Suzanne P. Blanchard

Hydroxyl Radical and Ferryl‐Generating Systems Promote Gel Network Formation of Myofibrillar Protein

UNLABELLED The objective of the study was to examine how oxidatively induced protein cross-linking would influence the gelation properties of myofibrillar protein (MP) under meat processing conditions. MP suspensions in 0.6 M NaCl at pH 6 were treated with an iron-catalyzed oxidizing system (IOS: 10 microM FeCl(3), 0.1 mM ascorbic acid, 0.05 to 5 mM H(2)O(2)) or a H(2)O(2)-activated metmyoglobin oxidizing system (MOS: 0.01 to 0.1 mM metmyoglobin/H(2)O(2)) that produced hydroxyl radical and ferryl species, respectively. Both oxidizing systems promoted MP thermal gelation, which was evidenced by rapid protein-protein interaction and the enhancement in storage modulus (elasticity) of the gel network as revealed by dynamic rheological testing in the 20 to 74 degrees C temperature range. This gelation-enhancing effect was attributed to the shift of myosin aggregation in the early stage of heating from predominantly head-head association (nonoxidized control samples) to prevalently tail-tail cross-linking through disulfide bonds. However, both hardness and water-holding capacity of chilled gels tended to decline when MP was exposed to >or=1 mM H(2)O(2) in IOS and to all concentrations of metmyoglobin in MOS. Microscopic examination confirmed a more porous structure in oxidized gels when compared with nonoxidized protein gels. The results demonstrated that mild oxidation altered the mode of myosin aggregation in favor of an elastic gel network formation, but it did not improve or had a negative effect on water-binding properties of MP gels. PRACTICAL APPLICATION Mild oxidation promotes protein network formation and enhances gelation of myofibrillar protein under normal salt and pH conditions used in meat processing. This oxidative effect, which involves disulfide linkages, is somewhat similar to that in bakery product processing where oxidants are used to improve dough performance through gluten protein interaction.

Thermal and dynamic rheological properties of wheat flour fractions

Abstract A commercial high gluten flour (HGF) was fractionated into prime starch (PS), tailing starch (TS), and gluten (G). Fractions were examined alone or in various combinations. Dynamic rheological properties of samples were measured in an oscillatory rheometer (strain 0.02; frequency 0.1 Hz) during heating at 1°C/min. Thermal characteristics of samples were determined by differential scanning calorimetry (DSC) at a heating rate of 10°C/min. The loss (G″) and storage (G′) moduli of PS and mixed G/PS, G/TS, and G/PS/TS increased after 60°C, reaching peak values (e.g. 81, 301, 313, and 3000 Pa in G′, respectively) around 75°C after which the moduli decreased. HGF showed a steady increase in G′ from 32 to 2490 Pa as temperature increased from 65 to 90°C, indicating continuous formation of elastic networks. Cooling increased G′ for G/PS/TS, decreased G′ for HGF, and produced no rheological transitions for all samples. TS and G alone did not exhibit appreciable viscoelastic responses to the heating and cooling temperatures. DSC measurements revealed a major endothermic transition in HGF. This transition, with a peak around 60°C, was due to starch gelatinization. The presence of G or TS resulted in reduced melting enthalpies of starch in the PS fraction. Gluten or TS fractions alone or in combination did not exhibit any endothermic transitions.

Effects of freezing and thawing methods and storage time on thermal properties of freshwater prawns (Macrobrachium rosenbergii)

Thermal stability of proteins in frozen and thawed freshwater prawns was measured by differential scanning calorimetry. The onset and peak melting temperatures corresponding to myosin denaturation, as well as total enthalpy of denaturation of prawn muscle, decreased after freezing–thawing treatments. There were no significant differences in the thermal properties of prawns with changes in the rate of freezing, ie blast (fast) vs still (slow) freezing. However, the thermal properties were influenced by the rate of thawing. Rapid thawing using a combination of microwave and tap water resulted in a lower (P⩽0·05) thermal stability of prawn proteins compared to slow (refrigeration) or moderately fast (tap water) thawing methods. Keeping prawn shells intact or not intact during freezing–thawing did not alter the thermal properties of the prawn proteins.

Postmortem proteolytic and organoleptic changes in hot-boned muscle from grass- and grain-fed and zeranol-implanted cattle☆

Abstract A total of 21 yearling steers (Angus sires × crossbreed dams) were allotted to three forage management systems: (a) pasture on Johnstone fescue (G); (b) grain on grass (GG); and (c) grain on grass with zeranol implant, a growth promoter (GGP). After approximately 150 days on experiment (May to October), three randomly selected steers from each dietary group were slaughtered, and composition, sensory characteristics and proteolytic changes of semimembranosus muscle were examined during postmortem storage at 2 °C. Overall, muscle chemical composition was not affected (P> 0.05) by dietary regimen with or without the implant. Grass-fed beef had a stronger (P ≤ 0.05) grassy flavor at 2 days postmortem and developed more (P ≤ 0.05) off-flavor after 10 days of aging than grain-supplemented beef. Postmortem storage generally improved beef tenderness. The implantation did not (P> 0.05) affect weight gain nor carcass yield. However, GGP beef was more tender (P ≤ 0.05) than G and GG beef after 2 days storage; a similar trend was observed in overall beef acceptability. Proteolysis of the muscle from the three forage systems was similar in that all showed major changes beyond 2 days postmortem with the disappearance of titin and troponin-T and the appearance of a 30 kDa component being most noticeable. These results suggest postmortem differences in beef palatability among the different nutritional treatments were not closely related to muscle composition and proteolytic degradation.

Frozen storage stability of antioxidant-treated raw restructured beef steaks made from mature cows ☆

Previous research has shown that beef quality decreased with the age of cattle. In this study, beef trimmings from nine mature cows (n=9), equally representing three animal age groups (2-4, 6-8, and 10-12yr), were restructured into steaks formulated with propyl gallate, alone or in combination with a beefy flavoring agent, to enhance palatability and stability during 6months of frozen storage at -29°C. Lipid oxidation, rancidity, and loss of beefy flavor in restructured steaks during extended storage were reduced by propyl gallate. The beefy flavoring agent inclusion masked mature, forage-fed beef off-flavors, intensified beefy flavor, and improved steak tenderness, juiciness and cooking yield. Thus, the combination of propyl gallate and beefy flavoring offers an effective means to enhance the palatability and storage stability of restructured beef prepared from mature cows.

Proximate, mineral and fatty acid composition of semimembranosus and cardiac muscles from grass- and grain-fed and zeranol-implanted cattle

Chemical composition (proximate, minerals, and fatty acids) of semimembranosus (SM) and cardiac muscle from cattle fed grass (G) and grain on grass without (GG) or with (GGP) zeranol implant were determined. The protein content of SM muscle from GG and GGP cattle was higher (p≤0.05) while the moisture content was lower (p≤0.05) than that from G cattle. The lipid content of cardiac muscle from GG cattle was higher (p≤0.05) compared to that of G cattle. Grain supplementation (GG and GGP) increased the potassium level in SM muscle while a decrease was observed in cardiac muscle. Grain supplementation also increased linoleic acid but decreased polyunsaturated (PUFA) fatty acids in both muscles. There was 3 times more PUFA, particularly linolenic and arachidonic acids, in cardiac muscle than in SM muscle irrespective of the feed type. The concentrations of PUFA in SM and cardiac muscle were higher for G cattle than for GG and GGP cattle, which could make muscles from G cattle more prone to oxidation.