Sodium Chloride and Tripolyphosphate Effects on Physical and Quality Characteristics of Injected Pork Loins

Transcription

1 JOURNAL OF FOOD SCIENCE FOOD ENGINEERING AND PHYSICAL PROPERTIES Sodium Chloride and Tripolyphosphate Effects on Physical and Quality Characteristics of Injected Pork Loins N.A. Detienne and L. Wicker ABSTRACT Whole, boneless pork loins were needle-injected to a final concentration of up to 1.5% NaCl and/or 0.45% sodium tripolyphosphate (STPP) in a 4 4 factorial, randomized, complete block design. Percent weight gain, internal meat ph, purge loss, final product yield, cook loss, Warner Bratzler shear, expressible moisture, and total moisture were determined. Response surface methodology was employed to create regression models and identify optimum ingredient parameters for each characteristic. NaCl and STPP improved weight gain, purge, final product yield, and moisture content. Predicted Warner Bratzler shear was reduced approximately 50%. A salt-phosphate interaction was observed for weight gain, purge, cook loss, and expressible moisture. Key Words: marination, muscle foods, tenderness, tripolyphosphate INTRODUCTION POLYPHOSPHATES ARE COMMONLY USED IN THE PRODUCTION OF value-added meat and poultry products. Injection of phosphate-containing solutions (marinades) increases the palatability and shelf-life of a wide variety of meat products (Teicher, 1990). Previous published work has demonstrated improved yields, tenderness, and moisture retention (Farr and May, 1970; Shults and Wierbicki, 1974; Young and Lyon, 1986), but much of the data were based on ground or cured products. Sodium tripolyphosphate (STPP) improved sensory characteristics in fresh, intact pork cuts (Smith et al., 1984; Cannon et al., 1993). However, published studies have not included optimization of marination technology in fresh, whole pork loins. Consumers of pork products have traditionally over-cooked pork because of concerns about the potential health risk of Trichina spiralis. Trends toward lowering fat content in cuts, such as whole loins from 24.14% to 12.58% (USDA-HNIS, 1983; 1992), introduce the likelihood that untreated, cooked, whole pork loin products will have less desirable attributes of juiciness and tenderness. A case ready marketing approach is being employed by many processors to meet demands of consumers for consistent, acceptable, ready-to-cook products (Robinson, 1997; Sutton et al., 1997). A fundamental reason for increases in phosphate usage in meat products may be the pressure from consumer groups to reduce dietary sodium levels (Kijowski and Mast, 1988). Salt levels in processed meats could be reduced by nearly 50% without storage or processing difficulties when 0.5% phosphate was used in the formulation (Choi et al., 1987). Meat products account for about 15% of the total sodium consumption in the Western diet. Thus, phosphates could provide considerable potential reduction in dietary sodium levels (Barbut et al., 1988). Among the phosphates commonly The authors are affiliated with the Food Process Research and Development Laboratory, Dept. of Food Science and Technology, Univ. of Georgia, Athens, GA Direct inquiries to Dr. L. Wicker ( lwicker@arches.uga.edu). used in the meat industry, STPP accounts for nearly 80%, added as a single agent or in blends (Barbut et al., 1988). Polyphosphates can be used in the United States up to 0.5% of the final product (USDA-FSIS, 1997). The interaction of polyphosphates with muscle tissue and the mechanism of meat hydration and tenderization are not fully understood. Some factors hypothesized by researchers have been increased meat ph (Oreskovich et al., 1992; Karlsson et al., 1996), increased ionic strength (Hamm 1970; Young et al., 1992), sequestration of metal ions, and dissociation of the actomyosin complex (Offer and Trinick, 1983; Lewis et al., 1986). Of these, an increased ph and ionic strength are the most widely hypothesized explanations. A well known, but not well understood, interaction has been reported between NaCl and STPP (Mahon, 1962; Shults and Wierbicki, 1974; Lawrie, 1985; Young et al., 1992). A clear understanding of this interaction could lead to more effective methods for commercial pork marination. The objectives of this study were to determine how varying levels of NaCl and STPP concentrations (within regulatory guidelines and solubility properties) affect the physical and textural characteristics of whole, boneless pork loins and to optimize parameters for each characteristic within