A 2 (PSE and normal pork trimmings) x 2 (standard brine and MDTM extract) factorial comparison of the physiochemical properties in four comminuted sausage products was performed.
Raw Material
Fresh MDTM was obtained from a local processing facility (Cooper Farms, St. Henry, OH). The MDTM was immediately extracted to minimize any further lipid oxidation during processing. Normal and PSE pork trimmings were obtained from The Ohio State University Meat Lab, Columbus, OH. The evaluation of PSE was determined by subjective evaluation based on color, texture and the amount of drip. Normal and PSE pork trimmings were ground with 1/4" (6.4 mm) plate openings and stored at 39.2 ± 3.6oF (4 ± 2oC) prior to the sausage manufacture.
Standard Brine (STB)
The standard brine formula was modified from the Ohio State Meat Lab, Columbus, OH, which includes: 1.4 M sodium chloride (Fisher Scientific, Fair Lawn, NJ), 0.1 M sodium tripolyphosphate (Food grade; Kemira Kemi AB, Helsingborg, Sweden) and 0.05 M sucrose (Domino® granulated sugar; Tate & Lyle North American Sugars Inc., New York, NY), pH 7.6 (n = 3).
MDTM Extract
Mechanically deboned turkey meat extract consisted of salt soluble proteins extracted at a MDTM:STB ratio of 1:3— (w/w). The MDTM and STB were mixed manually with a glass stir-rod for 1 h at 39.2oF (4oC). The salt-soluble proteins were recovered in the supernatant following centrifugation at 10,000 x g, 39.2oF, 15 min (6 x 250 ml per batch in a GSA rotor) in a Sorvall® RC-5B Refrigerated Superspeed Centrifuge (Sorvall Instrument, Newton, CT). Fat, collagen, and meat residue pellets were separated from the salt soluble protein supernatant and discarded. The supernatant was then sieved through a 1/16" (1.6 mm) mesh filter to further remove any solidified fats and meat residues. The protein concentration of the MDTM extract was determined using the Kjeldahl procedure in triplicate employing a Kjeltec Auto Sampler system 1035 Analyzer (Foss Tecator, Foss North America, Inc., Eden Prairie, MN). The pH of the MDTM extract (slurry), pH 6.4, was determined with a pH meter (Denver Instrument Company, Arvada, CO).
Sausage Preparation
Pork sausages were made in 3.3 lb (1.5 kg) batches from PSE or normal pork trimmings by preblending the trimmings with either STB alone or MDTM extract at a ratio of 100: 35 (w/w) manually with a glass stir-rod for 1 h at 39.2oF (4oC). Thus, each batch consisted of 2.44 lb (1110 gm) of trimmings and 0.86 lb (390 gm) of STB or MDTM extract. Sausage batters were stuffed into 2 cm diameter cellulose casings using an electric food grinder/stuffer (The Rival Company, Kansas City, MO). Sausage links were refrigerated and analyzed within 24 hours.
Protein concentration of MDTM extracts was performed using the Kjeldahl procedure in triplicate by a Kjeltec Auto Sampler system 1035 Analyzer (Foss Tecator, Foss North America, Inc., Eden Prairie, MN). The pH of the MDTM extract (slurry) was determined with a pH meter (Denver Instrument Company, Arvada, CO).
Sodium Dodecylsulfate Polyacrylamide Gel Electrophoresis
Sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) was performed as described by Laemmli (1970), using 1.5 mm x 10 cm polyacrylamide slab gels consisting of 10% resolving gel (37.5:1 acrylamide: N,N'-bis-methylene acrylamide) and a 3% stacking (37.1:1) gel containing 0.1% SDS. A sample of the supernatant was combined with an equal volume of SDS-PAGE reducing buffer and electrophoresed at a constant voltage of 150 V MiniProtean II gel apparatus (Bio Rad, Richmond, CA) until the tracking dye was within 1-2 mm from the bottom of the gel. Gels were stained with Coomassie Brilliant Blue R-250 (Bio Rad, Richmond, CA) and destained with a solution containing 25% methanol and 7% acetic acid.
