Application of spray-dried bacteriocins as cheese biopreservatives

Listeria monocytogenes can contaminate refrigerated ready-to-eat foods, such as cheeses. Enterocins, with a strong listericidal effect, constitute a natural alternative to control this pathogen in food. To optimize their antimicrobial action in food matrices, bacteriocins can be immobilised in edible coatings through spray drying technology which allows the large-scale production of microcapsules of bioactive molecules. The aim of this work was to evaluate the antimicrobial effectiveness of Enterococcus avium DSMZ17511 bacteriocins, obtained in a low-cost culture broth (HS-L), spray-dried assaying different thermoprotective materials (maltodextrin, cheese whey and brea gum), and incorporated into agar-based active coatings applied on goat cheese pieces artificially contaminated with L. monocytogenes 99/287. The bacteriocin solution (BS) powders, labelled HS-L BS, maintained the antimicrobial activity even after 90 days of storage, with titres up to 128,000 UA/g, with the least thermoprotective effect exerted by brea gum (64,000-32,000 UA/g). An increase in antimicrobial titre was observed for all bacteriocin powders after 3 months, despite storage conditions; probably due to a release effect from the encapsulated bacteriocin or a combined release and gradual dehydration effect of the encapsulating matrix. Also, the dried products stored at 25 °C hydrated easily, while refrigeration or freezing did not affect the powders texture. For coatings applied on fresh goat cheese, only a difference of 0.5 log cfu/mL was observed between the viability of L. monocytogenes in the contaminated active-coated cheese and the control without coating. Instead, for the commercial goat cheese, with a drier matrix, the viability values stood 1.0 log cfu/mL below the control uncoated cheeses for up to 10 days. These spray dried bacteriocin powders provide an alternative for their application as food biopreservatives, since stable dehydrated products were obtained, with prolonged antimicrobial activity, and with verified inhibitory action in a food matrix.