this range using response surface methodology (RSM). MATERIALS & METHODS Sample preparation and marination Twenty-four whole, boneless center cut pork loins (longissimus muscle) were purchased from a commercial distributor (Buckhead Beef, Atlanta, Ga., U.S.A.). The loins were quartered into uniform 15-cm sections (N 96). Preliminary studies indicated that variation might exist within each longissimus muscle. An experimental blocking factor was defined for experimental units derived from the anterior and posterior sections of each loin, such that 48 homogeneous loin sections were assigned to each block. Within each block, each section was randomly assigned to 1 of 16 treatment combinations of NaCl (0%, 0.5%, 1.0%, or 1.5%) and STPP (0%, 0.15%, 0.30%, or 0.45%), so that 3 replications were made for each treatment combination in each block. Sections were injected to a target weight gain (marinade uptake) of 12% to14% of the original (green) weight using a multineedle injector (Schroeder N40, Wolf-Tec Inc, Kingston, N.Y., U.S.A.), set at 200 kpa brine pressure and a belt speed of 4. Pumped loins were allowed to equilibrate for 5 min following injection to allow free water to expel and re-weighed for pump yield determination. The loins were then individually vacuum-packaged (Multivac Model AG500, W.R. Grace Co., Duncan, S.C., U.S.A.) in oxygen barrier bags (Cryovac Model B-620) and stored at 4 C for 96 h. The loins were weighed (post-storage weight), and internal meat ph was determined using a spear-probe (Model 81-63, Orion, Beverly, Mass., U.S.A.) attached to a hand-held meter (Accumet 1003, Fisher Scientific, Pittsburgh, Pa., U.S.A.). The loins were placed in uncovered pans and cooked in a convection oven (Model JBP90, GE, Louisville, Ky., U.S.A.) at 177 C to an internal temperature of 72 C, as monitored by a scanning thermometer (Digi JOURNAL OF FOOD SCIENCE Volume 64, No. 6, Institute of Food Technologists

2 Sense , Cole-Parmer, Vernon Hills, Ill., U.S.A.) that was equipped with a thermocouple (type T, Omega Engineering Co., Stamford, Conn., U.S.A.) inserted into the center of each loin. The loins were cooled to 25 C, weighed (cooked weight), and sampled for further analysis. Each meat sample was stored at 4 C in sealed, minimum-sized, plastic cups (25 to 100 ml), for 12 h, and equilibrated to room temperature prior to final analysis. Experimental treatments Loins were injected with a mixed solution (marinade) of NaCl and STPP (Sigma Chemical Co., St. Louis, Mo., U.S.A.) prepared with deionized water. Each marinade was formulated to contain 0%, 0.5%, 1.0%, or 1.5% NaCl and 0%, 0.15%, 0.30%, or 0.45% STPP, relative to the final packaged raw product weight as part of a 4 4 factorial arrangement. The controls were the injected samples with the 0% NaCl and 0% STPP combination. Product analysis Purge loss from each loin section was calculated as: % 100 (pumped wt post-storage wt) / (pumped wt green wt). Final product yield, defined as yield-to-green, was calculated as: % 100 (post-cooking wt green wt) / green wt. Cook loss, defined as yield-to-pump, was calculated as: % 100 (post-cooking wt - poststorage wt) / post-storage wt. Moisture content of cooked pork loins was determined using the standard procedure (AOAC, 1995). Water-holding capacity (WHC) was defined as the ability of meat to retain its own and/or added water during application of a force (Forrest et al., 1989). Jauregui et al. (1981) related expressible moisture to WHC as the release of free water from a protein system under application of force. Expressible moisture was determined using a modification of the filter paper press method (FPPM). A 2.0-cm slice was obtained from each cooked loin and two 2.5-cm-dia subsamples were cored parallel to the muscle fibers. Using a Universal Testing Machine (Model 5500R, Instron Corp., Canton, Mass., U.S.A.), the disc was pressed between paired #1 Whatman filter sheets and parallel plates. The Instron was set with a load cell of 500 kg and a crosshead speed of 100 mm/min. Samples were pressed to 75% deformation and held at that point for 15 s. The WHC was defined as the expressible moisture, calculated as: % 100 (initial wt final wt) / initial wt. For instrumental tenderness determination, a 2.5-cm slice was obtained from each cooked loin and subsampled for four 1.27 cm cores cut parallel to the muscle fibers for the Warner Bratzler shear determination. The shear force was measured with the Instron fitted with a Warner Bratzler shear attachment, and the peak force