were measured by the two-bite method using a texture analyzer, Tensipresser TTP-50BX (Taketomo Electric Inc., Tokyo, Japan). The 5 mm diameter hollow plunger penetrated the heat-induced gels (9 mm diameter, 20 mm thickness) in PP tubes at a speed of 6 mm/sec. The clearance was 14.0 mm. Figure 1 shows the H1, A1, A2, P1 and P2 given by the Tensipresser. H is the compression force (N) of the plunger, P is the moving distance (mm) of the plunger, and A is the area (mm2) surrounded by the stress profile and abscissa (workload). Hardness, H1, cohesiveness, A1/A2, gumminess, H1×A1/A2, and springiness, P2/P1×100, were determined from the texture profile by using the software provided with the Tensipresser. Animal Science Journal (2014) 85, 595–601
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Figure 1 Texture profile of heat-induced gels generated by the two-bite method using a Tensipresser. Physical properties of heat-induced gels were measured using the two-bite method with a Tensipresser TTP-50BX. H, compression force of the plunger; P, moving distance of the plunger; B, breaking point.
Sensory evaluation Sensory evaluation of three types of heat-induced gels with 9 mmol/L KPP or 36 mmol/L IMP and without KPP and IMP, designated as KPP gels, IMP gels and control gels, respectively, was conducted twice by trained panelists. The panelists were one female and six males (age 30 s, two; age 40 s, three; age 60 s, two) affiliated with Japan Meat Science and Technology Institute, Tokyo. The heat-induced gels were 28 mm in diameter and 3 mm thick. Gels were kept at room temperature (25°C) for 1 h before the test. The texture evaluation parameters were hardness, springiness, binding property and juiciness. The flavor evaluation parameters were umami, saltiness, astringency, odor and overall preference. Differences were expressed within a seven-point scale (−3 to +3), setting the value for the KPP-added gels as zero.
Statistical analysis The values of WHC and physical properties are expressed as mean ± standard error of triplicate determinations. In the sensory test, the scores between the KPP-added gels and the other gels were analyzed using Student’s t-test.
RESULTS AND DISCUSSION Effects of IMP on WHC of heat-induced gels from porcine meat Figure 2A, B and C show the WHC of 0-h and 12-h gels prepared with extraction solutions containing various concentrations of NaCl and 0–36 mmol/L IMP or 9 mmol/L KPP. KPP was used for comparison with the effect of IMP. In the case of the 0.3 mol/L NaCl extraction solution (Fig. 2A), the WHC of 0-h gels was 32% in the absence of IMP and KPP. The addition of 9 and 18 mmol/L IMP into the extraction solution slightly increased the WHC. The addition of 36 mmol/L IMP resulted in a fairly high WHC of 80%. The WHC of 12-h gels was 35% in the absence of IMP and KPP. The addition of 9, 18 and 36 mmol/L IMP increased WHC to 39, 70 and 96%, respectively. These values are higher than the corresponding values of the 0-h gels, indicating that Animal Science Journal (2014) 85, 595–601
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the WHC of the IMP-added gels is enhanced in a time-dependent manner. On the other hand, the addition of 9 mmol/L KPP into the 0.3 mol/L NaCl extraction solution increased the WHC of the 0-h and the 12-h gels to 87 and 97%, respectively. Thus, it was found that IMP enhanced the WHC of heat-induced gels and that the enhancing effect of 36 mmol/L IMP for the 0-h and 12-h gels was comparable to that of 9 mmol/L KPP. In the case of the 0.4 mol/L NaCl extraction solution (Fig. 2B), the WHC of the 0-h gels was 35% in the absence of IMP and KPP. The addition of 9, 18 and 36 mmol/L IMP into the NaCl solutions resulted in fairly high values: 61, 77 and 91%, respectively. These values are higher than the corresponding values of the IMP-added gels at 0.3 mol/L NaCl. This showed that the increase in the NaCl concentration from 0.3 to 0.4 mol/L enhances the WHC of the IMP-added gels. The WHC of the 12-h gels was 37% in the absence of IMP and KPP. The addition of 9, 18 and 36 mmol/L IMP increased the WHC to 71, 97 and 100%, respectively. These values are higher than the corresponding values