Effects And Mechanism Of Raw Material Moisture Content On Quality Properties Of Pork Cooked

In this paper, the changes in physical-chemical properties of dehydrated pork with water content at which the quality properties of pork changed significantly were studied. Furthermore, effects of water conditions on the quality properties of pork were investigated based on the view point of protein molecular structure and muscle microstructure of pork. The results provide a theoretical foundation for controlling the quality of dehydrated or semi-dehydrated meat products and establishing correct drying and thermal processing parameters. The details are listed as follows:1. Sensory hardness, sensory chewiness and tightness increased with moisture content decreasing, scores of sensory hardness ranged between 3.3 and 7.0. According to TPA analysis, a growth spurt in hardness was found around moisture content of 45%; there was a highly significant correlation between hardness, chewiness, shear force and moisture content(P < 0.01), and a non-linear negative correlation was also found between springiness, resilience and moisture content(P<0.05); textural properties of pork changed significantly between 30% and 50% moisture content.2. pH value of pork increased with increasing temperature when heated, but the changes was not obviously; cooking loss of dried samples were found to be significantly lower than the control group(P<0.05), especially those with moisture content lower than 45%. Pork with different moisture content showed different variation pattern when exposed to thermal treatment. With heating temperature rising, hardness and chewiness of pork increased and then decreased, the amplitude of variation was higher in dried samples; two increasing sections were found in shear force of pork with moisture content higher than 40%, while hardness and shear force of 30% samples had little change in higher temperature phase.3. Protein solubility of pork decrease with increasing temperature, while samples with lower moisture content showed smaller decrease, which showed that the heat-stability increased; surface hydrophobicity of myofibrillar proteins increased and sulfhydryl groups decreased after drying, along with the results of SDS-PAGE gel electrophoresis analysis, we can conclude that protein structure changed significantly during drying procedure, myosin heavy chain(205kDa) of samples with 30% moisture content had little change when temperature increased, while the stripe color of actin(43kDa) was deeper than other sample groups.4. The results of LF-NMR showed that peak area of immobilized water decrease obviously with increasing drying degree, and transverse relaxation time(T2) of bound water, immobilized water and free water were also decreased. The results of scanning electron microscope analysis indicated that, with moisture content decreasing, the gap region between muscle fibers vanished and granules disappeared gradually; cross section of muscle fiber changed from a nearly-circular shape to irregular lathy one, and better integrity of fiber bundle was observed in lower moisture samples.5. With regard to protein secondary structure of samples without drying procedure, β-sheet content was high(>30%), and α-helix content was relatively low. But the content of α-helix increased and β-sheet decreased when moisture content decreased, content of random coil from 30%~40% moisture groups was less than high moisture groups.6. Results of correlation analysis showed that conspicuous correlation was found between total peak area of T2 and textural properties(except springiness), sensory hardness, sensory tightness and chewiness(P<0.01), whereby content of immobilized water had a close relationship with pork quality. As for protein structure, hardness, shear force and chewiness had a positive correlation with α-helix content, and a negative one with β-sheet content; sensory tightness and sensory chewiness also had a relationship with content of α-helix and β-sheet.In conclusion, volume shrinkage as well as loss of immobilized water and free water was found during drying procedure, protein interaction was strengthened by hydrophobic effect and balance of protein – protein and protein – water changed, which resulted in various resistance of proteins to thermal denaturation. Thus higher content of α-helix was found in cooked pork with drying procedure. Consequencely, quality properties of pork varied with moisture content.