was recorded (Young and Lyon, 1989). The full-scale load was set at 10 kg, and the crosshead speed was 200 mm/min. Statistical analysis The data from this 4 4 factorial, randomized complete block design were first analyzed using the General Linear Models (GLM) procedure of SAS Institute Inc. (1997). Treatment means were compared using the Least Significant Difference method (P < 0.05). A second analysis was performed to fit a response surface for each block as follows: y b 0 + b 1 x 1 +b 2 x 2 + b 11 x b 22 x b 12 x 1 x 2 Where y is the dependent response variable, b is the equation parameter estimate (regression coefficient), and x 1 and x 2 are the STPP and NaCl concentration, respectively. b 1 /b 2 and b 11 /b 22 represent the parameter estimates for linear and quadratic terms, respectively. Likewise, b 0 and b 12 represent the parameter estimates for the intercept and interaction terms, respectively. For each equation, the quadratic model was assessed for adequacy using the lack of fit test. Lack of fit was determined as significant at p < Predicted responses were then plotted against percentage STPP and NaCl. RESULTS & DISCUSSION TREATMENT-WISE COMPARISONS WERE MADE TO DETERMINE significant differences between observed treatment means. The evaluations focused on the maximum or minimum response of each parameter and identification of the treatment(s) that provided such a response at either the lowest NaCl or phosphate concentration. Regression analysis calculated a prediction formula, determined an optimum response for each characteristic studied, and identified the factor(s) responsible for each response. Treatment-wise comparisons The treatment means of the physical characteristics of samples were summarized and compared (Table 1). Defining the block factor in the model of the analysis of variance(anova) enabled pair-wise comparisons to focus on the 16 treatment combinations, rather than the 32 block-treatment combinations. High variation in weight gain was observed between treatments although operating controls of the needle injector remained constant. The marinade weight gain (Table 1) in boneless pork loins ranged from 8.3% to 14.3%. Under certain conditions in the absence of either salt or phosphate, maximum weight gains were observed. In each case, maximum levels of the other ingredient, STPP (treatment 13) and NaCl (treatments 3 and 4), respectively, were required. Mean meat ph values ranged from 5.73 to The ability of the muscle to retain the injected marinade over a 96-h storage period varied greatly between treatments. Mean purge losses ranged from 73.8% in the injected control (treatment 1) to 4.8% with maximum levels of STPP and salt (treatment 16, Table 1). Minimal purge losses were found with 1% NaCl in the absence of STPP (treatment 9) or with 0.5% NaCl in the presence of 0.15% STPP (treatment 6). The final product yield was defined as the net yield of product after storage and cooking relative to the raw, non-injected green weight. Observed final product yields exceeded 92% with either 0.30% or 0.45% STPP at the 1.5% salt level (treatments 15 and 16, respectively), as compared to 65.2% in the injected control (Table 1). Young et al. (1987) had reported a similar result with a maximum yield observed with 0.5% STPP and 1.5% salt in chicken breast patties. Final product yield and cook loss (only the weight lost during cooking) were similar. The maximum final product yield and minimum cook loss with the lowest level of salt were observed at 0.45% STPP and 1.0% salt. Maximum responses of total moisture were observed with as little as 0.15% STPP and 1.5% salt (treatment 14) or with a lower salt level of 1.0% and 0.30% STPP (treatment 11). Expressible moisture, often associated with WHC, may be partially responsible for many other physical and structural properties of meat, including color, texture, firmness, and tenderness (Forrest et al., 1989). Only 0.45% STPP/1.0% salt and 0.30% STPP/1.5% salt treatments 12 and 15, respectively demonstrated lower expressible moisture than the injected control and other treatments (Table 1). These same treatments demonstrated the highest means for total moisture, indicating the ability of the muscle proteins to bind or immobilize a higher proportion of water molecules. Minimum Warner Bratzler shear values were achieved at lower levels of one ingredient while increasing the level of the other. Minimum shear values were observed at or near a force of 14 Newtons (N). These values were observed with minimal phosphate at 0.15% STPP and 0.50% salt (treatment 6) or in the absence of salt with 0.45% STPP (treatment 4). In a published study, in which pork loins were randomized according to location and not blocked, polyphosphates were evaluated at 5% and 10% injection levels without salt (Sheard et al., 1999). In that study, polyphosphate improved water holding capacity and yield, and a sensory panel reported that the polyphosphate treated loins were more tender and juicy than water injected or untreated controls. Thus, phosphate/salt marination has resulted in quality improvement in loins similar to that observed for poultry. Volume 64, No. 6, 1999 JOURNAL OF FOOD SCIENCE 1043