Preparation of a Purified Actomyosin Standard
Purified actomyosin was prepared from MDTM extract by mixing 1 vol. of MDTM with 3 vol. of a high salt buffer, 1.4 M sodium chloride, 0.05 M dextrose, 0.06 M sodium tripolyphosphate manually with a glass stir-rod for 1 hour at 39.2oF (4oC). After centrifugation at 10,000x g, 39.2oF (4oC), 15 min, the supernatant (pH 7.6) was recovered and diluted with 7 vol. of ice-cold double de-ionized water. The pellet was recovered after centrifugation at 10,000x g, 39.2oF (4oC), 15 min. The precipitated actomyosin was resuspended 0.04 M sodium pyrophosphate, 0.001 M MgCl2, 0.001 M EGTA (pH 9.6), 50% glycerol, and stored at 20oC for use as a standard for SDS-PAGE analysis.
Cooking Loss
All sausage links were cooked in an automatic time/temperature controlled smokehouse (DEC International, Inc., Lodi, WI) at 60oC, RH 100% for 1 hour (Pietrasik, 1999) to achieve maximal meat binding (Ishioroshi et al., 1979 & 1981; Samejima et al., 1985). Sausages were weighed individually and the final weight of each link was recorded. The cooking loss % was calculated as follows.
Texture Analysis
All sausage links were stored at 50oF (10oC) to optimize rigidity (Foegeding, 1988) and measured within 24 hours. After removal of the cellulose casing from the sausage, the force required to rupture the sample to 1/2 of the original height was used to evaluate the rigidity. The rigidity of 2 cm high x 2 cm diameter sausage cylinders was determined using a TA-XT2 Texture Analyzer (Texture Technologies Corp., Scarsdale, NY). A compression speed of 0.05 cm s-1 was applied using a 1" (2.5 cm) diameter piston. Means for sausage samples (n = 6) were expression in terms of peak force (g/cm2).
Water Holding Capacity
|
| Figure 1. Sodiumdodecylsulfate-10% polyacrylamide gel electrophoresis of myofibrillar proteins from mechanically deboned turkey meat (MDTM) and purified actomyosin from MDTM extract. Lane 1 contains high molecular weight standards. Numbers to the left indicate the approximate molecular weights: Myosin Heavy Chain (MyHC), 200 kDa; β-galactosidase, 116 kDa; Phosphorylase b, 97 kDa; Bovine Serum Albumin (BSA), 66 kDa; Ovalbumin, 45 kDa. Lane 2 contains mechanically deboned turkey meat (MDTM) extract. Numbers to the right of the lane correspond to the approximate molecular weights: MyHC, 200 kDa; Actin (A), 45 kDa; and Myoglobin (Mb), 18 kDa. Lane 3 contains actomyosin precipitated from MDTM extract. Numbers to the left of the lane indicates the approximate molecular weights of myosin heavy chain (MyHC), 200 kDa; and Actin (A), 45 kDa. |
The analysis of WHC of each sausage batter was modified from the Hamm procedure (Grau and Hamm, 1957). Briefly approximately 500 mg of meat sample was placed between two Whatman® No.1 filter papers. Filter papers were then placed between two Teflon® plates then placed between the plates of a Carver Press and subjected to a mechanical force of 500 psi for 1 min. After compression, the filter papers were separated from the plates, and the images scanned by a BioRad® Model 700 Imaging Densitometer (BioRad, Inc., Hercules, CA). The compression produced two circles, an inner circle corresponding to meat film area and an outer circle corresponding to the total surface area (Figure 1). The % moisture of each sausage sample was determined by air-drying method (100oC, 18 hours), described by AOAC (1990). Total moisture (mg) was calculated using the following equation:
The areas of the two circles were determined by image analysis and the area between the two traced circles on the filter paper was defined as amount of free water in meat. The compression procedure was also employed to determine the wet area of 20 mg of water as a reference for free water (n = 5). The result from each sample was recorded, and WHC (%) was calculated as follows:
Statistical Analyses
All analyses were performed in triplicate. Data were analyzed by using SAS® statistical analysis system (SAS, 1998). Statistical significance (P < 0.05) of the differences between means was determined by Tukey's multiple comparison procedure.