Developing a novel colorimetric indicator for monitoring rancidity reaction and estimating the accelerated shelf life of oxygen-sensitive dairy products

A colorimetric mixed pH dye-based indicator to real-time monitoring rancidity reaction of infant milk powder formula is described. Milk powder stored in 30, 40, and 50°C was analyzed in terms of peroxide value (PV), moisture content, volatile compounds and sensory score. In addition, moisture sorption isotherms of infant milk powder formula were assessed at various temperatures including 30, 40, and 50°C. It was found that milk powder kept at higher temperature had a shorter shelf life, whereas milk powder with higher moisture content yielded a higher PV, and vice versa. A rancid sensory score revealed a similar fashion to PV. Both hexanal and acetic acid concentrations increased with increasing moisture content of milk powder. An indicator label consisting of mixed pH-sensitive dyes of both bromothymol blue and methyl red responds through visible color change to volatile compounds e.g. hexanal and acetic acid released from oxidation and hydrolytic reaction during storage period. Indicator labels placed in headspace of milk powder bottles that stored in 30°C. Indicator label characteristics were studied, as well as their response to volatile compounds by changing color from light green to orange. An orange was a sign of either warning or rejecting. An accelerated shelf life of milk powder was estimated at 26 days.