3 Properties of Marinated Pork Loins... Response surface regression analysis The RSM models predicted (p < 0.05) measured characteristics for both head and tail portions (Table 2, 3). In the model of tail portions (Table 3), all coefficients in the full quadratic model were significant in predicting % weight gain, including linear effects (p < 0.01) of both STPP and salt, b 1 and b 2, respectively. However, in the model of the head portions (Table 2),only a linear salt term (b 2 ) and a negative interaction term were significant (Fig. 1). Table 1 Physical characteristics of injected, whole, boneless pork loins Weight Overall Cook Warner NaCl STPP gain Purge yield loss Bratzler, WHC Moisture Treatment % % % ph % % % (N) % % e 5.81 bcde 73.8 a 65.2 i 36.1 a 28.1 a 13.8 a 60.0 f bcd 5.88 abcde 64.9 ab 69.0 hi 33.6 abc 23.7 ab 14.3 a 64.0 def d 5.96 abc 34.0 c 70.0 ghi 34.6 ab 24.2 ab 13.9 a 63.6 def abcd 6.10 a 21.8 cd 72.7 fgh 33.8 abc 15.3 def 14.2 a 65.0 cde d 5.69 e 53.8 b 67.3 hi 35.8 ab 22.4 bc 14.0 a 62.0 ef abcd 5.91 abcd 19.7 cde 75.2 efg 31.8 bcd 17.5 cdef 13.9 a 63.2 def abc 6.00 ab 16.0 de 78.2 def 29.3 edf 17.9 cdef 13.8 a 65.1 bcde bcd 6.02 ab 5.8 de 84.2 bc 24.5 gh 17.0 def 14.1 a 66.2 bcde a 5.75 cde 15.8 de 78.7 cde 29.8 cde 19.9 bcd 12.5 ab 63.7 def abcd 5.84 bcde 14.8 de 75.0 efg 32.4 abcd 19.5 bcde 12.1 ab 63.7 def bcd 5.87 bcde 17.7 cde 80.3 cde 27.0 efg 17.5 cdef 12.9 ab 66.6 abcd bcd 6.10 a 5.8 de 91.6 a 17.7 ik 13.8 f 10.2 bc 69.0 ab abcd 5.73 de 12.8 de 83.1 bcd 25.2 fgh 20.1 bcd 13.2 a 65.3 bcde ab 5.83 bcde 12.4 de 87.4 ab 21.8 hi 19.2 bcde 13.2 a 68.4 abc ab 5.93 abcd 7.6 de 92.7 a 17.5 k 14.6 ef 8.6 c 70.2 a cd 5.85 bcde 4.8 e 92.7 a 16.3 k 14.5 ef 11.5 abc 67.1 abcd a-k Means within same column with different superscripts are different (p < 0.05) Fig. 1 Response surface of sodium chloride and sodium tripolyphosphate (STPP) concentration on marinade weight gain of needleinjected anterior and posterior pork loin sections. Fig. 2 Effect of sodium chloride and sodium tripolyphosphate (STPP) concentration on meat ph JOURNAL OF FOOD SCIENCE Volume 64, No. 6, 1999

4 Linear (b 1 ) and quadratic (b 11 ) regression coefficients of phosphate level in tail sections were found for meat ph (p < 0.01), which increased with increasing STPP concentration (Fig. 2). However, no terms in the model were significant in predicting ph of head sections. Purge loss values decreased with added salt and STPP in tail sections, but only salt was effective in reducing purge in head portions. A positive interaction coefficient (b 12 ) in both heads and tails indicated an antagonistic interaction of STPP and salt on purge (Table 2, 3). All coefficients in predicting purge loss in tails were significant (p < 0.05), whereas only the linear and quadratic salt terms and the interaction were significant in head portions (p < 0.05). Purge loss near an optimum of 0% was approached in both head and tail portions (Fig. 3). Final product yields in tail sections increased in linear fashion with added STPP and salt as indicated by b 1 and b 2, respectively (Table 3). Although a similar response surface was fitted (Fig. 4), only a quadratic effect of STPP (b 12 ) predicted final product yield of head portions. Maximum predicted final product yield increased Table 2 Regression equation coefficients a (REQ) for physical characteristics and ph of loin head sections REQ a Weight gain ph Purge Overall yield Cook loss Warner Bratzler WHC Moisture b *** 5.80*** 60.99*** 66.91*** 34.87*** 27.92*** 15.57*** 62.88*** b b *** *** ** b ** 63.20** b * * ** b *** * (p-value) abased on the full quadratic equation: y 0 + x x x x x 1 x 2, where x 1 STPP (%) and x 2 NaCl (%). y x x x x x 1 x 2, where x 1 STPP (%) and x 2 NaCl (%). 1, 2 are parameter estimates for the linear terms; 11, 22 are parameter estimates for quadratic terms; 0 is the parameter estimate for the intercept; 12 is the parameter estimate for the interaction. * p <0.10; ** p <0.05; *** p <0.01. Fig. 3 Effect of sodium chloride and sodium tripolyphosphate (STPP) concentration on purge loss. Fig. 4 Effect of sodium chloride and sodium tripolyphosphate (STPP) concentration on final product yield. Volume 64, No. 6, 1999 JOURNAL OF FOOD SCIENCE 1045

