Researchers at UNSW Sydney, led by A/Prof. Rona Chandrawati, have developed a chemical sensor that changes colour as the milk spoils. This is based on the fact that milk becomes more acidic as bacteria convert the lactose to lactic acid.
After testing a range of compositions, the best is a combination of a polydiacetylene polymer and zinc oxide (PDA/ZnO). By altering the chemistry of the sensing molecules used, the team was able to adjust the sensor so it works over the precise acidity range needed to see the change from fresh milk to spoiled milk. Fresh milk turns the sensor blue, ageing milk shows as purple and spoiled milk shows as pink. Transmission electron microscopy (TEM) was used to visualise and monitor structures formed by the different chemical combinations tested for the sensor.
In other previous studies, the colour stability of the PDA/ZnO sensor in food was seen to be unstable. The researchers’ new method stabilises the nanocomposite by pre-exposure to the food matrix prior to locking together the structure of the composite. Hopefully this new sensor technology will be in milk packaging in the
M. Weston et al., Colloid and Interface Sci. 2020