The effect of temperature on the development of browning of amorphous and crystalline lactose

When lactose crystals are dried in industrial driers the temperatures used can, when exposure time is too long, cause the crystals to undergo non-enzymatic browning. This leads to a defect in the final product. Understanding the kinetics allows driers to be designed to avoid this. To examine the non-enzymatic browning kinetics of amorphous and crystalline lactose, samples were heat treated for 2-120 min at 110 °C, 120 °C, 130 °C, 140 °C and 150 °C. The evolution of colour was followed by spectrophotometry at 420 nm and colorimetry (L* a* b*). The absorbance and the b* values increased while L* value decreased with time and temperature. A first order reaction model with Arrhenius temperature dependence provided a good fit to the data. A difference was seen between crystalline and amorphous lactose, with the latter having more intensive browning under the same conditions due to the increased surface area available.