of the 0-h gels, indicating that the WHC of the IMP-added gels is enhanced in a time-dependent manner. On the other hand, the addition of 9 mmol/L KPP into the extraction solution increased the WHC of the 0-h and 12-h gels to 89 and 96%, respectively. These values were comparable to those obtained for 18 and 36 mmol/L IMP. In the case of the 0.5 mol/L NaCl extraction solution (Fig. 2C), the WHC of the 0-h gels was 48% in the absence of IMP and KPP. The addition of 9, 18 and 36 mmol/L IMP into the extraction solutions increased the WHC to 78, 81 and 94%, respectively, which were almost equal to the corresponding values of the IMPadded gels at 0.4 mol/L NaCl. The WHC of the 12-h gel was 40% in the absence of IMP and KPP. The addition of 9, 18 and 36 mmol/L IMP increased the WHC to 95, 98 and 99%, respectively. These values are higher than the corresponding values of the 0-h gels, indicating that the WHC of the IMP-added gels is enhanced in a time-dependent manner. On the other hand, the addition of 9 mmol/L KPP into the extraction solutions increased the WHC of the 0-h and 12-h gels to 82 and 98%, respectively. These values were comparable to those obtained for 9, 18 and 36 mmol/L IMP. From the results described above, it was found that IMP has the ability to enhance the WHC of the heatinduced gels, and that this ability is enhanced by three factors: the increased concentrations of IMP and NaCl, and the increased incubation time of the meat homogenates at 4°C. We showed previously that the extractability of actin and myosin from porcine meat is enhanced by the three above-mentioned factors (Nakamura et al. 2012, 2013). Thus, because there is a similarity in the effectiveness of the three above-mentioned factors © 2014 Japanese Society of Animal Science
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Figure 2 Effects of disodium inosine-5′-monophosphate (IMP) and tetrapotassium pyrophosphate (KPP) on the water-holding capacity (WHC) of heat-induced gels. Meat homogenates were prepared by mixing minced meat with nine volumes of 0.3 mol/L (A), 0.4 mol/L (B) and 0.5 mol/L (C) NaCl solution containing 0–36 mmol/L IMP incubated for 0 (○) and 12 h (•) or containing 9 mmol/L KPP incubated for 0 (□) and 12 h (■). Homogenates were then subjected to heating. The WHC of the obtained heat-induced gels was determined. Each result is presented as the mean ± SE of three independent measurements. Other conditions are described in the ‘Materials and Methods’ section.
between WHC and extractability, the improvement of the WHC appears to be a result of the increased extractability. We showed in our previous paper (Nakamura et al. 2012) that the IMP-induced enhancement of the extractability of actin and myosin is ascribable to the dissociation of actomyosin to actin and myosin. Therefore, the dissociation of actomyosin appears to be the trigger for the improvement of WHC. The KPPinduced improvement of WHC also seems to be attributable to the increased extractability of actin and myosin, caused by the dissociation of actomyosin to actin and myosin. However, in the correlation between WHC and extractability, there is a noticeable difference between IMP and KPP in the case of the 0.3 mol/L NaCl extraction solution. As mentioned above, with respect to the WHC of 12-h gels, 36 mmol/L IMP (96%) has an enhancing effect equal to 9 mmol/L KPP (97%). On the other hand, as described previously (Nakamura et al. 2013), with respect to actin and myosin extractability with a 12-h extraction, 36 mmol/L IMP showed an extraction of 32% for actin and 30% for myosin, while 9 mmol/L KPP showed an extraction of 55% for actin and 93% for myosin, although 36 mmol/L IMP and 9 mmol/L KPP were assumed to almost completely eliminate the interaction between thin and thick filaments. As the reason for the discrepancy between IMP- and KPP-induced extraction of actin and myosin, we proposed the following scheme. The thin filaments containing actin and the thick filaments containing myosin are connected with scaffolds of myofibrils. Thus, it is necessary for actin and myosin to be © 2014 Japanese Society of Animal Science
