Preparation of particle-filled meat protein gels

All composite meat gels were prepared in a household food processor. Batters containing crystalline particles were formulated to have a final protein content of 10.6% in the batter (i.e. the gel phase), while the starch-filled gels had a protein content of 10.25%. The batters were formulated independent of the m_f employed so that the protein content of the gel matrix was constant for each class of particles. This was done to ensure the physical properties of the continuous phase in the composite was consistent across all m_f tested. Filler particles were added on a wt% or mass fraction basis; for the crystalline particles, a filler content of 0, 5, 10, and 15% was used, while for the starches, the meat batters were prepared with 0, 1.25, 2.5, 3.75, 5.0, 7.5, and 10.0% filler. All fillers were added after the chopping procedure to maintain the original size distribution, and were incorporated by hand mixing. Prior to preparation, the meat was completely defrosted overnight under refrigerated conditions (~4 °C). The meat batters were prepared by first chopping two parts meat for 60 sec, followed by the addition of one part deionized water (10 sec chopping), and 2.5% NaCl (10 sec chopping). The slurry was then held in an ice bath for 5 min to allow for the extraction of salt-soluble myofibrillar proteins. The ionic strength of the mixture during extraction was ~0.42 M. After extraction, the remaining water was added and the mixture was further chopped for a total of 80 sec. To ensure the batter was chopped homogeneously, the walls and base of the food processor were scraped at regular intervals throughout the preparation procedure. After chopping, the particles were thoroughly mixed into the batter by hand (~2 min), and each sample was equilibrated under refrigeration conditions (~4 °C) for a minimum of 1 hr prior to thermal processing. All formulations were independently prepared, and each was repeated three times in a randomized block design.

After chilling, for each composite batter, 40 g samples were stuffed into four 50 ml polypropylene centrifuge tubes and centrifuged at a low speed for 30 sec to remove air pockets. The composite batters were cooked by gradually heating to an internal temperature of 72 °C in a water bath. The heating process took approximately 75 min and the core temperature was monitored using a thermocouple unit fed through a rubber stopper. Upon reaching the target temperature, the samples were transferred to an ice bath to arrest the cooking/gelation process. Once the core temperature was below 40 °C, liquid loss was determined (see below), and the samples were then refrigerated overnight prior to performing texture profile analysis.