Effects of Heat on Quality Attributes

8 where C t is the concentration at time t, C is the initial concentration, t is time, and k is rate constant. a b Figure 1 a First order reaction curve Villota and Hawkes 2007 and b Relationship between rate constant and temperature Berk 2009. All chemical reactions are accelerated when the temperature is elevated Berk 2009. The temperature dependence of a reaction rate constant can be expressed by the Arrhenius equation Villota and Hawkes 2007, Berk 2009: k=k o exp - E a RT ⁄ ln k o k = E a RT where k o is the frequency or collision factor, E a is the activation energy, R is the gas constant 8.314 JK mol or 1.987 calK.mol, and T is the absolute temperature K. The design of optimal thermal processes relies on relevant kinetic data for bacterial inactivation and quality changes Van Loey et al. 1995. Generally, every 10 o C rise in temperature the rate of chemical reaction increases two-fold, while the rate of microbial destruction rises ten-fold or otherwise quality degradation is less temperature sensitive than microbial destruction Holdsworth 1985. There are differences in thermal behaviour between safety and quality factors during heating. Therefore, optimization is needed to ensure the product safety and maximize retention of quality attributes. Greenwood et al. 1944 were the first to observe thermal behaviour between safety and quality attributes. They studied the destruction of thiamin in cured pork luncheon meat at three levels, 50, 20, and 10, compared with microbial destruction. The rate of thiamine destruction is doubled with an 18 o F increase in temperature as contrasted with a tenfold increase in the rate of destruction of heat-resistant bacteria. They assumed that rapid heating method at the higher processing temperatures were more favorable to thiamine retention. Since then many publications have referred to this technique to optimize processing conditions Holdsworth 1985. 9 Figure 2 represents the effect of different time –temperature combinations on quality retention and microbial inactivation for thermal process. It can be seen from the graph that the acceptable combinations of time and temperature for thermal process fall within the sterile area. Heating of a product in non-sterile area was unacceptable because the microbiological requirements was not achievable. Figure 2 Diagram of t-T relationship for microbial destruction F and cooking C Holdsworth 1985.