Moisture Movement Characteristics and Their Effect on the Ultrastructure of Cooked Meat during Vacuum Cooling

A study was conducted to investigate cooling characteristics, the variations of moisture content of cooked meat and evaporation rate of moisture and the effect of moisture movement on the interior tissue structure of cooked meats by using a transmission electron microscopy (TEM). Experimental results showed that the cooling rate was higher at the beginning of the cooling. It took only about the first 4–5 min for the vacuum cooling to reduce the surface temperature of the cooked meat from 63 to 10 °C. The average moisture content of cooked meat decreased from 71 to 60·7% during vacuum cooling. The weight loss of cooked meat was 10·3%. For evaporation rate during vacuum cooling, there were two periods: an accelerating period and a falling period. It can be concluded from theoretical analysis and experimental results that moisture movement of free water within cooked meat during vacuum cooling consists of two parts. One is free water migration within cooked meat caused by chemical potential; the other is water vapour movement produced by evaporation or ebullition caused by pressure drop. In addition, the latter dominates in the process of moisture movement of free water. At the same time, TEM observations revealed that morphology of muscular tissue at the surface and the core of cooked meat treated by vacuum cooling remained intact. However, muscle fibre separation and formation of large inter-cellular spaces occurred in the intact muscle fibre of muscular tissue treated by vacuum cooling.