Smart packaging tools for selected Indian traditional buffalo milk products: a case for on-package freshness indicators
Authors: Panjagari Narender Raju , Singh Ashish Kumar , Ganguly Sangita , Sharma Rajan , Sharma Vivek 
Published: February 2025

Among the intelligent packaging systems, freshness indicators have been proven to provide real-time quality status of packaged food. They supplement or complement the printed “best before” or “expiry date” and give consumers an informed choice. Freshness indicators work on the principle of colorimetric changes with changes in the headspace volatile components of the packaged food product. With the growing consumer demand for real-time quality status, there is a need to develop colorimetric on-package freshness indicators for dairy products. The current study aimed to develop on-package freshness indicators for selected traditional Indian buffalo milk products, namely khoa, burfi, dahi, and misti dahi, and correlate their colorimetric responses with quality attributes. The prerequisites for developing freshness indicators were to identify the critical volatile headspace markers using solid phase microextraction (SPME) coupled with gas chromatography-mass spectrometry (GC-MS) for the respective dairy products, selection of suitable innovative ink components, namely dyes (methyl red, and methyl red sodium salt), plasticizer (glycerol), choose appropriate polymer support (methylcellulose, polyvinyl alcohol or paper), and adopt a suitable production technique such as casting, dipping, or electrospinning. SPME coupled with GC-MS revealed that the key volatile markers for all the products belonged to ketones, aldehydes, acids, and alcohols. The smart ink components were selected based on the key volatile markers, and a suitable fabrication technique was adopted for developing the respective freshness indicators. Later, the developed indicators were exposed to different concentrations of key volatile markers, such as hexanal, heptanal, 2-pentanone, 2-hexanone, 2-heptanone, acetic acid, butanoic acid, among others, in the range of 0.1 to 40 μL and their dose-dependent color responses were noted. The selected freshness indicators were characterized and suitably integrated with the closures to effectively detect and interact with the dynamic headspace volatile compounds while storing the packaged product. Finally, the real- time performance of the developed freshness indicators was evaluated. It was found that the initial yellow color of freshness indicators was changed to reddish-dark brown in the case of khoa and burfi while to pale pink in the case of dahi and misti dahi at the end of the storage periods, indicating loss of freshness. The total color difference (TCD) in the freshness indicators was correlated with the quality attributes of the products. Among all the freshness indicators, the TCD was found to be very highly positively correlated with titratable acidity, thiobarbituric acid value, free fatty acids value, and total viable bacterial count while significantly negatively correlated with pH, sensory flavor, and overall acceptability scores. The developed freshness indicators could successfully depict the freshness status of the stored products through visual color changes distinguishing between the fresh and spoiled products.