Studies On Effects Of Different Processing Conditions On Characteristics Changes Of Collagen And Meat Quality Of Beef Muscle

Acceptability of meat is a common concerned attribute both by meat producers and consumers, it was also called eating quality of meat. Tenderness is one of the most important meat palatability attributes, and it is mainly attributed to the properties of myofibrillar components (contraction part), and characteristics of intramuscular collagen (background tenderness). And the contribution of collagen components to meat tenderness and other quality attributes were affected by the different processing conditions post mortem. Therefore, this study was designed to track the changes of intramuscular collagen characteristics and related to meat tenderness and other meat quality of’beef Semitendinosus muscle, under the different postmortem treatments (heating, ultrasound, curing and high pressure processing), with the analysis methods of Differential scanning calorimetry (DSC), Scanning electron microscope (SEM) and Texture profile analysis (TPA) and so on. Meanwhile, more emphasis were placed upon the relation of intramuscular collagen characteristics to meat quality, and then to provide theoretical guidance for practical problems in beef production and also for some scientific researches. The paper includes four parts, the specific contents and results are as follows:1. Effect of water-bath and microwave heating on characteristics of intramuscular collagen and meat quality of beef muscleComparative studied the effects of heat-induced changes of intramuscular connective tissue (IMCT) and collagen of beef Semitendinosus muscle on meat tenderness and other quality attributes during water-bath and microwave heating, under the different internal endpoint temperature from 40℃to 90℃. The results showed that cooking loss and WBSF value increased with increasing in heating temperature for both water-bath and microwave heating (P<0.05). Heating internal core temperature of 60℃and 65℃were critical for affecting meat textural properties in water-bath and microwave heating respectively. Collagen contents increased with increase in heating temperature.Endomysial portion contents showed a gradual decrease during water-bath and microwave heating. Perimysial portion contents of microwave heated meat were increased with internal core temperature (P<0.05), but there were no obvious changes for perimysial portion contents in water-bath heating. There were fewer effects on thermal stability of endomysium for microwave heated meat than water-bath heated.60℃was critical heating temperature which affected the maximum shrinkage temperatures (Tmax) of perimysium and endomysium for both heated meat. Thermal treatments in this paper affected the structure of perimysium and endomysium in different extent, the thickness of perimysium were decreased and granulation appeared. With the increasing in heating temperature, coagulation and gelatinization changes of collagenous fibers were became. The microstructure changes for beef Semitendinosus muscle heated in microwave were less than heated by water-bath. The correlation analysis showed that the decrease in thermal stability of collagen induced by thermal treatments had significant effects on meat quality and textural charactersitics (P<0.05).2. Effect of low-frequency and high-power ultrasound treatments on characteristics of intramuscular collagen and meat quality of beef muscleLow-frequency and high-power ultrasound (40 kHz,1500 W) was tested for its effects on the characteristics of intramuscular collagen and meat quality and texture properties of beef Semitendinosus muscle. Meat steaks were sonicated for 10,20,30,40,50 and 60 min at ambient temperature respectively. Characteristics changes of collagen and meat quality and texture were estimated. The results indicated that using ultrasonic processing reduced WBSF values of meat (P<0.05). However, sonication had no significant effect on cooking loss. Ultrasound treatment had no significant effects on L* (lightness) and a* (redness) values, but decreased b* (yellowness) value significantly when sonicated for 30 min (P<0.05). Ultrasonic processing had significant effects on meat textural properties excepted for adhesiveness and resilience. The structure of cell and lysosomal were destroyed because of the cavitation effects of ultrasound, this contributed to the release ofβ-galactosidase and (3-glucuronidase, and promoted the degradation of intramuscular proteoglycans. In view of this, the structure of IMCT was weakened, decreased the WBSF value and contributed the improvement of meat tenderness.Sonication had little effect on collagen contents and solubility, especially no effect on insoluble collagen content, but significantly affected the thermal stability of collagen (P<0.05). After ultrasounding treatment, muscle fibers shrank and separated from each other, perimysial and endomysial net were destroyed, fibers diameter and perimysial thickness were decreased (P<0.05). Those changes contributed the improvement of background tenderness of meat. After ultrasounding for 10 min or even longer time, collagenous fibers were disordered and staggered significantly, the denaturation, granulation and aggregation of collagenous fibers appeared in the extracellular space. Those changes on microstructure of perimysium and endomysium and on collagen characteristics had significant effects on meat texture properties during ultrasounding treatment. The results suggested that low-frequency and high-power sonicating had effect on collagen characters and meat texture properties significantly.3. Effect of weak organic acids and