Inactivation of Barotolerant Listeria monocytogenes in Sausage by Combination of High-Pressure Processing and Food-Grade Additives

Abstract

Food-grade additives were used to enhance the efficacy of high-pressure processing (HPP) against barotolerant Listeria monocytogenes. Three strains of L. monocytogenes (Scott A, OSY-8578, and OSY-328) were compared for their sensitivity to HPP, nisin, tert-butylhydroquinone (TBHQ), and their combination. Inactivation of these strains was evaluated in 0.2 M sodium phosphate buffer (pH 7.0) and commercially sterile sausage. A cell suspension of L. monocytogenes in buffer (10(9) CFU/ml) was treated with TBHQ at 100 ppm, nisin at 100 IU/ml, HPP at 400 MPa for 5 min, and combinations of these treatments. Populations of strains Scott A, OSY-8578, and OSY-328 decreased 3.9, 2.7, and 1.3 log with HPP alone and 6.4, 5.2, and 1.9 log with the HPP-TBHQ combination, respectively. Commercially sterile sausage was inoculated with the three L. monocytogenes strains (10(6) to 10(7) CFU/g) and treated with selected combinations of TBHQ (100 to 300 ppm), nisin (100 and 200 ppm), and HPP (600 MPa, 28 degrees C, 5 min). Samples were enriched to detect the viability of the pathogen after the treatments. Most of the samples treated with nisin, TBHQ, or their combination were positive for L. monocytogenes. HPP alone resulted in a modest decrease in the number of positive samples. L. monocytogenes was not detected in any of the inoculated commercial sausage samples after treatment with HPP-TBHQ or HPP-TBHQ-nisin combinations. These results suggest that addition of TBHQ or TBHQ plus nisin to sausage followed by in-package pressurization is a promising method for producing Listeria-free ready-to-eat products.

Relationship between Sublethal Injury and Microbial Inactivation by the Combination of High Hydrostatic Pressure and Citral or tert -Butyl Hydroquinone

“…Synergistic inactivation effects have been described when HHP treatments were combined with low pHs (15,25) or with different antimicrobial substances, such as lysozyme (16,18,30), pediocin (17,21,22), nisin (8,17,18,21,30,55), and lacticin (34). Several workers have reported the lethal effect of HHP in combination with phenolic antioxidants, such as TBHQ or butylated hydroxyanisole (8,27,58), or with plant essential oils, such as citral (41).…”

“…TBHQ and HHP treatment also act synergistically when simultaneously applied to L. monocytogenes at pH 7.0 (8,58). We found that 100 ppm of TBHQ acting alone at pH 7.0 did not affect the survival of L. monocytogenes, in agreement with Vurma et al (58), but caused extensive sublethal injury following refrigerated storage for 24 h. This sensitizing effect might explain the efficacy of the combined treatment of HHP and TBHQ in L. monocytogenes, which allowed the inactivation of Ͼ6 log 10 cycles at pH 7.0.…”

“…Several workers have reported the lethal effect of HHP in combination with phenolic antioxidants, such as TBHQ or butylated hydroxyanisole (8,27,58), or with plant essential oils, such as citral (41).…”

“…Published data have demonstrated that the application of specific additional hurdles such as antimicrobial peptides, the lactoperoxidase system, and phenolic compounds in combination with HHP treatments have synergistic inactivation effects (8,16,17,18,21,22,30,31,34,55,58). One of the most effective phenolic compounds is tertbutyl hydroquinone (TBHQ), which sensitizes some barotolerant Listeria monocytogenes strains to HHP (8,58).…”

“…Where indicated, 100 ppm of TBHQ or 1,000 ppm of citral was added to the buffer. These concentrations were chosen from those previously described in published literature (8,11,58). Cell suspensions (2 ml each) were then placed in sterile plastic pouches that were heat sealed and kept on ice before pressurization.…”