The objective of the study was to investigate the role of emulsified fat (lard) and oil (peanut oil) in the rheology and microstructure of porcine myofibrillar protein (MP) gels. Heat-induced composite gels were prepared from 2% MP with 0% to 15% pre-emulsified lipids at 0.6 M NaCl, pH 6.2. Dynamic rheological testing upon temperature sweeping (20 to 80 degrees C at 2 degrees C/min) showed substantial increases in G' (an elastic modulus) of MP sols/gels with the addition of emulsions. Gel hardness was markedly enhanced (P < 0.05) by incorporating >or=10% emulsions, and the composite gel with 15% lard was 33% more rigid (P < 0.05) than that with 15% peanut oil. Incorporation of both emulsions at 10% or higher levels improved the water holding capacity of the gels by 28% to 44% (P < 0.05). Light microscopy revealed a compact gel structure filled with protein-coated fat/oil globules that interacted with the protein matrix via disulfide bonds. The results indicated that both physical and chemical forces contributed to the enhancements in the rheology, moisture retention, and lipid stabilization in the MP-emulsion composite gels.

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The thermal transitions of starch-fish protein mixtures were investigated by a thermal scanning rigidity monitor technique and differential scanning calorimetry. Three transitions due to protein denaturation and one transition due to starch gelatinization were identified by both techniques during thermal processing of these mixtures. The gelatinization of starch caused an increase in rigidity of the system to a degree dependent upon the starch type. Thermal transitions of starch and fish protein seemed to proceed independently in mixture systems. However, the presence of salt and sucrose, necessitated by the inclusion of fish protein, caused starch gelatinization to shift to higher temperatures.

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