Abstract
The essential oils of clove bud, cinnamon bark and thyme, and their individual compounds including allyl isothiocyanate (AIT), carvacrol, cinnamaldehyde, cinnamic acid, eugenol, and thymol were initially assessed for antimicrobial activity against 9 lactic acid bacteria (LAB) species. Carvacrol and thymol were the most inhibitory with MICs of 0.1% (v/v and w/v, respectively). Cinnamaldehyde, cinnamon bark oil, clove bud oil, eugenol, and thyme oil were moderately inhibitive (MICs = 0.2% v/v), while cinnamic acid required a concentration of 0.5% (w/v). AIT was not effective with MICs in excess of concentrations tested (0.75% v/v). The bactericidal capability of the oil components carvacrol, cinnamaldehyde, eugenol, and thymol were further examined against Pediococcus acidilactici, Lactobacillus buchneri, and Leuconostoc citrovorum. Thymol at 0.1% (w/v) was bactericidal against L. citrovorum (>4-log reduction), but resulted in a 2-log CFU/mL reduction against L. buchneri and P. acidilactici. Cinnamaldehyde at 0.2% to 0.25% (v/v) was effective against L. citrovorum, L. buchneri, and P. acidilactici, resulting in a >2-log reduction. All 3 organisms were susceptible to 0.2% carvacrol with >3-log reduction observed after exposure for 6 h. Eugenol was the least effective. Concentrations of 0.2% and 0.25% (v/v) were needed to achieve an initial reduction in population, >3-log CFU/mL after 6 h exposure. However, at 0.2%, P. acidilactici and L. buchneri recovered to initial populations in 48 to 72 h. Results indicate essential oils have the capacity to inactivate LAB that are commonly associated with spoilage of shelf stable low-acid foods.
Practical Application
Essential oils are plant derived compounds that consumers may view as more natural and preferred alternatives to synthetic preservatives. These oils have been demonstrated to have antibacterial and antifungal activity within food systems, and may be ideal additives to food formulations in order to meet the growing consumer demand for clean-label, organic or natural food products while preserving the quality and shelf-life of the product. These compounds have yet to be evaluated for their activity against common food spoilage organisms such as lactic acid bacteria, which is a first step in their adoption by the food industry.
Abstract
This study evaluated the antilisterial activity of hops beta acids (HBA) and their impact on the quality and sensory attributes of ham. Commercially cured ham slices were inoculated with unstressed- and acid-stress-adapted (ASA)-L. monocytogenes (2.2 to 2.5 log CFU/cm2), followed by no dipping (control), dipping in deionized (DI) water, or dipping in a 0.11% HBA solution. This was followed by vacuum or aerobic packaging and storage (7.2 °C, 35 or 20 d). Samples were taken periodically during storage to check for pH changes and analyze the microbial populations. Color measurements were obtained by dipping noninoculated ham slices in a 0.11% HBA solution, followed by vacuum packaging and storage (4.0 °C, 42 d). Sensory evaluations were performed on ham slices treated with 0.05% to 0.23% HBA solutions, followed by vacuum packaging and storage (4.0 °C, 30 d). HBA caused immediate reductions of 1.2 to 1.5 log CFU/cm2 (P < 0.05) in unstressed- and ASA-L. monocytogenes populations on ham slices. During storage, the unstressed-L. monocytogenes populations on HBA-treated samples were 0.5 to 2.0 log CFU/cm2 lower (P < 0.05) than control samples and those dipped in DI water. The lag-phase of the unstressed-L. monocytogenes population was extended from 3.396 to 7.125 d (control) to 7.194 to 10.920 d in the HBA-treated samples. However, the ASA-L. monocytogenes population showed resistance to HBA because they had a higher growth rate than control samples and had similar growth variables to DI water-treated samples during storage. Dipping in HBA solution did not adversely affect the color or sensory attributes of the ham slices stored in vacuum packages. These results are useful for helping ready-to-eat meat processors develop operational procedures for applying HBA on ham slices.
Practical Application
This study validated the antilisterial activities of HBA on commercially cured ham slices undergoing an HBA dipping treatment. Our results indicated that dipping the commercially cured ham slices into a 0.11% HBA solution (4.44 mg/kg of HBA on ham surfaces) inhibited unstressed-L. monocytogenes growth during storage, and the ASA-L. monocytogenes was cross-protected by HBA treatment. Moreover, application of 0.11% HBA to ham slices did not have negative effects on the color and sensory properties of the ham slices.
FoodWorld 