NaCl marination on characteristics of intramuscular collagen and meat quality of beef muscleBeef Semitendinosus muscle was marinated at 4℃for 24 h in 2% NaCl solution,1.5% lactic, acetic and citric acid solutions individually and in mixed marinades for the combination of NaCl and three kinds of weak organic acids respectivly. The effectiveness of marinades on beef Semitendinosus muscle was investigated. Changes in denaturation characteristics of connective tissue collagen, microstructural changes of collagenous fibers, meat quality and textural properties were studied. The results showed that marinating with organic acids and NaCl increased the water-losing rate (P<0.05), but no significant effects on cooking loss. After marinating, WBSF values were all lower than the control group, and the presence of NaCl in three kinds of weak organic acids as marinades resulted in a high WBSF value than marinated in acid solutions individually (P<0.05). L* (lightness) values were increased and a* (redness) values were decreased after marinating, and pH values were decreased. In addition, marinating had significant effects on meat textural properties (P<0.05).Marinating with organic acids and NaCl had no significant effects on total collagen and insoluble collagen contents, but significantly affected the soluble collagen contents (P<0.05). After marinating, part of connective tissue collagen were turned into the soluble components and the thermal stability of collagen was decreased, those changes suggested that marinating treatments in this study can weak the structure of connective tissue and contributed to the improving in meat tenderness and textural properties. Marinating with organic acids and NaCl resulted in denaturation of perimysial collagen and the disappearance of endomysial portion, fiber diameter and perimysial thickness were decreased (P<0.05) and the arrangements of collagenous fibers were disordered. For some treatments, the denaturation and aggregation of collagenous fibers lead to the lamellar or granular appeared on the surface of meat steaks. The results of this study showed that marinating with organic acids and NaCl can make significant effects on the microstructure of perimysial and endomysial collagenous fibers, those changes of collagen characteristics (solubility and thermal stability) contributed to the significant effects on meat quality and textural properties.4. Effect of high pressue processing (HPP) on characteristics of intramuscular collagen and meat quality of beef muscleThe effects of characteristics changes of intramuscular collagen of beef Semitendinosus muscle on meat tenderness and other quality attributes during high pressue processing (HPP) were studied, beef muscle was treated by high pressure (200～600MPa) at ambient temperature for 10 min and 20 min respectivly. Characteristics changes of collagen and meat quality and texture were estimated. The results indicated that HPP resulted in the decreasing in water-losing rate and WBSF value, and increasing in cooking loss, moreover, WBSF values for pressure processed for 20 min were lower than treated for 10 min significantly (P<0.05). For pressure processed meat, there were increases in L* (lightness) and b* (yellowness) values, but decrease in a* (redness) value (P<0.05). When pressure below 300MPa, pH values were lower than control samples, and when pressure increased above 300MPa, pH values were increased with the increasing in pressure applied. There was an increase in hardness with increasing in pressure, when pressure up to 300MPa, meat hardness reached the maximum for both treated for 10 min and 20 min, and when pressure increased above 300MPa, meat hardness was decreased. For processed 10 min at 300MPa, there were the maximal values for cohesiveness and resilience, and the values were all decreased after the pressure above 300MPa.When pressure below 400MPa, there were high enzyme activity ofβ-galactosidase andβ-glucuronidase, and can degrade the intramuscular proteoglycans and lead to the decreasing in contents, and when pressure above the 400MPa, enzyme activity were deactivated because of the passivation of themselves. Total collagen and soluble collagen contents were increased with increasing in pressure (P<0.05), but there was a decreasing in insoluble collagen contents. After HPP, soluble components of connective tissue collagen were increased, the solubility of collagen was increased (P<0.05), and contributed to the improvement in meat tenderness. In this study, the thermal stability of collagen was not affected by HPP significantly.The structure of perimysia and endomysia were fractured when pressure above 400MPa. After HPP, fibers diameter were decreased significantly (P<0.05), surface structures of endomysium were ruptured and honeycomb-like structures were disappeared, collagenous fibers were disordered and aggregated. Gelatination of collagen can be occurred during longer time pressure processing, and it was favorable for the improvement in meat tenderness. HPP in the study affected the microstructure of perimysial and endomysial collagenous fibers and meat quality attributes significantly.To sum up, in the present study, the effects of different processing conditions (heating, ultrasound, curing with organic acids and NaCl, HPP) on the characteristics of intramuscular collagen were mainly reflected on the collagen contents and solubility, thermal stability, microstructure of collagenous fibers, mechanical strength of collagen, changes of related enzyme activity and proteoglycans. And those changes of collagen characteristics contributed to the significant effects on meat quality and textural properties.