Effect Of Key Processing Technology On The Quality Of Prepared Beef Steak

Prepared beef steaks are very popular worldwide owing to easy cooking and high nutritional value. Lacking of uniform Processing standard, from material selection to cooking, the quality of commercially prepared steaks varies considerably. Many factors may affect the edible quality of beef steak, including cattle breed, age, pre-slaughter caring, stress management, parts of origin and carcass hanging after slaughter, electrical stimulation, cooling way, mature condition, processing and cooking methods. Beef silverside was used to evaluate the effects of phosphate free water-holding reagents, tumbling and cooking methods on beef quality. Water-holding capacity, shear force, color and texture were tested as evaluation indicators, afterwards low field nuclear magnetic resonance（NMR） technology and myofibril protein gel characteristics were used to analyze the reasons of the improvement in steak quality.Experiments were conducted by single factor and orthogonal design respectively, to evaluate the effects of sodium citrate, Na Cl, Na₂CO₃ and Na HCO₃ on p H value, cooking loss, expressible moisture, tenderness and color. Results showed that: Na Cl decreased cooking loss, expressible moisture, shear force, L* and a* significantly（P <0.05）, but p H value and b* were not affected（P >0.05）. Sodium citrate, and Na₂CO₃, Na HCO₃ when the mass fractions were less than 1%, significantly increased the p H value, water-holding capacity and tenderness of beef（P <0.05）, while the effects on color were different: Na HCO₃ and sodium citrate made L* decreased significantly（P <0.05）, but a* and b* changed little, while Na₂CO₃ made L*, b* decreased significantly（P <0.05）, a* increased significantly（P <0.05） when mass fraction was less than 1%. By orthogonal test, when the mass fraction of 2.5% Na Cl, 0.5% sodium citrate, 0.4% Na₂CO₃ and 0.6% Na HCO₃ were added, cooking loss reduced by 15.14%, but tenderness did not improve much（P> 0.05）. Analysis of low-field NMR technique showed that the improvement of water holding capacity, when sodium citrate, Na Cl, Na₂CO₃, Na HCO₃ were added, is due to the decrease of free water content, increase of free water mobility and immobilized water.Based on the results above, researches were conducted by adding Na Cl, Na₂CO₃, Na HCO₃, sodium citrate and TG enzyme respectively to beef myofibril protein to evaluate their impacts on myofibril protein gel characteristics, gel whiteness, water retention, gel hardness, and gel rheological properties. Results proved that a moderate amount of these additives can improve the gel properties and rheological properties of myofibril protein, and thus improve the quality and texture of meat products. The myofibril protein dehydrated severely in the formation of heating induced gel when no additive was added or the concentration of Na Cl was lower than 0.3 mol/L, Na HCO₃ was less than 0.2 mol/L, sodium citrate was less than 0.2 mol/L and mass fraction of TG enzyme was less than 0.4%. The use of Na Cl, Na₂CO₃, Na HCO₃, sodium citrate and TG enzyme increased water retention and hardness of the gel substantially（P < 0.05）, and greatly reduced gel whiteness value（P < 0.05）. While the mass fraction of Na₂CO₃ exceeded 0.2 mol/L, gel water retention reached 100%, and hardness of the gel began to decrease significantly（P < 0.05）. These additives had different effects on rheological characteristics of myofibril protein. As Na Cl, sodium citrate, or TG enzyme were added, along with the increasing of concentration, the final storage modulus G’ increased significantly（P < 0.05）, and the phase transition temperature reduced significantly（P < 0.05） except the groups added TG enzyme. Adding Na₂CO₃ from 0 to 0.2 mol/L or Na HCO₃ from 0 to 0.4 mol/L, the final storage modulus G’ increased significantly（P < 0.05）, phase transition temperature reduced, as the concentration increased, the final G ’decreased, phase transition temperature increased.Tests of tumbling mileage effects on prepared steak quality showed that: when mileage increased from 0 to 6000 m, cooking loss, shear force and hardness increased at the beginning and then decreased, L* increased significantly（P < 0.05）, while a* decreased remarkably（P < 0.05）. These impacts were caused by the improvement of the beef protein solubility and changes of water state and liquidity. When the beef was not tumbled, T21 peak intensity was weaker and the peak area was smaller, T22 peak appeared in 100 1000 ms which represents free water existence. With the extension of tumbling mileage, P21 increased firstly and then dropped, P22 almost disappeared, and T22 kept decreasing constantly, meant that the free water combination got tighter. Through the orthogonal test, process parameters were confirmed: tumbling mileage was 3000 m, tumbling speed was 10 r/min, run for 20 min and pause for 10 min. Compared with the non-tumbled control group, cooking loss reduced by 8.44%, tenderness increased by 18.53%.Experiments on influence of cooking process on edible quality showed that: water-holding capacity, tenderness, texture, and sensory evaluation score of prepared steak was significantly affected by cooking methods and maturity degree（P < 0.05）. With the same cooking process, the cooking loss, shear force value, hardness and chewiness was greater as the maturity increased, while the elasticity increased firstly and then decreased. When the maturity remained the same, the edible quality and capacity of prepared steaks vary with different cooking process. Steaks had the lowest cooking loss, shear force value, hardness and chewiness processed by sous vide cooking, and fried steaks had the maximum hardness and chewiness, cooking loss and tenderness was lower than low-temperature vacuum cooked steaks. Sensory evaluation results showed that medium well steak processed by sous vide cooking got the highest score, in other words, the evaluators preferred steaks with higher maturity and lower water loss.