Effect of the glycerol content on the A511 bacteriophage release in films made with whey protein isolated

The effect of glycerol concentration on the release of Listeria monocytogenes A511 phage from whey protein isolate (WPI)- based films to water and cheese was examined. For that, A511 phage was incorporated in WPI films with different glycerol content (2, 3, and 4%). Antilisterial ability of phage added-WPI films was evaluated, and physicochemical, mechanical, and barrier properties were characterized. Phage release profiles ranged about 0–1.22 log PFU· mL ⁻¹. After 24 h, phage release in cheese samples was 0, 0.2 and 1 log PFU· mL ⁻¹ for films with 2, 3 and 4 % glycerol, respectively. Phage release in water was 0, 0.2 and 1 log PFU· mL ⁻¹ for films with 2, 3 and 4 % glycerol, respectively. Antilisterial assays showed inhibition zones of 1.6, 2.1 and 2.7 mm for films with 2, 3 and 4 % of glycerol, respectively. Addition of phages into WPI films did not affect the film thickness, the hydrophilic character as well its barrier properties. However, phage addition into WPI films with 2 % glycerol did change the lightness, whiteness index, tensile strength, and elasticity modulus of films. Addition of glycerol from 2 to 4 % caused a reduction in the tensile strength (7.03–1.05 MPa), and elasticity modulus (243.88–17.04 MPa), whereas percent elongation (21.22–56.01 %), moisture content (63.67 %–83.28 %), and swelling power (223.57–609.43 %) were increased. The results show phage are suitable to be used as natural antimicrobials in food packaging.