Development of a novel colorimetric food package label for monitoring lean pork freshness

The aim of this work was to develop an easy-to-use food package label for pork shelf-life assessment. Meat samples were packaged in polyethylene terephthalate trays with on-package indicator labels and kept at 5 °C for 8 days. These indicators contained three groups of pH-sensitive dyes, i.e., bromocresol purple, bromothymol blue, and a mixture of bromothymol blue and methyl red. Results of pH, total volatile basic nitrogen (TVB-N) contents, aerobic plate counts and sensory scores of pork differentiated between fresh (on 0–3 days), medium fresh (on 4–5 days), and spoiled lean pork (on 6–8 days). Results of total color difference and principal components analysis carried out with colorimetric data of different indicator labels showed that the indicator label made by a mixture of bromothymol blue and methyl red at 3:2 proportion (at an initial pH of 5.0) was able to discriminate fresh (red), medium fresh (goldenrod), and spoiled (green) pork in cold storage. The statistical models obtained by partial least squares, with the color change of label, successfully predicted TVB-N contents and aerobic plate counts of pork. These results suggest the potential feasibility of this particular indicator system for monitoring freshness of packaged pork via color change detected directly using the naked eye.