Antimicrobial Effect of Natural Food Preservatives in Fresh Basil‐Based Pesto Spreads

Potential hurdle effect of biopreservatives – bacteriocin nisin and sugar alcohol xylitol (at pH = 5.2 and 4.8) – on indigenous flora and water activity (Aw) of fresh basil‐based pesto spreads was studied as alternative to traditional pasteurization or acidification treatments. Addition of 4% xylitol in pesto spreads (at pH 5.2) resulted in a 0.8‐log decrease in the total number of bacteria, after 14 days of storage at 4C, and depression of Aw from 0.886 to 0.864. Nisin (0.015%, at pH 4.8) decreased the bacterial growth by 1 log after 14 days, at 4C. The antimicrobial activity of nisin and xylitol was evaluated against several microorganisms isolated during the preparation of pesto spreads: Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus sp., and on laboratory cultures of Listeria innocua and Lactobacillus sp. An additive effect of 0.005% nisin and 5% xylitol on growth inhibition of pure culture of S. aureus was found. PRACTICAL APPLICATIONS: Application of natural antimicrobial substances may extend the microbiological life by minimizing food safety problems associated with uncooked processed products. Findings obtained in this study suggest a potential future application of bacteriocin nisin combined with additional hurdles: short temperature treatments of components, pH 4.8 and intermediate NaCl concentration in preservation of food.