Cure color ratio is not a reliable non-destructive indicator of microbial spoilage in sliced beef Hungarian-style salami

This study investigated whether color changes reflect the microbiological quality of vacuum- or modified-atmosphere-packaged sliced beef Hungarian-style salami during refrigerated storage. Products of five commercial brands were stored unopened at 4 ± 1°C and analyzed on days 0, 7 and 14 for color (L*, a*, b*, cure color ratio R650/R570, a*/b*), microbial counts (total aerobic mesophilic bacteria [TAMB], Lactobacillus spp., Enterobacteriaceae, yeasts and molds) and pH. Color changes were expressed relative to each brand’s day-0 values. Storage time significantly affected all microbial groups (n = 45; p < 0.001): TAMB increased from 5.81 to 7.47 log CFU/g and lactobacillus spp. from 5.74 to 7.34 log CFU/g, four of five brands exceeded 7 log CFU/g by day 14, and mean pH decreased by 0.375 units. In contrast, the cure color ratio did not change significantly (p = 0.341; −4.3%). Total color difference (ΔE) correlated with TAMB (r = 0.607), but not after controlling for storage day (partial r = 0.333). In principal component analysis (76.8% of variance explained), color and microbiological variables loaded on different components. pH showed the highest discriminative performance for the spoilage threshold (area under the curve [AUC] = 0.843), whereas the cure color ratio performed below chance level (AUC = 0.481). The cure color ratio was therefore not a useful non-destructive spoilage indicator: the products exceeded the spoilage threshold while their color change remained mostly below the threshold of visual perception, consistent with nitrosylhemochrome stability during dark storage in sealed packages.