Simultaneous application of microbial transglutaminase and high hydrostatic pressure to improve heat induced gelation of pork plasma.

The effects of treating porcine plasma with microbial tranglutaminase (MTGase) under high hydrostatic pressure (HHP) were studied as a means of improving its gel-forming properties when subsequently heated at pH 5.5, near the pH of meats. Plasma containing varying levels of commercial MTGase was pressurized (400MPa, room temperature, pH 7) for different times, and adjusted to pH 5.5 prior to heating to induce gelation. MTGase-treatment under HHP led to greater enhancement of heat-induced plasma gel properties as compared to control samples. The greatest improvements were achieved by pressurising plasma with 43.3U MTGase/g protein for 30min, thereby achieving recoveries of 49% and 63% in fracture force (gel strength) and fracture distance (gel deformability) of the subsequently heat-induced gels, respectively, relative to gel properties obtained by heating untreated plasma at physiological conditions (pH 7.5).

Inhibition of protease in intact fish fillets by soaking in or injection of recombinant soy cystatin or bovine plasma.

Arrowtooth flounder (AF) fillets are known to contain a heat-activated cysteine protease similar to that found in Pacific whiting, which results in soft texture upon cooking. A crude recombinant soy cystatin (CRSC) produced by Escherichia coli, which has been shown to inhibit the protease(s) in Pacific whiting, was introduced into AF fillets by immersion or injection at one of three levels of inhibitory activity: 10 times less than, equal to, or 10 times greater than that of a 20% bovine plasma protein (BPP) solution, a known inhibitor of AF protease(s). Fillets treated with CRSC or BPP at equal inhibitory strength subsequently exhibited the same degree of protection against textural degradation during cooking. Fillets treated with CRSC at lesser or greater levels of inhibitory activity than those of BPP exhibited lesser or higher protection, accordingly. As revealed by SDS-PAGE, the outer portion of fillets soaked with inhibitory solutions was more effectively protected than the inner portion. Such differences between the outer and inner portions of the fillets were not evident when inhibitory solutions were injected into the fillets.

High pressure processing effects on fish proteins.

Salted pastes of surimi, a myofibrillar concentrate of fish muscle, gel at pressures near 300 MPa. High pressure processing has been thought to induce denaturation and gelation of myofibrillar proteins mainly by disruption of protein intramolecular hydrophobic interactions which subsequently reform intennolecularly. We have shown that pressure-induced surimi gels evidence disulfide bonding as well. Endogenous transglutaminase (TGase) evidently survives the pressure treatment, and subsequent TGase-mediated setting of Alaska pollock surimi pastes at 25 degrees C results in very strong gels as compared to those prepared without prior pressurization. High pressure during freezing or thawing greatly accelerates these operations and can reduce ice crystal size and associated tissue damage. Yet pressure treatment can destabilize proteins which might lower fish quality. Infusion of certain carbohydrates into muscle prior to pressure-assisted freezing/thawing can achieve both baroprotection and cryoprotection of the muscle proteins. Pressure treatment has not proven useful for inactivation of proteolytic enzymes that degrade fish quality.

Use of chuck muscles and their acceptability in restructured beef/surimi steaks.

Ten major muscles along with any unidentifiable lean, were carefully excised from 16 Choice square-cut chucks Yield Grade 2, and placed according to previously determined tenderness rankings, into one of three muscle groups. Group 1 was composed of the most tender muscles, and contained the infraspinatus, longissimus, and triceps brachii. Group 2 contained intermediate tenderness muscles and was composed of the serratus ventralis, deep pectoral, and complexus. Group 3 contained the least tender muscles and was composed of the biceps brachii, supraspinatus, rhomboideus, trapezius, deltoids, and neck muscles. Each group was restructured into beef/surimi steaks and was evaluated. Total muscle yield before trimming accounted for 66.2% of the chuck. Careful fat trimming, desinewing, and internal seam cutting on individual muscles resulted in 34.7% lean available for the restructuring of steaks. The triceps brachii, longissimus, supraspinatus, and infraspinatus required the least trimming and were easiest to excise. These muscles made up 49% of the trimmed meat and 13.7% of the total chuck. Steaks were evaluated by a consumer sensory panel for tenderness, flavor, overall preference, and intent to purchase. There were no differences detected by consumers among the muscle groups for the sensory traits studied. Tenderness and flavor were rated equal to intact steaks for all muscle groups studied. The consumer sensory panel indicated that Groups 1 and 2 would be purchased twice a month and Group 3 once a month.