Evolution of surface temperature and its relationship with acrylamide formation during conventional and vacuum-combined baking of cookies

In this study, the mechanism by which vacuum baking reduces acrylamide in cookies was elucidated by continuous measurement of average surface temperature during conventional and vacuum-combined baking experiments. Heat transfer coefficient was also determined under atmospheric and vacuum baking conditions. Cookie dough samples (0.3 cm thickness, 5 cm diameter) were baked at 180 °C either completely under atmospheric pressure (101 kPa) or under a combination of atmospheric and reduced pressure (61 and 41 kPa). Baking times were adjusted accordingly to yield cookies with a moisture content between 3.0 and 3.5%. Surface and internal temperatures were recorded throughout baking treatments by using a thermal camera and a thermocouple, respectively. The degree of thermal load (energy input to the product) was then computed from the time - temperature profiles and related to acrylamide level in the finished product by using the total risk calculation approach. Acrylamide concentration of cookies prepared by vacuum-combined baking was found to be around 300 ng/g, a level which is about 30% lower in comparison to that of the conventionally baked sample (445 ng/g). A slight decrease in convective heat transfer coefficient was observed upon pressure reduction. Evaporative cooling effect created by sudden pressure reduction was found to be mainly responsible for limited temperature increase and hence acrylamide mitigation.