| Water-holding capacity (WHC) refers to the ability of meat muscles to retain their own moisture and moisture added during processing. It is one of the most important quality characteristics of raw products and the important quality indexes of other quality indicators such as meat flavor, color, tender degrees are so closely related. Many index are used to valuate water holding capacity of chilled meat, however, drip loss and purge loss are the most widely used in meat industry.In order to reduce the fluid loss, better understand on the mechanism of formation of the fluid loss are needed. Over the past 60 years, the studies on WHC of pork were more, until recent 15 years, the studies on WHC of poultry gradually began. In this paper, transort distance, pre-chilling methods, frozen-thaw treatment on the fluid loss of chickens were studied.With the help of DSC (Differential Scanning Calorimetry), transmission electron microscope,the protein denaturation,muscle structure and protein solubility were scanned. Based on this, the relationship of mucle protein and structural changes postmortem and water-holding capacity with fluid loss were studied, providing theoretical guidance for the improvement of WHC of chickens. Research results are as follows:1. Effects of transport prior to slaughter and chilling methods after slaughter on WHC of chickenTwo kinds of chickens were subjected to the same slaughter processing and exposed to stress during the different transport distance, that is transported by long distance(7-8h) and by short distance(1-2h), then after slaughter, two different chilling methods were used(-18℃,1.5h and 0-4℃,5h). The aim of the present study was to investigate how transport distance and chilling method affect postmortem pH value decrease and water-holding capacity of chicken breast muscle. The results showed that short distance transport increased the pH value pos-mortem(P <0.05). Short distance transport and fast chilling decreased drip loss of chicken breast muscle by 18% and 30% than the slow chilling and long distance transport.2. Effects of pre-chilling methods on WHC of chicken The same chickens come from the same chicken house are subjected to the same slaughter processing and then one stage, two stages and the three stages pre-chilling methods were used respectively. The aim of the present study was to investigate how pre-chilling methods affect postmortem pH value decrease, color and water-holding capacity of chicken breast muscle (P <0.05). The results showed that the pre-chilling of one stage increased the pH value early post-mortem, but the drop rate of PH value increases, as well as the drip loss. The pre-chilling of two stages increased the pH value, reduced the drip loss significantly. The pre-chilling of two stage decreased drip loss of chicken breast muscle by 22% and 38% than the three stage and the one stage pre-chilling methods.3. Comparison of meat quality with different WHC and determining of chicken muscle proteinsEighteen samples were divided into lower drip loss group(drip loss<2%)and higher drip loss group(drip loss≥2%)with cluster analysis. The meat quality attributes were investigated. The results showed that fluid loss and L* value were significantly different between groups (P <0.05). pH value from higher drip loss sample were lower than those from lower drip loss sample. There are no difference in sacoplasmic protein solubility and muscle protein between lower drip loss group and higher drip loss group, but Tmax peak I and Tmax peakⅡ( denaturation enthalpy of peak I and peakII )were lower in higher drip loss sample.There was a significantly negative relationship between WHC and denaturation temperature .These results indicated that more pronounced denaturation of myosin protein in meat from high drip loss group than that from low drip loss group. The ratio of extracellular space of higher drip loss sample was higher as opposed to sample of lower drip loss,where the of sacomere was shoter.4. Repeated freezing and thawing on WHC of chickens in the circulation processThe effects of repeating freezing at -18℃and -40℃and thawing on the WHC, the protein denaturation,muscle structure,protein solubility and color were investigated using chicken breast as raw materials. The results showed that compared with -40℃, freezing at -18℃and thawing resulted in significant decrease in the total protein and sarcoplasmic protein solubility and increased drip loss (P <0.05); With the freezing and thawing time increasing, the drip loss was significantly increased, total protein and sarcoplasmic protein solubility were significantly reduced; while the lightness value and other index of chromatic aberration were not affected. The ratio of extracellular space of samples from freezing at -18℃was higher as opposed to samples from freezing at -40℃,where the of sacomere was shoter.Tmax peakⅡand DHpeakII from samples freezing at -18℃were lower than those from samples freezing at -40℃at the second time freezing and thaw.5. Effects of different thawing methods on water holding capacity of muscle The effects of repeating freezing at -18℃and thawing in hydrostatic and air on the WHC, the protein denaturation,muscle structure,protein solubility and color were investigated using chicken breast as raw materials. The results showed that: fluid loss were significantly increased, and the fluid loss of samples thawing in hydrostatic was significantly greater than the samples thawing in air; compared with samples thawing in air,thawing in hydrostatic resulted in significant decrease in the total protein and sarcoplasmic protein solubility (P <0.05); With the freezing and thawing time increasing , total protein and sarcoplasmic protein solubility were significantly reduced; and there are no difference in muscle protein solubility, while the lightness value and other index of chromatic aberration were not affected. The ratio of extracellular space of samples from thawing in hydrostatic was higher as opposed to samples from thawing in the air,where the of sacomere was shoter.Until the third time,muscle cells of samples thawing in the water were dissolved. Regular sarcomere disappeared.6. Measures to improve the WHC of chickensThrough the determination of thaw loss, centrifugal loss, cooking loss of chickens, the effect of compound phosphate, glycerin, propylene glycol, xanthan gum and kara glue, guar gum and several other absorbent agent on WHC of chickens were studied separately in repeated freezing and thawing process. The results showed that the more compound phosphate, the greater the effect on WHC; In repeated freezing and thawing process, the best choice of glycerin concentration is 3g/100g, because of the lowest thawing loss. the thawing loss between the concentration of xanthan gum at 0.6% and 0.8% groups is no significant difference in the first freezing and thawing process, but in the second and third freezing and thawing process, samples at 0.6% less than other groups of concentration significantly, so 0.6% of xanthan gum is the best choice; with the increase of freeze-thaw time, the thawing loss of carrageenan at 0.4% is significantly different, so 0.4% of the xanthan gum is proposed to be chosen as the absorbent agent; and the best choice of guar gum concentration is 0.6% because of the lowest thawing loss. Compared among these absorbent agents, compound phosphate, glycerin, xanthan gum had the best effects. |
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