extracted so that both filaments are released from the scaffolds, as well as to eliminate interaction between these filaments. Hence, we assumed that the scaffoldreleasing activity of 36 mmol/L IMP was lower than that of 9 mmol/L KPP, resulting in the low extractabilities of actin and myosin induced by IMP. It is possible that the scaffold connected to the thin filaments is comprised of Z-disks, because the α-actinin of Z-disks interacts with F-actin of the thin filaments (Goll et al. 1972). On the other hand, the scaffold connected with thick filaments is possibly connectin and/or Z-disk, because Funatsu et al. (1993) observed the interaction of connectin filaments along with thick filaments and the interaction of both ends of connectin filaments with Z-disks. On the basis of the above scheme, the present results that 36 mmol/L IMP exhibited the same high level of WHC as 9 mmol/L KPP in spite of its low actin and myosin extractabilities, suggests that WHC is enhanced by the elimination of interactions between thin and thick filaments and is not influenced by the connection of both filaments with the scaffold of myofibrils. When the interaction between both filaments is weakened, the thin filaments are freed from myosin and thick filaments are freed from actin. Thus, the heat-induced gels from these free filaments may construct a fine, three-dimensional network to hold large amounts of water.
Effects of IMP on physical properties of heat-induced gels from porcine meat Figure 3 shows the physical properties of gels containing 0.3 mol/L total salt and 9, 18 and 36 mmol/L IMP or 9 mmol/L KPP. Animal Science Journal (2014) 85, 595–601
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Figure 3 Effects of disodium inosine-5′-monophosphate (IMP) and tetrapotassium pyrophosphate (KPP) on physical properties of heat-induced gels. Meat homogenates were prepared by mixing minced meat with 0.5 volumes of NaCl solutions containing 0–36 mmol/L IMP (○) or 9 mmol/L KPP (□) and then heated. The hardness (A), cohesiveness (B), gumminess (C) and springiness (D) of the obtained heat-induced gels were determined. The salt (NaCl plus KCl) concentration of the heat-induced gels was 0.3 mol/L. Each result is presented as the mean ± SE of three independent measurements. Other conditions are described in the ‘Materials and Methods’ section.
As for hardness (Fig. 3A), in the absence of IMP and KPP, the gel exhibited a value of 4.2 N. In the presence of 9, 18 and 36 mmol/L IMP, the gels exhibited increased values of 5.4, 6.3 and 7.9 N, respectively. On the other hand, in the presence of 9 mmol/L KPP, the gels exhibited a value of 8.1 N. As for cohesiveness (Fig. 3B), in the absence of IMP and KPP, the gels exhibited a value of 0.28. In the presence of 9, 18 and 36 mmol/L IMP, the gels exhibited increased values of 0.32, 0.39 and 0.46, respectively. On the other hand, in the presence of 9 mmol/L KPP, the gels exhibited a value of 0.43. As for gumminess (Fig. 3C), in the absence of IMP and KPP, the gels exhibited a value of 1.2 N. In the Animal Science Journal (2014) 85, 595–601
presence of 9, 18 and 36 mmol/L IMP, the gels exhibited increased values of 1.7, 2.5 and 3.6 N, respectively. On the other hand, in the presence of 9 mmol/L KPP, the gels exhibited a value of 3.5 N. As for springiness (Fig. 3D), in the absence of IMP and KPP, the gels exhibited a value of 57%. In the presence of 9, 18 and 36 mmol/L IMP, the gels exhibited increased values of 64, 71 and 73%, respectively. On the other hand, in the presence of 9 mmol/L KPP, the gels exhibited a value of 74%. The results described above indicated that 36 mmol/L IMP enhances physical properties, such as hardness, cohesiveness, gumminess and springiness, of heat-induced gels from porcine meat to the same level © 2014 Japanese Society of Animal Science
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Figure 4 shows the results of the sensory evaluation of texture. As compared with KPP gels, IMP gels