5 Properties of Marinated Pork Loins... from 66.9% to 94.4% and 62.2% to 96.6% for heads and tails, respectively (Fig. 4). Cook losses were reduced by a quadratic effect of phosphate (b 11, Table 2) in head portions and by an interactive effect in tails (b 12, Table 3). Warner Bratzler shear values were reduced by the presence of salt only (Table 2, 3). Considering head and tail portions, Warner Bratzler shear values were reduced by nearly 50% from 27.1 N in the injected control to 13.8 N in the 0.45% STPP and 1% salt-injected loins (Fig. 5). Sutton et al. (1997) reported no decrease in Warner Bratzler shear in injection of pork loins using up to 0.40% STPP. However, in their study the marinades did not contain salt. The importance of NaCl in phosphate marination has been documented (Shults and Wierbicki, 1974; Lawrie, 1985; Young et al., 1992). Cannon et al. (1993) reported only marginal reductions in Warner Bratzler shear values of phosphate-marinated pork loins with salt levels at about 6 times less than we used. Neither NaCl nor STPP alone affected predicted expressible moisture of head or tail portions. The only notable observation (p < Table 3 Regression equation coefficients a (REQ) for physical characteristics and ph of loin tail sections REQ a Weight gain ph Purge Overall yield Cook loss Warner-Bratzler WHC Moisture b *** 5.71*** 92.42*** 62.23*** 37.81*** 26.26*** 12.38*** 57.67*** b *** 2.18*** *** 44.92*** *** b *** *** 14.37*** * ** b ** 2.72*** ** ** b ** *** b ** *** ** * 5.92 (p-value) a Based on the full quadratic equation: y x x x x x 1 x 2, where x 1 STPP (%) and x 2 NaCl (%). y x x x x x 1 x 2, where x 1 STPP (%) and x 2 NaCl (%). 1, 2 are parameter estimates for the linear terms; 11, 22 are parameter estimates for quadratic terms; 0 is the parameter estimate for the intercept; 12 is the parameter estimate for the interaction.* p < 0.10; ** p < 0.05; *** p < Fig. 5 Effect of sodium chloride and sodium tripolyphosphate (STPP) concentration on Warner Bratzler shear force. Fig. 6 Effect of sodium chloride and sodium tripolyphosphate (STPP) concentration on total moisture content JOURNAL OF FOOD SCIENCE Volume 64, No. 6, 1999

6 0.10) was a negative interaction coefficient (b 12 ) in tail sections (Table 3). However, phosphate in heads and salt and phosphate in tails affected total moisture. An apparent maximum moisture level in tail portions of around 69% appears to have been achieved as the moisture level decreased slightly at high STPP levels (Fig. 6). The maximum moisture level for head portions appears to lie outside our range of experimentation. CONCLUSIONS THE USE OF NACL AND STPP IN NEEDLE INJECTION OF PORK loins improved quality characteristics and increased yield. The complementary action of salt and phosphate demonstrated the ability to reduce the level of one while compensating with the other. Response differences, specifically to phosphate, of different portions of the pork loin demonstrated potential processing variations within the longissimus muscle. The variation of the muscle tissue between anterior and posterior portions may influence the ability of the phosphate to adequately disperse into the muscle tissue. Possibly, this could be controlled by changing brine pressure of the needle injector to increase dispersion for specified muscle types. Marination of whole, boneless pork loins using needle injection demonstrates a strong potential for meeting consumer preferences. REFERENCES AOAC Official Methods of Analysis, 16 th ed. Association of Official Analytical Chemists, Arlington, Va. Barbut, S. Maurer, A.J., and Lindsay, R.C Effects of reduced sodium chloride and added phosphate on physical and sensory properties of turkey frankfurters. J. Food Sci. 53: Cannon, J.E., McKeith, F.K., Martin, S.E., Novakofski, J., and Carr, T.R Acceptability and shelf-life of marinated fresh and precooked pork. J. 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Food Sci. 57: Ms 0429 received 1/29/99; revised 4/30/99; accepted 6/21/99. This project was funded by the National Pork Producers Council (NPPC, Project #1807). Volume 64, No. 6, 1999 JOURNAL OF FOOD SCIENCE 1047