Study On Relationship Between Structural Changes And Water/Fat-binding Capacity Of Pork Meat Proteins

The structure-function relationship is a main determinant factor for the usefulness and suitability of a protein ingredient in food applications. Emulsification and heat-induced gelation properties of meat proteins play an important role in processing of meat batter products, and are correlated closely with rheological properties, textural properties, water-and fat-holding capacity, and mouth feeling. Previous research mainly focused on gelation mechanism of meat proteins, effects of intrinsic and environmental factors on gel and emulsification properties. However, the mechanisms responsible for stabilizing/binding the fat within the product have not been clearly elucidated. The overall objectives of this research were to use low field nuclear magnetic resonance (NMR), Raman spectroscopy technique to investigate the influence of the protein structures on the functionality of meat proteins in the development of well-texture emulsion meat products, especially on the water- and fat-holding capacity. The ultimate aim was to offer theoretical foundation for improving the quality of emulsion meat products.1. Influence of proteins different states on the mobility water and fat in processing of meat batterFirst, the influence of proteins with different states on the mobility water and fat in processing of meat batter based on water and fat added was investigated. The changes in water/fat mobility and rheological properties observed were consistent with a three-stage model of protein matrix development in imitation meat batter manufacture. These stages included the salt-soluble proteins extractability, swelling of proteins and formation of a matrix and the development of a homogeneous meat batter mass contain emulsified fat particles. Results showed that there were three relaxation components in pure meat and fat, and the third relaxation time, T22,50ms, corresponded to the water or fat moderately bound within the meat or fat matrix. The component with the short relaxation time, T2b and T21, both of them lower 10ms, related to water or fat that was tightly bound within the proteins. These results suggested that the relaxation times in meat batters can be assigned to the signals of water and fat. The number of relaxation components in meat batters was not affected by water or fat, the position of the major component T22 clearly shifted longer relaxation times (from 50ms to 66ms), loss modulus (G") and the gelatin properties decreased with added water and fat, and the effect of fat was greater than the water. The relaxation components shifted to lower relaxation times with heating in meat batters, indicating. that limited water and fat proton mobility. In addition, a new relaxation component (T23,200～300ms) appeared with heating, this relaxation time was attributed to free water and fat in emulsion gel. The effect of water and fat on relaxation time T22 of emulsion gel was fat higher than water, but the influence of water and fat on relaxation time T23 in emulsion gel was water higher than that of fat. The textural characteristic of the emulsion gel was affected by water and fat. In general, the pure meat had the highest hardness, gumminess and chewiness, and the influence of fat on hardness, gumminess and chewiness higher than that of water. On the other hand, the influences of water on springiness, cohesiveness, resilience was higher than fat.2. The effects of chopping on physical and chemical properties and water/fat stabilizing of meat battersSecond, the effects of chopping on physical and chemical properties and water/fat stabilizing of meat batters were investigated combined with the low-field NMR, Rheology, TPA technology etc. Cooking loss and L* increased with the extend of chopping time, on the other hand, the colors of a* and b*, the values of TPA index decreased with the increasing of chopping time. All of these changes showed significant difference (P<0.05) between chopping 5min and chopping 6min. The position of the component T21 clearly shifted shorted relaxation times, and the proportion of peak area of T21 decreased with the increasing of chopping time. The results suggested that the binding of proteins with water and fat was tighter and the contein of this part of water and fat decreased. These changes of T21 would induce the decrease of a*, b*, cohesiveness and resilience and lead the increase of L* and cooking loss. The proportion of peak area of T22 in raw meat batters was gradually higher (P<0.05) with the extend of chopping time, however, the peak area of T22 significantly decreased (P<0.05) and the peak area of new component T23 significantly increased (P<0.05) in heated emulsion gel after chopping 5min, indicated that the water/fat-binding capacity of proteins beginning to decline. The results of rheology and viscoelasticity showed that the initial damping factor (δ) gradually decreased with the extension of chopping time. And there were significant difference (P<0.05) between chopping 4min and chopping 5min. The shear viscosity coefficient and velocity of gel of raw meat batter showed the highest values under chopping 6min, but the storage modulus (G’) and the loss modulus (G") indicated the best properties under chopping 5min. In addition, a significantly negative correlation (r=-0.85, P<0.01) was found between the proportion of peak area of T22 and T21 in raw meat batter, and there were significantly positive correlation (P<0.01) between the proportion of peak area of T22 and chopping time (r=-0.89), cooking loss, and the color of L*.3. Evaluation of structural changes in raw and heated meat batters prepared with different lipids using Raman spectroscopyThe goal of this work was to use Raman spectroscopy to determine the structures of components of meat batters manufactured in situ with different types of lipids. The ultimate aim was to gain a thorough understanding of the behavior of these emulsions with different fat ingredients. Structural changes, textural properties, water-and fat-binding properties and their relationships in meat batters prepared with different lipids and with heating were studied by Raman spectroscopy. Results revealed that the meat batters prepared with soybean oil (SO) showed the lowest fluid losses, greatest (P<0.05) hardness, springiness, cohesiveness, chewiness, resilience values compared with batters prepared with pork fat (PF) or butter (DB). There was a significant decrease (P<0.05) in a-helix content accompanied by a significant increase (P<0.05) in β-sheet structure after heating in PF and SO samples, but no significant (P>0.05) difference was found in DB batters. A positive significant (P<0.05) correlation between β-sheet structure and textural properties was found in heated samples. Further, there was a significant positive (P<0.05) correlation between α-helical structure and total expressible fluid and a significant negative (P<0.05) correlation between β-sheet structure and total expressible fluid. Results suggest that different lipid additions and thermal treatments induced different changes in meat proteins structural, expressible fluid, and textural properties of meat batters.4. A Raman Spectroscopic Study of Meat Protein-Lipid Interactions at Protein/Oil or Protein/Fat InterfacesIn this work, our objectives were to use Raman spectroscopy to determine the changes in proteins structures following emulsification with different types of lipids, and to study the interactions of meat proteins and lipids (animal fat or soybean oil) at the protein/lipid interface. The ultimate aim was to gain a thorough understanding of the behavior of these emulsions with different fat ingredients for the manufacture of emulsion-type meat products. Structural changes in proteins of meat, FC (fat cream layers) and OC (soybean oil cream layers) were studied by Raman spectroscopy. Results revealed that adsorption of proteins to the cream layers resulted in a maximum scattering change from 1657cm-1 to 1661cm-1, the intensity of amide I was significantly increased (P< 0.05). The percentages of secondary structures of proteins in the raw meat and meat-cream layers, were significantly different (P< 0.05), indicating that lipid emulsions can induce changes in the conformation of proteins. This mainly involved increasing the β-sheet component at the expense of a-helical structures. The bands near 540cm-1 and 475cm-1 were significantly (P< 0.05) higher in intensities in the soybean oil cream layer samples compared to raw meat alone, indicating that soybean oil caused changes of meat proteins in the disulphide bands. The increase in the normalized intensity of the tryptophan band near 758cm-1, from 0.52 in the raw meat to 1.11 (fat cream layer,) or 0.72 (soybean oil cream layer) indicated that hydrophobic interactions were involved in the formation of cream layers. Intensities of all bands assigned to aliphatic and aromatic amino acids were higher in the case of raw meat, confirming the active role of muscle proteins in conformational rearrangements during emulsification. The protein-lipid interaction at the interface (with either fat or oil) caused structural changes to protein molecules, and different lipids induced different changes to the protein molecules. Disulphide bonds, hydrophobic interactions and hydrogen bonding were the main interactions observed in proteins and lipids at the emulsion interface.