I. Inactivation of Salmonella and Listeria monocytogenes in steamed fish paste using an integrated treatment of malic acid-incorporated edible coating and in-package cold plasma treatment
An in-package atmospheric dielectric barrier discharge cold plasma (CP) treatment integrated with malic acid-incorporating whey protein isolate (MA-WPI) antimicrobial coating treatment (MA-WPI + CP) was developed for the inactivation of food-borne pathogens in steamed fish paste packaged in a polyethylene terephthalate (PET) container. The effects of MA-WPI + CP treatment on the Salmonella and Listeria monocytogenes inactivation and color of steamed fish paste were investigated. The inactivation effect was further evaluated with Salmonella and L. monocytogenes during storage at 4 and 10 ℃, and the effect of CP treatment on the diffusion coefficient (D₁) of malic acid in MA-WPI film were measured. The MA-WPI coating solution consisted of WPI (9%, w/w wet basis), glycerol (1%, w/w), and MA (3%, w/w). The fish paste samples were dip-coated with MA-WPI coating solution, placed in polyethylene terephthalate containers, treated with in-package CP at 28 kV for 3 min, and stored at 4 and 10 ℃ for 28 and 21 days, respectively. The diffusion coefficients for the diffusion of malic acid in the MA-WPI film with or without CP treatment were also determined. In MA-WPI coating and MA-WPI + CP treatment, MA-WPI coating increased the lightness of steamed fish paste. The reduction rate of Salmonella survival was greater with the coated samples treated by CP at both storage temperatures (4 and 10 ℃). MA-WPI coating and MA-WPI + CP treatment inhibited L. monocytogenes growth of steamed fish paste during storage at 4℃. The diffusion coefficients increased by CP treatment from 2.11 x 10-14 m²/s and 3.27 x 10-14 m²/s to 2.79 x 10-14 m²/s and 4.83 x 10-14 m²/s at 4 and 10 ℃, respectively. The results demonstrated that the inhibition of Salmonella by MA-WPI coating was enhanced by the in-package CP treatment and the enhancement was expected due to the increased diffusion of malic acid in the MA-WPI film by CP treatment.
II. Effect of in-package atmospheric dielectric barrier discharge cold plasma treatment on the antimicrobial efficacy of malic acid-incorporating edible films against food-borne pathogens in chicken breast processed meat
This study investigated the effects of in-package atmospheric dielectric barrier discharge cold plasma (CP) treatment on malic acid-incorporating whey protein isolate (MA-WPI) coating on the antimicrobial efficacy of the coating against foodborne pathogens in chicken breast processed meat (CBPM). The effects of a combined treatment of MA-WPI coating and in-package CP treatment (MA-WPI + CP) on the inactivation of Salmonella and Listeria monocytogenes contaminated in CBPM. The inactivation effect was further evaluated with Salmonella during storage at 4 and 10 ℃, and the effects of MA-WPI + CP treatment on the color and lipid oxidation of CBPM during storage at 4 ℃. Also, the effect of glycerol concentration or CP treatment on the diffusion coefficient (D₁) of malic acid in MA-WPI film, and D₂ and K12 values in CBPM and MA-WPI film according to CP treatment were measured. The CBPM samples were dip-coated with MA-WPI solution [3% (w/w) MA], placed in polyethylene terephthalate containers, treated with in-package CP at 24 kV for 3 min, and stored at 4 and 10 ℃ for 28 and 21 days, respectively. The diffusion coefficients (D1) for the diffusion of malic acid in the MA-WPI film with or without CP treatment were also determined. The reduction rate of Salmonella survival was greater with the coated samples treated by CP at both storage temperatures. The diffusion coefficients (D₁) increased by CP treatment from 1.93 x 10-14 and 3.00 x 10-14 m²/s to 4.65 x 10-14 and 6.39 x 10-14 m²/s at 4 and 10 ℃, respectively. CP treatment did not influence the D₂ (from 1.16 x 10-10 m²/s to 1.31 x 10-10 m²/s) and K₁₂ values (from 0.57 to 0.48) of CBPM at 4 ℃. MA-WPI + CP treatment did not influence the color and lipid oxidation of CBPM during storage at 4 ℃ (p 〉 0.05). The CP treatment did not alter the water vapor permeability and tensile properties (elongation at break and elastic modulus) of MA-WPI film (p 〉 0.05). The results demonstrated that the inhibition of Salmonella by MA-WPI coating was enhanced by the in-package CP treatment and the enhancement was expected due to the increased diffusion of malic acid in the protein film by CP treatment. Also, the study demonstrated the potential of applying MA-WPI + CP treatment for foodborne pathogens decontamination of CBPM without quality properties change.