Beef heart surimi was prepared in the presence or absence of propyl gallate and blended with or without cryoprotectants (sorbitol, sucrose) prior to frozen storage at Ϫ15Њ, Ϫ29Њ, and Ϫ70ЊC up to 52 wk. Protein solubility, gelling characteristics, water-holding capacity, cooking yield, and emulsifying properties decreased during storage at Ϫ15Њ and Ϫ29ЊC for control surimi (without cryoprotectants). Propyl gallate alone did not influence functionality changes. However, functional properties were largely protected by cryoprotectants as well as at Ϫ70ЊC independent of cryoprotectants. Thus, unless extremely low temperatures are used, beef heart surimi subjected to long-term cryogenic storage should be mixed with cryoprotectants and antioxidants to preserve functionality.the methods of Wan et al. (1993). The pellet of BHS was diluted to a protein concentration of 50 mg/mL with 0.6M NaCl, 50 mM sodium phosphate buffer (pH 6.0). The sol was set at 4ЊC for 18h to ensure maximal protein solubility prior to rheological measurements. A Model VOR rheometer (Bohlin Instruments, Inc., Cranbury, NJ) equipped with parallel plates (upper plate dia 3.0 cm) was used for dynamic rheological measurements during protein gelation. Protein gels were formed by heating the BHS sol from 20 to 73ЊC at 1ЊC/min, and the sample temperature during heating was verified with a thermocouple. The gelling samples were sheared at a fixed frequency (0.1 Hz) with a maximum strain of 0.02.To determine gel strength, gels were prepared by heating 5 g of the above BHS sol in glass vials (15 mm i.d. ϫ 65 mm l) from 20 to 75ЊC at 1ЊC/min in a water bath, followed by chilling in an ice slurry. After overnight setting at 4ЊC, gels, while still in the vials undisturbed, were equilibrated at room temperature (24ЊC) for 40 min and subsequently penetrated using a steel rod (12.5 mm dia with flat end) attached to the load cell (1 kg capacity) in a Model 4301 Instron universal testing machine (Instron Corp., Canton, MA). The crosshead speed was set at 20 mm/min. The force required to disrupt the gels (first peak) was used to represent gel strength.
Cooking yield and water-holding capacityCooking yield and water-holding capacity (WHC) were determined as described by Daum-Thunberg et al. (1992). About 2 g aliquots of protein sol were weighed into glass vials (15 mm dia ϫ 40 mm l) and set at 4ЊC for 18h. The protein sol was cooked in a water bath at 1ЊC/min to 75ЊC. Cooked gels were chilled in an ice slurry and stored at 4ЊC for 18h. Gel weights were recorded after the vials were inverted and the cooked-out liquid was absorbed with a paper towel. Cooking yield was calculated as the weight of blotted gel divided by the weight of protein sol then multiplying by 100. Gels after the cooking yield determination were placed in thimbles folded with filter paper (2 pieces with a 5.5 cm dia at the outer layer and 1 piece with a 7.5 cm dia at the inner layer) and centrifuged at 30,000 ϫ g (Sorwall RC-5B, Du Pont Instruments, Fairview, TN, Rotor SS34 16,000 rpm) for 15 min. Afte...