Effect of secondary heat-induced aggregation on pork meat batter protein conformation, hydration characteristics, textural quality and in vitro digestibility

Secondary heating (SH, 30 min at 100 degrees C), which has a great influence on elastic gels, has been widely applied to emulsified meat products to extend their shelf life. The effects of SH on the textural and nutritional qualities, water migration of meat batter and on the conformations, aggregation and in vitro digestibility of the meat proteins were investigated. Various heat treatments were tested, and the results revealed that an initial heating at 75 degrees C yielded the highest low-field NMR relaxation time T-22 and peak area P-22 and the highest in vitro digestibility. As this initial heating time was increased, the alpha-helix content, water-holding capacity (WHC) and protein digestibility all decreased. Furthermore, SH yielded a much more obvious decrease in the pepsin activity on the protein digestibility than just the initial heating, and also yielded increases in beta-sheet content, hardness, gumminess, and chewiness. This result implied that gel shrinkage and protein aggregation occurred, causing decreased WHC and protein digestibility. Also, SH resulted in significantly decreased (P < 0.05) intensities of myosin light chain gel electrophoresis bands. Therefore, SH was concluded to have reduced the textural quality and nutritional value of the meat.