In the present study, model gel systems of myofibrillar protein (MP) and various concentrations of konjac glucomannan (KG) were evaluated for textural properties, spatial distribution and MP gel networks using a texture analyzer, the paraffin section method and scanning electronic microscopy (SEM), respectively. The regulatory mechanism of the microstructure of MP-KG gel systems on their textural properties was elucidated in order to provide a theoretical basis for the application of KG as a fat replacer in low-fat sausages. The textural analysis results showed that the fracture stress and fracture strain exhibited a parabolic trend with KG concentration, but they reached their maximum at different KG concentrations. The results of low-field nuclear magnetic resonance (NMR) showed that the shortest relaxation time (274 ms) and highest percentage (92.79%) were observed for immobile water in composite gels with 1% KG, suggesting that KG could promote cross-linking of MP and consequently enhance MP binding to water molecules. Paraffin section showed that the spatial distribution of MP-KG gels was transformed from the “trapped structure” to the “penetrated structure” with increasing KG concentration. The SEM micrographs showed that the MP gel networks in the control group were filled with crisscrossed moisture channels and consequently were loose. Addition of a small amount of KG reduced the cross-linked moisture channels, and promoted the formation of compact and well-aggregated MP gel networks. On the other hand, excess addition of KG resulted in the formation of a continuous phase, damaging the MP gel networks. In conclusion, KG could improve the gel strength through stabilizing the water phase and deteriorate the texture of composite gels through the penetrated structure.
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The effects of replacing starch with cellulose on the gel properties of myofibrillar protein were investigated to provide a theoretical basis for the application of replacing starch with cellulose in sausage.
Different proportions starch/cellulose-myofibrillar protein were set as the simulation system to study the water holding capacity, color, texture properties, and stress and strain during fracture deformation, to analyze the dynamic rheological properties and creep recovery properties, and to observe the spatial distribution and three-dimensional network structure of starch/cellulose-myofibrillar protein.
By increasing the proportion of starch and cellulose, the water holding capacity and storage modulus of the composite gel were improved. When the addition proportion of starch and cellulose increased from 0 to 2.0%, the hardness and chewiness of composite gel gradually increased to the maximum; compared with the control group, the hardness was increased by 29.47% and 43.69% respectively, and the chewiness was increased by 34.82% and 41.58%, respectively; however, L* and whiteness had a tendency to decrease. The maximum stress (9 681.86 Pa) and the minimum strain (1.14) were obtained when 2.0% cellulose was added. The value of the creep modulus of the composite gel decreased gradually with the increase of the proportion of starch and cellulose, while the value of the composite gel in the cellulose group decreased more obviously under the same proportion. Paraffin sections showed that starch and cellulose were simply embedded in the gel network structure, but did not cross-link with the protein, and the cellulose formed larger irregular regions in the myofibrillar protein gel system. Based on microstructure analysis, the surface of the control group was rough and there were more cavities. When starch and cellulose were added, the composite gel became uniform and compact, and the cavities were reduced. The protein network structure of cellulose group had better uniformity and compactness under the same addition ratio.
The addition of starch and cellulose to myofibrillar protein could improve the water holding capacity, color, texture properties, stress and strain during fracture deformation, rheological properties and microstructure of the composite gel, but cellulose had a more significant improvement effect on the composite gel. Therefore, the application of cellulose as starch substitutes in gelatinous sausage was feasible.
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