Purpose: To produce and apply on foods, Na-alginate films incorporated with Janthibacterium sp. and assess the physicochemical parameters of films that allow the appearance of purple color on the film when food spoilage occurs.
Methods: Na-alginate films without or with different concentrations of nutritional substances (yeast, meat extract, tryptophan, skimmed milk powder, cooked meet at concentrations of 0.6% and 1.2% and NaCl: 0.6% and their respective combinations) were prepared and inoculated with 2, 4 or 7 log CFU/ml Janthinobacterium sp. The films were applied on Tryptone Soy Agar (TSA) and on i) pork ii) minced pork iii) beef iv) minced beef, v) minced chicken, vi) ham, vii) Gouda-cheese viii) Haloumi-cheese and viii) turkey-ham. The TSA samples were stored at 5°, 10° and 25°C, whereas the food samples at 5°C. Microbiological and image analysis in addition to pH measurements took place throughout the storage.
Results: Yeast and meat extract Na-alginate films were documented as the most efficient carriers for Janthinobacterium sp. These films retained the viability of Janthinobacterium sp. in contrast to Na-alginate films with no additives where a reduction of Janthinobacterium sp. population (up to 2 log CFU/g) was observed during their preparation. In addition, image analysis showed that the color of yeast and meat-extract films on TSA changed into purple 2 and 4 days earlier compared to the films with no additives, at 25°C and 5°C, respectively. During storage of minced pork at 5°C, coated with yeast (0.6%) or meat-extract films (0.6%) purple color appeared in films after 6 days.
Significance: The combined use of alginate films and Janthinobacterium sp. could be a promising food-spoilage indicator.