| The gel-forming properties of proteins are essential to the development of protein-based products in that it contributes to textural properties, shaping the product, retaining water, and holding other food components in the product. During gelation, the molecular transitions of the protein from its native state to the denatured state are influenced by pH, protein concentration, ionic conditions, vary muscle sources and additives. These changes determine the final structure and textural properties of the protein gels. The effect of pH, ionic type and strength, protein type on the functional properties and biochemical characteristics of myofibrillar protein gel were studied by combined low field nuclear magnetic resonance (NMR), Raman spectroscopy and Scanning electron micrograph (SEM)technique. The aim was to provide more insight into the functional properties of proteins, allowing the manipulation of processing conditions in order to obtain products with the desired structural and textural attributes. The detailed contents and results are shown as follows.1 Sensory properties of blood curd related to results of mechanical testsIn order to study the textural property of blood gel, sensory evaluation and mechanical tests have been conducted to assess textural characteristics of seven blood products manufactured from porcine or duck blood. When sensory evaluation or mechanical tests were adopted as grading standard separately, two case cluster analyses got similar results. The sensory and mechanical variables could be divided into two and three major groups, respectively, when variables'cluster analysis was carried on. The canonical analyses performed have shown that there were robust correlations (P<0.001) between mechanical tests and sensory evaluation. The first sensory evaluation canonical variate was positively associated with tenderness and juiciness(0.7050, 0.6669)while the corresponding mechanical tests canonical variate was negatively associated with hardness, gumminess and chewiness (–0.9629,–0.8930 and–0.8490). The Texture Profile Analysis (TPA) test could be a useful method for rapid control of the textural properties. In the processing industry, juiciness and tenderness were more important indices for good acceptability of blood curd from the sensory point of view; however, excessive hardness resulting from mechanical tests could bring negative quality.2 Texture and water holding quality mechanism of animal blood gelCompared with the WHC of duck blood gel with pressure method, pig blood gel showed relatively poor performance. But if replacing 3 / 4 of porcine blood with duck blood, the water retention of porcine blood gel can be significantly enhanced. Heated porcine blood gel showed lower value in hardness than heated duck or mixed blood gel, but possesed higher resilience and cohesiveness value. There was no significant difference on texture index between duck blood curd and mixture blood curd.Duck blood had 3 times gelation rate during 37℃holding and 6 times final storage modulus than pig blood. After heating, ratio of immobile water of pig blood gel increased compared with mobile water domination before heating. Protein interactions emerged during gelation. Disulfide bonds, secondary structure and aliphatic CH stretching vibration increased, but heat treatment decreased this interaction. The result of SEM showed that the plasma protein gel had continuous and flaky structure, and obvious link between plasma protein and blood cell can be observed. The pig blood plasma protein presented a mess of filamentous connection on microstructure contrasting with pig blood plasma gel.3 Heat-inducted gealtion between myofibrillar and plasma influenced by pHThe effect of pH on WHC, textural, rheology, low field NMR and Raman spectroscopy property of plasma protein gel was investigated. With the increase of pH, more immobile trend appeared on the water of blood heat-induced gel. Duck plasma proteins gel show broader pH dependence on WHC. With the increasing of pH over 6.5, significantly increasing of WHC appeared. Porcine plasma protein gel was better than duck plasma proteins gel on texture and WHC at pH 6.0. Porcine plasma protein has higher storage modulus and different gelation rate comparing duck plasma protein.4 Heat-inducted gealtion characters of myofibrillar protein influenced by plasma protein at normal meat processing conditionHardness of spent hen myofibrillar protein was significantly high compared with broiler myofibrillar protein and plasma protein. Plasma protein exhibited highest stickiness among three samples. When spent hen myofibrillar protein and plasma protein were mixed with equal amount, storage modulus of mixed protein has similar value to broiler myofibrillar protein.Thermally-induced plasma protein gels possessed the higher proportion of immobile water compared to myofibrillar protein heat-induced gels. After mixing with the plasma protein, the broiler and spent hen myofibrillar protein heat-induced gels increased the proportion of immobile water, but no statistically significant increase on WHC. Gel pore size of mixed protein heat-induced gel was small and showed uniform distribution.5 Heat-inducted gealtion characters of myofibrillar protein influenced by plasma protein at low sodium conditionThe effect of KCl,MgCl2 and TPP on WHC, textural, rheology, low field NMR and microstructure property of myofibrillar and plasma protein gel was investigated at low sodium (0.4mol·L-1NaCl)condition. 0.1mol·L-1MgCl2 significantly decreased WHC of plasma protein gel. Plasma proteins gel showed high ratio of immobile water contrasted with myofibrillar protein. Compared to myofibrillar protein gel, WHC of plasma protein gel is low. However, no significantly decrease appeared when 5% plasma protein was added to myofibrillar protein. 5% plasma protein bring WHC increase effect at 0.4mol·L-1NaCl or 0.4 mol·L-1NaCl+0.5%TPP comparing to 100% myofibrillar protein. 0.2mol·L-1KCl brought hardness increase effect at 0.4 mol·L-1NaCl, however, 0.5%TPP had adverse effect at same condition. 0.1mol·L-1MgCl2 showed adverse effect to storage modulus of rheology test and produce unordered big hole SEM structure.
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