exhibited a slightly low score in hardness and no differences in springiness, binding property and juiciness, whereas control gels exhibited very low scores in all evaluation items except juiciness. The texture of IMP gels was evaluated as comparable to that of KPP gels. This result is consistent with the results of the WHC and physical properties obtained in the previous section. A low score in hardness might be ascribable to a lower extractability of actin and myosin obtained by IMP, in comparison with KPP, as described above. Figure 5 shows the results of the sensory evaluation of flavor. As compared with KPP gels, IMP gels exhibited high scores in umami and overall preference and no differences in saltiness, astringency and odor, whereas control gels exhibited no differences in umami, saltiness and astringency and low scores in odor and overall preference. This is reasonable since IMP is an umami agent. It was noticeable that the control gels exhibited a rancid odor resulting from lipid oxidation, whereas IMP gels did not. Inorganic polyphosphates, including pyrophosphate, are able to prevent the generation of rancid odors (Matlock et al. 1984a, b; Sofos 1986). Thus, IMP, an organic polyphosphate, appears to possess the same ability. On the basis of the results described above, it was found that IMP improves the sensory properties of heat-induced gels and that the increased sensory scores of IMP gels are higher or at the same level as those of KPP gels.
Figure 4 Sensory evaluation of heat-induced gel texture. Sensory evaluation of the heat-induced gels was conducted using three heat-induced gels with 9 mmol/L tetrapotassium pyrophosphate (KPP) (KPP gels, a standard expressed as dotted line) or 36 mmol/L disodium inosine-5′monophosphate (IMP) (IMP gels, ○) and without KPP and IMP (control gels, é). Differences were expressed within a seven-point scale (−3 to +3), setting the value of the KPP gels as zero. Other conditions are described in the ‘Materials and Methods’ section. *P < 0.05 (vs. KPP gels); **P < 0.01 (vs. KPP gels).
Figure 5 Sensory evaluation of heat-induced gel flavor. Sensory evaluation of heat-induced gels was conducted using three heat-induced gels with 9 mmol/L tetrapotassium pyrophosphate (KPP) (KPP gels, a standard expressed as dotted line) or 36 mmol/L disodium inosine-5′monophosphate (IMP) (IMP gels, ○) and without KPP and IMP (control gels, é). Differences are expressed within a seven-point scale (−3 to +3), setting the value of the KPP gels as zero. Other conditions are described in the ‘Materials and Methods’ section. *P < 0.05 (vs. KPP gels); **P < 0.01 (vs. KPP gels).
as obtained by 9 mmol/L KPP. Protein extractability of beef myofibrils is positively correlated with the strength of the gel prepared with beef myofibrils (Samejima et al. 1985). Thus, we suggest that the IMPinduced enhancement of physical properties of the gels is ascribable to the increased extractability of actin and myosin obtained by IMP. In the previous section, we proposed a possible reason why 36 mmol/L IMP exhibited the same high level of WHC as 9 mmol/L KPP in 0.3 mol/L NaCl in spite of its low extractability of actin and myosin. As for the heat-induced gels used here for determination of physical properties, we assumed that 36 mmol/L IMP exhibited the same level of WHC as 9 mmol/L KPP. Thus, the high level of the physical properties induced by 36 mmol/L IMP might be related to the 36 mmol/L IMP-induced high level of WHC and not to the low extractability of actin and myosin induced by 36 mmol/L IMP. As observed with WHC, the IMPinduced elimination of the interaction between thin and thick filaments renders the thin filaments free from myosin and the thick filaments free from actin. Thus, the heat-induced gels from those free filaments may construct fine, three-dimensional networks to account for the favorable physical properties.
Effects of IMP on sensory properties of heat-induced gels from porcine meat
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In conclusion, IMP is expected to be a practical substitute for pyrophosphates to improve the quality of sausages. Furthermore, we expect that IMP has the ability to improve the quality of other meat products, such as ham and bacon. Thus, we are examining the effect of IMP on the quality of ham and bacon. Further studies are needed to clarify this subject.
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