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Antilisterial effects of different hop acids in combination with potassium acetate and potassium diacetate at 7 and 37 °C

Sansawat, T., Lee, H.C., Zhang, L., Ryser, E.T., Kang, I.
Food control 2016 v.59 pp. 256-261
Listeria monocytogenes, acetates, alpha acids, antibacterial properties, beta acids, exposure duration, heat, minimum inhibitory concentration, potassium, salts, synergism, temperature, yeast extract
This study was conducted to assess the effect of eight hop acid extracts (α-acid, β-acid, acid-iso, acid-tetra, potassium-iso, potassium-hexa, potassium-tetra, and potassium-rho) with/without potassium acetate/potassium diacetate salts (PAPD) on inhibition of Listeria monocytogenes in trypticase soy broth with yeast extract (TSBYE). Following overnight incubation at 37 °C, 50 ppm α-acid decreased Listeria from 6.0 to <1.0 log CFU/mL, with significant reduction to 3.6–3.8 log CFU/mL using β acid, acid-tetra, K-tetra, or K-hexa.No inhibition was seen for acid-iso, K-iso, K-rho and the control. After incubating Listeria with the five hop acids (α-acid, β-acid, acid-tetra, K-tetra, and K-hexa) at 25 ppm with/without 0.5% PAPD, Listeria population decreased from 5.7 log CFU/mL) to < 1.0 log CFU/mL in PAPD/α-acid, PAPD/β-acid, or PAPD/acid-tetra, with reduction to 1.8–4.2 log CFU/mL for the remaining except the control. When the hop acids at 25 ppm were exposed to 85 °C up to 30 min, α-acid maintained the most effective antilisteiral activity by reducing Listeria from 5.0 to <2.9 CFU/mL, regardless of heat exposure time. The minimal inhibitory concentration was 6.3 ppm for α-acid, β-acid and acid-tetra, with 12.5 ppm seen for K-tetra and K-hexa. During the incubation of hop extracts at 5 ppm/7 °C for 6 days, listeristatic effect was observed in the hop/PAPD mixtures and PAPD at 0.5 and 1%, with no listeristatic effect seen for a single addition of hop acids except β-acid. These findings indicated that the combination of hop/PAPD provided both stable and synergistic effects against Listeria growth compared to any single addition, regardless of incubation temperature and addition amount.